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TRANSPORT AND ROAD RESEARCH LABORATORY Department of Transport RRL Contractor Report 164 Accident analysis methodologies and remedial measures with particular re- gard to cyclists by R D Hall, J H Harrison, M McDonald (Transportation Research Group, University of Southampton) and D G Harland (TRRL) The first three authors of this report are employed by the University of Southampton The work reported herein was carded out under a contract placed on them by the Transport and Road Research Laboratory. The views expressed are not necessarilythose of the Department of Transport. This report, like others in the series, is reproduced with the authors' own text and illustrations. No attempt has been made to prepare a standardised format or style of presentation. Road Safety Division Safety and Transportation Group Transport and Road Research Laboratory Old Wokingham Road Crowthorne, Berkshire RG1 1 6AU 1989 ISSN 0266-7045

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Page 1: RRL - Transport Research Laboratory · 2016-10-02 · TRANSPORT AND ROAD RESEARCH LABORATORY Department of Transport RRL Contractor Report 164 Accident analysis methodologies and

TRANSPORT AND ROAD RESEARCH LABORATORY Department of Transport R R L

Contractor Report 164

Accident analysis methodologies and remedial measures wi th part icular re- gard to cycl is ts

by R D Hall, J H Harrison, M McDonald (Transportation Research Group, University of Southampton) and D G Harland (TRRL)

The first three authors of this report are employed by the University of Southampton The work reported herein was carded out under a contract placed on them by the Transport and Road Research Laboratory.

The views expressed are not necessarily those of the Department of Transport.

This report, like others in the series, is reproduced with the authors' own text and illustrations. No attempt has been made to prepare a standardised format or style of presentation.

Road Safety Division Safety and Transportation Group Transport and Road Research Laboratory Old Wokingham Road Crowthorne, Berkshire RG1 1 6AU

1989

ISSN 0266-7045

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CONTENTS

2

LIST OF TABLES

LIST OF FIGURES

ABSTRACT

INTRODUCTION

I.I Background 1.2 Objectives 1.3 Approach 1.4 Literature Review

INFORMATION FROM SELECTED COUNTIES

2.1 Approach 2.2 Policy and Programme towards Cyclist Safety 2.3 Structure within Counties 2.4 Accident Data Systems 2.5 Problem Identification 2.6 Monitoring 2.7 Cycle Schemes

2.7.1 With-flow cycle lanes 2.7.2 Shared use footwavs 2.7.3 Contra-flow cycle lanes 2.7.4 Other schemes

2.8 Conclusions with respect to Cycle Accident Problems

ACCIDENT ANALYSIS METHODOLOGY

3.1 Objectives and Criteria 3.2 Accident Data Collection and Processing 3.3 Data Presentation and Analysis 3.4 Problem Identification 3.5 Initial Ranking 3.6 Problem Investigation 3.7 Identification of Possible Remedial Measures 3.8 Accurate Costs and Benefits 3.9 Priority Ranking with Special Regard to Cyclists 3.10 Implementation and Monitoring

PORTSMOUTH ACCIDENT DATA ANALYSIS

4.1 Approach 4.2 Data Collection

4.2.1 Data Verification 4.2.2 Link-Node-Cell System

4.3 Overview Analysis and Data Presentation 4.3.1 Plotting by Grid Reference 4.3.2 Cross-Tabulations

Page

(iii)

(iii)

(iv)

3 3 3 3 4 6 8 8 9 9 I0 I0

II

II 13 13 14 ]4 14 14 15 15 16

17

17 17 17 17 20 20 20

(i)

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Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1 st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

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Page

4.4 Problem Identification and Ranking 23 4.4.1 Sites Chosen for Further Investigation 27

4.4.1.1 Nodes 27 4.4.1.2 Links 28 4.4.1.3 Cells 28

4.5 Site Investigation 28 4.5.1 Accident Sketch Plans and Dominant Accident Type 28 4.5.2 Cross-Tabulation of Factors 32 4.5.3 Stick Diagram Analysis 32 4,5.4 Site Inspections 34

4.6 Remedial Measures 37 4.6.1 Identification of Possible Schemes 37 4.6.2 Node 51 37 4.6.3 Link 29-104 37 4.6.4 Node 9 38

4.7 Costs. Benefits and First Year Rate of Return 38

5 SU~Y AND CONCLUSIONS 41

ACKNOWLEDGMENTS 43

REFERENCES 44

APPENDIX A 45

Crown Copyright. The views expressed in this Report are not necessarily those of the Department of Transport. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

(ii)

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Page

LIST OF TABLES

I

2

3

4

5

6

7

Casualties at 24 Accident Remedial Sites Treated during 1980-1984 in County A

Casualties at 13 Accident Remedial Sites Treated during 1983 in County B

Casualties at 54 Accident Remedial Sites Treated during 1981-1983 in County C

Accidents Before and After Implementation of 4 With-flow Cycle Lanes

Accidents Before and After Implementation. of 2 Shared Use Footways

Accidents Before and After Implementation of a Contra-flow Cycle Lane

Casualties.by Road User Class and Severity for All Accidents

8 Nodes in Portsmouth with 3 or more Cycle Accidents in 3 years (1984-1986)

9 Links in Portsmouth with 3 or more Cycle Accidents in 3 years (1984-1986)

I0 Cells in Portsmouth with 3 or more Cycle Accidents in 3 years (1984-1986)

II Cycle Casualties by Age and Time of Day on Link 29-104 12 Cycle Casualties by Cycle Manoeuvre and Direction on

Links 29-104 13 Stick Diagram Analysis for Link 29-104 14 Stick Diagram Analysis f0r Node 9 15 Calculation of Estimated Costs, Benefits and First Year .Rate

of Return for Node 51 16 Calculation of Estimated Costs, Benefits and First Year Rate

of Return for Link 29-104

A1 All Accidents by Severity and Year A2 Cycle Accidents by Severity and Year A3 Cycle Accidents by Year and Month A4 Cycle Accidents by Day of Week and Hour of Day A5 Cycle Accidents by Junction Control and Type A6 Cycle Accidents by Speed Limit and Carriageway Type A7 Cycle Accidents by Road Surface and Weather Conditions A8 Cycle Accidents by Light and Road Surface Conditions A9 Vehicles involved in Cycle Accidents by Year and Class AI0 Casualties in Cycle Accidents by User Class and Age

LIST OF FIGURES

Example of Computer Generated Accident Map Methodology Flow Chart Plan of Link-Node-Cell System for Portsmouth Plot of Cycle Accidents in 1 km square of South Portsmouth Plot of Worst Cycle Accident Nodes and Links Sketch Plan of Rudmore Roundabout (Node 51) Sketch Plan of Kings Road/Elm Grove (Link 29-104) Sketch Plan of New Road/Copnor Bridge T-Junction (Node 9)

7

7

7

9

9

I0 22

24

25

27 33

33 35 36

39

40

45 45 45 46 47 47 48 48 49 49

5 12 19 21 26 29 30 3]

(iii)

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ABSTRACT

This report describes the development and testing of an accident analysis methodology with particular concern for the accident problems of cyclists. A comprehensive review of the literature concerning accident analysis and the provision of cycle facilities was made and is published as a separate document. From this review and the methods used in five selected local authorities a cycle accident analysis methodology was developed. Important features of the methodology are that separate consideration is given to the accident problems of cyclists, and that remedial schemes should be selected so as to give expected casualty reductions by road user type approximately in proportion to the level of casualties of each type. The methodology was tested by its application to the accident data for Portsmouth for the three years 1984-1986, and was successful in clearly identifying the worst accident locations for cyclists and enabling dominant accident types and feasible remedial measures to be established.

(iv)

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1 INTRODUCTION

I.I Background

Over the last 10-15 years, there has been a marked increase in the level of use and ownership of pedal cycles following a general decline up to the early 1970's. This increase has been accompanied by a rise in the number of accidents involving cyclists together with an increase in the accident rate per distance travelled. This increase in accident rate for cyclists is set against a steadily decreasing rate for accidents involving other road users (Department of Transport, Scottish Development Department, and Welsh Office, 1986a & b), so that now cyclists are about 5 times more likely to be involved in a road

accident per kilometre than car drivers.

Being unprotected, cyclists are also more liable to injury when involved in an accident and this additional factor makes them some 18 times more likely to be injured per kilometre travelled than car drivers (Downing, 1985). Cyclists are particularly vulnerable at certain types of location; in particular at roundabouts their involvement in accidents is some 15 times that of car users (Layfield and Maycock, 1986). Another factor which is of considerable concern is the proportion of children involved in cycle accidents; about 40~

of cyclist casualties are aged 16 or under.

The above figures are based on the Stats 19 data recorded by the police at the time of an accident and are recognised as being understated due to the considerable level of under-reporting of cycle accidents, estimates varying between 35% (Hepworth et al, 1984) and 87% (Pedder et

al, 1981).

As a result of such trends and statistics, there has been an increase in awareness and interest at both local and national government levels in finding ways to reduce the accident risk to cyclists with guidelines being produced on the provision of facilities for cyclists as well as experimental schemes being implemented and monitored.

As an integral part of this, however, there was need to be able to readily identify cycle accident problems and select appropriate remedial measures, so the Transport and Road Research Laboratory (TRRL) invited the Transportation Research Group (TRG) of Southampton University to undertake, under contract, such a study of cycle accident

analysis methodologies.

1.2 Objectives

The objectives of the study were :

(a) To conduct a review of selected local authorities in order to :

(i) Establish the methods of analysis of accidents and associated data used in identifying cycle accident

problems.

(ii) Establish the methodologies remedial measures.

for selecting appropriate

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(iii) Collect information on particularly trying to effectiveness in terms attractiveness to cyclists.

cycling schemes implemented, establish their level of of accident savings and

(b) To test and develop the methodology established above by making detailed studies of cycle accidents in Portsmouth.

1.3 App roach

The study was carried out in three main phases as follows : -

(i) A literature survey was conducted bringing together as much as possible of the published work in the areas of accident investigation and prevention and the provision of on and off road cycle facilities; the survey included an extensive bibliography produced by both conventional and on-line computer search

techniques.

(ii) A review of five County Councils was conducted to establish their methods of accident analysis and remedial measure selection. This also included investigation of cycle schemes already implemented, their cost and effectiveness in terms of their level of usage and accident reductions. In addition, the proportion of benefit of all accident remedial work to the vulnerable road user groups, i.e. pedal cyclists, pedestrians and motor cyclists was examined.

(iii) From the information gathered from the local authorities and from the literature, a methodology was developed for the whole process of accident data collection and analysis, problem identification and ranking, and remedial treatment choice. This methodology was then tested and developed by its application to the analysis of accident data for Portsmouth for the three year period

1984-86.

1.4 Literature Review

The literature review has been published as a separate document (Harrison, Hall and Harland, 1989). The review aimed to gain as full an appreciation as possible of the current methods of accident data collection and analysis in general, and as they relate to cycle accidents in particular. The areas covered encompassed all aspects of data collection and analysis, remedial treatments and the provision of

cycle facilities, installed for any reason.

The review showed that :

(i) None of the reported accident analysis methodologies specifically address the accident problems of vulnerable road users or of

cyclists in particular.

(ii) There is clear need for the development of an accident investigation and prevention methodology aimed specifically at

the problems of vulnerable road users.

(iii) There is very little published evidence at present of the effectiveness of cycle facilities in reducing accidents.

