Metered entrance

Roundabouts operate effectively only when there are sufficient longer and acceptable gaps between vehicles in the circulatory lanes. If there is a heavy movement of circulating drivers, then entering drivers at the next downstream entry may not be able to enter. This situation occurs most commonly during the peak periods, and the performance of the roundabout can be greatly improved with entrance metering.

The concept of entrance metering at roundabouts is similar to ramp metering on freeways. A convenient sign is a changeable one that reads “Stop on red signal” and shows the usual yield sign for a roundabout otherwise. The sign would also include a yellow and red signal above the sign. The operation of the sign would be to show drivers the roundabout sign, display the yellow light and the sign “Stop on red signal,” and finally display the red light and the same text sign. This would cause entering vehicles to stop and allow the vehicles at the downstream entrance to proceed. A queue length detector on the downstream entrance may be used to indicate to the signal controller when the metering should be activated and deactivated. Once on the circulatory roadway, vehicles are not stopped from leaving the roundabout.