qhdm cross sections

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Cross Sections

Notice:

This document is issued for the sole purpose of stakeholder engagement in advance of astakeholder workshop to be held on 18 and 19 June 2013.

The contents of the document are draft and must not be used for any purpose other thanpreparation for the said workshop.

Note that the document is a work-in-progress and as such may contain inaccuracies in crossreferencing, table and figure referencing and page numbering. It may also contain rough drafts offigures and could include inconsistencies and areas of text yet to be developed.



Cross Sections

Contents

1 Introduction ................................................................................................................................. 1

1.1 General .............................................................................................................................. 1

1.2 Departures ........................................................................................................................ 2

2 Design Principles .......................................................................................................................... 3

2.1 Network Objectives ........................................................................................................... 3

2.2 Cross-Section Elements ..................................................................................................... 6

2.2.1 Paved Width ......................................................................................................... 6

2.2.2 Shoulders .............................................................................................................. 6

2.2.3 Hard Strips ............................................................................................................ 7

2.2.4 Medians ................................................................................................................ 8

2.2.5 Verges ................................................................................................................. 10

2.2.6 Parking Bays and Lanes ...................................................................................... 10

2.2.7 Side Slopes .......................................................................................................... 12

2.3 Auxiliary Lanes ................................................................................................................. 13

2.4 Service Roads .................................................................................................................. 14

2.5 Pedestrian Facilities ........................................................................................................ 14

2.6 Clearances ....................................................................................................................... 152.6.1 Utilities ............................................................................................................... 17

2.7 Road Restraint System .................................................................................................... 17

2.8 Fencing ............................................................................................................................ 18

2.9 Road Closure and Partial Closure .................................................................................... 18

3 Level of Service .......................................................................................................................... 21

3.1 Introduction .................................................................................................................... 21

3.2 Level of Service ................................................................................................................ 21

Tables

Table 2.1 Shoulders and Hard Strips ................................................................................... 7

Table 2.2 Parking Bay Dimensions (m) .............................................................................. 11

Table 2.3 Standard Headroom at Structures .................................................................... 16

Table 2.4 Sag Radius Compensation ................................................................................. 16

Table 3.1 Level of Service Flow Rates for Different Operational Speeds .......................... 23

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Figures

Figure 2.1 Cross-Section Design Flow Chart ......................................................................... 5

Figure 2.2 Angled Parking Bay Elements ............................................................................ 11

Figure 2.3 Typical Parking Lane Treatment at Tee-Junctions ............................................. 12

Figure 2.4 Typical Turning Head Details ............................................................................. 20

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1 Introduction

1.1 GeneralThis Standard gives details of the cross-sections and headroom requirements to beused for all rural and urban roads, both at and away from structures.

The information covers freeways, expressways, arterials, collectors and local access

roads, both single and dual carriageway, together with associated connector roads.

This standard does not give mandatory requirements for headroom near airports or atpower lines, the Designer should contact the relevant authorities to agreerequirements as part of the design process.

In general the different road reservations are intended to provide drivers withadequate sight distances and allow the public utilities sufficient space for existing andproposed plant. Where space for utilities is limited, “way leaves” outside the roadreservation may be obtained by contacting the relevant planning authority.

Figures at the end of this Part [replace with figure numbers 2.xx to 2.yy] show crosssections depicting the essential elements in typical sections for two way singlecarriageways and dual carriageways for urban and rural roads. The cross sectionsshown are typical and the final layout of the reservation should be agreed with theOverseeing Organisation.

The recommended reservation details for rural roads are similar to those for urbanroads but reflect the reduced access and drainage requirements of the rural situation.Generally for rural roads the near side of the carriageway would not be kerbedalthough flush kerbing may be considered at certain locations. Raised kerbing to themedian of rural dual carriageways should only be provided at specific location, in thevicinity of bridges and at grade junctions. In all cases an edge strip shall be providedbetween the kerb and lane edge. Verges shall be designed to fall away from thecarriageway in the rural situation and thus water will drain to surrounding ground.

Shoulders are not normally required on rural single carriageway roads and wherethese are omitted, hard strips must be included in the design. Replacing full hardshoulder construction with hard strips on rural and urban dual carriageways shall bepermitted on economic grounds pending agreement with the Overseeing Departmentbefore inclusion in the final design.

A standard lane width of 3.65m has been used on all typical cross sections illustratedand should be provided for all rural and urban single and dual carriageway roads with

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posted speeds of 80kph or greater. Exceptions are permitted where it is necessary tomaintain continuity with the remainder of an existing route, and for roads providingaccess to residential and some commercial and industrial areas. Permitted variations

are described in Section 2.2.1 below.

In order to provide adequate drainage, a standard crossfall of 2% has been applied forcarriageways and medians.

Where existing or proposed land use requirements necessitate amendments to thestandard carriageway cross sections then approval from the Overseeing Departmentmust be sought. In such instances amendments to the utilities layout may be requiredto suit the specific road cross section proposed. In such circumstances any proposedrevisions to the standardised utility locations must have the approval of theappropriate Utility Authorities.

Certain special routes, such as abnormal or exceptional load routes or scenic routes,may require specific requirements and in these situations consultation should besought with the Overseeing Department to agree appropriate solutions.

