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M4 Corridor around Newport Stage 1 Road Safety Audit – M4 Reclassification – Response Report

Welsh Government

M4 Corridor around Newport

Stage 1 Road Safety Audit - M4 Reclassification – Response Report

M4CaN-DJV-GEN-ZX_GEN-RP-CH-0001

P02 | 23 November 2016

This report takes into account the particular

instructions and requirements of our client.

It is not intended for and should not be relied

upon by any third party and no responsibility

is undertaken to any third party.

Job number 242707

CVJV/AAR

3rd

Floor

Longross Court,

47 Newport Road,

Cardiff

CF24 0AD

Welsh Government M4 Corridor around Newport


Issue Document Verification with Document �

Contents

Page

Authorisation Sheet 1

1 The Project 2

2 Scope of this Report 4

3 Key Personnel 6

4 Issues Raised by this Stage 1 Road Safety Audit 7

Appendices

Appendix A

Drawings and Documents Provided

Appendix B

Location of Problems



M4CaN-DJV-GEN-ZX_GEN-RP-CH-0001 | P02 | 23 November 2016

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1 The Project

1.1 Context

1.1.1 The Welsh Government has awarded a Professional Services Contract for the

next stage of Scheme development and environmental surveys for the M4

Corridor around Newport (M4CAN) up to publication of draft Orders and an

Environmental Statement. The contract has been awarded to a Joint Venture of

Costain, Vinci and Taylor Woodrow with consultants Arup and Atkins, supported

by sub-consultant RPS. The team shall be developing proposals in anticipation

of publishing draft Orders and an Environmental Statement in Spring 2016 and a

Public Local Inquiry later that year. This process will then inform the next stage of

Ministerial decision making.

1.1.2 Since 1989 there have been various studies to identify the problems and propose

possible solutions. The M4 Corridor around Newport WelTAG Stage 1 (Strategy

Level) Appraisal concluded that a new section of 3-lane motorway to the south of

Newport following a protected (TR111) route, in addition to complementary

measures, would best achieve the goals and address the problems of the M4

Corridor around Newport and should be progressed for further appraisal. These

options have subsequently formed the basis for the development of the draft

Plan, which was published in September 2013 and was the subject of public

consultation from September to December 2013.

1.1.3 Having taken into account the responses to this participation process, as well as

the assessments of the draft Plan, the Welsh Government has decided to publish

a Plan for the M4 Corridor around Newport. Alongside this Plan, the Welsh

Government has published updated strategy-level reports, including a Strategic

Environmental Assessment Statement, to demonstrate how the participation

process has informed its decision making. It also announced in July 2014 a

revised preferred route, which will protect a corridor for planning purposes.

These documents can be accessed from the website http://m4newport.com.

1.2 Scheme objectives and reason for the scheme

1.2.1 The aims of the Welsh Government for the M4 Corridor around Newport are to:

a) Make it easier and safer for people to access their homes, workplaces and

services by walking, cycling, public transport or road.

b) Deliver a more efficient and sustainable transport network supporting and

encouraging long-term prosperity in the region, across Wales, and enabling

access to international markets.

c) To produce positive effects overall on people and the environment, making a

positive contribution to the over-arching Welsh Government goals to reduce

greenhouse gas emissions and to making Wales more resilient to the effects

of climate change.

1.2.2 The Scheme aims to help to achieve or facilitate these aims as part of a wider

transport strategy for South East Wales, as outlined within the Prioritised National

Transport Plan.





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1.2.3 The Transport Planning Objectives (TPOs), or goals, are:

TPO 1: Safer, easier and more reliable travel east-west in South Wales.

TPO 2: Improved transport connections within Wales and to England, the Republic of Ireland and the rest of Europe on all modes on the international transport network.

TPO 3: More effective and integrated use of alternatives to the M4, including other parts of the transport network and other modes of transport for local and strategic journeys around Newport.

TPO 4: Best possible use of the existing M4, local road network and other transport networks.

TPO 5: More reliable journey times along the M4 Corridor.

TPO 6: Increased level of choice for all people making journeys within the transport Corridor by all modes between Magor and Castleton, commensurate with demand for alternatives.

TPO 7: Improved safety on the M4 Corridor between Magor and Castleton.

TPO 8: Improved air quality in areas next to the M4 around Newport.

TPO 9: Reduced disturbance to people from high noise levels, from all transport modes and traffic within the M4 Corridor.

TPO 10: Reduced greenhouse gas emissions per vehicle and/or person kilometre.

TPO 11: Improved travel experience into South Wales along the M4 Corridor.

TPO 12: An M4 attractive for strategic journeys that discourages local traffic use.

TPO 13: Improved traffic management in and around Newport on the M4 Corridor.

TPO 14: Easier access to local key services and residential and commercial centres.

TPO 15: A cultural shift in travel behaviour towards more sustainable choices.

