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Safety effects of by-pass lanes at T-junctions

Authors: Alena Katharina Høye, Ingeborg Storesund Hesjevoll
Report nr: 1909/2022
ISBN (digital version): 978-82-480-1965-7
Language: Norwegian
Attachments Summary
Full report - in Norwegian only

By-pass lanes at a T-junctions consist of a widened through lane on the main road to allow through traffic to pass waiting left-turning vehicles in the presence of oncoming traffic. By-pass lanes can under certain conditions be used instead of left-turn lanes. Among countries using by-pass lanes are Norway, Finland, USA, Denmark, and Australia. How by-pass lanes affect safety varies between studies. International studies found mostly crash reductions. Analyses of Norwegian crash data indicate unchanged or increased crash numbers at T-junctions where by-pass lanes were installed. Conditions under which by-pass lanes may be an acceptable alternative to left-turn lanes are, according to the Norwegian studies: (a) Traffic volume above 3000, speed limit 50 km/t or higher; (b) Many through vehicles pass waiting left-turning vehicles on the right side; (c) By-pass lane harmonizes with the roads curvature and sight conditions; (d) Not exceptionally many head-on collisions.


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