1.2 DeparturesIn difficult circumstances Departures may be considered by the Designer, havingregard to all relevant local factors. Careful consideration must be given to layoutoptions incorporating Departures, having weighed the benefits and any potential

disbenefits. Particular attention must be given to the safety aspects (includingoperation, maintenance, construction and demolition) and the environmental andmonetary benefits/disbenefits that would result from the use of Departures. Theconsideration process must be recorded. The preferred option must be comparedagainst options that would meet full Standards.

In these situations, the Overseeing Organisation may be prepared to agree to aDeparture from Standard where the standard is not realistically achievable. Designersfaced by such situations and wishing to consider pursuing this course must discuss anysuch option at an early stage in design with the Overseeing Organisation. Proposals toadopt Departures from Standard must be submitted by the Designer to the Overseeing

Department and formal approval received BEFORE incorporation into a design layout.

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2 Design Principles

There are many components in a highway provided for specific purposes and eachinvolves a number of interrelated design decisions. Integrating all these componentsto satisfy the numerous competing demands for highway space and functionalityrequires carefully balanced decisions. Features included in the cross-section can affectthe overall width and their relationship and interaction is often complex. Thepreferred locations for features in verges and the central reserve may often coincideor overlap and the Designer should be aware of the potential for such conflicts.Generally, there is far more equipment below the surface of verges and centralreserves than is apparent on the surface and some underground features must bereadily accessible for routine maintenance.

Towards the end of the design process, Designers are occasionally faced with fittingadditional detailed design features into the available highway. Problems can beavoided by ensuring that the approximate sizes and locations of detailed designfeatures are identified during the very early stages of the design so that the requiredspace can be determined. Designers may need to consider the possibility of future

widening, particularly at structures.

The Designer should ensure that the blend of the various components within theavailable space balances considerations of safety, environmental impact, cost,buildability, operation and maintenance. Where there are options for dimensions, thedecision making process should include due consideration of the often complexinteraction between these factors and any other design constraints. Properconsideration of the basic design will help ensure that both new roads andimprovements to existing highways fit harmoniously into their surroundings.

2.1 Network ObjectivesThe aim is to deliver an economic, accessible, integrated, safe, reliable, efficient andenvironmentally acceptable network for all users. This includes the need for safe,efficient and effective maintenance as well as the necessity to adapt and improvesome highways for the benefit of non-motorised users. The Designer must ensure thatthe proposed cross-section and lane widths are adequate to enable maintenance to beundertaken safely. These factors must be taken into account throughout the designprocess. A flow chart has been provided in Figure 2.1 . to assist with this process.

In urban areas there are likely to be numerous items of street furniture andunderground equipment within the highway cross-section offering less scope for co-ordinating features than in rural areas. The Designer will need to ensure a careful

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balance between the many competing demands wherever economically andenvironmentally practicable to do so.

While there may be fewer items of underground equipment in rural areas, those thatdo exist are likely to be high capacity services, which could have a bearing on theeconomical and effective delivery of subsequent maintenance and operation of thenetwork.

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Figure 2.1 Cross-Section Design Flow Chart

CROSS SECTION ANDHEADROOM

ALIGNMENT

Determine side slopes

according togeotechnical data,

stabilisation treatment,maintenance,

environmental andaesthetic values.

Determine future maintenancerequirements and Health &

Safety responsibilities

Determine appropriate medianand verge widths

Assess conditions againststandards and identify

deficiencies

Determine appropriate treatmentfor hazards within the cross

section

Adjust cross section componentsto accommodate stabilisation,

landscaping, drainage and

environmental requirements

Confirm that construction widthcan be accommodated within the

available highway boundary

DESIGN

Design Speed

Horizontal/VerticalAlignment (adjusting for

avoidance of adjacenthazards as required e.g.

headlight glare

Visibility Requirements

Establish long term functional needsof corridor, including public transport

and other transport considerations(e.g. NMU provision, abnormal load

requirements).

Highway Corridor Classification forpredicted design traffic volume

and NMU usage.

Consider requirements forStructures, NMU's, Laybys,

communication equipment, busstops, utility apparatus, drainage,

vehicle restraint systems etc.

Yes

No

Accommodateenvironmental and

heritage factors

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2.2 Cross-Section ElementsThis chapter identifies the components of the cross-section and presents guidance ondetails of their design. It applies to all cross-sections other than those through or

across structures for which specific requirements are given in Chapter 5. Figure B1 toFigure B14 shows sections with detailed dimensions to indicate how the variouscomponents should be brought together to form the cross-section of different types ofroad. Numerous changes in the cross-section are not desirable and a consistent widthis to be preferred whenever practicable along a route.

2.2.1 Paved WidthThe dimensions of the components of the Paved Width must be as given in Figure B1to Figure B14, based on a standard lane width of 3.65m. Any reduction or increase inthese dimensions is a Departure from Standard, with the exception that:

• Lane widths of 3.65m are provided in industrial areas where large vehicles forma significant proportion of the traffic.

• Lane widths of 3.30m are provided in urban commercial/retail areas wherespeeds are 50kph and below.

• Lane widths of 3.00m are provided in urban residential areas where trafficvolumes are low and speeds are 30kph and below.

• Curve Widening on curves of low radius to allow for the swept path of longvehicles as provided for in Part 3, Section 3.5.

Lane widths outside the above guidance may be provided under a departure process

with full justification provided by the Designer to the Overseeing Department.