1.2.4 The scheme-specific environmental objectives (EO), as set out in the Strategic

Environmental Assessment of the Plan, are as follows:

EO1 - Improved air quality in areas next to the existing M4 around Newport;

EO2a - Reduce greenhouse gas emissions per vehicle and/or person kilometre;

EO2b - Ensure that effective adaptation measures to climate change are in place;

EO3 - Reduce disturbance to people from high noise levels, from all transport modes and traffic within the existing M4 Corridor;





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EO4 - Ensure that biodiversity is protected, valued and enhanced;

EO5 - Improved access to all services and facilities and reduce severance;

EO6 - Protect and promote everyone’s physical and mental wellbeing and safety;

EO7 - Reduce transport related contamination and safeguard soil function, quality and quantity;

EO8 - Minimise transport related effects on surface and groundwater quality, flood plains and areas of flood risk;

EO9 - Ensure the prudent and sustainable use of natural resources and energy;

EO10 - Ensure that diversity, local distinctiveness and cultural heritage are valued, protected, celebrated and enhanced;

EO11 - Ensure that landscape and townscape is properly valued, conserved and enhanced;

1.2.5 In addition, the Wales Transport Strategy includes the following environmental

outcomes (WTSEO):

Outcome 11: The sustainability of the transport infrastructure - Increase the use of more sustainable materials in our country’s transport assets and infrastructure;

Outcome 12: Greenhouse gas emissions - Reduce the impact of transport on greenhouse gas emissions;

Outcome 13: Adapting to climate change - Adapt to the impacts of climate change;

Outcome 14: Air pollution and other harmful emissions - Reduce the contribution of transport to air pollution and other harmful emissions;

Outcome 15: The local environment - Improve the positive impact of transport on the local environment;

Outcome 16: Our heritage - Improve the effect of transport on our heritage;

Outcome 17: Biodiversity - Improve the impact of transport on biodiversity.

2 Scope of this Report

2.1.1 This Road Safety Audit Response Report relates to the Stage 1 Road Safety

Audit Report (document reference: 8002-845-001D Rev1) for the reclassified

section of the M4 as part of the M4 Corridor around Newport Scheme.

2.1.2 The Design Team have carefully considered the problems and recommendations

in the Stage 1 Road Safety Audit Report. This Road Safety Audit Response

Report includes all of the problems and recommendations raised by the Road

Safety Audit Team, as well as the Design Team’s response to these issues.





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2.2 Scope of the Stage 1 Road Safety Audit

2.2.1 Atkins Arup Joint Venture (AAJV) was commissioned by the Joint Venture of

Costain, Vinci and Taylor Woodrow on behalf of the client, Welsh Government, to

undertake a Stage 1 Road Safety Audit (RSA) on the proposed reclassified

section of the existing M4 motorway. The proposals involve the provision of a

new section of motorway and reclassification of the existing M4 motorway.

Works associated with the proposed new M4 motorway are considered in a

separate RSA.

2.2.2 The RSA comprised a desktop review of the information provided in:

• the RSA Brief (dated March 2016);

• a subsequent email providing the Departures from Standard report on 14th

June 2016; and

2.2.3 A site visit was carried out during daylight hours on Wednesday 18th May 2016.

During the site visit the weather was dry and bright.

2.2.4 The RSA has been conducted with reference to the procedures and scope set

out in the Welsh Government’s ‘Design Manual for Roads and Bridges’ (DMRB),

Volume 5, Section 2, Part 2, ‘Road Safety Audit’ Standard HD 19/15. The RSA

Team has examined and reported only on the road safety implications of the

measures as proposed, and has not specifically examined or verified the

compliance of the design to any other criteria.

2.2.5 Details of the information forming the RSA Brief, received from Ian Wilson of

Arcadis on behalf of the Design Organisation and approved by the Project

Sponsor, Martin Bates of Welsh Government, are included in Appendix A.

Problems and recommendation locations are indicated on the plan of the scheme

included in Appendix B.

2.3 Report Structure

2.3.1 Following this introduction, the report is structured as follows:

• Chapter 3 provides information on the Key Personnel from the Overseeing

Organisation, the Road Safety Audit Team and the Design Organisation.

• Chapter 4 details the issues raised by the Stage 1 RSA and the Design Team

Responses.





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3 Key Personnel

3.1 Project Sponsor – Welsh Government

3.1.1 Martin Bates Project Director Welsh Government

3.1.2 Matthew Jones Project Engineer Welsh Government

3.2 Road Safety Audit Team

3.2.1 Rob Hunt CEng MICE MCIHT MSc (Eng) BEng (Hons)

Team Leader Managing Consultant Atkins

3.2.2 Fraser Arnot MCIHT CMILT BSc (Hons)

Team Member Principal Consultant Atkins

3.2.3 Stuart Kay IEng FCIHT FSoRSA Team Member Group Engineer Atkins

3.2.4 Tansin Brown IEng AMICE AMCIHT Team Member Senior Engineer Arup

3.2.5 Fraser Arnot, Rob Hunt and Stuart Kay all hold a Highways England-approved

Certificate of Competency in Road Safety Auditing gained via the TMS

Consultancy course route.

