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