It should be noted that lines marking the edge of carriageways are outside of thetravelled way and are provided within the hard shoulder or hard strip whereas lanelines provided within the travelled way are ignored when determining lane widths.

High Occupancy Vehicle (HOV) lanes provide priority to road based public transportprovision. Public transport strategy for Qatar identifies routes as part of the roadnetwork but provision of HOV lanes is not considered as part of standard cross-sections and will be dealt with as scheme specific documentation.

2.2.2 ShouldersThe presence of a shoulder to the nearside edge of a road has many advantages.Shoulders provide structural support for the pavement edges, emergency parkingspace for stopped vehicles and also provide side clearance between moving vehiclesand stationary objects. They also provide an additional running lane for emergencyservice vehicles and can be utilised during road maintenance operations. The shouldermust be constructed to the same standard as the adjacent carriageway and anyreduction in provision will be considered a Departure and must be agreed with theOverseeing Department.

Where shoulders are provided as shown in the standard carriageway cross-sections,they should be constructed with a standard crossfall of 2% or as an extension of the

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crossfall of the superelevated carriageway. Shoulders shall be provided with cross-section dimensions as follows:

• 3.0m for all dual carriageway roads in rural areas• 3.0m for all urban freeways, expressways and arterial roads where the design

speed is 100kph or greater. For design speeds less than 100kph the shoulderwidth may be reduced to 2.5m.

2.2.3 Hard StripsHard strips provide a safer carriageway, facilitating the removal of surface water andproviding additional carriageway width to manoeuvre around stopped vehicles in caseof an emergency. Hard strips keep roadside debris away from the running width of anoutside lane and maintain pavement integrity and stability.

Hard strips are to be provided as shown on Figure B1 to Figure B14.

A width of 1.0m is deemed sufficient for a hard strip for a median edge on a dualcarriageway where design speeds are greater than 80kph and reduced to 0.5m wherethe design speeds are less than or equal to 80kph. The hard strip width shall beallowed for within the standard median width and shall not reduce the lane width.Hard strips are to be provided adjacent to the outer travelled lanes on all unkerbedroads unless replaced by a shoulder. For rural dual carriageways a width of 0.5m shallbe provided reducing to 0.35m for rural single carriageways. Refer Table 2.1.

Where a kerb is provided there is a tendency for drivers to steer a distance away fromthe kerb, this is termed "shy distance". At slower speeds the requirement for shydistance is reduced and conversely, at higher speeds, an increased shy distance isrequired. An additional function of the Hard Strip is to provide the shy distance.

A Hard Strip of 0.5m must be added to the road width, for each kerbed road edge onroads with a design speed greater than 80kph. On kerbed dual carriageway roads ofdesign speed less than or equal to 80kph, a Hard Strip of 0.35m shall be added to theoutside edge as a gutter. Refer Figures 5.1 -5.7. The Hard Strip is an additionalpavement width and the lane width shall not be reduced. The provision of Shouldersand Hard Strips at junctions is discussed further in Part 4: Intersections and

Interchanges.

Table 2.1 Shoulders and Hard Strips

Road TypeShoulder/ and Hard Strips (m)

Outside Edge Median Edge

Rural

Dual Carriageway (Shoulder) 3.00 -

Dual Carriageway (Hard Strip) 0.50 1.00

Single Carriageway (Hard Strip) 0.35 -

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Road TypeShoulder/ and Hard Strips (m)

Outside Edge Median Edge

Urban

Dual Carriageway (Shoulder)> 80kph 3.00 -

Dual Carriageway (Shoulder)< 80kph 2.50 -

Dual Carriageway (Hard Strip)> 80kph 0.50 1.00

Dual Carriageway (Hard Strip)< 80kph 0.50 0.50


Hard Strips for Kerbed Roads *

Dual Carriageway > 80kph 0.50 0.50

Dual Carriageway (Shoulder) <80kph 0.35 0.35


Note: * - Whilst awaiting installation of services and kerbs a temporaryadditional hard strip of 0.35m shall be provided.

2.2.4 MediansMedians are used to separate opposing traffic lanes on dual highways. They provideprotection from interference by opposing traffic, minimise headlight glare, provide

space for utilities and future lane width, provide additional space for crossing andturning vehicles at at-grade junctions, and allow pedestrian refuge in urban areas.

A median may vary in composition from say a 1.2m width with a pedestrian barrier toa 20m wide median with street lighting, drainage and landscaped areas. Medians aredependent on the width of reservation available and the functional requirements ofthe median. Often, consultation with the relevant planning authority is required priorto agreement of the width and function of the median.

Narrow medians are those in the range 1.2m to less than 4.0m and are used inrestricted conditions. Medians 1.2m wide do not provide a refuge area for pedestriansbut do provide the minimum space permitted for clearance of opposing trafficprovided the lane edge is kerbed. Narrow medians are used where there is a need to

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provide a divided road, but where the available reservation does not permit a greatermedian width. Narrow medians are not wide enough to provide effective left turnlanes. The minimum allowable median width to provide a safe pedestrian refuge is

3.5m. Pedestrians’ ability to cross at narrower medians shall be controlled or activelydiscouraged by the provision of barriers/high kerbs, continuous planting and otherfeatures.