3.3 Design Organisation – Arup Atkins Joint Venture

3.3.1 Ben Sibert CEng FICE MIStructE MCIHT BEng

Design Project Manager Arup

3.3.2 Simon Westwood CEng MICE MSc MEarthSc (Oxon) Highway Design Leader Arup

3.3.3 Andrew Jones CEng MICE MIHT BEng Highway Design Leader Arup





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4 Issues Raised by this Stage 1 Road Safety Audit

4.1.1 This section details the issues raised by this Stage 1 RSA; the issues have been

presented by geographical location (from west to east) within each issue

category, with issues relevant to all locations presented separately.

4.2 General

Problem 1

Location: Throughout the scheme.

Summary: Introduction of all vehicle types leading to conflicts between

user types.

4.2.1 The reclassification of the existing M4 alignment will enable use of the

reclassified road by vehicles that are currently prohibited under motorway

regulations. This would include cyclists between Junctions 23A and 24. Given the

limited changes proposed to the physical environment, driver behaviour may not

change significantly (particularly amongst regular users) thus resulting in speed

differential conflicts with slower-moving vehicles such as agricultural and

construction vehicles. This could result in a variety of collision types throughout

the section of reclassified road.

Recommendation

4.2.2 Whilst it is acknowledged that the decision to reclassify the M4 and A48(M) is a

strategic decision it is considered that the road safety implications of the

proposed changes are relatively unknown given the lack of comparable schemes

in the UK. Therefore it is recommended that a Safety Risk Assessment in

accordance with GD 04/12 (Volume 0 of the Design Manual for Roads and

Bridges) is undertaken to fully inform the decision. This should take account of

the impact upon the affected populations (as defined in GD 04/12) and any

mitigation measures deemed appropriate to ensure the safety risk is at an

acceptable level.

Design Team Response

4.2.3 Agreed – The GD 04/12 (Volume 0 of the Design Manual for Roads and Bridges)

Safety Risk Assessment will be undertaken to fully inform the decision to remove

the prohibitions associated with the motorway classification of the existing road.

To date this assessment has been completed for Non-Motorised User classes.

Problem 2


Summary: Signal control following re-classification.

4.2.4 Although the existing M4 is not classified as a Smart Motorway, it does contain

elements of technology ‘control’ in the form of MIDAS, Variable Speed Limit

(VSL) via advanced motorway indicators (AMIs), MS4s and associated gantries.

It is generally recognised that gantries and signing are unequally spaced, which

anecdotally suggests a low level of compliance with the VSL on certain sections.





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This is potentially connected with the large number of nose-to-tail collisions into

stationary traffic throughout the length of the scheme.

4.2.5 Retention of the existing infrastructure and signalling on the reclassified M4 may

lead to AMIs being positioned over redundant carriageway giving the user the

impression that the existing lane allocation has not changed. This may lead to

inadvertent lane changes followed by sudden manoeuvres back into the correct

lanes, increasing the risk of side-swipe type collisions.

4.2.6 This issue is evident currently on the Junction 26 eastbound merge where a

signal has been placed over the existing merge, giving the impression that it is

Lane 1 and therefore a lane gain. This may lead to side-swipe collisions as a

result of poor lane discipline and lack of user guidance.

4.2.7 In addition to this, the composition of traffic permitted on an all-purpose trunk

road will be different to that permitted under motorway regulations. As such,

slower moving vehicles (agricultural, construction or low cc powered two

wheelers) may result in longer queues, stationary traffic and the intervention of

the VSL via MIDAS. Users may not anticipate this and it could lead to nose-to-

tail collisions into stationary or slowing vehicles.

Recommendation:

4.2.8 A comprehensive ITS strategy should be developed to review the

appropriateness of all existing technology, gantries and associated infrastructure

for operation and management on the reclassified M4.


4.2.9 Agreed – A comprehensive ITS strategy has been developed in conjunction with

Welsh Government’s network operator and is currently the subject of review.

Problem 3


Summary: Unauthorised use of hatched area or carriageway to the rear of

the proposed hard strip.

4.2.10 There are some sections of the proposed reclassified M4 to the rear of the

proposed nearside hard strip that will have an unknown status.

4.2.11 Where such a large area is proposed:

• this could encourage injudicious comfort breaks and stops on what will

effectively be a high speed road with a proposed rural clearway order

introduced. This could result in stationary vehicles being hit by other vehicles

or the area to the rear of the proposed hard strip being obstructed during an

emergency;

• additionally, the area to the rear of the proposed hard strip could be used

during times of congestion by those wishing to undertake stationary or slow-

moving traffic (particularly at merges and diverges) which could result in

multiple vehicle collisions;





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• closure of the nearside carriageway area for maintenance activities (sign

replacement and vegetation clearance etc.) could become more hazardous

for operatives;

• signs located to the nearside of the carriageway could become less effective

as the distance between Lane 1 and the signs will increase; and

• existing lighting may be adversely affected if the carriageway is lit from the

nearside only and not amended to take account of the proposed alignment.

