LPI – Leading Pedestrian Interval
Leading Pedestrian Intervals (or LPIs) are a traffic signalization strategy that assigns pedestrians an exclusive 3 to 5 second signal (in some cases much longer) to begin crossing the street before cars get a green light. Consequently, they are also known by their sassier nickname, Pedestrian Head Start. But in my view the best variation on what LPI stands for comes from Christine Berthet of the Hells Kitchen Neighborhood Association who proposes: "Life Preserving Interval". That's what it is.
Transportation Alternatives has recently begun a push to make these more common in NYC. Here's hoping our video (featuring some nice visuals from TOPP's own Carly Clark) can help aid the case and explain what this arcane phrase means.
I've heard that Denver, CO has a more extreme version of the "Leading Pedestrian Interval". The timing of some of the signal lights has 3 phases. In one phase, vehicles on one street have the right-of-way. In the second phase, vehicles on the other street have the right-of-way. In the third phase, pedestrians own the whole intersection, so they can cross either street, or both at once diagonally. Pedestrians don't just get a head start--they get a car-free intersection with enough time to cross completely in any direction.
A few years ago, downtown Seattle WA would sometimes develop gridlock, when there were so many pedestrians in crosswalks that vehicles could never turn right or left, over many signal-light cycles. Eventually the car drivers would get impatient, and nudge their way through the fully occupied crosswalks. The Denver idea would solve this problem, I don't know whether or not Seattle has implemented it yet.