A narrow median should not be considered if it is possible to provide an intermediateor wide median at that particular location. Acceptable standards for the remainingcross section elements should be maintained. Where narrow medians are beingconsidered these should discussed with the Overseeing Department prior to beingincluded in the final design.

Intermediate width medians are those in the range 4.0m to less than 8.0m and aregenerally wide enough to provide for a left turn lane. A width of 8.0m is the desirableminimum to provide a left turn lane and a residual median, and a width of 8.0m is thedesirable minimum to shelter a crossing vehicle undertaking a U-turn manoeuvre.Where intermediate medians are being considered these should discussed with theOverseeing Department prior to being included in the final design.

Wide Medians 8.0m or greater in width provide space for effective landscaping andmay be used for signing, services and drainage. Wide medians may also be used toabsorb level differences across the road reserve. Rural medians should be a minimumof 8.0m wide with a central safety barrier.

A disadvantage of wide medians occurs at signalised junctions, where the increasedtime for vehicles to cross the median may lead to ineffective signal operation.

Wide medians should not be implemented at the expense of reduced verge widths.Verge widths are required for pedestrian walkways, installation of services, trafficsigns, drainage channels, parking etc. Any significant reduction in verge width mayresult in hazards in the verge which negate the advantages of a wider median.

It is recommended that urban medians should be kerbed and that rural mediansshould be provided with a hard strip and not kerbed. A kerbed median is desirable

where there is a need to control left turn movements and is also used when themedian is to be landscaped. In the rural situation, a depressed median is preferred asthis improves drainage of the road.

Special attention should be given to drainage of medians. If the median is kerbed, themedian surface should be designed to have slopes of 2%, and should fall towards thecentre of the median if unpaved, or towards the carriageway if paved. Depending onwhether the median is paved or open, planted or not, median drainage should notinterfere with the operation of the highway. Paved medians may require positivestorm water drainage systems incorporating manholes, pipes etc. Non-paved mediansmay be self-draining, but again, consideration should be given to the provision ofadditional storage capacity or outlets to allow for storm conditions. All drainage inlets

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in the median should be designed with the top flush with the ground, and culvert endsprovided with safety grates to minimise the risk to errant vehicles.

It is common practice to landscape medians. This is seen to provide a betterenvironment and reduce driver stress. Careful consideration should be given to thechoice of planting to ensure that visibility and stopping sight distances are notimpaired. Furthermore, the upkeep of the landscape and growth of the plants shouldbe designed for minimal maintenance and hence less disturbance to the road user.

Watering shall not require tankers to obstruct the trafficked lanes at any time.

Where two abutting sections of highway have different carriageway widths it isdesirable that a smooth transition should accommodate this difference. The transitionshould be as long as possible for aesthetic reasons and preferably occur within ahorizontal curve.

2.2.5 VergesThe verge is a width of the reservation which facilitates additional functions essentialfor the operation of the road. Verges must be able to accommodate highway signs,structures, utility services, drainage, traffic signals, street lighting and associatedducting. Where a verge is adjacent to a development a set back may be required.Verge widths may vary from a desirable minimum of 3.0m up to the limits of thereservation, which could be in excess of 15.0m. Paved verges should be designed witha 2% fall towards the carriageway for drainage purposes. However, in larger paved

areas, falls shall be designed to specific drainage collection points in the verge.

It is important to ensure that objects in the verge (such as structures, signs orlandscaping) do not affect the sight distances required for the particular design speedof the road. Additional care should also be taken at traffic signals and junctions whereadditional signage is provided.

Verges may be paved, landscaped or graded depending on the intended use of theverge. Due consideration must be given to the proposed width of verges if soakawaysare to be provided in the verge as part of the drainage design solution.

Detailed investigations for the provision of services and utilities in verges must beundertaken during the design stage for both new roads and where existing roads arebeing improved such that all can be accommodated within the verge provision.

2.2.6 Parking Bays and LanesThe need for parking is determined by the existing and future development of theimmediate surrounding area. Consultation will be required with the Traffic Section andthe Planning Department to determine the future development plans and the amountof on-street and off-street parking required.

In urban locations, parking shall be provided away from the carriageway and in specificlots or contiguous with Minor Urban Collector and Local Access roads. Parking should

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not be provided near junctions or opposite access points as this is likely to increase theprobability of accidents and also hinder sight distance.

Parking lanes provide parallel parking adjacent to the outside lane edge of thecarriageway, i.e. Lane 1. The standard width required for a parking lane is 2.5m, eachbay being nominally 6.5m in length. Care should be taken when providing a parkinglane to ensure there is sufficient forward visibility to accommodate the desirableminimum stopping sight distance for the design speed of the road. It is recommendedthat parking lanes should only be provided on single carriageway roads, with postedspeeds of 50 kph or less. The design speed, stopping sight distance and trafficvolumes should also be appropriate to allow minimal interruptions to traffic flowwhen vehicles are entering or leaving the parking lane.

Angled parking bays may be provided contiguous with the trafficked lane where onstreet parking demand is high. This should only be considered if there is sufficientwidth within the available Right of Way. The perpendicular parking bay should bemade up of stalls 3.0m wide and 6.0m in length. The dimension requirements forangled parking are shown in Table 2.1 and Figure 2.2.

