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Signal Systems

​Found at every major intersection, signal systems are the most common and easily understood type of intelligent transportation system. The newest systems utilize the latest technologies and are truly “intelligent” – adapting to changing traffic conditions in real time.

How “smart” can a signal get?

The most basic traffic signals are timed, going through a pre-set sequence of green, yellow and red lights based on the time of day. A “smart” (actuated) traffic signal can sense the presence of approaching vehicles and adapt to change the length of each light cycle. This reduces delays that cause traffic jams, lowers emissions caused by vehicles sitting at the light and helps relieve driver frustration.

A series of “smart” intersections can coordinate to allow traffic to progressively flow along an arterial street. This “open network” of signals greatly reduces total trip time by pushing groups (platoons) of vehicles along a corridor at a steady pace. North Carolina’s U.S. 70 from Raleigh to the coast is the most impressive example of this type of signal system.

In centralized business districts, such as in city centers, an isolated group of coordinated intersections, called a “closed loop,” is utilized to improve traffic flow in and around these areas.

Centralized computer systems blend these two components to provide coordinated traffic flow in metropolitan areas.

Other Components

Other components that are often used in concert with signal systems are described below.

​Device​Purpose
​Lane control signs​Lane control signs are used to change designated lane use based on traffic conditions.Ramp meters, also called on-ramp signals, regulate the number of vehicles entering a high-volume freeway to prevent congestion
​Ramp meters​Ramp meters, also called on-ramp signals, regulate the number of vehicles entering a high-volume freeway to prevent congestion
​Traffic cameras​Traffic cameras allow operators to verify reported incidents on roads and change traffic patterns to alleviate congestion.


7/10/2018 10:19 AM