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.
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.
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.
James A. Bonneson, Srinivasa R. Sunkari, and Michael P. Pratt, Traffic signal operations handbook (College Station: Texas Transportation Institute, 2009).
Adapted from the Urban Street Design Guide, published by Island Press.