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DESIGN MANUAL FOR ROADS AND BRIDGESVOLUME 6SECTION 1ROAD GEOMETRYLINKSPART 4TD 70/XXDESIGN OF WIDE SINGLE 2+1 ROADSContentsChapter1. Introduction2. Design Principles3. Geometric Standards4. Junctions5. Traffic Signs and Road Markings6. Road Users’ Specific Requirements7. Economics8. References9. EnquiriesAppendix A: Traffic Signs and Road Markings(Sample layouts)
Volume 6 Section 1 Chapter 1Part 4 TD 70/XXIntroduction1. INTRODUCTIONGeneral1.1 A Wide Single 2+1 (WS2+1) road consistsof two lanes of travel in one direction and a singlelane in the opposite direction. This providesovertaking opportunities in the two lane direction,while overtaking in the single lane direction isprohibited.Scope1.2 This Standard applies to single carriagewaytrunk roads in rural areas. TD 9 (DMRB 6.1.1) isto be used to derive the design speed and theassociated values for geometric design.1.3 This Standard also provides guidance onthe design of Differential Acceleration Lanes, aform of WS2+1 road.1.4 This Standard is not applicable to climbinglanes. For guidance on the design of climbinglanes refer to TD 9 (DMRB 6.1.1).Implementation1.5 This Standard must be used forthwith forthe procurement of Trunk Road Works at anystage from conception through design tocompletion of construction except where theprocurement of such works has reached a stage atwhich (in the opinion of the OverseeingOrganisation) use of this Standard would result insignificant additional expense or delay progress(in which case the decision must be recorded inaccordance with the Overseeing Organisation’sprocedure).Definitions1.6 The terminology used in this Standardfollows the definitions contained in BS6100:Subsection 2.4.1, where possible.1.7 Terms relevant to this particular Standardare defined below:Changeover: A carriageway layout which effectsa change in the designated use of the middle laneof a WS2+1 road from one direction of traffic tothe opposite direction.Climbing Lane: An additional lane added to asingle or dual carriageway in order to improvecapacity and/or safety because of the presence ofa steep gradient.Conflicting Changeover: A changeover wherethe vehicles using the middle lane are travellingtowards each other.Differential Acceleration Lane (DAL): AWS2+1 road on which the overtaking lane isprovided for traffic accelerating away from aroundabout to cater for the differentialacceleration between vehicles.Non-Conflicting Changeover: A changeoverwhere the vehicles using the middle lane aretravelling away from each other.Overtaking Lane Section: That section of aWS2+1 road on which two lanes are provided inone direction to facilitate overtaking, with theopposing traffic confined to one lane. Refer toFigures 2/1 and 2/2.Single Lane Section: That section of a WS2+1road on which traffic is confined to a single lanerunning parallel to an overtaking lane section inthe opposite direction. Refer to Figures 2/1 and2/2.Wide Single Carriageway (WS2): A wide singlecarriageway road with one lane in each direction.Wide Single 2+1 (WS2+1): A wide singlecarriageway road with two lanes of travel in onedirection and a single lane in the oppositedirection.WS2+1 Interface: The interface between aWS2+1 road and a two-lane single carriagewayroad.December 20101.1
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