To the knowledge of the Audit Team, the degree of separation between live traffic and traffic

signs/street lighting proposed in this scheme has never been used before over

such a length. With a higher proportion of large vehicles in the space currently

occupied by Lane 2, users in the space occupied by Lane 3 may find the signs

and lighting to be less effective, potentially being blocked by the closer, larger

vehicles. A large area of lit but unused carriageway raises concerns for

distraction and also potential misuse of the non-trafficked area.

Recommendation

4.2.12 A consistent approach to the carriageway status and appearance to the rear of

the proposed hard strip should be taken throughout the scheme such that it does

not alternate between different levels of provision. This could include hatching of

all areas to the rear of the proposed hard strip and associated measures to

discourage the use of the area of carriageway to the rear of the hard strip.

4.2.13 Additionally, a review of existing signs and lighting (most significantly their

distance from the nearside traffic lane) should be undertaken which could help

inform a decision on hard shoulder provision.


4.2.14 Agreed – The designer notes that this comment only applies to discrete lengths

of the reclassified M4; from J23a to J24 and through J28 in both directions, and

Westbound between J24 and J25. Through these areas, the hatched area of the

reclassified M4 to the rear of the proposed hard strip will be reviewed at Detailed

Design to provide a consistent hard shoulder width. A review of the existing signs

and lighting will be undertaken at detailed design.

Problem 4


Summary: Inconsistency between slip road layouts.

4.2.15 The current grade separated layouts between Junctions 29 and 23 are

inconsistent, with a mix of tapers, auxiliary lanes and lane gain/drop. The

proposed scheme would not alleviate any of the existing inconsistency and could

largely make it worse by removing some of the consistency between successive

junctions and introducing a wider variety of vehicle types on an all-purpose road.

4.2.16 To illustrate the problem, the eastbound mainline/junctions would be, in order:

• 3-lane dual carriageway

Lane drop at ghost island diverge






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Lane gain at taper merge


Parallel diverge


Parallel merge


Lane drop at taper


Taper merge


Taper diverge


Lane gain at ghost island merge


Lane drop at ghost island diverge


Taper merge


Taper diverge

This would represent 4 types of diverge, 4 types of merge and 5 changes of

number lanes.

4.2.17 Inconsistency at a series of junctions leads to user confusion and late and/or

unnecessary lane changes. Users intending to continue on the mainline may find

themselves needing to change lanes at the last minute if they are travelling in a

nearside lane that diverges away from the mainline. Similarly, users may be

reluctant to use the nearside lane if they expect a lane drop where the slip road is

actually a taper, leading to users in the nearside lane undertaking those in the

offside lane.

4.2.18 Late lane-changing and undertaking can lead to side-swipe and loss-of-control

collisions.

Recommendation

4.2.19 The proposed junction layouts should be reviewed to provide greater consistency

wherever possible.


4.2.20 Agreed – The merge and diverge layout types have been designed in

accordance with the DMRB and have been derived from TD22/06 Design of





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Grade Separated Junctions (with Departures from Standards) and based upon

the Design Year (2037) Traffic Forecast. Proposed layouts provide highest

possible capacity for a junction within the available road space and minimise the

risk of queuing or stationary traffic on the main carriageway.

4.2.21 Implementation of alternative layouts from those proposed would reduce the

capacity on the finished road layout. As a result, the risk of shunt and side swipe

type collisions on the mainline and vehicle queuing on connector road and

consequently on junctions gyratory would significantly increase. The layouts

proposed are consistent with those provided on the wider road network and the

most appropriate layout to fit within the land constraints whilst providing for the

design traffic flows.

Problem 5


Summary: Possibility of existing road restraint system becoming less

effective.

4.2.22 The proposed replacement of the existing Lane 1 and hard shoulder (on existing

D3M sections) with a hard strip and hatched area (proposed D3AP) is likely to

mean that an errant vehicle could strike the nearside road restraint systems

(RRS) at a more direct (head-on) angle given the increase in distance between

the proposed Lane 1 and the RRS. This could lead to the RRS not working in the

way it was originally intended in the event of a collision (especially where these

are designed to flex and provide a less severe stopping motion for vehicles).

4.2.23 Whilst a vehicle can strike the nearside barriers from the existing Lanes 2 and 3

in the event of a loss of control collision, it is considered that the removal of lane

one and increased hatched area would represent a material increase in the

frequency of more direct vehicle strikes of the RRS. This could result in an overall

increase in the severity of injuries to vehicle occupants.

