2 + 1 roads with median

In Canada in 2011, 18.7% of fatal crashes were head-on collisions between two vehicles. They resulted in 23.5% of all fatally injured victims that year.

One way to reduce the likelihood of head-on collisions is through the application of a 2+1 road design. 2+1 roads are roads with a continuous three-lane cross section with alternating passing lanes. The directions of travel can be separated by line markings or a cable median barrier. They are installed in order to improve safety on two-lane highways with wide shoulders and wide lanes. They enable drivers to safely make passing manoeuvres in the additional third centre lane.

An evaluation of the 1,800 km of 2+1 roads in Sweden in 2008 revealed that the death rate per kilometre of road was 79% lower on these roads than on regular undivided roadways. Travel speeds were 2 km/h higher on 2+1 roads than on regular undivided roads with 90 km/h posted speed limits and identical to travel speeds on motorways with 110 km/h speed limits. However, the vehicle capacity over time per direction of travel was approximately 12% higher on regular undivided roads than on 2+1 roads) due to bottlenecks when two lanes of traffic transition into one (Carlsson, 2009).

A study carried out in 2003 on the application of 2+1 road designs in Finland, Germany and Sweden showed that there can be effective alternatives to two- and four-lane roads.

Road authorities in Finland estimated that the 2+1 roads, that separated the two directions of traffic with only pavement markings, had 22-46% lower collision rates than conventional two-lane highways. In Germany, collision rates on 2+1 roads, separated by pavement markings alone, experienced 36% lower collision rates than conventional two-lane highways. Sweden observed a 55% reduction in fatal and injury collisions with the implementation of 2+1 roads using a cable barrier design to separate the two directions of traffic. The author of the study recommended the implementation of 2+1 roads in the United States as an alternative design for rural roads with a traffic flow up to 1,200 vehicles per hour in one direction of travel (Potts, 2003).

A feasibility study was carried out on the suitability of implementing 2+1 roads on selected segments of rural highways in Alberta. Twelve control sections from Alberta’s rural two-lane highway network were identified for potential 2+1 road application on the basis of traffic volumes, collision rates, and Alberta Transportation’s planned programs for twinning and for climbing/passing lanes. The authors of the study determined that the 2+1 roads concept was not suitable for the general application of Alberta’s rural highway network due to the requirement for the accommodation of the large number of intersections in the 2+1 road design because of Alberta’s requirements for safety performance and sight distance. However, they indicated that 2+1 roads may be feasible elsewhere in Canada where sections of arterial two-lane highways are quasi-freeways with grade separated access control (McGregor et al., 2009).

Scope of the Problem

• Transport Canada (2013). National Collision Data Base. Retrieved from http://wwwapps2.tc.gc.ca/Saf-Sec-Sur/7/NCDB-BNDC/p.aspx?l=en

Evidence

• Carlsson, A. (2009). Evaluation of 2+1 roads with cable barrier. Final report. Swedish National Road & Transport Research Institute, Linköping, Sweden. Retrieved from http://www.vti.se/en/publications/pdf/evaluation-of-21-roads-with-cable-barrier--final-report.pdf
• Potts, I. (2003). Application of European 2+1 Road Designs, National Cooperative Highway Research Program, Research Results Digest, (April 2003-Number 275). Retrieved from http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rrd_275.pdf
• McGregor, R. V., Hassan, M., and Kenny, B. (2009). Feasibility of 2+1 Roads on Alberta Rural Highway Network. Presented at the 2009 Annual Conference of the Transportation Association of Canada Vancouver, British Columbia. Retrieved from http://conf.tac-atc.ca/english/resourcecentre/readingroom/conference/conf2009/pdf/Hassan.pdf