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2 INFORMATION FROM SELECTED COUNTIES

Five counties were contacted in order to establ~sh their methods of accident data collection and analysis, and choice of remedial measures. Counties were chosen which were considered to be particularly active in the provision of cycle facilities and/or accident remedial work.

2.1 Approach

Initially, information was gathered by means of meetings held with relevant officers of each County Council. For ease of comparison, a standard format was used aimed at giving an appreciation of :

(i) General policy and programme towards safety and cycling (ii) Structure within the County (iii) Accident data systems and methods of analysis (iv) Cycle accident remedial measures (v) Number and types of cycle schemes

Further meetings were then held to follow up on items of particular interest such as the success or otherwise of specific cycle schemes.

2.2 Policy and Programme towards Cyclist Safety

In general, the county councils seem to be in the early stages of considering cycle problems separately from those of other road users, though there is a largely common polic~ that cyclists should be specifically considered in the planning of any new highway schemes. In addition, most of the County Transport Planning Policies state that situations should be sought where specific cycle accident remedial schemes may be required and their feasibility studied.

2.3 Structure within Counties

Organisational structure varies from county to county with some counties having specific personnel and budgets for cycle planning whilst for others, this work comes under the road safety team. Even where a special cycling budget exists, it is usually small and any major schemes have to compete with those from other areas for funding from the maintenance or capital expenditure budgets.

Several of the counties have district or local road safety committees involving the relevant county or district staff and the Police as well as interested parties such as cycling organisations, parent-teacher groups, etc. These are thought to be particularly useful in pointing out local problems which may be overlooked by county level

investigations.

2.4 Accident Data Systems

Accident data is collected by the police at the scene of the accident and a local variation of the Stats 19 form is completed. Three of the counties do this for personal injury accidents only, whilst the other two also collect data for damage only accidents. In both cases,

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however, it is recognised that the damage only information may be biased (due to under reporting) and so it is not used in the detailed analysis but merely to provide supportive information.

It is recognised by all five counties that the data collected in this way is liable to quite a high degree of error (estimated as 3 errors per accident in the one case where this had been quantified). Validation is carried out either by computer or by hand. Clearly, logic checks made by computer have the advantage of being efficient but manual methods can make use of expertise and local knowledge. In fact, the county putting the highest priority on this aspect of data collection uses its own staff to check and then code the data for input to the computer at which stage further automatic validation checks are

performed.

The degree of effort put into the verification of data varies considerably between counties but clearly for any analysis to be meaningful it must be performed on data of the best possible quality.

The method used to plot accidents varies with some counties relying on manual plots using transparent sheets overlaid on road maps, while one county used computer plots on a computer drawn road network at any required scale. The locations of accidents are determined using grid references or by a system using links and nodes in some combination. Such a system can provide a useful cross-check of the grid reference and can take several forms but those used involve either : -

(i)

or

(ii)

each link is numbered so that any location can be defined as being a certain distance from the start of the link or at the

intercept of two or more links

each node is numbered and locations can be defined as being a distance from one node in the direction of the second.

One particularly good method uses a kilometrage system of accident location such that plots can be created by computer on road maps which are also generated by the computer from the digitised road network. Such a method allows easy access to high quality colour plots of either individual accidents of a particular type or cumulative 'blobs' of accidents within defined limits. Such plots are easy to read and also make for good visual impact in public awareness campaigns and road safety exhibitions. This method, however, relies on a computer system capable of storing and subsequently plotting the digitised road network. To initiate this type of system would require more time (and sophisticated plotting equipment) than is available in this study. It would be, however, a one-off task with continuing benefits so the time involved should not preclude its implementation by local authorities. An example of the output of such a system is shown in Figure I.

2.5 Problem Identification

All the counties produce an initial list of sites for further investigation. In some cases this is a list of a fixed number of 'worst sites' and in others it is a list of all the sites with more

than a fixed number of accidents.

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In all cases, this list contains more sites than can be treated within the limits of resources and time available and acts merely as a starting point for further investigation. The typical 'black-spot' definition is "12 or more personal injury accidents in 3 years".

Having produced this list of worst sites, the counties generally proceed along the lines of the Department of Transport's Accident Investigation and Prevention Manual (Department of Transport, Road Safety Directorate, 1974); (this has now been superseded by the Accident Investigation Manual (Department of Transport, 1986)). In general the accident problems of cyclists are not given any special priority but in some cases, where cyclists are found to be vulnerable at a site found by conventional means, a separate solution may be found to the cycle specific problem. In some cases this has involved special facilities at the site (such as a cycle phase at traffic lights), and in other cases, it has involved removal of cyclists by providing an

alternative route.

2.6 Monitoring

Often, due to pressures on staff time, little is done in the way of monitoring of accident remedial schemes. However, three counties provided 'before and after' data at general accident remedial sites in order to investigate the overall proportion of benefit to each road user type. The results of these analyses are shown in Tables 1 - 3.

Expected numbers of casualties have been calculated by applying correction factors to the 'before' figures taking into account the accident trends for the whole county or city as appropriate for the

relevant time period.

It can be seen in Tables I and 2, that pedal cyclist casualties hardly feature at the accident remedial sites and in the before period are a much lower proportion of the casualties than found in the county as a whole, albeit numbers are small. The reductions of 7 and 2 from expected cyclist casualties cannot be considered significant. A fairly similar pattern is also found for pedestrians and motor

cyclists.

In County C with a much higher level of cyclist casualties, a much larger proportion of casualties in the before period at the treated sites were cyclists and reflects a situation where cycle accidents dominate at many locations. The apparent low level of casualty reduction at such sites highlight the difficulties in tackling cycle

accident problems.

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TABLE 1 : CASUALTIES AT 24 ACCIDENT REMEDIAL SITES TREATED DURING 1980-1984 IN COUNTY A

Road User All Type Casualties

in County (1981-83) No. %

Casualties at Remedial Sites (3 years)*

Before After Expected Actual

% No. Number Number

Reduction for Road User Type from Expected

Pedal Cyclist 1149 6.7 2.7 12 14 7 Pedestrian 2450 14.3 4.6 20 20 I0 Motor Cyclist 4938 28.9 18.2 80 82 44 Car Occupant 7425 43.5 66.5 292 296 192 Other 1118 6.6 8.0 35 36 38

50.0 50.0 46.3 35.1 -5.5

Total 17080 I00.0 I00.0 439 448 291 35.0

* Except for 2 sites for which there were 2 and 2~ years data respectively both before and after

TABLE 2 : CASUALTIES AT 13 ACCIDENT REMEDIAL SITES TREATED DURING ]983 IN COUNTY B

Road User All Type Casualties

in County (1981-83) No. %

Casualties at Remedial Sites (3 years)

Before After Expected Actual

% No. Number Number

Reduction for Road User Type from Expected

%

Pedal Cyclist 1750 9.7 6.0 7 8 6 25.0 Pedestrian 332~ 18.4 14.7 17 18 16 II.I Motor Cyclist 4369 24.] 22.4 26 20 5 75.0 Car Occupant 7105 39.2 46.6 54 54 24 55.5 Other 157l 8.7 10.3 12 II 9 ]8.2

Total 18123 I00.0 I00.0 116 III 60 46.0

TABLE 3 : CASUALTIES AT 54 ACCIDENT REMEDIAL SITES TREATED DURING 1981-1983 IN COUNTY C

Road User All Type Casualties

in County (1981-83)

No. %

Casualties at Remedial Sites (3 years)

Before After Expected Actual

% No. Number Number

Reduction for Road User Type from Expected

%

Pedal Cyclist 1817 15.7 22.3 192 247 243 1.6 Pedestrian 1044 9.0 10.6 91 90 72 20.0 Motor Cyclist 2475 21.4 29.2 251 294 266 9.5 Other 6222 53.8 37.9 326 361 307 15.0

Total 11558 I00.0 I00.0 860 992 888 10.5

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" 2.7 Cycle Schemes

Each of the five counties has in recent years installed cycle facilities of some sort, either as accident remedial measures or for other reasons such as to provide more pleasant alternatives to busy roads. These facilities range from the provision of a with-flow cycle lane to some quite complex junction improvements. There are many problems in assessing the success of accident remedial schemes as

outlined below :

(i) Because the total number of cycle accidents is relatively small, many of the problem sites have not come to light as a result of the comventional 'worst sites' identification procedures, but rather from local pressure groups or the experience and knowledge of local engineers. Consequently, formal before and after studies are generally

not available.

(ii) It is difficult to identify the area of influence of a scheme which may attract cyclists to it from other locations. For example, where a grade separated cycle facility is installed at a roundabout, cyclists who had previously used a more circuitous route in order to avoid the roundabout, may revert to using the roundabout route. Thus, the number of cycle accidents may increase near the treated location although the overall accident rate per cyclist may be reduced.

(iii) Conversely, where the facility consists of an alternative route, the benefits at the sites which are being avoided have to be balanced with the possible creation of problems on the new route. The area of influence (as discussed in (ii)) is also particularly difficult to assess in the case of new routes using, for example, shared footways through parks which could have a very wide 'catchment' area.

For these reasons, whilst it is relatively straightforward to make a subjective assessment in terms of levels of use and perceived risk, it has proved very difficult to determine the effectiveness of schemes using formal monitoring techniques. In addition, the lack of 'after' accident data due to the predominantly recent implementation of schemes

currently hinders quantified appraisal.

Monitoring has been carried out for a few cycle schemes, a summary of the results being shown below by type of scheme. The data is very limited so any conclusions are necessarily tentative.

2.7.1 With-flow cycle lanes

Table 4 shows a summary of the accidents before and after at 4 with-flow cycle lanes. Unfortunately, at each site the before and after periods were of different durations so direct comparisons of accident numbers are not possible, and accidents per kilometre year are given as well as the expected number of accidents in the after period. The expected figures have been calculated by applying a local control factor based on accident trends for the type of vehicle in the relevant time period. In the region including these sites there was an increase of approximately 50% in the number of cycle accidents and it can be seen that at these 4 with-flow cycle lanes, a reduction in accidents from expected has been achieved for cyclists, though total

accidents have sharply increased.

8

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TABLE 4 : ACCIDENTS BEFORE AND AFTER IMPLEMENTATION OF 4 WITH-FLOW CYCLE LANES

Cycle Accidents Number Number/Km Yr

All Accidents Number Number/Km Yr

Before (35.0 Km Years) 56

Expected After (22.9 Km Yrs) 54

Actual After (22.9 Km Years) 46

I .6 130 3.7

2.4 77 3,4

2.0 133 5.8

2.7.2 Shared use footways

Table 5 gives a summary of accident monitoring at two shared use footways.

TABLE 5 : ACCIDENTS BEFORE AND AFTER IMPLEMENTATION OF 2 SHARED USE FOOTWAYS

Cycles All No Accs Number/Km Yr No Accs Number/Km Yr

Before (25.0 Km Years) 41

Expected After (30.7 Km Yrs) 65

Actual After (30.7 Km Years) 43

1.6 123 4.9

2.1 139 4.5

1.4 144 4.7

Again, the before and after periods are of different durations and the expected after figures have been calculated by applying a regional control factor for the relevant time period. The two sites are made of 6 parts of schemes, implemented over a three year period, some of which are two-way and some of which are one-way only. A good reduction between 'expected' and 'after' is shown for cyclists, while there is little difference for total accidents.

