The Benefits of Retiming Traffic Signals

Headnote

SIGNAL RETIMING IS ONE OF THE MOST COST EFFECTIVE WAYS TO IMPROVE TRAFFIC FLOW ALONG A CORRIDOR. TRAFFIC SIGNAL RETIMING CAN SIGNIFICANTLY REDUCE DELAYS AND STOPS EXPERIENCED BY MOTORISTS, WHICH CAN IMPROVE SAFETY AND REDUCE FUEL CONSUMPTION AND EMISSIONS. TYPICALLY, THE BENEFIT TO COST RATIO FOR SIGNAL RETIMING IS ABOUT 40:1.

WHAT IS SIGNAL RETIMING?

Signal retiming is a process that optimizes the operation of signalized intersections through a variety of low-cost improvements, including the development and implementation of new signal timing parameters, phasing sequences, improved control strategies and, occasionally, minor roadway improvements.

The signal timing process often includes the training of engineering and maintenance staff to use existing signal control equipment more efficiently and to support new technologies as they become available for implementation.

Each traffic signal operates under a unique set of timing parameters. These parameters include minimum and maximum green durations, pedestrian indication requirements, gap and extension times, overlaps and phase change intervals (yellow change plus red clearance). A fixed-time signal also must have fixed cycle and split lengths that accurately balance average demand over a period of time.

When signals are operated within a coordinated system, additional parameters are used: cycle (the time needed to serve all phases); offset (the time from a reference point, such as the start of green or yellow of the coordinated phase at one intersection, to the same reference point at the other intersections); and split (the time allowed for each movement or phase-their total is the cycle length).

The offset is used to allow vehicles moving at the proper speed to advance from intersection to intersection without stopping. This process is called progressive movement.

As traffic patterns change over days, weeks and times of year (such as holidays), it is appropriate to modify signal timing parameters. This often includes the development of different timing parameters for morning and evening peak periods, midday off-peak periods, weekends and nights.

Signal retiming is oriented toward optimizing a controller unit's response to the demands of roadway users, including all types of motor vehicles, bicycles and pedestrians. Signal timing strategies include the minimization of stops, delays, fuel consumption and air pollution emissions and the maximization of progressive movement through a system.

Occasionally, the signal retiming process includes the reconfiguration...