Differentiated speed limits allowing higher speed at certain road sections whilst maintaining safety standards are presently being applied in Denmark. The typical odds that higher speed limits will increase the number of accidents must thus be beaten by the project. The Danish Road Directorate has been asked by the Ministry of Energy and Transport based on a request from parliamentarians to suggest an approach to assess the potential for introduction of differentiated speed limits on the Danish state road network. A pilot project was carried in late 2006 and the entire state network will be assessed during the first half of 2007 - first of all to identify where speed limits may be raised. The paper will present the methodology and findings of a project carried out by the Danish Road Directorate and COWI aimed at identifying potential sections where the speed limit could be increased from 80 km/h to 90 km/h without jeopardising road safety and where only minor and cheaper measures are necessary. Thus it will be described how to systematically assess the road network when the speed limit is to be increased. Speed dependent criteria that should be fulfilled at speed limits 60 km/h, 70 km/h, 80 km/h and 90 km/h were identified. These include road class, cross sections, road side (safety zone), existence of non-motorised traffic, horizontal and vertical alignment, land use, density and type of junctions, sight distances, number of accesses, traffic level and density and frequency of accidents. Data on the road network was collected from the road data bank (VIS) and the data were inserted in the database where the road data were compared to the above criteria. This screening resulted in a list of road sections fulfilling the criteria for different speed limits and the results are presented on digital maps. The advantage of screening the network in office is that road sections that are far from the criteria for 90 km/h and thus generally too costly to upgrade can at an early stage be separated out. Focus can then be on the roads with a potential for higher speed limits and resources may then be used more efficiently during the more time consuming inspection in the field of the network. The inspection of the roads is used to confirm data from the road database and to register issues not in the road database such as too narrow safety zone, accesses, sight distances at junctions, etc. Based on the screening and inspection potential road sections are identified which have the potential for higher speed limits. Also measures to avoid negative consequences on road safety are identified and costs of the measures are assessed. The consequences of the changed speed limits are assessed. These indicators are traffic accidents, time, emissions and noise. When the effects are assessed these may be given a cost. This result may be used to describe the consequences for society of raising the speed limit. For the covering abstract see ITRD E137145.
Abstract