2.7.3 Contra-flow cycle lanes

Accident monitoring at only one contra-flow cycle lane was available. Before the implementation of the scheme, cyclists had to make a detour to avoid the one-way street in which the contra-flow lane was subsequently installed. For this reason, a simple before and after comparison at the site was not possible but accidents were monitored in a study area designed to encompass the whole area of influence of the

scheme. The results are shown in Table 6.

A worse than expected increase in cycle accidents was found, but no account is made of change in levels of cycle flows.

9

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TABLE 6: ACCIDENTS BEFORE AND AFTER IMPLEMENTATION OF A CONTRA-FLOW

CYCLE LANE

Cycle Accidents Before (3 years) Expected (3 years) After (3 years)

62 76 91

2.7.4 Other schemes

There are other schemes which are too recent to have been properly monitored. These include a number of potential solutions to roundabout problems which are one of the main areas of concern in this field. Other schemes include dual-use signalised crossings, separate cycle lanes at signalised junctions, joint use of pedestrian subways under roundabouts as well as complete routes, signposting cyclists to use alternative routes with some special facilities at major road

crossing-points.

2.8 Conclusions with respect to Cycle Accident Problems

The main finding with respect to accident investigation and prevention as it relates to cyclists is that whilst some cycle facilities are being installed by most counties, they do not have a specific methodology to deal with cycle accidents independently from those involving any road user. As a result many of the cycle schemes so far implemented have originated from a common sense approach to the problem

and, in some cases, purely in response to public pressure.

As can be seen from the above figures, the few schemes which have been installed as remedial treatments in the formal sense do not show great savings in the number of accidents. In fact, often an increase has occurred, but this should be regarded in the context of the gradually

increasing accident rate for cyclists nationwide.

In the subsequent sections of this report an accident analysis methodology is described which has been established in an attempt to formalise a procedure which could be expected to tackle cycle accident problems with the degree of success which is now considered normal for

road users in general.

l0

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3 ACCIDENT ANALYSIS METHODOLOGY

With the experience gained from discussions with the County Councils and from the literature, an accident analysis methodology was established, which was intended to incorporate the best techniques of established practice as well as introducing new ideas designed to overcome the inadequacies of such practices as regards cyclists.

Some consideration has also been given to other vulnerable road user groups (i.e. pedestrians and motor cyclists) as it is anticipated that the investigation of accidents to these groups could be tackled using a similar approach.

Figure 2 shows the simplified flow chart of the sequential processes involved in the methodology which are explained and discussed in the following sections. The flow chart is not intended to explain the procedure but provides a guide to the order and the interdependence of

the necessary steps.

3.1 Objectives and Criteria

The overall objective is to reduce the number and severity of accidents

in the area subject to the following criteria • -

(i)

(ii)

To achieve a required rate of return within a specified budget

To achieve a reduction in the number and severity of accidents

for ALL road users.

It was shown in section 2.6 that cyclists (and other minority groups) do not benefit from remedial schemes arising from conventional methodologies in proportion to their rate of involvement. A further objective should, therefore, be • -

(iii) To provide a balanced reduction of casualties by road user type.

Conventional methodologies have merely considered numbers of accidents rather than the types of road users involved. The main innovation of this methodology, therefore, is the principle of giving separate

consideration to each road user group.

The inclusion of such a criterion is further supported by the fact that some remedial schemes, such as replacing traffic signals by a roundabout, may reduce the overall number of accidents whilst actually

increasing the risk to groups such as cyclists.

The reasons for the phenomenon are as follows • -

(i) Different road users have different accident problems even at the

same site. (ii) There is a far greater number of cars than cycles or motorcycles

etc. (iii) Problems for the minority groups are swamped by the large numbers

of car accidents, and consequently rarely reach the top of the priority lists drawn up in the conventional manner.

ll

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Figure 2 : Methodology Flow Chart

Objectives and Criteria 1

i I Accident Data Collection and Processing

Y

I ata Presentation and Analysis

l

1 I n i t i a l Ranking

Problem Investigation

Identification of Possible Remedial Measures I

AccurateCosts and Benefits 1

I Priority Ranking I

Implementation

i I Monitoring I

I Further Depth as Necessary

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If each road user group is considered separately at each stage of the methodology, however, and given priority roughly in proportion to the numbers of casualties in each group then a balanced reduction of casualties could be achieved. The same economic criteria may still be used in the assessment of schemes, but now equally high benefit schemes for minority road user groups may be included, which otherwise would not be identified due to small numbers of total accidents. It should alsobe remembered that some schemes will benefit all road users, for example, removing cyclists from a roundabout by the provision of a separate cycle route, will also have the effect of increasing the capacity of the roundabout for the remaining traffic.

3.2 Accident Data Collection and Processing

This element involves : (i) Collection of the accident data by the Police on the Stats 19

form. (ii) Manually checking all of the data but especially the grid

reference. (iii) Adding a kilometrage code or link-node-cell code as an additional

location item. (iv) Inputting the data to computer, including the English language

description (v) Running computer validation checks to detect for any illogical or

suspect coding (e.g. weather : rain, Road Surface : dry) and subsequently correcting data.

(vi) Plotting the accidents on overlay sheets or stxip maps (if manual) or on road maps generated by the computer. This should be done for all accidents and for accidents involving each road user type.

It is particularly important at this early stage of the methodology to ensure the data is as free from error as possible, as the subsequent analysis critically depends on accurate information for confidence in the results and ease of use.

3.3 Data Presentation and Analysis

An overview of the basic accident characteristics is required for all accidents and separately for cycle accidents, by means of cross-tabulations of the relevant Stats 19 parameters. This enables comparisons to be made with national or regional data. Trends and local changes may also be detected.

Useful cross tabulations include :

Accidents by year and severity Accidents by month and year Accidents by day of week and hour of day Accidents by junction control and junction type Accidents by speed limit and carriageway type Accidents by light and road surface Accidents by road surface and weather Accidents by police accident cause (if available) Vehicles by class Casualties by road user class and sex Casualties by road user class and age

13

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Such tabulations may also bring to light errors in the data which have not previously been detected.

3.4 Problem Identification

Lists should be compiled of the worst accident locations of each type of site, i.e. nodes, links, cells and groups of locations suitable for mass action (such as sites with a predominance of skidding or night-time accidents). Separate lists should be compiled for total accidents and for each road user type so that accident problem sites can be identified for each type of road user. As a guideline, sites with a total of 12 or more accidents or 3 or more cycle accidents ~n a 3 year period should be included.

3.5 Initial Ranking

For each type of site, the above lists are then ranked. should be :

The ranking

for nodes by number of accidents for links by accidents per lO0 m of link for cells by accidents per unit of cell size, which could be road

network length and/or number of junctions in the cell.

for mass action sites by number of accidents

3.6 Problem Investigation

From the ranked lists of problem sites, the worst few from each category (numbers depending on resources) need to be investigated. This involves a detailed assessment of all the accidents at each site. The type of accident should be determined from the Stats 19 parameters in conjunction with the English language description, and the accidents plotted on a large scale site plan. Cross-tabulations of important accident characteristics, such as time of day, month, age of casualties, accident severity, etc., can be useful in identifying common factors in the accidents. However, the most useful method for identifying such common factors is a 'stick diagram analysis'. This may be done manually, but is a powerful method when used interactively on a computer.

3.7 Identification of Possible Remedial Measures

Having identified dominant accident types at a site it then remains to design appropriate remedial measures. This involves both studying scale plans and making site visits from which some possible solutions may be readily apparent. If not, however, further investigation of the problem may be necessary. This can be aided by reference to police records but in some cases, especially along links and in cells, it may be difficult to find a single solution. In particular, in the case of links with cycle accident problems, it may be easier and safer to encourage cyclists to use an alternative route.

Cyclists differ from other vehicle users in that in the appropriate circumstances, they can be allowed to use off-road facilities and be diverted from the road system (or part of it) altogether. Ideally a

14

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network of segregated routes could be developed using park land, disused railway lines, canal towpaths, etc., which would leave cyclists only needing to use the all purpose roads for access. More realistically, though, the majority of cycling will remain on the existing roads and so work must continue to develop ways of improving the safety of cyclists on those roads.

One of the problems in recommending cycle accident remedial schemes is the lack of clearly successful examples on which to base designs, as can be seen from the data given in section 2.7. One reason for this, however, is the relatively haphazard way in which such schemes have come about. It is hoped, therefore, that the application of the already successfully established procedures to specific cycle accident problems will redress the balance.

An example of this can be seen at a T-junction in Portsmouth (node 9 discussed in more detail later) where there is a very dominant right turn problem involving cyclists and, therefore, a potentially straight forward solution. This site is very unlikely to have come to light by conventional problem site identification techniques due to the relatively small total number of accidents.

3.8 Accurate Costs and Benefits

For each possible remedial scheme the costs of implementation and the expected reduction in number and severity of accidents should be estimated. The estimated costs of accidents are given in the Department of Transport's Highways Economic Note No. 1 (HEN1). Separate costs for each severity or an average accident cost could be used. The estimated accident savings should take account of the change in level of use likely to occur after implementation of the scheme.

3.9 Priority Ranking with Special Regard to Cyclists

The First Year Rate of Return (FYRR) is calculated as : FYRR = First Year Savings/Implementation Costs

Traditionally, all schemes are considered together and ranked purely in terms of FYRR. It is the priority ranking, however, which dictates the proportion of benefit to each road user group. For a balanced benefit to be afforded to each road user group, therefore, the following procedure should be followed.

(a ) The first list drawnup should include schemes from all the user group lists in order of FYRR

(b) The expected reductions in casualties for each road user group should be calculated. If these are not distributed among the user groups roughly in proportion to the distribution of casualties being experienced by these groups, then the list is

unbalanced and needs to be modified.

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A balanced list may then be achieved in the following way : -

(i) If the best excluded FYRR of a deprived group is close to the worst included FYRR of an over-supplied group, then given the uncertainties of FYRR calculation it may be reasonable to

exchange these two schemes.

(ii) If a selected site provides benefit to an over-supplied group at the expense of a deprived group then this (deprived) group could be compensated by allowing its best excluded FYRR to substitute

for the worst included FYRR of the benefitting group.

(iii) It may be possible to enhance the FYRR of a scheme by taking non-transport benefits into account. For instance, environmental and recreational benefits may be provided by an off-road cycle route. Ideally, the cost of such a scheme would be shared with other local authority budgets. Thus, by reducing the cost to the Accident Investigation and Prevention budget, there is a virtual increase in the FYRR. Where this is not possible, some attempt should be made to assess the additional

benefits which would also increase the FYRR.

If, after such adjustments, the list still remains unbalanced, a different approach may be needed. It may be that the accidents involving the deprived groups are difficult to treat due to their dispersed nature. If this is the case, an area treatment needs to be considered, and since this is likely to exceed the cost of a single scheme, a special budget may have to be approved.

3.10 Implementation and Monitoring

The final stage in the methodology is to monitor schemes once they have been implemented. This is important for two reasons. Firstly, if the scheme does not work from the accident remedial point of view, it is important that this is discovered as soon as possible. Secondly, the advantages and disadvantages of the scheme need to be quantified so that the experience gained can be applied to future schemes. Conflict studies may be used to give an immediate appreciation of the performance of the scheme rather than waiting for accidents to actually occur. However, there may be a tendency for road users to approach any new scheme with caution and, therefore, longer term studies should also be carried out to allow for this settling in period.

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4 PORTSMOUTH ACCIDENT DATA ANALYSIS

4.1 Approach

The accident analysis methodology established above was tested by its application to accident data from Portsmouth for the 3 year period 1984-1986. Portsmouth was chosen as it is local to Southampton University and also has quite a high proportion of travel by bicycle.

