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Urban Street Design Guide Index

Urban Street Design Guide
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Signal Cycle Lengths

Though often invisible to the public, traffic signal cycle lengths have a significant impact on the quality of the urban realm and consequently, the opportunities for bicyclists, pedestrians, and transit vehicles to operate safely along a corridor.

Long signal cycles, compounded over multiple intersections, can make crossing a street or walking even a short distance prohibitive and frustrating. This discourages walking altogether, and makes streets into barriers that separate destinations, rather than arteries that stitch them together.

Short cycle lengths of 60–90 seconds are ideal for urban areas.

Corridor-Based Signal Timing with Longer Cycles

Corridor-based cycle lengths (sec)

Longer signal cycles and corridor-based timing schemes make large avenues into barriers that separate neighborhoods rather than joining them.

Under the initial conditions shown above, all users approaching from side streets incur significant delay when crossing the major corridor. The major corridor receives almost four times as much green time (96 seconds) as the minor streets (24 seconds). As a result, motorists avoid minor streets, increasing congestion on main routes. Pedestrians frequently cross the street out of frustration before receiving a WALK signal.

Balanced Signal Timing with Shorter Cycles

Balanced cycle lengths (sec)

Shorter signal cycles help city streets function as a complete network, rather than a series of major corridors.

In the balanced scenario, the signals are re-timed with 60-second cycle lengths. The amount of green time at each minor intersection is apportioned in a 3:2 ratio (36 seconds for the major street, 24 for the minor). The increased turnover improves pedestrian compliance and decreases congestion on surrounding streets.

Benefits & Considerations

Short signal cycles reduce overall pedestrian wait times as well as side street delay.
Shortening cycle lengths can come at the expense of reducing the amount of time that a pedestrian has to cross the street. While long cycle lengths may increase pedestrian non-compliance and risk-taking behavior, short cycle lengths may not always be achieved without resorting to a 2-stage pedestrian crossing, especially on wider streets and boulevards. Determination of the appropriate cycle length must always be correlated with the pedestrian crossing distance on a given street.1

See Crosswalks

Cycle lengths influence the desired progression speed of traffic along a corridor. They may be used to keep speeds to a minimum as part of a coordinated signal timing plan. Longer cycle lengths result in wider variability in speeds.

Critical

A minimum WALK time of 7 seconds is required (MUTCD 4E.06).

Recommended

Short cycle lengths of 60–90 seconds are ideal for urban areas and permit frequent gaps and consistent crossing opportunities, creating a more permeable network.
The length of a pedestrian crossing should be taken into account when using shorter cycle lengths. In some cases, elderly pedestrians and children may be unable to cross in a single cycle. In these cases, efforts must be made to shorten the crossing via road diets, curb extensions, and other measures.
While short cycle lengths are desirable, ensure that cycle lengths are long enough for pedestrians to cross wide streets in a single leg without getting stuck in the median, unless the median is a destination in and of itself.
Adaptive signal control should have limited variation in their cycle length. Operations for adaptive signal control should be limited to suburban settings and event venues where traffic is highly variable. Adaptive signal control can result in a longer cycle length that degrades multi-modal conditions.

Optional

Cycle lengths may be adjusted according to the time of day to account for fluctuating vehicle or pedestrian volumes. Cycle length adjustments should be minimal and consider both pedestrian and vehicle volumes at peak and off-peak times.
Cycle lengths shorter than 60 seconds are only recommended where a city uses “feathering” (intervals that decrease as they approach a pinch point) to relieve an upstream bottleneck. In such cases, adequate crossing time for pedestrians should be taken into account based on a crossing speed between 2.5–3.5 feet per second.2

Footnotes

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  1. Ron Van Houten, Ralph Ellis, and Jin-Lee Kim, “Effects of Various Minimum Green Times on Percentage of Pedestrians Waiting for Midblock “Walk” Signal,” Transportation Research Record No. 2002 (2007).
  2. When actuated, the direction of travel with a green phase should be given ample time to safely change from green to yellow then red. The amount of time for the yellow change interval is dependent on approach speed (presumably 25 mph or less), which would require 3 seconds. The time that should be given for the clearance interval (red signal for all legs of intersection) is dependent on the approach speed and intersection width. An approach speed of 25 mph and an intersection width of 70 feet would recommend a clearance interval of 2.5 seconds.

    James A. Bonneson, Srinivasa R. Sunkari, and Michael P. Pratt, Traffic signal operations handbook (College Station: Texas Transportation Institute, 2009).

References

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

References

References for Signal Cycle Lengths: 4 found.