Leebo,
Concurrent crossing phases help to keep automobile traffic moving (traffic engineers love this), provide shorter wait times for pedestrians and are the default choice for a great many traffic engineers. They do have their problems, especially where there are few pedestrians crossing and drivers don't expect them, much of the USA falls into this category.

Exclusive pedestrian phases (also know as scramble or Barnes dance) stops all traffic and give pedestrians free reign in the crosswalk. The downside for pedestrians is that the time between pedestrian phases is increased. When frequency of pedestrian phases goes beyond 60 seconds, jaywalking tends to increase as pedestrians become impatient. In areas with high pedestrian traffic this phasing can reduce automobile throughput and significantly downgrade the Level of Service (LOS). Automobile LOS is frequently the Holy Grail for traffic departments and not surprisingly, traffic engineers don't like to downgrade automobile LOS to make things easier for pedestrians.

Adding a leading pedestrian interval (LPI) to the concurrent phase gives pedestrians a head start on traffic and allows them to be in the crosswalk giving them them the right of way and making it much more likely that turning traffic will yield, instead of barreling through to deny pedestrians their RoW. Not unlike taking the lane in cycling terms. The LPI is generally three or more seconds. Most pedestrian crossings are timed for a pedestrian walking speed of 4ft/second, elderly people and small children are slower and do better with 3.2 - 3.5 ft/sec. The LPI tends to balance out the problems with concurrent and exclusive phases, except where there is a large amount of turning traffic.

Of course, increased traffic enforcement is frequently needed to help make crossings safer and your eyes and ears are always your best defense when crossing or riding on the road.

Anyways, I hope I'm not totally highjacking The Sci Guys thread.