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U.S. Department of Transportation
Traffic Signal Timing Fundamentals
§Fixed
Timed Operation
□Does not
require traffic detectors at the
intersection
□Includes a
set programmed time to service all movements every cycle
□Services all
movements whether or not there is vehicle demand
□Assumes that the
traffic patterns can be predicted based on time of
day
§Actuated Operation (Semi-Actuated or Fully
Actuated)
□Consists
of actuated traffic signal controllers and traffic detectors placed in
or on the roadways approaching the intersection
□Primarily concerned
with when green intervals terminate
▪Maximum Green Time
▪Traffic Flow Ceases on the Approach
▪Force-off by the Signal System
▪Traffic Signal Pre-emption
§Adaptive Signal Operation
□Consists
of adaptive traffic control system and traffic detectors placed in
or on the roadways approaching the intersection
□Coordinates
control of traffic signals across a signal network, adjusting the lengths of
signal phases based on prevailing traffic conditions
