Locally Quickest Paths

One of the major improvements scheduled for Pathfinder 2011 is a change to how occupants plan their paths out of the building. Previously, occupants would identify the shortest path all the way to their exits, then follow that path in its entirety. As these paths stretched through the building, certain geometric features could produce very popular routes – leading to what we came to refer to as the “divided door” bug. This is a reference to one side of a divided door receiving all of the traffic.

Pathfinder 2011 will use a system we refer to as “locally quickest”. With this technique, occupants will only plot a path through the current room. When choosing between doors leading out of the current room, occupants will be aware of density and consider the time it will take to reach each door as part of the local path planning decision. To illustrate the difference, we have uploaded a couple before and after videos.

In the first case, occupants are in a room with two door doors (very near one another). For all of the occupants in the room, the lower of the two doors provides the shorter overall path to the exit. Previously (left side), almost all of the occupants used the lower door which resulted in an evacuation time much slower than might be expected based on the available doors. A few occupants do use the upper door, but only when they are forced far enough off their original paths that a path regeneration is triggered.

In the locally quickest version (right side), occupants review their local path at a regular interval and make changes based on the density between their current location and the target door. This produces a much more even usage of the doors.

The second case shows a large room with three exits. The room is designed to force all occupants closer to the center exit. In the previous version (left), very few occupants use the left or right exits. This causes the center exit to become very congested. The new version reduces congestion at the central exit considerably as occupants are able to detect the slow-moving queue and select an alternate exit.

We are still working out some details, but the new system should be available to beta testers soon.