Summary and Conclusions
Signalization is used to enhance the operational efficiency of roundabouts where pedestrian traffic causes unacceptable vehicle delay and where the volume of traffic from one entry is so high as to cause unacceptable queues at downstream entries. No evidence was identified to suggest that a properly designed signal system would degrade roundabout traffic operations. When traffic signals are installed that stop both entry and exit traffic at the same time while pedestrians cross both directions of traffic, queues back up into the circulating roadway and disrupt traffic operations. Stopping both directions of traffic at the same time is generally not done outside the U.S.
The only study identified that addressed the effect of signalization on roundabout safety showed a marked improvement in safety for vehicles and bicyclists, with no degradation in pedestrian safety.
Solar powered traffic signals that operate only when called by pedestrians could be installed at four legs of a multilane roundabout for about $140,000. The actual cost could be less, if fewer than four signal faces are used at each crossing. Additionally, if pedestrian traffic is unbalanced, then crosswalks can be omitted from some legs and substantial signalization cost reductions can obtain.
The estimate does not include the cost of: (1) installing barriers to prevent pedestrians from crossing at locations other than the crosswalk; (2) drilling through concrete or other work that might be required to install mounting poles in difficult locations; or (3) maintenance or operations. Because ADA standards govern only new constructions or alterations, the estimate does not include the cost to modify an existing roundabout, such as the cost of moving crosswalks and ramps.
Additional research is needed to support signal implementations that do not meet current MUTCD standards. This includes research into the effects of using two-lens amber-red signals instead of red-amber-green signals, and study of the effects of only operating the signals when the pedestrian call button is pressed. Research is also needed to verify that U.S. drivers will comply with roundabout signals, and that drivers will continue to observe the circulating traffic priority rule after responding to pedestrian traffic signals.