Recommendation

4.2.24 The RRS should be reviewed in accordance with RRRAP procedures to

determine the most appropriate solution along the proposed route. Measures to

reduce the likelihood of vehicles striking the RRS at a more direct angle than

originally intended should be progressed as part of the overall scheme design.


4.2.25 Agreed – The designer notes that this problem only applies to a discrete length of

the reclassified M4; between J23a and J24 and through J28 in both directions

and westbound between J24 and J25. In these lengths the existing RRS will be

reviewed in accordance with TD19/06 using RRRAP as appropriate.

4.3 The Junctions

Problem 6

Location: Junction 27 eastbound and westbound diverges and merges.

Summary: Changes to the layout may be ignored by users.





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4.3.1 The existing parallel merge and diverge layouts are proposed to be modified

‘existing parallel merge/diverge layout to be modified’. Details of the modifications

or (reasoning for them) are not provided on the drawings at this stage of design

development. There is a concern that some regular users may continue to use

the carriageway as they currently do and this could lead to variations in the way

the slip road is used. This could result in collisions between vehicles on the slip

roads or with vehicles on the main carriageway.

Recommendation

4.3.2 As the design is progressed the layouts of the slip roads should either be

retained as existing or designed to avoid mis-use of the carriageway.


4.3.3 Agreed – The layouts of the slip roads have been designed to minimise the risk of

mis-use of the carriageway. Detailed design will consider (via risk assessment)

whether further specific design measures are required to further reduce the risk

of mis-use of the carriageway.

Problem 7

Location: Junction 26 eastbound diverge.

Summary: Slip road layout amendments may lead to new conflicts.

4.3.4 The proposed change to the layout would increase the length of the two-lane

section of diverge and this would appear to involve shortening of the

chevron/nose and replacement of continuous longitudinal lines with intermittent

lines. Extensive observation of the existing use of the junction over many years

indicates late lane changing from the mainline to the diverge occurs frequently.

The proposed layout may increase the levels of late lane changing from the main

carriageway to the slip road with subsequent side-swipe or nose-to-tail collisions.

This problem is supported by the existing collision history at this location which

consists of nose-to-tail collisions.

Recommendation

4.3.5 The layout should incorporate measures to discourage mis-use such as late lane-

changing. These could include continuous longitudinal lines and a longer nose.


4.3.6 Agreed – Measures to discourage late lane changing, such as lining, enhanced

signing or other physical measures will be appraised and included as appropriate

at detailed design.

4.3.7 The designer notes that this comment relates to observation of the performance

of the existing road layout which includes a longer nose and continuous

longitudinal lines. The observed behaviours that underlie this comment relate to

driver frustration resulting from queuing on this slip road back along the

motorway. The designer considers that the behaviours described by the auditor

are best managed by measures aimed at reducing slip road queues, which are

beyond the scope of this scheme.

Problem 8





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Location: Junction 26 westbound diverge.

Summary: Potential increase in conflicts between exiting and mainline

traffic.

4.3.8 The proposed change from a parallel diverge to a taper diverge would be

expected to guide diverging users to leave the carriageway further downstream

over a shorter length. The width of the taper may also prevent exiting vehicles

fully leaving the mainline until they are close to the diverge nose. These issues

raise concerns for potential conflicts between exiting and mainline vehicles

resulting in nose-to-tail collisions.

Recommendation

4.3.9 The proposed diverge layout should allow exiting vehicles to leave the mainline in

an expedient manner with a smooth transition from the mainline.


4.3.10 Agree – The proposed taper diverge layout meets the requirements set out by the

auditor. The designer notes that the taper diverge layout meets the requirements

for a diverge taper at the proposed 60mph speed limit for this section of the

reclassified road, and that a parallel diverge would fall below the required

standard for this type of road layout.

Problem 9

Location: Junction 26 eastbound merge.

Summary: Proposed changes could lead to higher differential speeds.

4.3.11 The proposal would replace the existing parallel merge with a taper merge. The

slip road has a steep uphill gradient and a short merge length prior to the tunnel

portal. Any reduction in slip road ‘space’ may result in slower slip road users

merging suddenly with faster mainline traffic and this could lead to side-swipe or

nose-to-tail collisions. Alternatively familiar users may choose to use the slip road

carriageway as per the current layout which would be unexpected for main

carriageway users. This in turn could also lead to side-swipe or nose-to-tail

collisions.

Recommendation

4.3.12 The existing merge layout should be retained. If changes are to be made these

should maximise the available space for joining traffic to reach similar speeds as

mainline traffic whilst acknowledging the hazard of the tunnel portal downstream

of the merge.


4.3.13 Agree – The proposed taper merge layout is designed to fully meet the required

standard for a taper merge and the design is cognisant of the issues explained by

the auditor. The designer notes that a parallel merge layout (as existing) would

fall significantly short of the required standard for that type of merge, and would

allow very limited space for drivers to abort a merging manoeuvre into the area

downstream of the merge. In the case of the proposed taper merge, the area

downstream of the merge (into which a driver may abort a merging manoeuvre) is

significantly increased in size. The designer believes that the proposed taper





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merge layout minimises the likelihood of drivers colliding with the tunnel portal in

the event of an aborted merge.

