Split-phase traffic signals protect pedestrians and cyclists by separating them from turning drivers — people walking and biking across the street get their own signal phase, and drivers turning into the crosswalk get another. Research indicates that split-phase signals are highly effective at preventing traffic injuries and deaths. But when DOT revealed its strategy to reduce crashes caused by left-turning drivers, there was no commitment to increase the use of split-phase signals.
DOT is scaling up a similar intervention — leading pedestrian intervals, which allow pedestrians to enter intersections a few seconds before turning drivers get a green light. LPIs reduce injuries too, but not as much as split-phase signals, according to a 2014 DOT-funded study published in the journal “Accident Analysis and Prevention” [PDF].
The study analyzed crash data from 68 New York City intersections with either LPIs or split phases between 2000 and 2007, though the vast majority — 59 — had LPIs. Both types of signal adjustments performed better than a control group of intersections where turning drivers were permitted to proceed at the same time as pedestrians and cyclists. The improvement was more pronounced, however, at split-phase signals.
At intersections equipped with split-phase signals, pedestrian and cyclist injuries declined a precipitous 67 percent. At intersections with LPIs, pedestrian injuries declined 38 percent and bicyclist injuries 52 percent. (For the control group, the reduction was 25 percent for pedestrians and 44 percent for cyclists.) The data on split-phase signals was limited, however — it came from only nine intersections, with no locations in Manhattan.