Table 2.2 Parking Bay Dimensions (m)

Dimension ElementAngle

45◦

60◦

75◦

90◦

Stall width

parallel tolane

A 4.25 3.50 3.25 3.00

Stall Length B 9.00 7.75 6.80 6.00

Stall Depth C 6.40 6.70 6.60 6.00

x

Figure 2.2 Angled Parking Bay Elements

A reduction in the minimum parking lane width of 2.5m to 2.2m for Local Access roadswill be considered. Any proposed reduction in width below either 2.5m or 2.2m willbe a Departure and approval from the Overseeing Department will be required beforeinclusion in the final design.

Edge of Contiguous Trafficked Lane

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Provision for parking in parking lanes or angled parking shall be excluded from thefollowing locations:

• Junctions; to provide space for pedestrians to cross and to maintain adequatevisibility. See Figure 2.3.

• Bends; to maintain adequate forward visibility for drivers.• Pedestrian crossing points; to minimise crossing width and enable crossing

pedestrians to be seen clearly by drivers.• Any other location where parking would cause unsafe conditions.

In all cases parking must not encroach on visibility splays.

Figure 2.3 Typical Parking Lane Treatment at Tee-Junctions

The dimension “D” indicated in Figure 2.3 is the distance between the end of thecircular arc forming the side road junction bell mouth and the end of the parking lanetaper on the principal road. As an absolute minimum this should be 5.0m but must beincreased to ensure that parked vehicles in the parking lane do not encroach withinthe junction visibility envelop required by the design speed of the principal road.

2.2.7 Side SlopesSide slopes should be designed to ensure roadway stability and to provide areasonable opportunity for recovery for an out-of-control vehicle. Earth cut and fillslopes should be flattened and liberally rounded as fitting with the topography andconsistent with the overall type of highway. Effective erosion control, low-costmaintenance, and adequate drainage of the subgrade are largely dependent uponproper shaping of the side slopes. The rounding and flattening of slopes minimisesdrifting and wash out of loose material such as sand and hence reduces maintenancecosts. Slope and soil data are used in combination to approximate the stability of theslopes and the erosion potential. Overall economy depends not only on the initialconstruction cost but also on the cost of maintenance, which is dependent on slopestability. Furthermore, flat or rounded natural slopes with good overall appearance

are appropriate for any roadside located near developed and populated areas.

D D

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Where possible the embankment side slopes should fall away from the verge at aslope of 1 in 5, or flatter if conditions permit. Generally, it is better to use flatterslopes, providing there is adequate fall for drainage. It is usual to consider the

provision of a safety barrier when slopes are between 1 in 5 and 1 in 3, and the heightof the embankment is greater than 6m. For embankment slopes between 1 in 2 and1 in 3 inclusive a safety barrier will be required when the embankment height isgreater than 2m. Where embankment slopes are steeper than 1 in 2 safety barrierswill be required at all locations when the embankment is a minimum of 0.5m.However where slope rounding is employed it is unlikely that slopes steeper than1 in 2 will occur until the embankment height is greater than 0.85m.

Slopes in cutting should not be steeper than 1 in 2 and preferably should be 1 in 3 toallow mechanical maintenance equipment to be used on the slope. If there isinsufficient width which would require slopes steeper than 1 in 2, then partial or fullretaining walls should be used or some method of slope stabilisation. Retaining wallsshould be set back from the carriageway to avoid a constricting feeling and reducestress for the driver. Steep sided cuttings or earth bunds greater than 1 in 2 within theclear zone must be protected by a safety barrier.

An adequate geotechnical investigation along the route of the proposed new roadsworks must be carried out prior to specifying slopes. The investigation will determinethe slopes for long term stability for both cut and fill and the criteria for benching orerosion protection if required.

Where benching is required, benches should ideally be 4.0m in width and laid to fallsof approximately 1 in 20 to avoid ponding of water and consequential slip failure.

In rock cuttings it is recommended to include ditches and a debris verge to provide asafe landing and catchment area for possible rock fall and removal of surface waterrun off. This additional width also provides a useful area for rock face maintenance. Itis becoming common international practice for rock outcroppings to be left in placefor reasons of economy or aesthetics. This may be considered for application in Qatar.However in such situations, the conditions described above with respect to steepsided cuttings would apply and a safety barrier must be provided if the rock faceoutcrop occurs within the clear zone.

Vehicle restraint systems are discussed in Part 12 Road Safety.

For details of sand slopes, wind blown sand and dune control refer to the Kingdom ofSaudi Arabia, Ministry of Communications, Highway Design Manual, Book 2, Section1.16, Sand Dune Control.

2.3 Auxiliary LanesAuxiliary lanes serve as speed change lanes, storage lanes, additional access lanes or acombination of all three. They may also be either right turn or left turn facilities at

junctions or provide a continuous contiguous trafficked lane between interchangesand grade separated junctions (refer Part 4: Intersections and Interchanges). A speed

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change lane is primarily for the acceleration or deceleration of vehicles entering orleaving the through traffic lanes. A speed change lane should be sufficient in lengthand width to enable a driver to make the necessary change between the speed of

operation on the through highway and the lower speed necessary to turn withminimal disruption to the speed of following vehicles. Speed-change lanes can havedifferent layouts depending on the alignment of the highway, frequency ofintersections and the distance required to effect the necessary change of speed.Generally all auxiliary lanes should have a cross-section width of 3.65m.

