Roundabouts are becoming more common in urban areas and with good reason. They are known to improve traffic flow and safety in comparison to other forms of intersection control such as traffic signals. However, problems can arise from using roundabouts since traffic signals and signs have been the standard for so long. Understanding how to best optimize roundabouts and prevent accidents will ensure that traffic flow is being optimized.
According to a research conducted by the Insurance Institute for Highway Safety (IIHS), most of the accidents at roundabouts were run-off-road, rear-end, sideswipe, and entering-circulating. Drivers may not slow down sufficiently or early enough on high speed roads and can result in a collision with another vehicle, pedestrian or street furniture.
To increase awareness of an upcoming roundabout, municipalities have posted advance signage to alert drivers. Countdown markers and chevron signs have been throughout the UK to indicate upcoming roundabouts. Transverse yellow bar markings have been effective as well over longer distances on approaches to large roundabouts on high-speed roads. It has been shown that there is 11-18% reduction in collisions when applied to motorway slip roads.
In the UK, high-friction (or anti-skid) surfacing has been implemented as a signal. It’s used not only on the basis of indicating stopping distance from the roundabout but also taking into consideration the length of queues regularly occurring on the approach. This is useful for wet road conditions and has reduced accidents by 57%.
Decreasing the speed limit on the approaches to a roundabout is also an effective safety measure to reduce accidents as well as the severity of them. This has been implemented in Edmonton, Alberta and Victoria, Australia among many other cities. Splitter islands are also considered to assist in controlling approach speeds.
Having appropriate signs and landscaping helps signify upcoming roundabouts and ensures crashes are less severe. High curbs, walls or other obstacles can intensify crashes. In order to prevent this, within the UK, cities removed these obstacles and utilized signs made of multiple flexible marker posts to alert drivers.
In order for roundabouts to be effective, they need to be placed in the appropriate locations. Space constraints or highly unbalanced traffic flows are generally not desirable intersections for roundabouts. However, in desirable intersections, IIHS found that roundabouts have been shown highly effective and reduce accidents by 39%, carbon emissions by 30% and improve traffic flow by 62-75%. Utilizing roundabouts as a result is beneficial, even more so when any potential safety concerns are addressed early on.