Safety standards for express roads

The objective of the SAFESTAR project is the formulation of design standards or recommendations exclusively based on safety arguments. Workpackage 3 (WP3) of SAFESTAR, of which this report is the concluding report, should result in design recommendations for single and dual-carriageway express roads of the Trans European Road Network (TERN). The objective was to formulate the design recommendations on the basis of an extensive accident analysis (WP3.1), a description of decision-making processes in EU member states (WP3.2), the conclusions and findings of a workshop (WP3.3), and a literature review. The main conclusion of this Workpackage (WP3.4) is that the amount of information and knowledge on safety effects of design parameters of express roads is very limited. The reports of WP3.1 to WP3.3 and of the literature review conducted in WP3.4, could therefore not result in design recommendations or safety standards. To be able to give design recommendations for express roads, elaborate research on the safety effects of the different design parameters yet has to be carried out. In contrast with the situation for express roads, extensive research on safety effects of design characteristics has been carried out on motorways and on rural two-lane roads. Because function, design, and use of these particular road-types differ too much from express roads, this research information however cannot be simply translated to the situation on express roads. Some of the information of this research on road-categories just above and just below the express road category can however give some indication of possible effects. These indicators can therefore serve as a guide in future research on express roads. It is recommended to restrict use of express roads to high speed motorised traffic exclusively and to limit the number of access points as much as possible. The horizontal alignment has to be consistent and allow for a constant design speed along the entire road section. In order to distinguish clearly between situations where overtaking is, or is not, possible, intermediate curve radii (between approximately 800 m and 2,000 m) must be avoided. The distance between two successive curves or between a straight section and a curve should be large enough to judge and interpret the situation (a recommendation is expected to be around 3 seconds driving time). Narrow curves should be avoided because of the proven increase in accident rates (510 m could be used as an indication for the minimum curve radius). Research indicates a probably positive effect on traffic safety of transition curves . Because of some contradicting results however, further research is advised. Super-elevation values larger than approximately 8 % are not recommended. Research indicated 3.5 m as an optimum value for lane width on express roads. An unequivocal value for the optimum shoulder width on express roads could not be given on the basis of past research. Because of their considerable improvement of traffic safety, climbing lanes must be recommended on upgrade sections on two-lane express roads. Minimum values for obstacle-free zones on express roads probably vary between 3.5 and 5 metres. Research on motorways and two-lane rural roads indicate a maximum sideslope of 5:1. Steeper slopes have to be considered as dangerous areas, and should therefore be protected with guard rails