Road Tunnels Manual

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6.4. Carriage way geometry

Fig. 6.4-1 : Example of cross section

The terminology has to be defined as follows:

  1. Carriageway, comprising the area inside the inner edges of the outermost traffic lane markings
  2. Off-carriageway, comprising those areas in plan outside the carriageway, including edge lane markings, clearances, emergency lanes, sidewalks and safety barriers.

More information is available in Chapter 2 "Terminology" of Report 05.11.B.

To aid good management, roads are classified on a hierarchical basis according to function. Road networks of highest classification are interstate connections such as the Trans European Road Network or the Interstate Highways in the USA. National networks consist of roads that connect urban regions and national economic centres. Regional networks provide connections between regional towns. Functional requirements to the distinct functional networks or roads are formulated such as speed, congestion level, distances between intersections.

Most countries have their own directives and guidelines regarding requirements to carriageway geometry. A comparison of international guidelines is given in the Chapter 5 "Traffic lanes and carriageway" of Report 05.11.B.

Fig. 6.4-2 : Comparison of international guidelines (Excerpt of table 5.1 of the Report 05.11.B)
Country and name of source Design speed or reference speed (km/h) Width of traffic (m) Width of traffic lane marking (m) Width of carriageway (m)
Austria RVS 9.232 80 - 100 3,50 0,15 7,00
Denmark (Practise) 90 - 120 3,60 0,10 7,20
France (CETu) 80 - 100 3,50 ? 7,00
Germany 100 (26 T, 26 Tr) 3,50 0,15 7,00
Germany RAS-Q 1996 70 (26 t) 3,50 0,15 7,00
Germany RABT 94 110 (29,5 T) 3,75 0,15 7,50
Japan 80 - 120 3,50   7,00
Japan Road Structure Ordinance 60 3,25   6,50

It is recommended that the width of traffic lanes in tunnels with design velocities of 100 km/h shall not be less than 3.50 m. When it is acceptable/necessary to impose speed limits (80 or even 60 km/h) in tunnels on roads (i.e. unavoidable sharp curves, noise reduction in built up area, limited capacity necessary, cost reduction) a restriction of the width of traffic lanes (for example to 3.25 m ) may help drivers to reduce speed and thus act as a psychological support of the speed limit. This generally has to be enforced with frequent controls and high fines. In some urban tunnels, where only light vehicles are allowed, more narrower lanes are accepted ; in curves attention has to be given to the influence of the bending of the pavement on the width of the structure.

More information is available in Chapter V "Traffic lanes and carriageway" of Report 05.11.B and Sections 7.1 to 7.5 of Chapter 7 "Geometric cross section" of Report 05.12.B.

Reference sources

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