2.4 Service RoadsService roads are roads which run roughly parallel with, and are connected to the mainthrough highway. They are generally of low design speed and preferably restricted toone-way traffic. Figure YY shows a typical reservation with a service road.

Service roads provide a number of functions depending on the development of thesurrounding area. The provision of service roads reduces the number of access pointsonto the main highway and segregates the higher speed through traffic from the lowerspeed local traffic. This reduces interruption of traffic flow, makes the best use of roadcapacity and results in a safer environment.

Service roads may also provide an alternative route if maintenance is required on thethrough road or in case of an emergency.

The width of the service road is dependent on the classification of traffic expected touse the service road such as light vehicles, delivery lorries or heavy goods vehicles, andmust comply with the lane widths described in sub-Section 2.2.1 of this Section.Further consideration should be given to the turning requirements of such vehicles,the type and number of access points and type of street parking, if required.

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2.5 Pedestrian FacilitiesPedestrian facilities are generally found within the verge and at road crossing points.

The provision of paved pedestrian areas is related to the function of the roadsidedevelopment. To obtain reliable estimates of pedestrian volumes and movements,studies should be carried out at the concept and preliminary design stage. All urbanroads and junctions shall allow space for footpaths unless the area strictly forbidswalking. A width of 2.0m should be provided depending on pedestrian needs. Thewidth of paved pedestrian areas should be increased to a minimum of 3.0m nearschools, large sports venues, commercial areas or other areas with high pedestrianvolumes. Footpaths may be constructed with paving blocks or concrete and laid tocrossfalls of 2% towards the roadway to facilitate drainage. In the event thatfootpaths are remote from the carriageway a separate drainage system must beprovided.

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Where possible a separation area should be included within the verge which acts as abuffer between vehicular and pedestrian traffic. A minimum separation width of 1.2mis desirable. A separation width is not required in commercial areas with on street

parking where wider footpaths are usually provided.

Pedestrians should be actively discouraged from crossing roads along the length ofdual carriageways. Special pedestrian refuge sections should be provided at selectedpoints, or ideally at junction locations. It is recommended that these refuge areas be aminimum of 3.5m wide and should be staggered so that pedestrians are not able toapproach and cross both carriageways in one line.

On roads with a posted speed of 60kph or less, it is recommended to provide a pelicancrossing (signalized pedestrian crossing) or a zebra crossing (pedestrian crossingdefined by road markings) as a crossing point for pedestrians. These crossings shouldbe located, signed and marked in accordance with this manual and with the QatarTraffic Manual.

In areas with high volumes of pedestrian traffic, footpaths should be provided on bothsides of the road. Some urban areas and most frontage roads can be served with afootpath on one side only. In these areas, footpaths must be continuous for the fullpedestrian route.

On rural roads, footpaths are not usually required, except along sections of roadwhere there is substantial residential or commercial development. In such situations,

footpaths are usually located between the bottom of the embankment and theproperty line.

2.6 ClearancesGenerally, no structures apart from roadside furniture, such as signs and lightingcolumns, are allowed to fall within the road reservations. The positioning of signs andother street furniture should be in accordance with the Qatar TrafficControl Manual. If it is not possible to position structures outside the reservation,consideration should be given to providing a road restraint system or safety cushions,refer Section 12: Road Safety.

Structures should not be placed within 1.2m of the edge of the hard shoulder, or 0.6mof a kerbed road. Setback of road restraint systems is dealt with in Section 12: RoadSafety.

The minimum vertical clearances are specified to prevent vehicles or their loads fromcoming into contact with any structure or roadside furniture.

The minimum clearances for structures are given in Table 2.3. These clearances are tobe provided across all trafficked lanes including verges and shoulder or hard strips. Theclearances allow for 200mm of pavement construction which may be applied duringthe maintenance of the road.

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Table 2.3 Standard Headroom at Structures

Category of Road/Structure Type Clearance Required

High Load Routes 6.5mGantries/Lightweight Structures 6.5m

Pedestrian Over Bridge 6.5m

Freeway and Expressway Bridges 6.0m

Camel Underpasses 6.0m

All Other Road Structures 5.7m

Pedestrian Underpasses 3.5m

OHPS Equal to the vertical clearance of theprotected structure

Minimum clearance shall be provided to all structures or roadside furniture thatoverhangs the carriageway. These include any bridge or building structure, sign gantry,overhead cables or suspended lighting.

Where a public utility specifies a minimum vertical clearance to its plant then thegreater of the clearances must be provided for. Protective measures may be requiredat overhead cable crossings such as guard wires. Guidance may be sought from theMinistry of Electricity and Water when planning works in the vicinity of theirinstallations.

Where a road passing underneath a bridge is on a sag curve, the headroom givenabove shall be increased in accordance with Table 2.4. The sag radius is measuredalong the carriageway over a 25m chord.

Table 2.4 Sag Radius Compensation

Sag Radius(m)

AdditionalClearance

(mm)

100 801200 701500 552000 453000 256000 15

>6000 nil

Nominated existing structures over highways with non-conforming clearances shall beprotected against accidental damage from over height vehicles by adopting thefollowing protective measures:

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• Rerouting of over height vehicles to service roads or ramps to prevent theirpassage beneath bridges with clearances less than shown in Table 2.3. Warningsystems shall be implemented highlighting height restrictions and indicating

alternative routes. This can be done via an integrated traffic system (ITS) (e.g.OVDS, CCTV cameras VMS, etc.).

