or — Why am I Sitting at a Red Light?
Traffic signals and timing may be controlled in a variety of different ways depending upon the city or county where you’re driving. The most familiar setup is a control box located near the intersection where the folks in charge of local roadways can set a program of signal light changes and times for different times of day based upon past traffic volume data. Many localities, however, are trying to be more quickly reactive to changing traffic conditions by setting up live monitoring and signal control at important intersections. In Sacramento County, California, for example, the Traffic Operations Center uses more than 100 traffic cameras to monitor live conditions on the county’s roadways in order to directly control traffic signals and timing at most of at those intersections. In addition to being able to react more accurately to changing traffic volume, this type of system is especially helpful when unexpected conditions occur such as accidents, weather events, fires, or other situations that may suddenly change traffic.
In addition to the signal programming — and live cameras where those are installed — an important feedback element for traffic signals and timing is the system of sensors built into the roadway that detect vehicles approaching intersections. Not only do these help trigger the light changes, they also provide the local transportation agency with live information about the volume and speed of traffic passing over the sensors. The green, yellow and red traffic information we can see on live traffic maps is drawn from this constantly updated information.