The microcomputer accident analysis package (MAAP) developed jointly by T.R.R.L. and the University of Southampton was used in the analysis. This package can sort, plot and cross tabulate accident data by reference to one or more of the Stats 19 parameters. Stick diagram analysis can also be performed.

4.2 Data Collection

The full Stats 19 accident data was obtained from Hampshire County Council on magnetic tape and stored on the University IBM Mainframe Computer. However, the data then had to be modified into a form suitable for down loading in to the MAAP. The main problem here was that the data was held in variable length records which included the English language description. A Fortran program was written to create a file of fixed length Stats 19 parameter records and the data was then successfully input to the MAAP. In addition, a printout was obtained of the records including the English language description. Further amendments were made to the data, these mainly consisted of individual corrections but locations were also entered by coding them according to a Link-Node-Cell system as described in 4.2.2 below.

4.2.1 Data verification

With the exception of one record which was completely corrupted and two or three which had been repeated, the data seemed to be of quite high quality at first glance. It is only when looking closely at individual accidents that inaccuracies become evident. The majority of these were errors in the grid references which is one of the reasons for developing the Link-Node-Cell system. This provides a check on all locational data as well as classifying locations in a useful way.

4.2.2 Link-Node-Cell system

The type of Link-Node-Cell system chosen was as follows : -

(i) Node : defined as the junction of two or more major roads

(ii) Link : defined by the nodes at either end

(iii) Cell : defined as an area bounded by but not crossed by Links

This system allows all accident locations to be uniquely defined as either at a node, on a link or in a cell. The system was developed by initially setting up links and nodes and refining as was necessary until at least 75% of all accidents were accounted for by the links and

nodes. This was done as follows • -

17

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(i) The link-node system was originally set up using just the A and B classified roads. This produced a system involving 45 nodes and

accounted for 60% of a sample of 50 accidents.

(ii) The second level was to include those roads which are coloured yellow on the Ordnance Survey 1:50,000 map; these are local distributor roads in urban areas. This increased the number of nodes to 95 and accounted for 75% of a sample of 50 accidents. Also 74% of a sample of 50 cycle accidents were detected by this

system.

(iii) The grid was further refined by the inclusion of bus routes, junctions with traffic signal control, and roundabouts not

already included. This final version, consists of 143 nodes, including 9 'false nodes' where links go beyond the boundary of the region, and one which was included to divide a particularly long link on a busy main road. The link-node system now

accounts for just over 81% of all accidents and just under 81% of accidents involving cyclists. A plan showing the link-node system is given as Figure 3, the numbering system used being as

follows ' -

A and M roads : - in the range 1 - 99 B roads : - in the range I01 - 199 Other roads • - in the range 201 - 299

As far as was possible, the nodes were numbered sequentially along a route but it is clearly not possible to maintain this over the whole system. As the node numbers are purely arbitrary, it was not considered necessary to spend much time on optimising the numbering

system.

In order to gain an overall view of the accidents not detected by the

link-node system, the remaining accidents were assigned to cells. Only those cells in which an accident had occurred were numbered. This method produced a total of 58 cells which cover the majority of the built-up areas and could, of course, be extended to cover the whole

region. These cells are also shown on the plan and numbered from C1 to C58. The cells vary widely in size and land use to such an extent that comparison should be made with care; nevertheless, the cells are

useful for plotting purposes and have potential in analysis.

Several points arise from the close inspection of the Stats 19 data : -

(i) The location needs to be very carefully recorded - there are many cases where the grid reference and the English language

description of location are incompatible. The English language locations should be precise and identifiable from a map, so descriptions such as 'outside no. 61' or 'by Joe's Garage'

require detailed local knowledge and are not very useful.

(ii) The link-node-cell system took approximately ten man-weeks to

fully define and code the 3000 accidents and a further two weeks to input the codings to the data set but the system definition would normally be only a one-off job and the coding would form

18

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h l i n d

""\.,"PORTSMOL • : .."~<~-~ B O RO, ,

,, .,,'/. -'~, ~ . ~ ; , . .~o~, • " ~. . ~ " - : ._ . . ' ,

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Founlain Lake

~ ~ ~ #~¢,.~,~- "" \ .-'/ -

I \

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FIGURE 3 : PLAN OF LINK-NODE-CELL SYSTEM FOR PORTSMOUTH

19

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part of the ongoing process of checking and recording accidents as they occur. Once set up, the system allows easy analysis of the most important nodes and routes in a network.

(iii) The English language description of an accident gives the most direct information about circumstances surrounding the incident. If this is concisely and accurately phrased, it provides valuable confirmation o~ many of the additional coded details which are used subsequently for numerical analysis such as that performed by the Accident Analysis Package described in more detail below.

( i v ) Some problems do seem to arise from confusion of 'to and from' directions and these might well be eased by the inclusion of a sketch diagram on the Stats 19 form. At sites like roundabouts, there is also the particular confusion of origin and destination with the actual direction of movement at the time of impact.

In summary, it is clear that time spent verifying and cross-checking data at the input stage is an essential element in an effective and efficient accident analysis methodology.

4.3 Overview Analysis and Data Presentation

In order to gain an overview of the accident situation of an area, it is important to look at the overall picture in terms of who is involved (vehicle type, casualty age, male/female, etc.) and where the accidents are happening (area, type of location, etc.). This was done using the MAAP to plot the accidents by grid references and to cross tabulate the data by a selection of the Stats 19 parameters. In this way, regional norms can be established for comparison with data from particular sites which may help in identifying common causes of accidents at black

sites.

4.3.1 Plotting by grid reference

Plots by grid reference using MAAP were produced at increasing scales for both total accidents and cycle accidents. Figure 4 shows a plot of cycle accidents at a scale where it is possible to identify problem links and nodes when the plots are studied in conjunction with a road map. An obvious improvement to the plotting routines would be for the road map to be generated by the system with accidents plotted directly

onto it.

It should be noted, however, that at the larger scales, the grid references may not be accurate enough for use in formal analysis but do, nevertheless, give pointers to problem areas. This is an area which could be greatly improved using more accurate locational data.

4.3.2 Cross-tabulations

The main characteristics of the accidents are shown through cross-tabulations of the Stats 19 parameters, most of the Tables being given in Appendix A. In total there were 3074 reported injury accidents in the 3 years with little difference in the distributions between the years (Table AI). Of these accidents 795 were cycle accidents, being some 26% of all the accidents in Portsmouth (Table A2). This percentage may be compared with statistics for Great Britain, where

20

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Each

Character

Covers an

400 425

0 1 2

1

-25 ........

Area of

i

1

450 475

1 t l

3

1 1 1

1 ! 4 t

............... - .............. 1-

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! 1

1 "50m x 50m" 1 -50 ....... - ...................... 2-2-

1 1

1 1

2 5

I

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-75 ............

500

-25

• -50

-1---2-4 ........... 75

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400 425 450 475 500 i t l !

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

. . . . 50 I I I I I I

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. . . . . . . . .

FIGURE 4 : PLOT OF CYCLE ACCIDENTS IN 1 KM SQUARE OF

SOUTH PORTSMOUTH

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nearly 11% of all accidents are cycle accidents (Road Accidents Great Britain, 1986). Table 7 gives the distribution of casualties by main road user class for all accidents and shows that pedal cyclists were nearly 22% of all reported casualties in Portsmouth.

TABLE 7 : CASUALTIES BY ROAD USER CLASS AND SEVERITY FOR ALL ACCIDENTS

Injury Severity

Road User Class

Pedestrian Pedal Motor Car,Goods Veh Total Cyclist Cyclist PSV User

Fatal 19 3 8 9 39 Serious 187 138 274 174 773 Slight 435 638 760 976 2809

Total 641 779 1042 1159 3621 % 17.7 21.5 28.8 32.0 I00.0

For Great Britain about 10% of all casualties on built-up roads are cyclists while in Hampshire as a whole, cyclist casualties average 13% of all casualties. The high level of cycle accidents in Portsmouth may partly reflect a higher level of cycle use, but is nevertheless of

particular concern.

The distribution of casualties by main road user type, given in Table 7, also forms the desired distribution of expected casualty reductions to achieve a balance of benefit when ranking remedial

schemes, as discussed in section 3.9.

The following characterstics of the cycle accidents were also noted : -

(i) The distribution of cycle accidents by month (Table A3) shows October to have the highest frequency with June and July also at

a high level.

(ii) The distribution by day of week and hour of day (Table A4) shows no real difference between the weekdays, while Saturday and especially Sunday have much lower cycle accident numbers. During the weekdays, there is both a morning and evening peak, but the level and duration is much higher during the evening peak.

(iii) Analysis of cycle accidents by type of junction and control shows that 72% of the cycle accidents occurred at a junction (Table A5). Cycle accidents at T or staggered junctions were 40% of the total, while roundabouts accounted for a further 19%. Only 4% of the cycle accidents occurred at signalled junctions.

(iv) The distribution by speed limit and carriageway type, shows that 90% of the cycle accidents occurred on 30 mile/hr roads and, excluding the roundabout accidents, 78% were on single

carriageway 2-way roads (Table A6).

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(v) Some 18% of the cycle accidents occurred in the dark, with only 7 on unlit roads (Table A7). Nearly 23% occurred on wet, snowy or icy road surfaces, while 19% occurred during inclement

weather (Table A8).

(vi) Cars formed 76% of the non-cycle vehicles involved in the cycle accidents, powered two-wheelers were nearly 7%, the remainder being other motor vehicles (Table A9).

(vii) Cyclists formed nearly 93% of the casualties in the cycle accidents (Table AI0), pedestrians were 2% of the casualties, users of powered two-wheelers were just over 3%, while users of cars and other motor vehicles were only 2% even though such vehicles formed 93% of the non-cycle vehicles involved.

(viii) Of the cyclist casualties, the 16-20 age group had the highest number, with the 11-15 and 21-25 age groups having the next highest levels (Table AI0).

Tables such as those described above provide an essential background to the detailed accident investigation, and permit comparisons with national and county wide data as well as with the small sub-sets

considered in the detailed investigation.

4.4 Problem Identification and Ranking

The identification of the accident locations was carried out using MAAP to produce lists of the links, nodes and cells by number of cycle accidents as shown in Tables 8, 9 and I0 respectively. About 25% of accidents in Portsmouth involve a pedal cycle and for this reason the lower limit used was 3 injury accidents involving cyclists in the three years (generally, 12 accidents, of all types, are required for a s~te to be regarded as a hazardous location). For each site, the total number of all accidents and the proportion involving cyclists was also listed, wh~le for links, the number of accidents per I00 m was

calculated.

It is useful to note that the three tabulations identifying sites with 3 or more cycle accidents in the 3 years include 74% of all the 795 cycle accidents in Portsmouth, whereas only 55% of cycle accidents would be included in similar tables identifying sites with 12 or more

accidents of all types in 3 years.

The links and nodes fulfilling the initial criterion of 3 injury cycle accidents in three years were identified on a monochrome copy of the street plan using a colour code for each accident level. A copy of this is shown as Figure 5, though a monochrome accident level coding is used for ease of reproduction. This presentation proved useful as an 'at a glance' reference but more importantly it showed up the continuity of combinations of links and nodes with high cycle accident frequencies which might otherwise have been overlooked. The links were coded and plotted twice, once in terms of numbers of cycle accidents and once in terms of cycle accidents per I00 m, the latter

providing a more meaningful presentation.