• Over height protection system (OHPS) shall be used on structures withheadroom less than 5.7m.

• OHPS shall be made integral with the existing structures.• OHPS shall be designed to resist highway collision load in accordance with the

UK Highways Agency DMRB BD 65 (Design Criteria for Collision ProtectionBeams).

• OHPS will be positioned at strategic locations taking into consideration thesafety of the public in the event that the top boom is damaged or becomesdetached.

• All OHPS shall have headroom equal to the vertical clearance of the structurebeing protected.

• The design of the OHPS shall take into consideration ease of construction, futuremaintenance, the safety of the public and aesthetics.

2.6.1 UtilitiesRoad corridors are given in Figures XX-YY. These are intended to provide adequatespace for road cross section requirements and at the same time allow the publicutilities sufficient space for existing and proposed plant. Where space for utilities islimited, “wayleaves” outside the road reservation may be obtained by contacting the

planning department. Full details for the provision of Utilities is given in Part 9Utilities.

2.7 Road Restraint SystemA road restraint system is the general name for a vehicle restraint system or apedestrian restraint system used on the road comprising longitudinal barriers toprotect motorists and pedestrians from natural or man-made hazards located in theroad reserve, and to protect non motorised users from out of control vehicular traffic.Safety fences may be located in the verge or median depending on the particularrequirements and location.

The safety barrier is designed to prevent an errant vehicle from leaving thecarriageway and striking a fixed object or feature located in the Clear Zone bycontaining and redirecting the errant vehicle.

The Clear Zone is the total width of traversable land on the nearside or offside, withinthe road boundary, which is to be kept clear of unprotected hazards. The zone ismeasured from the nearest edge of the trafficked lane and includes the hard shoulderor hard strip where these occur. The zone does not normally include the boundaryfence or areas of land beyond the road boundary. However, in some circumstances, itmay be necessary to consider hazards on or beyond the road boundary.

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Please refer to Section 12 Road Safety for full details of road restraint systems, typesand provision.

2.8 FencingThere are many different types of fences used within the road reservation, each typehaving particular applications. The main types of fencing are listed below:

• Right of Way Fencing to delineate and separate private property from the roadreservation.

• Road Restraint Systems erected where considered necessary.• Animal Fencing prevents animals from entering the highway reservation. The

size and type of fencing is dependent on the type of animal the fencing isintended to control, e.g. camel or goat.

• Acoustic Fencing may be required in sensitive locations such as residential areasto lower the traffic noise level. The fence forms a barrier and the sound isreflected away from the sensitive area.

• Headlight Barriers may be implemented at locations where it is desirable tominimise the glare of the headlights of oncoming vehicles, such as at unlit bendson rural roads.

• Pedestrian Access Fencing may be required where there are significant numbersof pedestrians such as on commercial streets, outside schools or large sportscomplexes where crowds may gather. The fencing controls the movement ofpedestrian traffic and lowers the risk of a pedestrian accidentally moving onto a

live carriageway.

2.9 Road Closure and Partial ClosureThe transition between the previous road hierarchy and the new hierarchy will involvethe upgrading and downgrading of existing roads to ensure compatibility with the newcriteria.

It is acknowledged that the adoption of the new hierarchy will requireupgrading/downgrading of some roads to meet the new classification. The extent ofthe difference between the previous road hierarchy classification and the new

classification will influence the physical engineering extent of the upgrade/downgraderequired. It may be necessary to upgrade/downgrade a specific road in order to allowother roads to meet their new roles within the road hierarchy or to ensure thatadverse rerouting of traffic does not takes place. This will depend to a great extent onthe type and extent of land use development adjacent to the road and the status ofany potential new development and will influence the integration of on-road parkingand the access strategy to serve adjacent land uses. This will be pertinent with respectto current access and parking provisions associated with existing service roads.

The main aims of full or partial road closures are to:

• Deter non-access traffic from using residential roads as through routes;• Limit the number of minor accesses onto major routes;

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• Remove the crossroad type junction which is generally considered unsafe. ReferPart 4 Intersections and Interchanges.

Amendments to existing roads to conform to the new road hierarchy will require theprovision of clear and concise warning and/or diversion signs that must be providedduring the first two to three months of operation. This will help assist the travellingpublic in understanding the new road layout. Refer to Qatar Traffic Signs Manual foradvice and layouts.

Typical turning heads are shown in Figure 2.4. The choice of layout is dependent onthe width of carriageway available and the positions of existing property accesses thathave to be accommodated by the closure.

Any barriers or turning heads shall be designed in such a way as to ensure thatemergency vehicles are able to gain access. This may be achieved by the use oflockable barrier gates or demountable bollards. Whichever is chosen, it must becapable of preventing private vehicles from passing through the restriction. For thisreason, solutions such as a route through a landscaped area are not recommended asthey are open to abuse, particularly by drivers of four wheel drive vehicles.

Partial closures allow restricted access into the areas by the use of width restrictionsor raised humps to make alternative routing unattractive for the general road user.

Partial closure is often incorporated at undesirable locations along the major road to

discourage use such as at accesses near to major junctions. Where the minor road hasto remain open for emergency vehicle access or to provide limited access into thedevelopment then partial closure is a preferred method for controlling general use.

