Suggested design changes for safer biking in roundabouts:
1. Eliminate reliance upon drivers to make decisions which maintain the safety of cyclists or give way on behalf of cyclists. For every approach, cyclists intending to the use the interior of the roundabout are forced to merge into vehicular traffic at their own risk. Drivers are allowed to maintain their speed and trajectory in spite of the merging action being forced upon them.
a. Entry angle, or the angle by which vehicles enter the roundabout, should be as close to 90 degrees as possible – any angles less than 20 degrees is too flat to enforce 15mph design speed.
b. View angle, or the angle by which drivers must look left over their shoulder to assess oncoming traffic (and bicycles) within the roundabout should be less than 15 degrees. A view angle of 15 degrees or more confuses priority messages about yielding and encourages unsafe merging behaviors.
c. Fast path describes a near straight-line route through the roundabout which allows drivers to accelerate at any point of the roundabout’s entry or interior. Fast paths are created with entry angle and view angles are misaligned and the interior design of the roundabout fails to discourage acceleration.
2. Vehicular approaches should be modified to improve sight lines and reduce travel speed, not prioritize intersection efficiency. Any multi-lane approaches should be eliminated in favor of single lane approaches.
a. Eliminate right-turn bypass lanes.
The NCHRP Report 672 Roundabouts an Informational Guide has this warning about Right-Turn Bypass Lanes: “A right-turn bypass lane (or right-turn slip lane) should be implemented only where needed, especially in urban areas with bicycle and pedestrian activity. The entries and exits of bypass lanes can increase conflicts with bicyclists and with merging on the downstream leg. The generally higher speeds of bypass lanes and the lower expectation of drivers to stop may increase the risk of collisions with pedestrians. They also introduce additional complexity for pedestrians with visual impairments who are attempting to navigate the intersection.” Section 6.8.6.
3. The interior of the roundabout should encourage cars to slow down, not allowing for acceleration until they have fully exited the roundabout. Recommended width of travel lane in roundabout is 14ft (the existing design is several feet wider than this). The roadway could provide an adverse camber, and the angles of entry/exit from the interior should be more acute.
Making Roundabouts Work for Pedestrians and Bicycles
Some of the concepts in this report are correct, but it fails to fully deliver the keys to safe roundabout design for bicycles.
4. The safest path for cyclists to navigate the roundabout is by never entering the interior at all. Unfortunately, the current layout of the roundabout does not provide an adequately safe off-street alternative.
Safest Roundabout Design for cyclists. The best of Dutch infrastructure is worth emulating.
Test ride the safest roundabout in Assen
a. 90 degree crossings between cyclists, pedestrians, and drivers improve sight-lines of all users. Bicycle and pedestrian crossings (each should have their own separated pathways, not combined into a shared-use pathway) should be set back in advance of vehicles entering the roundabout, and if necessary, include speed humps that alert drivers of the crossing and encourage slower speeds.
b. Refuges between streams of motor traffic which are wide enough to accommodate a whole bicycle. It may be necessary for a person riding a bike to find refuge in an island while exiting traffic clears the intersection. These islands should be large enough for an entire bicycle to fit.
c. Bidirectional cycle-paths allow cyclists to cross fewer streams of traffic – crossings are where the dangerous interactions occur. To allow cyclists maximum flexibility for navigating the roundabout safely and efficiently, the cycle paths circumnavigating the roundabout should be bi-directional.d. Right turns take place with no interaction at all between cyclists and motor vehicles. A bicyclist should be able to approach a roundabout and make a right-hand turn without ever interacting