Problem 10

Location: Brynglas Tunnels/proposed Junction 25A eastbound diverge.

Summary: Lack of carriageway in advance of the eastbound diverge.

4.3.14 Traffic heading eastbound through the Brynglas Tunnels are banned from

changing lanes in the tunnel by means of a continuous white centre line. Upon

exiting the tunnel, there will be a relatively short section of carriageway before the

proposed eastbound diverge to the local road network at Junction 25A. Drivers in

Lane 2 through the tunnel may therefore have limited time to move across to

Lane 1 and use the diverge facility. This could result in nose-to-tail or side-swipe

collisions immediately downstream of the eastbound tunnel.

Recommendation

4.3.15 Advanced lane destination signing should be provided west of the Brynglas

Tunnels to encourage eastbound drivers into the correct lane for the diverge

when they exit the tunnel.


4.3.16 Agreed – The use of advanced lane destination signing would be included at

detailed design.

Problem 11

Location: Junction 25 and 25A.

Summary: Large number of Departures from Standard over a relatively

short distance.

4.3.17 The proposed introduction of west facing slip roads (merge and diverge) has

resulted in the creation of 9No. Departures from Standard (DfS). Individually, the

DfS contain both risks and mitigation measures as well as an acknowledgement

of adjacent DfS. However, cumulatively the risks and mitigation measures do not

appear compatible and may lead to inappropriate stop/start or lane change

manoeuvres resulting in an increased occurrence of side-swipe or nose-to-tail

collisions.

4.3.18 The collisions analysis report revealed an unusually high number of single vehicle

loss-of-control collisions involving westbound M4 mainline traffic passing though

Junction 25. The introduction of west-facing slip roads at Junction 25 and the

removal of east-facing slip roads at Junction 25A may not alleviate the apparent

indecision by users, potentially increasing the risk of sharp changes of direction

or sudden manoeuvres and subsequent side-swipes and nose-to-tail collisions.

Recommendation:

4.3.19 An assessment of the cumulative impact of all of the DfSs relating to the

proposed merge and diverge should be undertaken and appropriate mitigation

measures designed to reflect a holistic approach to the surrounding highway

network.






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4.3.20 Agreed – a holistic appraisal of the Departures from Standards in conjunction

with the merge and diverge has been undertaken with a view to identifying a

suitable mitigation strategy. The Departures from Standards have been submitted

to the Overseeing Organisation, and are currently in the process of being agreed.

A significant component of this mitigation strategy is the introduction of a fixed

60mph speed limit over this length of carriageway. The designer notes that the

standard of provision made is much nearer the required standard for a 60mph

dual carriageway, but that the departures from standards are (necessarily)

measured against an unrestricted speed of 70mph.

Problem 12


Summary: Loss of control due to sudden change in direction.

4.3.21 The proposed diverge alignment appears to have a nose ratio of about 1:8. This

leads to a sudden change of direction for traffic exiting the mainline, with traffic

swerving to the left on the slip road before merging into a right-hand bend on the

link road. Users would not be able to adequately see the road layout ahead.

4.3.22 Eastbound traffic diverging from the motorway at Junction 25 may not appreciate

the sudden changes in direction of the layout ahead, leading to vehicular loss of

control.

Recommendation

4.3.23 The alignment should be amended as far as possible within the existing

constraints so the changes in direction are less severe.


4.3.24 Agreed – Amendments to the alignment will be appraised at detailed design

stage, taking into account the constraints upon design. The designer notes that

the current constraints to the alignment, such as the gantry, may require

relocation/redesign in conjunction with any alignment changes.

Problem 13

Location: Junction 25.

Summary: Proposed westbound on-slip.

4.3.25 The proposed westbound on-slip at Junction 25 will enable westbound travel

along the reclassified road from the nearby Junction 25, where there is currently

a westbound off-slip to areas such as Cwmbran via the A4042 at Junction 25.

During peak periods, the existing M4 experiences significant congestion around

Junction 25. Should the reclassified road experience similar levels of congestion,

some users may mis-use the westbound on-slip in order to escape congestion at

Brynglas Tunnels. This could result in vehicles travelling the wrong way (or in

reverse gear) along the westbound on-slip (where this would not be subject to

motorway regulations) in order to access the link to the A4042. This could result

in nose-to-tail or head-on collisions.

Recommendation





Page 16

4.3.26 The design of the on-slip should include physical measures to discourage mis-

use of the on-slip. This could be achieved through the physical alignment and

associated signing.


