Signal timing
Signal timing is the technique which traffic engineers use to determine who has the right-of-way at an intersection. Signal timing involves deciding how much green time the traffic lights shall provide at an intersection approach, how long the pedestrian WALK signal should be, and many numerous other factors.
Coordination
Coordination refers to the timing of the signals so that a "platoon" of cars traveling on a street arrives at a succession of green lights and proceeds through multiple intersections without stopping. A well coordinated signal system can enhance traffic flow, reduce delay and minimize pollution. However, it is not always possible to retain progression throughout a network of signals. It is also difficult to maintain signal progression on a two-way street. An early traffic engineer Henry Barnes, who served as Commissioner of Traffic in many cities including Baltimore, Maryland and New York, New York, developed coordinated traffic signal timings, so that large amounts of traffic could be accommodated on major traffic arterials.
Traffic signal timing is a very complex topic. For example timing a 'WALK' signal for a wide pedestrian crossing and slower pedestrians (for example the elderly) could result in very long waits for vehicles, and thus increases the likelihood of cars running the light, which could potentially cause accidents. Therefore, optimizing the safety of intersections involves multiple factors like street width, lane width, number of intersecting streets, availability of electricity for a signal, number of cars per unit of time and even/uneven nature of flow, number and type of pedestrians, and many other factors.
Traffic signals can be programmed to have different signal timing plans, depending on the time of day.
Research
Standardizing signal timing procedures, standards, and best practices has recently been completed in the form of the The Signal Timing Manual, a tabletop resource compiled by Kittelson & Associates, Inc., the Texas Transportation Institute, the Institute of Transportation Engineers, and the University of Maryland.