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TABLE 8 : NODES IN PORTSMOUTH WITH 3 OR MORE CYCLE ACCIDENTS IN 3 YEARS (1984-86)

Node Type of Junction Number of Accidents

Involving Total Cyclists

% Involving Cyclists

51 Roundabout 37 Roundabout 1 Roundabout 2 Roundabout

66 Roundabout 36 Roundabout 57 Roundabout 9 T-junction

72 Roundabout 53 Roundabout Ii Roundabout 29 Roundabout 78 Roundabout

106 T-junction 17 Roundabout 30 Roundabout 43 T-junction 45 Roundabout

105 Signalled Cross-roads i0 T-junction 31 Roundabout 48 T-junction 71 Roundabout

104 Signalled Cross-roads 7 Signalled Cross-roads

13 T-junction 26 Cross-roads 55 Roundabout 76 Signalled T-junction 80 T-junction 84 Roundabout

112 Roundabout 230 T-junction 239 Roundabout

19 55 34.5 16 24 66.7 14 57 24.6 13 29 15.4 I0 30 33.3 9 20 45.0 9 25 36.0 7 9 77.8 7 22 31.8 7 20 35.0 6 9 66.7 6 9 66.7 6 23 26.1 6 9 66.7 5 6 83.3 5 16 31.2 5 13 38.5 5 16 31.2 5 7 71.4 4 6 66.7 4 6 66.7 4 6 66.7 4 9 44.4 4 ii 36.4 3 12 25.0 3 16 18.7 3 3 i00.0 3 5 60.0 3 14 21.4 3 8 37.5 3 13 23.1 3 12 25.0 3 8 37.5 3 7 42.9

Total 210 535 39.25

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TABLE. 9.- : LINKS IN PORTSMOUTH WITH IN 3 YEARS (1984-86)

3 OR MORE CYCLE ACCIDENTS

~ink

Number Length(m)

Accidents

Involving Cyclists

No. Per 100m

Total

No. Per 100m

% Involving Cyclists

42.43 634 45.46 724 29.104 670 41.42 290 4.5 905

37.38 996 36.105 724 6.7 616

46.47 887 51.52 905

109.230 724 37.39 489

2.48 1358 56.239 742

108.109 616 229.230 887 11.40 941 73.74 959 57.101 869 37.230 362

218.240 272 220.221 1122 11.12 597 7.45 1068 9.42 996

53.54 507 78.79 2172 7.221 742

10.223 380 106.107 543 109.110 398 205.206 1448 12.13 272 18.19 724 35.36 724 3.47 362

39~40 453 43.51 398 49.51 996 72.76 996 53.112 380 80.219 290

104.105 326 104.237 362 213.217 1249

15 2.4 Ii 1.5 ii 1.6 i0 3.4 9 1.0 9 0.9 9 1.2 8 1.3 8 0.9 8 0.9 8 i.i 7 1.4 7 0.5 7 0.9 7 1.1 7 0.8 5 0.5 5 0.5 5 0.6 5 1.4 5 1.8 5 0.4 4 O.7 4 0.4 4 0.4 4 0.8 4 0.2 4 0.5 4 1.1 4 0.7 4 1.0 4 0.3 3 1.1 3 0.4 3 0.4 3 0.8 3 0.7 3 0.8 3 0.3 3 0.3 3 0.8 3 1.O 3 0.9 3 0.8 3 0.2

43 6.8 41 5.7 25 3.7 19 6.6 21 2.3 29 2.9 15 2.1 25 4.1 41 4.6 30 3.3 18 2.5 25 5.1 24 1.8 18 2.4 20 3.2 14 1.6 16 1.7 17 1.8 26 3.0 I0 2 . 8 15 5.5 ii 1.0 16 2.7 12 1.1 25 2.5 17 3.4 32 1.5 ii 1.5 4 1.1

19 3.5 16 4.0 8 0.6 9 3.3 5 0.7

II 1.5 14 3.9 22 4.9 II 2.8 14 1.4 15 1.5 7 1.8 8 2 . 8 5 1.5 6 1.7

28 2.2

34.9 26.8 44.0 52.6 42.9 31.0 60.0 32.0 19.5 26.7 44.4 28.0 29.2 38.9 35.0 50.0 31.2 29.4 19.2 50.0 33.3 45.5 25.0 33.3 16.0 23.5 12.5 36.4

I00.0 21.i 25.0 50.0 33.3 60.0 27.3 21.4 13.6 27.3 21.4 20.0 42.9 37.5 60.0 50.0 10.7

Total 33074 250 0.75 818 2.47 30.56

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~ , . ~ . C . . 5 i

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FIGURE 5 : PLOT OF THE WORST CYCLE ACCIDENT NODES AND LINKS IN PORTSMOUTH

26

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TABLE I0 : CELLS IN PORTSMOUTH WITH 3 OR MORE CYCLE ACCIDENTS IN 3 YEARS (1984 - 1986)

Cell Number of Accidents % Involving Number Involving Total Cyclists

Cyclists

4 21 42 50.0 19 12 29 41.4 16 9 23 39.1 9 9 29 31.0

13 8 33 24.2 6 7 16 43.7

II 7 17 41.2 23 7 36 19.4 12 6 27 22.2 1 5 14 35.7

15 5 14 35.7 31 5 20 25.0 3 4 12 33.3 5 4 14 28.6

25 4 11 36.4 18 3 25 12.0 26 3 7 42.9 30 3 I0 30.0 34 3 I0 30.0

Total 125 389 32.1

The proportion of accidents involving cyclists also provided a most useful indicator of potentially treatable sites. In one case (Node 9), there were only 9 injury accidents in total and as such, this site would not have been considered in a conventional investigation but with 78% of the accidents involving a cyclist it became one of the priority sites. Further investigation led to the ready identification of a dominant, and potentially treatable, cause.

4.4.1 Sites chosen for further investigation

Apart from the obvious s~tes with the highest number of cycle accidents, other sites were chosen for further investigation according

to one of the following criteria : -

(i) A higher than average proportion of cycle accidents

(ii) A high number of cycle accidents per I00 m for links

4.4.1.1 Nodes

In all, five nodes were chosen. These were the three with the highest number of cycle accidents : nodes 51, 37 and I, (all roundabouts) and two T-junctions with very high proportions of cycle accidents (78% and 67% respectively) : nodes 9 and 106. It is interesting to note that the roundabouts would all have been included in an initial accident site

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list (albeit near the bottom) in a conventional investigation, but neither of the T-junctions (with 9 total accidents each) would have been included in the initial lists and so would have gone undetected.

4.4.1.2 Links

Four links were chosen. These were : -

(i) The link with the highest number of (15) cycle accidents :

Link 42-43

(ii) One of two links with the second highest number of (II) cycle accidents, but with a higher accident frequency per I00 m and also a higher proportion involving cyclists : Link 29-104

(iii) The two other chosen links were 4th and 7th in terms of numbers of cycle accidents but both had quite high numbers per I00 m and also high proportions of cyclists involved : Link 41-42 and

Link 36-105.

4.4.1.3 Cells

The cells vary widely in size and density of road network so it was decided merely to consider the three cells with the highest number of cycle accidents, i.e. Cells 4, 19 and 16. The cells also had a high proportion of cycle accidents. If the cells had been considered in terms of all accidents, they would have ranked Ist, 4th and 8th.

4.5 Site Investigation

Site investigations and subsequent procedures within the methodology were carried out for all the sites given above. For the purposes of this report, however, two sites have been chosen as examples for presentation, though further examples are occasionally shown where they are of particular interest. The example sites are Node 51 and

Link 29-104

4.5.1 Accident sketch plans and dominant accident type

The first process in the site investigation procedure involved reference to the English language description of the accident in conjunction with location and movement parameters. This allows, in most cases, the location to be pinpointed quite precisely, e.g. which arm of a roundabout or at which point along a link, as well as giving an indication of the possible cause (such as 'vehicle turning from

minor road failed to give way').

For each site, all accidents were plotted on a sketch plan and collision diagrams were drawn for those involving cyclists. In some cases, this led to a good understanding of the problem but additional analysis was performed which it was hoped would lead to greater

appreciation of the problems and to remedial solutions.

Figures 6 and 7 show sketch plans of the two example sites with all accidents marked in their approximate positions. The collision diagrams which refer only to the cycle accidents, show the relative movements of the vehicles involved and the number in the top left hand

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~l i ±..

i //.

• ~ ~ . , . ~

Q

J -£

-?

~) Cycle Accidents

X Non Cycle Accidents

FIGURE 6 : SKETCH PLAN OF RUDMORE ROUNDABOUT (NODE 51)

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.I2' '" e l 3

i . I ~ . L I ~ 7.~

v

L~

~O,.o~ ~,o~ o

N

m 4-1 o ~

¢...) u

.~C u

o L~ Z

r.~ ==¢; c/3

o °

r ' ~

r ~

c_3 I , - - I

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- ° _ _ _ •

O

Q &2

Cycle Accidents

Non Cycle Accidents

FIGURE 8 : SKETCH PLAN OF NEW ROAD/COPNOR BRIDGE T-JUNCTION (NODE 9)

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corner of the box indicates the number of occurrences of that type of accident. Figure 8 is included as it shows, very clearly, the

dominant accident type at node 9.

These examples show the variety of results from different types of site. The first, node 51, is a large and busy roundabout at the Portsmouth end of the M275. Whilst the accidents here are quite evenly spread between the five arms of the roundabout (and 2 on the circulating sections) this is typical of the problems faced by cyclists on large roundabouts, with the majority of accidents involving circulating pedal cycles in conflict with entering vehicles.

The second site (link 29 - 104) shows a wide variety of accidents with no particular locations being dominant. The interesting points here are the involvement of parked cars and the fact that the majority of pedal cycles are going ahead on the link rather than trying to cross

it.

The third site (Node 9) shows very clearly the sort of dominant accident type which could reasonably be expected to be treatable, with all but one of the pedal cycle accidents being of a very similar type (i.e. a vehicle turning right from the minor road in collision with a

pedal cycle going ahead on the major road).

4.5.2 Cross-tabulation of factors

To further assist the understanding of the accidents occurring at each site, a number of cross-tabulations of the accident characteristics were made using MAAP. The most useful of these were of cycle

casualties : (i) by age and time of day (ii) by vehicle direction and vehicle manoeuvre.

Examples of both of these tabulations are given for Link 29-104 in Tables II and 12 respectively. Table II clearly shows that 10 of the II cyclist casualties are in the age range 16-30 and, therefore, do not include children, and that the accidents are mainly occurring during the evening peak period or after I0 pm. Table 12 shows 4 of the accidents involve a cyclist overtaking and only 2 a cyclist making a

turning manoeuvre.

Some historical traffic flow data, was extracted from files provided by Portsmouth City Council and whilst counts were not always available at the exact site in question, for most sites it was possible to get a reasonable indication of the level of flows.

