#17 Protected Turns
- Duc Phan
- Mar 24
- 2 min read
Protected turns are highly effective for reducing traffic conflicts and are the default position for signalised intersections in a safe system framework. Common turn-related crash types involve vehicles turning right across the path of oncoming through traffic and rear-end collisions of same-direction vehicles turning left or right. Research in the US shows that auxiliary right-turn lanes (US left-turn) produce crash reductions of 28 – 48%, while 14 - 26% reductions are attributable to left-turn lanes (US right-turn)[1]. Protected turns are also used to minimise traffic delay and improve network efficiency.
Protected turns are generally characterised by auxiliary turning lanes and associated signs and guidance, often including turn signals in urban areas especially. Dedicated turning lanes provide opportunities for vehicles to decelerate on approach to the turn, and storage of stopped vehicles waiting for a turning opportunity. However, there are many types of protected turn treatments, the selection of which depends on a complex combination of factors such as road configuration and alignment, road user types, traffic volumes, speed limits, intersection type and other variables.
Right-turn treatments
Two relatively simple T-junction solutions for both rural and urban roads are the Basic right-turn (BAR) and Channelised Right-turn (CHR) treatments. The BAR treatment is the least complex and offers the least protection, with through vehicles passing right-turning vehicles to the left on a shoulder of sufficient width. CHR treatments provide a channelised auxiliary turning lane as some measure of protection, removing right-turning vehicles from the through traffic stream.
More complex treatments provide greater protection through the default provision of auxiliary lanes, but typically also require more space to implement. These include staggered T-intersections with overlapping or back-to-back right-turns, two-stage crossings on divided roads, offset right-turn lanes, and (rural) ‘seagull’ and wide median treatments. Right-turn bans are sometimes appropriate, including where auxiliary lanes cannot be provided, sight distance is poor, and/or there is a noted risk of conflicts.
Left-turn treatments
As with BAR, the Basic left-turn (BAL) treatment is the least complex and offers the least protection. Auxiliary left-turn (AUL) treatments provide an auxiliary left-turn lane of appropriate length, removing turning vehicles from the through traffic stream and reducing rear-end collision risk. Channelised Left-turn (CHL) treatments include a traffic island separating turning traffic from through traffic and may also include an acceleration lane. Provision of the traffic island may help to reduce pedestrian crossing distances. Consideration must be given to heavy vehicle turning requirements.
[1] Information sourced from Austroads Guide to Road Design Part 4A and FHWA Proven Safety Countermeasures