For further reference on traffic calming and partial closures please refer to the“Manual for Streets” and the “Manual for Streets 2” published by the CharteredInstitution for Highways and Transportation and “A Policy on Geometric Design ofHighways and Streets (2011) published by the American Association of State Highwayand Transportation Officials.

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Note:

A central island radius of 10 metres will just allow the vehicle to turn about. In view ofthe restricted area available, the island may be reduced or omitted altogether.

Minimum Dimensions for Turning Heads

In situations where larger vehicles have to be accommodated, these dimensionsshould be increased to take account of the larger turning radius and swept path.

Figure 2.4 Typical Turning Head Details

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3 Level of Service

3.1 IntroductionIn addition to strategic importance and safety, the desired characteristics of trafficflow will generally determine the class of a road. For example, high volumes of trafficare generally associated with urban freeways and expressways, whereas low volumesare associated with rural routes.

In most urban situations, the capacity of intersections on a particular network willgovern the capacity of the network as a whole. Uninterrupted flow only takes placewhen the influence of at-grade intersections can be neglected. This is rarely the caseon most urban road systems.

The capacity of a highway is affected by the composition and the habits and desires ofthe traffic using the road system and the controls that the designer imparts onto thetraffic. These include:

• Horizontal, vertical and cross section geometry;• Traffic composition;• Lane distribution;• Variations in traffic flow;• Traffic interruptions;• Bus operations, cyclists and pedestrians

The highway infrastructure provides a service to road users and as such it is importantthat this infrastructure is of a high quality providing a good level of service.

3.2 Level of ServiceLevel of Service (LOS) is defined as a qualitative measure describing the operationalconditions on the highway network and road users’ perception of how effective thecombination of the various elements of a road contribute to the user experience inproviding an efficient network and journey reliability.

Under ideal conditions, analysis of all of the above factors will have an influence onthe capacity of a highway’s ability to carry the maximum number of vehicles in safetyat an appropriate level of service. In this situation level of service is a technicalconcept which attempts to describe the travel experience in terms of operating speed,the ability to overtake vehicles in safety, traffic congestion, overall safety and driver

and passenger comfort. In general there are six levels of service, designated from A toF, with level of service A (LOS A) representing the best operating condition (i.e. free

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flow) and level of service F (LOS F) the worst (i.e. forced or breakdown flow). For cost,environmental impact and other reasons highways are not typically designed toprovide LOS A conditions during peak periods, but rather some lower level of service

that reflects a balance between traveller demands and economic and environmentalconcerns.

The different levels of service can generally be described as follows:

• LOS A – free flow with high speeds in which individual drivers are virtuallyunaffected by the presence of others. Manoeuvrability, comfort andconvenience are extremely high.

• LOS B – stable flow with drivers still having reasonable freedom to drive at theirselected speed. Manoeuvrability, comfort and convenience are less than forLOS A.

• LOS C – stable flow with drivers becoming restricted in their choice of desiredspeed. Manoeuvrability, comfort and convenience begin to decline noticeablyat this level.

• LOS D – is close to the limit of stable flow and drivers are severely restricted intheir choice of desired speed. Manoeuvrability, comfort and convenience arepoor. Small increases in traffic flow will generally cause operational problems.

• LOS E – occurs when traffic volumes are at or close to capacity. Speed and theability to manoeuvre are dictated by the traffic stream. Flow is unstable andminor disturbances to the traffic flow will cause breakdown.

• LOS F – the amount of traffic demand reaches capacity, flow breakdown occurs

and queuing and delay result.

The level of service concept should be used as the basis for the capacity andoperational analysis for all new roads. Table 3.1 shows the relationship betweenoperational speed and vehicle flow rate for each level of service. In this context theDesigner should aim to provide as a minimum LOS C for rural roads and LOS D forurban roads. Traffic analysis should provide sufficient data to determine anappropriate operational speed.

When two or more lanes are available for traffic in a single direction, the distributionin lane-use will vary widely. The lane distribution will depend on traffic regulations,

traffic composition, speed and volume, number and location of access points, origin-destination patterns of drivers, development, environment, and local driver habits.

Due to the above factors, there are no typical lane distributions. The recommendationfor each LOS flow rate recognises that flow in some individual lanes will be higher andin others lower, and as such the figures in Table 3.1 should be considered an averagefor determining the number of lanes required.

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Table 3.1 Level of Service Flow Rates for Different Operational Speeds

Level of Service

Operational Speed

(kph)120 100 80 70 60 50

A 820 710 610 520 450 400

B 1280 1120 960 810 710 630

C 1840 1600 1370 1160 1020 900

D 2340 2040 1640 1470 1300 1140

E 2660 2320 1980 1670 1480 1300

Notes:1. The flow rates in the above table reflect changes in traffic flow densities

(vehicles/lane/hour) with respect to Operating Speeds. The flows in eachrow are the maximum for each LOS.

2. Flows in excess of those shown for LOS E for each operational speed areconsidered providing LOS F.

3. The flows above are Design Year flows, 15 years after opening.

At the planning stage, major routes should be planned and designed as multi-lanedivided, controlled access facilities even though they may be developed by stagedconstruction. In the plans for each stage of development, provision should be madefor further improvements to existing sections forming part of the level of serviceassessment.

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