Civil Engineering Reference
In-Depth Information
16.4.3 Cycle Phases
The number of phases should be kept at a minimum. Two-phase operation is
desirable wherever possible. As the number of phases increases the red time on each
approach increases and so does delay. A third phase, and sometimes a fourth phase,
is needed to serve left turns or accommodate a third street entering the intersection.
Additional pedestrian-only phases generally should be limited to locations with
heavy turning movements
and
heavy pedestrian crossings.
Design and operating strategies that restrict or divert left turns and simplify
intersection geometry can reduce both cycle lengths and delay.
16.4.4 Coordination
Coordinating traf
c signals along a roadway minimizes stops and delays during
both peak and off-peak hours. Coordination requires signals to operate on common
cycle lengths. In addition, uniform spacing of signals is desirable.
Signals should be coordinated on city streets (where they are spaced close
together), and on suburban roads where their spacing does not exceed one mile.
The traf
c speeds that result from coordination depend upon both the signal
spacing and the cycle length. Higher speeds require longer distances between signals;
shorter cycle lengths and closer spacing of signals produce lower speeds [
5
].
Figure
16.1
shows these relationships.
Fig. 16.1 Speed of traffic
progression as a function of
cycle length and signal
spacing.
Source
Reference
[
5
], p 57. Figure 7.1
