2+1 roads with cable barriers : a Swedish success story.

The objectives of this paper are to present the Swedish National Road Administration (SNRA) policies on cost-effective safety measures mainly on 2+1 roads with median cable barriers but also on separated 2+2 and 4-lane roads and to summarize important results and findings from projects opened to date, totally some 1000 km. In the 1990s almost 100 Swedes were killed and another 400 severely injured every year on the 3500 km network of 13 m wide two-lane roads due to the huge traffic load. This comprised 25% of all fatalities and 20% of all severe injuries on the 100,000 km of state roads. The main problem on all two-lane roads was run-off and head-on accidents causing more than 70% of all fatalities. The event process tended to be the same. The driver looses control for some reason and crashes against some obstacle in the roadside area or an opposing unlucky driver. The pressure grew on SNRA in the 1990s to explore more cost-effective measures to improve traffic safety. The alternative 4-lane road (i.e., with full access control and 18 m crown width including a 2.5 m median) was introduced for new constructions in the mid-90s in the aftermath of a political intervention with the objective to replace motorways to decrease costs and environmental intrusion without jeopardizing traffic safety. In 1998, SNRA decided on a full-scale program to improve traffic safety on six existing 13 m roads using low-cost measures, preferably within existing right-of-way. The main alternative was the 2+1 concept (i.e., with a central overtaking lane changing permitted direction every 1.25 km with a separating cable barrier preferably within the existing 13 m width) estimated to eliminate 20 to 50% of all severe link accidents. The design was soon judged to be a major success with now almost 1000 km opened. Traffic safety results for the 2+2 concept (i.e., to widen existing 13 m roads to 2 lanes in each direction separated with a cable barrier with a width of 16 m) and the alternative 4-lane roads are so far more disappointing, being no safer than 2+1 roads.