4.5.3 Stick diagram analysis

Of much greater help in the detailed understanding and analysis of the accidents at each site was the stick diagram analysis, also performed using MAAP. This analysis takes the form of a 'stick' of up to 15 of the Stats 19 parameters associated with each accident at a site. These 'sticks' can then be re-ordered on the microcomputer to group together accidents with similar characteristics such as night time accidents or accidents involving children on their way to or from school. Within the current MAAP system, the most useful stick included the following :

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TABLE ii : CYCLE CASUALTIES BY AGE AND TIME OF DAY ON LINK 29-104

AGE TWO HOUR PERIOD COMMENCING * 00" 02* 04* 06* 08* i0" 12" 14" 16" 18" 20* 22* *Total*

. . . . . . . . ~ - - - ~ - - - * - _ _ ~ _ _ _ * _ _ _ * _ _ - * - - - ~ - _ - * - _ _ * _ _ _ * _ _ _ * _ _ _ , * . . . . . *

0-5 0 0 0 0 0 0 0 0 0 0 0 0 0 6-10 0 0 0 0 0 0 0 0 0 0 0 0 0

11-15 0 0 0 0 0 0 0 0 0 0 0 0 0 16-20 0 0 0 0 0 0 0 0 2 0 0 2 4 21-25 0 0 0 0 0 0 0 0 2 0 0 1 3 26-30 0 0 0 0 1 0 0 0 2 0 0 0 3 31-35 0 0 0 0 0 0 0 0 0 0 0 0 0 36-40 0 0 0 0 0 0 0 0 0 0 0 1 1 41-45 0 0 0 0 0 0 0 0 0 0 0 0 0 46-50 0 0 0 0 0 0 0 0 0 0 0 0 0 51-55 0 0 0 0 0 0 0 0 0 0 0 0 0 56-60 0 0 0 0 0 0 0 0 0 0 0 0 0 61-65 0 0 0 0 0 0 0 0 0 0 0 0 0 66-70 0 0 0 0 0 0 0 0 0 0 0 0 0 71-75 0 0 0 0 0 0 0 0 0 0. 0 0 0 >75 0 0 0 "0 0 0 0 0 0 0 0 0 0

. . . . . . . . ~ - - - * - - - ~ - - - ~ _ _ _ * _ _ _ ~ _ _ _ * _ _ _ ~ _ _ _ ~ _ _ _ * _ _ _ * _ _ _ * _ _ _ * * . . . . . *

Total 0 0 0 0 1 0 0 0 6 0 0 4 ii

........ *---*---~---*___*___*___*___-~_--*__-*---~__-*---*--* ..... ~'~

TABLE .12 : CYCLE CASUALTIES BY CYCLE MANOEUVRE AND DIRECTION ON LINK 29-104

VEHICL VEHICLE DIRECTION MANVR *W E *E W *W N *N S * total* . . . . . • . . . . . ~ . . . . . * . . . . . * . . . . . * . . . . . . *

Rever 0 0 0 0 * 0* Park 0 0 0 0 * 0* WaitA 0 0 0 0 * 0* Stop 0 0 0 0 * 0* Start 0 0 0 0 * 0* UTurn 0 0 0 0 * 0* Left 0 0 1 0 * i* WaitL 0 0 0 0 * 0* Right 0 0 0 0 * 0* WaitR 0 0 0 1 * I* LaneL 0 0 0 0 * 0* LaneR 0 0 0 0 * 0* O/T 1 1 0 0 0 * i* O/T 2 2 1 0 0 * 3* O/T 3 0 0 0 0 * 0* BendL 0 0 0 0 * 0* BendR 0 0 0 0 * 0* Ahead 4 1 0 0 * 5*

Total 7 2 1 1 * ii* #o .,o .,. .,o * . . . . . . *

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reference number year month day of week hour of day darkness weather : rain/fog or not road surface : wet/icy or not severity : fatal, serious, slight vehicle turning right or waiting to vehicle turning left or wa~ting to breath test positive or refused school pupil on way to or from school pedal cycle involved parked vehicle involved

The MAAP was developed for use in general accident investigation work in developing countries and consequently had limitations when used for the investigation of accidents to a particular user group. The problem lay in associating particular manoeuvres and directions with particular vehicles in a stick, thus, although a stick could contain an item indicating that a right turning vehicle was involved, it could not show which vehicle. Ideally the following information would be included

in place of some of the above items : -

movement of pedal cycle movement of other vehicle direction of pedal cycle direction of other vehicle type of other vehicle age of pedal cyclist casualty

The first four of these would, in combination, form the conflict type while the last two would provide particularly relevant additional

information.

The provision of such enhancements to the MAAP system is now in hand and the revised version is expected to be available in the near future.

As examples, stick diagram analyses are shown for Link 29-104 in Table 13 and for Node 9 in Table 14. These stick diagrams include all accidents at the site. Table 13 clearly shows that 7 of the II pedal cycle accidents on Link 29-104 involve a parked vehicle, while at Node 9 a right turn is involved in 5 of the 7 cycle accidents.

4.5.4 Site inspections

Visits were made to all the chosen sites. This achieved the dual purpose of ensuring that the problem had been clearly understood from the sketch diagrams and plans, as well as allowing consideration of possible remedial solutions. One characteristic of sites which may not be readily apparent from sketches or scale plans is the gradient. Portsmouth is generally very flat but at two of the sites, gradients (due to railway bridges) seemed to be influential factors in the

dominant accident types.

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TABLE 13 • STICK DIAGRAM ANALYSIS FOR LINK 29-104

STICK:231 10: i : 3 I 25: 2 1 : 7 I 2 2 : 2 : 15: 11: 19: 20: 14 :161 131 18 :241

REF 335:032 085 111 368 191:333:217:095:307:108:137:1651298:363:145 118:364: YY 86 85 84 84 86 86 1 8 4 : 8 6 ' ' ,8 . : 8 5 : 8 5 : 8 6 86 8 5 : 8 5 : 8 5 8 6 : 8 6 MM ZZ O2 O3 O4 12 O 7 : 1 1 : 0 8 : 0 4 : 1 0 : 0 5 : 0 5 O6 I 0 : 1 2 : 0 6 O4 : IZ DoW 4 6 4 4 7 5 : i : i : 5 : 2 : i : 2 4 6 : 6 : 5 4 : 3 KH 6 7 I0 12 12 115 118 118 119 119 121 122 22 5 I 9 117 22 122

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

*N* I*N*I*N* '*N*I I '*N*IeN*I *N* *N*I *N* WET :WET:WET WET IWET: ' ' I l

RSF :RSF:RSF RSF :RSFI ' ' l I

SEV : 3 : 2 2 2 3 2 3 : 3 : 3 3 3 : 2 : 3 2 3 2 3 3 l , , => =>

=> I=> ', => I=> , , , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

<= <= <= <= <= ' I

B-T SCH l

P/C P/C P/CIP/CIP/C P P , , , I

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

STICK:4 ', 1 7 : 5 : 8 ', 9 : 6 : 1 2 : 0 ', 0 I 0 I 0 ', 0 : 0 I 0 : 0 : 0 : 0 ', 0

120:079 84:86 04:03 4',5

16 116

1931370 84:84 06 ii 2 5

17 17

REF YY MM DoW HH

5601207 84 84 12 07 5 6

17 22

139 85 06 5

23

*N* ' ' '*N* *N* *N* ', *N* , I

WET ' ' WET a WET I I

RSF ' ' RSF ', RSF l l

SEV 3 1 3 1 3 3 3 3 1 3 => ,' ,i ,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

< = 1 !

B-T SCH I

e/c IP/C',P/C',P/C',P/C P/C',P/C P/C', p ',p ',P ',P ~, P P ', P ',P , l I

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

REF=REF NO. HB=HOUR SEV=SEVERITY SCH=TO/FRO SCH

YY=YEAR *N*=DARKNESS =>=RIGHT TURN P/C=PEDAL CYCLE

MM=MONTH WET=RAIN/FOG <==LEFT TURN P=PARKED

DoW=DAY OF WEEK RSF=WET/ICY B-T=DRUNK

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TABLE 14 : STICK DIAGRAM ANALYSIS FOR NODE 9

STICK:8 ', 5 I 4 : 3 I 6 ', 1 1 2 I 7 I 9 I 0 ', 0 I 0 I 0 I 0 I 0 I 0 ] 0 I 0 '! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

REF :1391283 YY 186 185 MM I03 I05 DoW : 7 I 1 ~m I 4 116

164',5431319'1026 85 84 185 184 O3 O9:05 I01 2 51611 8 17 ',10 112

1421395 3541 84 85 86 03 06 06 7 7 5

12 14 18

*N* ',*N* ', WET ',WET', RSF ', RSF ', SEV ', 3 ', 3 => , ,, =>

i

I I I I

',WET ', ', RSF ',

3 ~ ', 3 ', 3 ,,=> I=>

I I

',WET ', RSF',

3 3 ' , 2 => => ', =>

< =

B-T SCH P/C

i t !

i I I

I I I !

SCH i

P/C P/C',P/C',P/C',P/C P/C',P/C

I , ! . . . . . . . . . . . . . . . . . . . . . . . . .~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

REF=REF NO. HH=HOUR SEV=SEVERITY SCH=TO/FRO SCH

YY=YEAR *N*=DARKNESS =>=RIGHT TURN P/C=PEDAL CYCLE

MM=MONTH WET=RAIN/FOG <==LEFT TURN

DoW=DAY OF WEEK RSF=WET/ICY B-T=DRUNK

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4.6 Remedial Measures

4.6.1 Identification of possible schemes

Having identified the dominant accident types and common factors of accidents at a site, an experienced engineer should be able to design remedial treatments which will either resolve or reduce the problem. Of course, it is important that no further problems are created, so consideration of the implications to ALL road users should be afforded to any scheme. Improvements can take the form of altering the site to make hazardous manoeuvres less risky, banning those movements or, in the case of cyclists removing the vulnerable users from the site by

the provision of a suitable alternative route.

If at this stage, no suitable remedial treatment can be designed, it may be necessary to perform a further or more detailed investigation using conflict studies and/or reference to police records. The whole procedure of site investigation and choice of remedial measure should

be regarded as iterative.

By way of example, the choice of remedial measures for the three sites previously considered is discussed in the following sections.

4.6.2 Node 51

As yet, there is no successful treatment of this type of roundabout problem, Clearly the conflicting movements cannot be banned nor can the volume or speed of the traffic be significantly reduced as the roundabout is already used to capacity at peak hours. There does exist, however, a comprehensive network of pedestrian subways with ramped approaches which could quite easily be converted to shared use. These subways are already illegally used by a large proportion of cyclists and there is no evidence of conflict between pedestrians and cyclists. Experience elsewhere suggests that pedestrian safety can be maintained using segregation by a white line and installing barriers at potential conflict points to slow cyclists down to a safe speed.

4.6.3 Link 29 - 104

The accident locations are spread along the length of the link. Some interesting points arise from the cross tabulations and the stick diagram analysis. Firstly, the predominant influence of parked cars; the link is partly residential but mainly commercial with shops, restaurants and other commercial premises. This makes it unlikely for parking to be banned (even on one side) to allow room for cYCle lanes to be installed. Such a measure would be unenforceable anyway in such circumstances. Also, despite relatively wide footways, shared use of these would be unsuitable due to the large number of pedestrians going

in and out of shops.

The other points of interest are 'age' and 'time of day'. The majority of accidents involve people aged 16 - 25 and all but one occurred in the evening peak period or between I0 and 12 at night. The Polytechnic (and the Students' Union) lie to the west of this link and the majority of student accommodation is to the east. These factors, in combination, suggest that the accidents may involve students returning from either lectures or evening social activities, who would

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travel the whole length of the link. These are the type of cyclists most amenable to using a suitable alternative route and this is the recommendation made. The proposed alternative route uses quiet residential roads parallel to and north of the link. Two special features would be required; namely, use of a short section of pedestrianised street and a section of contra-flow cycle lane on an adjacent one way street though it would also be appropriate to investigate reversion to 2-way flow here. The proposed route and the link itself are inter-connected at several points which would allow cyclists to use the new route as far as required before returning to

the link for access to the shops as necessary.

