General Considerations

The functional objective of signal timing is to alternate the right-of-way among the various phases in such a way as to:

• provide for the orderly movement of traffic.
• minimize average delay to vehicles and pedestrians.
• reduce the potential for accident-producing conflicts.
• maximize the capacity of each intersection approach.

Unfortunately, these desirable attributes are not compatible. For example, delay may be minimized by using as few phases as possible and the shortest practical cycle length. To reduce accident potential requires fewer conflicts. Therefore, multiple phases and longer cycles are indicated. Maximizing approach capacity requires the minimum number of phases to service the demand. Accordingly, it is necessary to exercise engineering judgment to achieve the best possible compromise among these objectives.

Timing for Pre-timed Control

There are several fundamental aspects of developing timing settings for pretimed signal control. Some of there fundamentals are also applicable to actuated signal timing. The essential elements include:

• Number of timing plans.
• Phase change intervals (yellow change plus all-red clearance)
• Pedestrian timing requirements (including decision whether or not to use pedestrian
• indications)
• Cycle length calculations
• Split calculations
• Flashing operation

To function effectively, pre-timed signal operations must take into account a number of local intersection variables and hardware characteristics. It is therefore difficult to set forth comprehensive guidelines to fit all possible situations. In many situations, it is desirable to monitor the initial operations and adjust the timing settings to reflect the unique character of the intersection and traffic flow.