The Leading Pedestrian Interval (LPI) helps put people crossing the road in a better position to be seen by drivers, much like taking the lane by cyclists. LPI's are combined with concurrent pedestrian phasing - you don't have a need for an LPI if you have exclusive phasing. LPI's give a person a head start when crossing so that drivers making a right turn can better see the people on foot.

Concurrent phasing helps reduce the amount of time between pedestrian phases so that pedestrians aren't tempted as much to cross against the light. FHWA studies show that concurrent phasing is no more unsafe than exclusive phasing.

Crossing times in the U.S. are dictated by the American's with Disabilities act (ADA) as 3.5' per second. Of course, this is very frequently ignored by those programming the signals.

Exclusive pedestrian phases are exactly that, all the traffic lights turn red and people on foot are allowed to cross. While simple, it does lead to much longer phases. If the walk phase doesn't come around every 60 seconds or less, people tend to cross anytime they have a break in traffic. This is why many pedestrian advocacy organizations try to get concurrent phasing wherever possible.

Of course, having pedestrian crossing lights that are on automatic recall (the crosswalks get a walk signal once every signal phase) is very important so that people can sometimes get a walk signal just as they approach the crosswalk, just like people in cars. Having to press a beg button to get a walk light means that people on foot nearly always have to wait more than a few seconds for a walk signal.

Protected intersection design does much the same as a Leading Pedestrian Interval except that people on foot and on bike get a start in space, not time.