4.3.27 The designer notes that the likelihood of queuing described by the auditor is

highly unlikely, particularly at the location described by the auditor. The existing

queuing described by the auditor is largely consequential to the existing traffic

flows along the westbound carriageway, and the lane drop junction arrangement

at Junction 25A. The forecast traffic flows are significantly lower than at present,

and the lane drop arrangement at J25/25A has been removed, by the removal of

lane 1 from J23A to J25 westbound.

4.3.28 Notwithstanding the above, the designer agrees with the auditor’s

recommendation to include measures to discourage mis-use of the on-slip at

detailed design. The designer notes that the existing diverge would be broken out

and kerbed.

Problem 14

Location: Junction 25 eastbound merge.

Summary: Potential for swooping across the ‘tiger tails’/ghost island.

4.3.29 The proposed lane gain at ghost island merge layout incorporates intermittent

longitudinal lines and this raises the concern that some faster-moving merging

users may choose to cut across the hatched areas to pass slower merging or

mainline vehicles such as goods vehicles. This raises concerns for conflicts

between these two types of user such as side-swipe collisions.

Recommendation

4.3.30 The design of the proposed layout should be developed to discourage mis-use,

which may include the use of continuous longitudinal lines on the ghost island

and other complementary measures.


4.3.31 Agreed – The use of continuous lines would be used for use on ghost islands at

detailed design.

Problem 15

Location: Junction 25 westbound diverge.

Summary: Loss of control due to sudden change in direction.

4.3.32 The proposed diverge alignment appears to have a nose ratio of about 1:8. This

would lead to a sudden change of direction for traffic, with traffic swerving to the

left on the slip road. Westbound diverging traffic would be at risk of losing control

on the slip road, with inadequate road space to take corrective actions. This could

result in either single vehicle collisions on the slip road or side- swipe collisions

with mainline vehicles.

Recommendation





Page 17

4.3.33 The alignment should be amended as far as possible within the existing

constraints so the changes in direction are less severe. It appears from the

drawings that there is scope for improvement to the proposed layout.


4.3.34 Agreed – The provision of a less severe diverge nose would be considered at

detailed design.

Problem 16


Summary: Late lane-changing on slip road.

4.3.35 The proposed layout is likely to encourage faster users to access the slip road

from the downstream taper and enter Lane 2 of the slip road. Extensive

observation of the existing use of the junction over many years indicates late lane

changing from the mainline to the diverge occurs frequently. Many of these users

would then wish to access Lane 1 of the slip road to join the A449 and this may

result in sudden lane changes close to the start of the segregated lane. This

could then result in side-swipe or nose-to-tail collisions.

Recommendation

4.3.36 As the design is progressed the layout of the slip road and the segregated lane

should be developed to minimise the potential for late lane-changing

manoeuvres.


4.3.37 Agreed – The risk highlighted above would be considered in the development of

the detailed design of this junction layout.

Problem 17

Summary: Ghost island merge into congested traffic during busy periods.

Location: Junction 24 westbound merge.

4.3.38 A ghost island merge layout is proposed westbound. The brief states that no

layout in this location would be compliant with standards and that the proposed

Type H requires a Departure from Standard. Traffic on the slip road would arrive

in platoons from the signal control at J24 and the forecast traffic flows show that

the mainline could be congested downstream. The slip road itself could also be

congested. Slow-moving or stationary traffic on the mainline would shorten gaps

for merging traffic, which could be particularly problematic for traffic in the

nearside lane of the slip road.

4.3.39 Congestion and limited gaps for merging traffic could lead to side-swipe collisions

as traffic tries to merge from the slip road. Nose-to-tail collisions could occur if

merging traffic fails to appreciate the slow speeds on the mainline. Congestion on

the slip road could lead to aggressive users trying to join the mainline at the tip of

the nose and needing to brake suddenly because the mainline speeds are slower

than expected.

Recommendation





Page 18

4.3.40 The number of mainline carriageway lanes downstream of the merge is fixed by a

strategic decision. Therefore it is recommended that measures to reduce the

levels (or control the movements) of joining traffic are investigated. Such

measures may include variable speed limits, strategic route signing and ramp

metering although the range of options is likely to be much wider.


4.3.41 The designer notes that the auditor refers to the possibility of congestion on the

mainline downstream of this junction. The traffic forecasting report indicates that

the probability of congestion is low, therefore the likelihood of the problems raised

by the auditor occurring is low, particularly taking into account the inclusion of a

continuous hard shoulder alongside the carriageway, which should improve the

overall performance of the road.

4.3.42 Agree – The designer notes that this slip road currently forms part of the strategic

route linking Swansea and Cardiff with the Midlands and Northern England. In the

opening year, the A465 would have become the strategic route for traffic bound

for Swansea and West Wales, and Junction 24 would remain part of the strategic

route for Cardiff traffic. Consequently measures to reduce the levels of joining

traffic are not realistic or feasible. Control of movements of joining traffic will be

effected through the retention of the Variable Speed Limit system, as shown in

the current design. The designer notes that ramp metering is not currently

permitted in Wales.

