How does the Road Commission determine when and where to put a traffic signal?
Often developers proposing a new subdivision or shopping mall hope to get the Road Commission to install a traffic signal at the entrance to their development to make it easier to get in and out. If there are already traffic problems in the area, frequently local residents will voice their agreement that what is needed to solve the problem is another traffic signal. It is as if signals are viewed as some sort of cure-all. They are not. Traffic engineers, in making a determination of whether a signal is or is not “warranted,” refer to a manual of guidelines known as the Michigan Manual of Uniform Traffic Control Devices. This manual covers everything from signals, to pavement markings, to signs. Virtually identical manuals are used in every state. This manual identifies no less than 11 warrants that may be reviewed in determining whether a signal should be installed. The warrants that receive the closest review, however, are: minimum vehicular volume, interruption of continuous traffic,
