The following excerpts were taken from the 1991 Manual of Traffic
Signal Design, 2nd Edition, published by the Institute of Transportation Engineers
(pp. 139-140)
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.