Left turns that take place from shared lanes impede the other movements in the shared lanes unnecessarily. This results in a very inefficient utilization of the available roadway space. Heavy left turns, even from exclusive lanes, require dedicated phases that rob time from the major movements and increase the total time lost due to startup and termination of traffic movements. Signals are mechanical devices that not only require maintenance but also periodically malfunction. They are also dependent upon electrical power and do not, therefore, provide any control during power failures.
Many signal violations occur at higher speeds so that the severity of accidents is often high.
Permitted left turns and right turns on red introduce additional conflicts. Even when TWSC capacity is not exceeded, there is often public pressure to install signals at TWSC intersections. AWSC treats the cross street movements more favorably, without the wasted time associated with traffic signals. Roundabouts A roundabout overcomes all of these disadvantages. Left turns are not subordinated to through traffic.