LPI – Leading Pedestrian Interval

Friday, July 18, 2008

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.

http://www.livablestreets.com/people/LevinN LevinN

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.
Dr. Errol C. Noel

An excellent solution that could reduce pedestrian-vehicle conflicts and crashed at crosswalks! But, we have to be careful about improper implementation. We need a standard for application. This will help the engineers in conducting the appropriate study to confirm need for and the duration of a lead ped interval. In the context of other solutions, we must be able to confirm when LPI is the best option on a case by case basis. Application to all intersections, including all those with substantial pedestrian traffic, is NOT RECOMMENDED. Opportunity for MUTCD consideration!
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Anonymous

This is a great idea that someone noted in the comments of this blogpost: http://blog.timesunion.com/gettingthere/walking-can-be-dangerous-to-your-health/2044/
Anonymous

LevinN - the Denver diagonal dance is dead, unfortunately: http://blog.timesunion.com/rogergreen/the-depressing-demise-of-the-denver-diagonal-dance/1908/
Guest

These sound like great ideas, love the UK style street markings. Now how do we stop Pedestrians from crossing the street when there isn't enough time on the "walk countdown?" Pedestrians cause gridlock too by taking up time at an intersection that was meant for cars turning etc, by crossing when there is 1 second left on the countdown. This needs to be addressed also.
Murray Henman

We have at least one of these in Brisbane, Australia (corner of Adelaide and Edward Streets). I haven't heard anyone suggest getting rid of it, so come and take a look.
Ian Dutton

In what situation could it possibly be harmful? The only drawback is that a few seconds have been removed from the green phase for that direction of flow. I think that in ANY situation where turning vehicles threaten pedestrians, it's a no-brainer and very effective measure to protect vulnerable street users. What could possibly be the "standard for application" - whether or not the pedestrians in question are worth not being run over?
NF

This isn't really a pedestrian problem, as much as it is a signal timing problem.

The answer is to separate the movements to that they cannot happen together. At locations where this is problem people driving should be given a clear green signal without conflicting pedestrian movements.

Alternatively, prohibiting the turning movement to prevent the conflict also works well.
NF

This is a fully MUTCD compliant treatment, no special experiments necessary. In fact, engineers already have the formulas necessary to calculating crossing time for pedestrians and cars, and are fully capable of using their engineering judgement to decide how many seconds to provide to the LPI.
Robert

Some situations might be better solved with a scramble crossing, or "Barnes Dance." However, in a city like NYC, with both aggressive pedestrians and drivers, this is probably a better solution. A scramble crossing would encourage enough people to commence crossing with inadequate time on the light (eg. five seconds across the Avenues) to cause a real safety hazard and some serious traffic problems as well.

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