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Urban Street Design Guide Index

Urban Street Design Guide
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Fixed vs. Actuated Signalization

Fixed vs. Actuated Signalization

In general, fixed-time signals are the rule in urban areas for reasons of regularity, network organization, predictability, and reducing unnecessary delay. In certain, less-trafficked areas, actuated signals (push buttons, loop detectors) may be appropriate; however, these must be programmed to minimize delay, which will increase compliance.

Actuated signals in general are not preferable because of the maintenance requirements and upkeep of the detection on the street.

Fixed-time signals incur lower initial and ongoing maintenance costs than actuated signals.

Critical

In coordination with traffic signal timing, designers must consider spacing between traffic signals, looking at desirable crossing intervals to achieve a pedestrian-friendly environment.

See Crosswalks

Benefits & Considerations

Drivers and others at downstream unsignalized intersections benefit from a series of fixed-time signals, as they produce routine gaps in traffic that may be used to turn onto or cross the street. Fixed-time signals help make pedestrians an equal part of the traffic signal system by providing them with regular and consistent intervals at which to cross.
Fixed-time signals incur lower initial and ongoing maintenance costs than actuated signals.
Actuated signals prioritize movement along the primary corridor and can present obstacles to cross traffic and pedestrians if timed to prioritize vehicle movements only.
Where used, actuated signals should be timed to be as responsive to activation as possible, with delay kept to a minimum.
Many existing traffic signals controllers have the capacity to reduce delay, but remain in coordination rather than a free setting. Coordination, paired with long signal cycles, can result in delays of 80 seconds or more, reducing pedestrian compliance, increasing risk-taking behavior, and creating the impression that a push button is either non-responsive or malfunctioning.
At crossings where the signal is uncoordinated with adjacent traffic signals (free setting), designers can further reduce pedestrian delay by reducing the minimum green time. At coordinated signal locations, designers have multiple options to decrease delay, including increasing the permissive window, adjusting signal timing for responsiveness at certain times of day, and setting the signal to recall on the pedestrian phase.

Optional

Fully-actuated signal control may be used where vehicle and pedestrian volumes vary considerably throughout the day. Full-actuation can reduce the amount of delay by being responsive to ongoing shifts and patterns in the traffic system.
Semi-actuated control prioritizes the through movement of a major road and is not recommended on streets with frequent cross traffic or pedes- trian demand from the minor approach unless a low cycle length is used (below 80 seconds). Any traffic signal with long delays for pedestrians may discourage crossings and become a barrier to travel, especially at busy intersections.
Actuated signals may be combined with a number of signalization treat- ments, including full signalization (of the major and minor approach) and pedestrian or half-signalization (stop sign on the minor approach).
Signalization is not always the best option for a given intersection. Stop or yield control may be preferable at intersecting local or residential streets.

Recommended

Fixed-time signals are recommended in all downtown areas, central business districts, and urban areas in which pedestrians are anticipated or desired and speeds are intended to be low.
Use of semi- or fully-actuated signal operations should mainly be restricted to suburban arterials and rural roads. In suburban corridors, motorist compliance can be increased and delay reduced through use of actuation.
In areas with lower pedestrian traffic, actuation may be used along priority rapid transit corridors to increase the schedule reliability of transit service and avoid unnecessary delays.
The responsiveness of an actuated signal should be prompt (as low as 5 seconds) based on the necessary transition time for approaching motorists to come safely to a stop. In cases where the pedestrian movement crosses a high capacity transit line, major bicycle facility, or critical freight route, longer delays are acceptable.
For major bicycle routes, use upstream passive detection as opposed to push-button activation to minimize the time lag between detection and crossing.

References

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Adapted from the Urban Street Design Guide, published by Island Press.

References

References for Fixed vs. Actuated Signalization: 11 found.