The objectives of this paper is to present the SNRA development program to upgrade traffic safety on existing 13 m using low cost measures and also to summarize all important results and findings until April 2001 from opened projects as yet, totally some 200 km. There is a significant gap in traffic performance, safety, investment and maintenance costs, land requirement and intrusion between normal two-lane and four-lane cross-sections. In Sweden, this gap so far has been filled with a 13 m road with 3.75 m traffic lanes and 2.75 m hard shoulders. The traffic performance of these roads is quite satisfactory but there are safety problems with fatal accidents. Almost 100 people are killed and about 400 people are severely injured every year on 13 m roads due to the huge traffic load, still being the safest two-lane road. The main problem on all two-lane roads is run-off and meeting accidents causing more than 50 per cent of all fatalities. The event process tends to be the same. The driver looses control for some reason and crashes against some obstacle in the roadside area or in the shape of an opposing unlucky driver. In 1998, the director general of SNRA decided on a full-scale programme to improve traffic safety on six existing 13 m roads using low-cost measures preferably within existing right-of-way. The main alternative is the 2+1-solution with a separating cable barrier preferably within the existing width 13 m. This solution was estimated to have a potential to prevent some 50 per cent of all severe link accidents. Findings so far have been judged so successful that SNRA has decided to replace the old 13 m road with the 2+1-solution on a general basis. The main results and findings up to May 2001 are as follows: (1) Level-of-service for normal traffic is better than expected. Speed performance on 2+1-roads with cable barrier is the same or even better compared with an ordinary semi-motorway at one directional flows up to 1 400 v/h. The capacity is estimated to be about 1650 v/h in one direction, some 300 v/h less than for an ordinary 13 m road; (2) Emergency and tow agencies are complaining as their working conditions and service at emergencies have deteriorated; (3) The transitions zones from 2 to 1 lane have performed well. The proportion of vehicles in the beginning of the zone is small. Drivers tend to handle the design of the transition zones in a cautious and responsible manner; (4) The traffic safety effect on severe accidents was expected to be high on 2+1 road with cable barrier. So far in eight objects there has not been any fatal accident but totally 6 persons with severe injuries. This is about 60 per cent less than on ordinary semi-motorways and supports the prediction that fatal and severe injuries can be reduced with up to 50 per cent; (5) Median cable barrier crashes are very frequent but normally without person injuries. They are often caused by skidding, flat tyre or lost control of the vehicle. A number of accidents have been prevented by means of the median cable barrier but instead turned out to be crashes against the cable with more slight injuries; (6) Driver attitude surveys show that drivers attitude to roads with cable barrier have been changed into a positive direction. About 40 per cent of the drivers say it is the best design; and (7) The maintenance costs are increased with about 120 Thousand SEK per km and year. The main costs are cable repairs with 80 Thousand SEK per km and year. Work zone safety at cable barrier repairs is a major concern. (A) For the covering abstract of the conference see ITRD no 207828. The reprints are also available at the web - http://www.vti.se/pdf/reports/K18APart1.pdf; http://www.vti.se/pdf/reports/K18APart2.pdf and http://www.vti.se/pdf/reports/K18APart3.pdf.
Samenvatting