4.6.4 Node 9

Although node 9 is not one of the examples for which details of treatment and cost have been calculated, it is possible to see potentially simple solutions. There is quite a lot of space to redesign the layout of the junction, or the right turns from the minor arm could be banned with traffic being directed to an alternative,

nearby junction.

4.7 Costs, Benefits and First Year Rate of Return

The costs, benefits and hence, the First Year Rate of Return (FYRR), have been roughly calculated for Node 51 and Link 29-104 and are shown in Tables 15 and 16 respectively. The estimated costs shown were

provided by Portsmouth City Council.

In the calculation of the FYRR, an accident saving of 50% was used fo~ each site. The likely change in the level of use was taken into account in the estimation of the accident savings. More properly this could be assessed from a survey of those cyclists and other road users

presently using the s~tes.

The FYRR was calculated in two ways, f~rstly using accident costs bv severity and secondly using average accident costs. For both sites, the second method gave much higher rates of return, because of the high proportion of slight accidents with associated low accident costs in the first method. The lower FYRR using the accident costs by severity are felt to provide a more realistic value in these cases, but would clearly be highly sensitive if fatal accidents with very high costs

were involved.

A FYRR of 50% was commonly required for remedial schemes to be acceptable. To approximately achieve such a return using the more conservative severity cost calculation, a saving of 2 accidents would be required at each of the sites considered.

In practice, the FYRR would be calculated for all feasible schemes and those sites with the highest FYRR from each road user group providing a proportional balance of road user casualty savings would be selected for implementation, following the procedure outlined in section 3.9.

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TABLE 15 : CALCULATION OF ESTIMATED COSTS, BENEFITS AND FIRST YEAR RATE

OF RETURN FOR NODE 51

(a) Implementation Costs

Proposed remedial measures : -

To allow shared use of the existing pedestrian subways

Traffic regulation order Dropped kerbs (6) Illuminated signs (4) Barriers (4 pairs) White lines

Approximate costs

£500 £2,400-£3,000

£1,440 £1,200

£150

Total £5,690-£6,290

(b) using accident cost by severity

Potential accident savings and first year rate of return (FYRR)

Accidents in 3 years (1984-1986)

Accidents Number Cost (£) Potential Accident Potential Reduction Saving (£)

Slight 16 26,976 8 13,488 Serious 3 54,546 1½ 27,273 Fatal 0 0 0 0

40,761

.. First year saving = £13,587

.. FYRR = 13,587/6,000 = 226%

(c) Potential accident savings and FYRR using average accident costs

Accidents in 3 years (1984-1986)

Number Cost (£) Potential Accident Reduction

Potential Saving (£)

19 217,512 9~ 108,756

.. First year saving = £36,252

.. FYRR = 36,252/6,000 = 604%

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TABLE 16 : CALCULATION OF ESTIMATED COSTS, BENEFITS AND FIRST YEAR RATE OF RETURN FOR LINK 29-104

(a) Implementation costs

Proposed remedial measures : -

To signpost an alternative backstreet route avoiding Elm Grove and Kings Road. This involves allowing cyclists to use a pedestrianised area and the provision of a short section of contra flow cycle lane.

Approximate Costs

Traffic regulation order Dropped kerb (2) Lit bollards (2) Ducting (for the above) Illuminated signs (3) Direction signs (6) Road markings

£500 £800-£1 ,O00

£200 £300-£1,000

£I ,080 £300 £300

Total £3,480-£4,380

(b) Potential accident savings and first year rate of return (FYRR) using accident costs by severity

Accidents in 3 years (1984-1986)

Accidents Number Cost (£) Potential Accident Reduction

Potential

Saving (£)

Slight ~0 16,860 5 8.430 Serious 1 18,182 ~ 9,091 Fatal 0 0 0 0

17,521

First year saving = £5,840 FYRR = 5,840/4,000 = 146% °°°

(c)

Accidents in 3 years (1984-1986)

Number Cost (£)

Potential accident savings and FYRR using average accident costs

Potential Accident Reduction

Potential Saving (£)

II 125,928 5~ 62,964

.. First year saving = £20,988

.. FYRR = 20,988/4,000 = 524%

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5 SUMMARY AND CONCLUSIONS

This report describes an investigation of cycle accident analysis and remedial measures. The objectives of the study were : to conduct a review of five local authorities so as to establish methods of accident analysis and selection of remedial measures; to collect information on cycle schemes implemented; and to develop and test a methodology for the analysis of cycle accidents and the application of remedial

measures.

A comprehensive review of the literature concerning accident analysis and the provision of cycle facilities was made and is published as a separate document. The best features of the accident analysis methodologies from this review and from the findings gathered from the five local authorities were used to develop a methodology for the analysis of cycle accidents and the application of remedial measures. This methodology was then tested and further developed by its application to accident data for Portsmouth for the three year period

1984-1986.

The main findings of the study are given in two parts : firstly relating to the information from the selected counties and secondly concerning the analysis methodology and its application to the

Portsmouth data.

A INFORMATION FROM SELECTED COUNTIES

The County Councils are generally in the early stages of considering cycle accident problems separately from those of other road users, though there is a largely common policy that cyclists should be specifically considered in the planning of new highway

schemes (Section 2.2).

Spec~a] budgets for cycle accident remedial measures 2.3).

schemes and particularly for cycle are rare and generally Small (Section

The findings from the literature review and the selected counties showed that the established methodologies hardly address tile problems of accidents involving vulnerable road users in general or

cyclists in particular (Section 1.4).

4 At local authority level, little is done in the way of monitoring

of accident remedial schemes (Section 2.6).

5 An analysis by road user typ e of casualties at all accident remedial sites was carried out for three counties. For two of the counties pedal cyclists and other vulnerable road users (pedestrians and motor cyclists) formed much lower proportions of the casualties than was found in each county as a whole. For the third county, with a high level of cycle use, cyclists formed a markedly larger proportion of the casualties at the remedial sites than in the county as a whole, but only a marginal reduction in cycle casualties had been achieved, illustrating the difficulties

in tackling cycle accident problems (Section 2.6).

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6

8

B

9

I0

II

12

13

14

15

16

Many of the cycle schemes so far implemented have originated from a common sense approach or in response to public pressure rather than as accident remedial measures (Section 2.8).

There is very little evidence at present of the effectiveness of cycle facilities in reducing accidents because it is very difficult to determine due to small numbers of accidents, lack of formal monitoring and the difficulty in identifying the area of influence of a scheme (Sections 1.4 and 2.7).

The few cycle accident remedial schemes with before and after data do not show great savings in the numbers of accidents, but the data is very limited. Further research is required to establish more clearly the performance in terms of accident savings and level of use of such schemes (Section 2.8).

ACCIDENT ANALYSIS METHODOLOGY

The main features of the methodology established are that cyclists and other main user groups are considered separately and that the proposed remedial measures should achieve a balance of benefit in proportion to the number of casualties of each main road user group (Section 3.1).

Raw Stats 19 data is liable to a high degree of error so manual checking and validation by computer is an essential prerequisite to any meaningful analysis (Sections 2.4, 3.2 and 4.2).

The plotting of accident data by computer on a computer generated road network provides an excellent means of identifying accident problems and displaying information (Sections 2.4 and 4.3.1).

The use of a link-node-cell system of coding accident location can provide a useful cross check of the grid reference and enable ready identification and analysis of accident problem locations (Sections 2.4 and 4.3.1).

In the analysis of the Portsmouth accident data, just over 81% of all accidents and just under 81% of cycle accidents were located on the links and nodes of the simple link-node-cell system developed (Section 4.2.2).

The lists identifying sites with 3 or more cycle accidents in 3 years included 74% of all cycle accidents in Portsmouth. A high proportion of accidents involving cyclists provided a most useful indicator of potentially treatable sites (Section 4.4).

The plotting of the worst accident nodes and links on an outline street plan using a colour code for each accident level, showed up the continuity of combinations of links and nodes with high cycle accident frequencies which might otherwise have been overlooked (Section 4.4).

The most useful method for identifying common factors at accident problem sites is the stick diagram analysis. This is a particularly powerful method when carried out interactively on a computer (Sections 3.6 and 4.5.3).

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17

18

In calculating the first year rate of return (FYRR) on proposed schemes use of accident cost by severity is highly sensitive to the inclusion of fatal accidents with very high associated costs (Section 4.7).

The methodology was successful in clearly identifying the worst accident locations for cyclists in Portsmouth and establishing the dominant accident types and feasible remedial measures (Section 4).

ACF~OWLEDGMENTS

The work described in this report forms part of the research programme of the Cycling Section of the Transport Planning Division of the Transport and Road Research Laboratory and this report is published by permission of the Director. The research was carried out under contract by the Transportation Research Group, Department of Civil Engineering, University of Southampton (Director Dr. M. McDonald).

The authors would like to thank the many officers of the Local Authorities for their valued cooperation and supply of information for the study and the Hampshire Constabulary and Hampshire County Council for the supply of the Stats 19 accident data for Portsmouth. They are also particularly indebted to Mr. Peter Rix and Mr. Brian Lyus of the Department of Transport for their valued guidance, discussion and support throughout the course of the work and to Mr. Geoffrey Hebditch of Portsmouth City Council and Mr. Peter Bayliss of Hampshire County Council for their help during the latter stages.

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REFERENCES

DEPARTMENT OF TRANSPORT, ROAD SAFETY DIRECTORATE, (1974), Accident Investigation and Prevention Manual

DEPARTMENT OF TRANSPORT, (1986 - updated annually), Highways Economic Note No. 1

DEPARTMENT OF TRANSPORT, (1986), Accident Investigation Manual

DEPARTMENT OF TRANSPORT, SCOTTISH DEVELOPMENT DEPARTMENT AND WELSH OFFICE, (1986a), Transport Statistics G.B. 1975-1985, H.M.S.O.

DEPARTMENT OF TRANSPORT, SCOTTISH DEVELOPMENT DEPARTMENT AND WELSH OFFICE, (1986b), Road Accidents Great Britain 1985, H.M.S.O.

DOWNING, C.S., (1985), Pedal Cycling Accidents in Great Britain, Paper to 'Ways to Safer Cycling' Conference, Department of Transport

HARRISON, J.H., HALL, R.D. and HARLAND, D.G., (1989), Literature Review of Accident Analysis Methodologies and Cycle Facilities, Department of Transport, TRRL Contractor's Report, Transport and Road Research Laboratory, Crowthorne.

HEPWORTH, J,, McDONALD, M. and HALL, R.D., (1984), Accidents to Cyclists, Report to Science and Engineering Research Council, Transportation Research Group, University of Southampton

LAYFIELD, R. and MAYCOCK, G., (1986), Pedal Cyclists at Roundabouts, Traffic Engineering and Control, June 1986

PEDDER, J.B., HAGUES, S.B., MACKAY, G.M. and ROBERTS, B.J., (1981), A Study of Two-wheeled Casualties at a City Hospital, Proceedings of 6th International Conference, IRCOBI, Gothenburg, Swede,s, September 1979

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APPENDIX A : TABULATIONS OF PORTSMOUTH ACCIDENT DATA

TABLE AI : ALL ACCIDENTS BY SEVERITY AND YEAR

YEAR ACCIDENT SEVERITY *Fatal*Serio*Sligt *-- ~ --*---

1984 18 241 765 1985 Ii 238 800 1986 I0 232 759

* . . . . . * . . . . . * . . . . .

