Traffic control devices are only effective if they are seen as reasonable by the drivers who use them. Usually after lesser forms of control have proven ineffective. Then traffic engineers follow specific, uniform, guidelines to determine whether a traffic signal is called-for. They look at daily and hourly traffic volumes on the intersection approaches, including through vehicles, turning vehicles, and pedestrians. When a location meets engineering criteria, traffic signals will improve safety and operational efficiency.
Problems can result.
Signals almost always create more overall delay to drivers. In fact, minor side street traffic may experience excessive delay, particularly during off-peak hours. Because of this, drivers may actually avoid the signalized intersection and switch to alternate routes or to residential streets not meant to handle through traffic. This leads to problems elsewhere in the area. People also seldom consider the cost of signals, both in public funds and out of their own pockets.