4.4 Non-Motorised Users

Problem 18

Location: Between Junctions 23A Magor and J24 Coldra.

Summary: Proposed cycle route.

4.4.1 The proposed scheme includes provision for cycling between Junctions 23A and

24 in both directions. It is not clear at this stage what form this provision will take,

but it is considered that the following issues are of relevance:

• The existing physical D3M layout is proposed to be reclassified (to D2AP)

and therefore the cycle route would, presumably, need to use the area of

carriageway to the rear of the proposed nearside hard strip, the hard strip

itself or the proposed mainline carriageway. It is likely that drivers will

continue to view the road as motorway standard and behave the same way

i.e. not expect cyclists to be present. Therefore, should cyclists be allowed to

use the carriageway at this point, they could be struck by errant vehicles

resulting in a fatality. Additionally, HGVs in Lane 1 would need to overtake

cyclists which may result in side-swipe collisions with other vehicles.

• It was noted during the site visit that some of the existing parapet heights

appeared to be too low to facilitate safe adjacent cycle use, potentially

increasing the risk of cyclists falling over the parapet resulting in fatal injuries.

• If the provision for cyclists is segregated from the mainline then this would

limit the number of areas for vehicles to pull over away from the mainline

carriageway in the event of a breakdown or emergency. This could result in

stationary vehicles in Lane 1 which may then be struck by other vehicles





Page 19

causing injuries to occupants. This could also result in vehicles stopping in a

cycle facility which could force cyclists in to Lane 1, where they would be at

an increased risk of being struck by vehicles.

• At Junction 23A, cyclists would need to negotiate the motorway junction

roundabout to access Magor which could put them at conflict with fast-moving

traffic on the eastbound off- slip (if they are not segregated from traffic).

Additionally, the existing Magor service area is located immediately adjacent

to the roundabout and thus attracts HGV traffic.

Recommendation

4.4.2 The prohibition of NMUs along the reclassified road should be extended to

include the section between Junctions 23A and 24.

4.4.3 If a cycle route along the existing M4 alignment is to be provided, then it should

be fully segregated from mainline traffic, using physical measures, to provide

protection from errant vehicles (and the parking of broken down vehicles) due to

the high speed nature of the existing (and proposed) road. Additionally, the

emerging design should consider the tie-in points at Junctions 23A and 24 to

ensure a segregated facility can be provided throughout and in both directions. A

review of existing parapet heights should also be undertaken to ensure that the

minimum appropriate height is achievable.


4.4.4 Agreed – The prohibition of cyclists along the reclassified road would be

extended to include the section between Junctions 23A and 24.

4.5 Traffic Signs, Road Markings and Street Lighting

Problem 19

Location: Local road (and connecting trunk road) approaches to the M4.

Summary: Inappropriate routeing of traffic and user indecision/hesitation.

4.5.1 The proposals do not include any measures to amend traffic signs on the local

road approaches to the reclassified M4 or elsewhere on the local road network.

This raises concerns for traffic either taking inappropriate routes to the new M4 or

becoming confused by the inconsistent signing and making unexpected

manoeuvres. This could bring them into conflict with other road users.

4.5.2 Southbound users on the A449 approaching the reclassified M4 at Junction 24

could travel in either direction to access the M4 to the west of Newport. Unclear

signing, or signing that does not seem the most attractive route, could lead to

sudden lane changes on the approach to or at Junction 24. This could lead to

loss-of-control or side-swipe collisions.

Recommendation

4.5.3 As the design is developed a strategy for routeing traffic on the local roads should

be developed. This should incorporate changes to the direction signs on the local

road network to ensure they are consistent with the reclassified M4 and also

ensure they provide the most direct and appropriate routes to the new M4

mainline.





Page 20


4.5.4 Agreed – The strategy for routeing on the local roads would be developed in

conjunction with a suitable signing strategy.

Problem 20

Location: Junctions throughout the reclassified M4 where changes are

proposed to slip road layouts.

Summary: Amended layouts may not be sufficiently lit.

4.5.5 A number of junctions along the reclassified M4 would have amended layouts

under the proposals. The lighting throughout the reclassified M4 is not to be

changed. The exact junction changes are generally not yet defined and therefore

the amended junction layouts could be outside the existing fully-lit area of

carriageway. Users may mis-read the road layout or fail to see obstructions in the

carriageway in areas with lower lighting levels, leading to single or multiple

vehicle collisions.

Recommendation

4.5.6 Lighting levels at amended layouts should be reviewed as part of the design

process to ensure the entire area of live carriageway is lit appropriately.


4.5.7 Agreed – The lighting levels would be reviewed throughout at detailed design

stage to ensure they are suitable for the revised road layout and classification.

Appendix A

Drawings and Documents Provided

A.1 Drawings

A.2 Documents

Appendix B

Location of Problems

Note: only location specific issues are shown on these plans)

6

16

18

17

10 11, 12

9

14 7

8 20 13

15