Total 39 711 2324 * ..... * ..... * .....

* Total*

* 1024" * 1049" * 1001"

* 3074*

TABLE A2 : CYCLE ACCIDENTS BY SEVERITY AND YEAR

YEAR ACCIDENT SEVERITY *Fatal*Serio*Sligt * Total*

..... . ..... . ..... , ..... , ...... ,

1984 0 51 231 * 282* 1985 3 51 227 * 281" 1986 0 48 184 * 232*

Total 3 150 642 * 795* * ..... '°___ - -* ..... * ...... *

TABLE A3 : CYCLE ACCIDENTS BY YEAR AND MONTH

MONTH YEAR "1984 "1985 "1986

Jan

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Total

* T o t a l * % * . . . . . * . . . . . * . . . . . * . . . . . . * . . . . . . .

26 ii 21 * 58* 7.3 17 14 13 * 44* 5.5 29 27 13 * 69* 8.7 18 15 26 * 59* 7.4 16 32 24 * 72* 9.1 32 29 16 * 77* 9.7 23 29 25 * 77* 9.7 25 19 14 * 58* 7.3 24 27 18 * 69* 8.7 30 31 24 * 85* 10.7 25 27 20 * 72* 9.1 17 20 18 * 55* 6.9

282 281 232 * 795* * . . . . . * - -,. , . . . . . . *

i00.0

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TABLE A4 : CYCLE ACCIDENTS BY DAY OF WEEK AND HOUR OF DAY

HOUR DAY OF WEEK * Sun *Mon * Tue * Wed * Thu * Fri * Sat

. . . . . ~ . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . .

0 1 i 0 0 1 0 1 0 0 0 0 0 0 2 0 0 0 0 0 0 3 0 0 0 0 0 0 4 0 0 0 0 0 0 5 0 0 1 0 0 0 6 0 3 0 2 0 2 7 1 lO II 17 12 9 8 i ii 14 8 20 15 9 4 7 13 5 6 Ii

I0 1 4 3 5 7 4 ii 8 6 2 2 6 7 12 3 5 7 6 8 ii 13 3 5 ii 8 6 4 14 8 8 7 1 3 3 15 6 6 9 I0 ii 14 16 3 26 12 17 18 6 17 3 22 16 14 22 20 18 1 7 i0 13 18 5 19 2 7 7 4 4 7 20 1 4 3 6 2 3 21 3 6 2 3 5 3 22 0 0 2 2 3 2 23 0 1 2 2 2 0

..... * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . .

Total 49 139 132 125 154 126 70 ..... * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . .

% 6.2 17.5 16.6 15.7 19.4 15.8 8.8 . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * . . . . .

* Total*

2 * 5* i * i* 0 * 0* 0 * 0* 0 * 0* 0 * i* 0 * 7* 1 * 61" 3 * 72* 6 * 52* 6 * 30* 6 * 37* 7 * 47* 3 * 40* 8 * 38* 7 * 63* 6 * 88* 5 * 102" 4 * 58* 2 * 33* 0 * 19" 1 * 23* 1 * I0" i * 8*

* . . . . . . *

* 795* * . . . . . . *

I00.0

%

0.6 0.1

0 . i 0 .9 7.7 9.1 6 .5 3.8 4.7 5 .9 5 .0 4 .8 7.9

11.0 12.8 7.3 4.2 2.4 2.9 1.3 1.0

i00.0

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TABLE A5 : CYCLE ACCIDENTS BY JUNCTION CONTROL AND TYPE

JUNC JUNCTION CONTROL TYPE *Not-J*AuthP*Signl*Stop *GveWy*Unctl * Total* ..... , ..... , ..... , ..... , ..... , ..... , ..... , ...... ,

Not-J 220 0 0 0 0 0 * 220* Round 0 0 0 1 130 15 * 146" MiniR 0 0 0 0 3 0 * 3* T/Stg 0 0 15 2 227 72 * 316" Y/Jun 0 0 0 0 6 5 * Ii* SlipR 0 0 0 0 2 4 * 6* Cross 0 2 13 0 25 i0 * 50* Multi 0 0 0 0 8 0 * 8* Entrc 0 0 i 0 1 3 * 5* Other 0 0 1 I i0 18 * 30* . . . . . . . . . . . . 4' . . . . . . • - _* . . . . . * . . . . . * . . . . . *_ ~ * . . . . . *

Total 220 2 30 4 412 127 * 795* . . . . . 4, _ - - - ~ , . . . . . . , . . . . . • . . . . . * . . . . .,. _ - - -*- - - ~ _-' . . . . .

% 27.6 0.3 3.8 0.5 51.8 16.0 i00.0 . . . . . -~ .,. _ - -* . . . . . * . . . . . *- . . . . * . . . . . * . . . . . . *

%

27.6 18.4 0.4

39.7 1.4 0.8 6.3 1.0 0.6 3.8

i00.0

TABLE A6 : CYCLE ACCIDENTS BY SPEED LIMIT AND CARRIAGEWAY TYPE

C'WAY TYPE *30 *40 *50 . . . . . * . . . . . * - - - . . . . . .

Round 102 17 0 1-Way 20 1 0 DC 2 24 i0 0 DC 3+ Ii 6 0 SC 1 15 0 0 SC 2 506 5 0 SC 3 8 0 0 SC 4+ 18 5 Q UnKwn 12 1 0

Total

%

SPEED LIMIT *60 *70 k Total* %

. . . . * . . . . . * . . . . . . * . . . . . . .

i0 9 * 138" 17.4 0 0 * 21" 2.6 2 3 * 39* 4.9 0 5 * 22* 2.8 0 0 * 15" 1.9 3 0 * 514" 64.7 0 0 * 8* 1.0 2 0 * 25* 3.1 0 0 * 13" 1.6

* . . . . . . * . . . . . . .

* 795* I00.0 * . . . . . . * . . . . . . .

I00.0 * . . . . . . *

* . . . . . * . . . . . * . . . . . * . . . . . * . . . . .

716 45 0 17 17 * . . . . . * . . . . . * . . . . . * . . . . . * . . . . .

90.1 5.7 - 2.1 2.1 , . . . . . * . . . . . -~ . . . . . * . . . . . * . . . . .

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TABLE A7 : CYCLE ACCIDENTS BY LIGHT AND ROAD SURFACE

CONDITION

LIGHT ROAD SURFACE

-*Dry *Wet *Snow *Ice *Flood * Total * ............ , ..... , ..... , ..... , ..... , ..... , , ....... ,

Day 530 115 2 3 0 650

Night Lit 74 45 2 1 0 122

Night Unlit 6 1 0 0 0 7

Night Unknown 6 i0 0 0 0 16 ............ , ...... , ..... , ..... , ..... , ..... , , ...... ,

Total 616 171 4 4 0 795 . . . . . . . . . . . . ~ . . . . . . * . . . . . * . . . . . * . . . . . * . . . . . * * . . . . . . *

% 77.5 21.5 0.5 0.5 0 i00.0 . . . . . . . . . . . . -~ . . . . . . * . . . . . * . . . . . * . . . . . * . . . . . *- - -* . . . . . . *

%

81.8

15.3

0.9

2.0

i00.0

TABLE A8 : CYCLE ACCIDENTS BY ROAD SURFACE AND

WEATHER CONDITIONS

WEATH

Fine

Rain

Snow

F+Wnd

R+Wnd

S+Wnd

Fog

Other

UnKwn

Total

%

ROAD SURFACE

*Dry *Wet *Snow *Ice *Flood * ..... * . . . . . * ..... * . . . . . ~ . . . . .

583 34 0 3 0

1 95 0 0 0

0 2 4 0 0

23 2 0 0 0

0 13 0 0 0

0 0 0 0 0

3 0 0 0 0

5 24 0 1 0

1 1 0 0 0 * ..... * . . . . . * . . . . . * . . . . . * . . . . .

616 171 4 4 0 * ..... * . . . . . * . . . . . * . . . . . * . . . . .

77.5 21.5 0.5 0.5 0 * ..... * ..... * . . . . . * . . . . . * . . . . .

* Total* * . . . . . . *

* 620*

* 96*

* 6*

* 25*

* 13"

* 0*

* 3*

* 30*

* 2* * . . . . . . *

* 795* * . . . . . . *

i00.0 * . . . . . . *

%

78.0

12.0

1.0

3.1

1.6

0.4

3.8

0.2

i00.0

b

9 ¸

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TABLE A9 : VEHICLES INVOLVED IN CYCLE ACCIDENTS BY ACCIDENT SEVERITY AND CLASS

VEHICL ACCIDENT SEVERITY

CLASS *Fatal*Serio*Sligt * Total * % • . . . . . * . . . . . . _ . _ _ _ * . . . . . . . * . . . . .

Cycle 3 153 660 * 816 * 52.2 Moped 0 4 7 * i i * 0.7

Scoot 0 0 0 * 0 * - M/Cyc i 12 26 * 39 * 2.5

Combo 0 0 0 * 0 * - InvTr 0 0 0 * 0 * - 3WCar 0 2 2 * 4 * 0.3 Taxi 0 4 14 * 18 * I. I Car i i00 468 * 569 * 36.4

M/Bus 0 0 7 * 7 n 0.4

PSV 0 2 18 * 20 * I. 3 LGV 0 15 38 * 53 * 3.4 HGV 1 5 17 * 23 * 1.5

OthM 0 1 2 * 3 * 0.2 OthNM 0 0 0 * 0 * - . . . . . • . . . . . * . . . . . * . . . . . * . . . . . . . * . . . . . .

Total 6 298 1259 * 1563 * I00.0 . . . . . • . . . . . n . . . . . * - - - - - . . . . . . . . n . . . . . .

TABLE AI0 : CASUALTIES IN CYCLE ACCIDENTS BY USER CLASS

AND AGE

AGE CLASS OF ROAD USER *Ped'n*Cycle*Moped*M/Cyc* Car *Other* Total %

..... n ..... n ..... n ..... n ..... , ..... * ..... n ..... n ......

0-5 2 4 0 0 2 0 n 8 i .0

6-10 4 29 0 0 0 0* 33 3.9 11-15 3 160 0 0 0 0* 163 19.4 16-20 0 184 5 8 i 0* 198 23.5 21-25 0 115 0 7 2 0* 124 14.7 26-30 0 62 0 3 2 0* 67 8.0 31-35 0 38 0 0 0 0* 38 4.5 36-40 I 44 0 2 0 0 n 47 5.6 41-45 0 29 0 1 0 0* 30 3.6 46-50 1 25 0 0 0 0* 26 3.1 51-55 0 28 0 0 1 0* 29 3.4 56-60 i 17 0 i 0 2* 21 2.5 61-65 0 14 0 0 0 0* 14 1.7 66-70 1 13 1 0 2 I* 18 2.1 71-75 1 8 0 0 3 0* 12 1.4 >75 3 9 0 0 0 i* 13 1.5

. . . . . , . . . . . . . . . . . , . . . . . , . . . . . * . . . . . * . . . . . * . . . . . n . . . . . .

Total 17 779 6 22 13 4* 841 I00.0 . . . . . ,_ - . . . . . _ _ _ _~ . . . . . * . . . . . * . . . . . * . . . . . n . . . . . .

49