Q: Sometimes when I press the button to cross intersections, nothing happens. At other times, there’s a quick response. Why is that?

A: Traffic signals for cars and pedestrians are on timers, and each timer varies in duration, which explains why the wait is longer at certain intersections than at others. At most intersections in Manhattan, the timers are “actuated,” which means that lights continuously change at regular intervals. In the outer boroughs, where intersections vary in configuration and volume, many intersections are “semi-attenuated” which means that either a person pressing a button on a pole or a car passing a sensor buried beneath the asphalt will cause the light to change. For example, at intersections where traffic from side streets is rare, the light may change only when a car passes a sensor. Certain waits, however, vary even at the same intersection. This is where things get complicated. Each timer cycles continuously on 60-90- and 120-second cycles. When the light will change is dependent on where the timer is in the cycle when you press the button. At a certain point in the cycle – which varies according to the volume of traffic at any given intersection – someone pressing the “walk” button will have to wait for the cycle to complete before getting a green light. Likewise, if you press the button before this cut-off point, you don’t have to wait for the next cycle. It’s like catching a train as it enters the station as opposed to arriving at the station just as a train leaves. In other words, it’s all in the timing.