Additional Thoughts on Pedestrian Detection

This is a continuation of a previous post, found at:

 http://ntcip-unleashed.blogspot.com/2012/02/pedestrian-detection-diagnostics.html

Generally, there are two pedestrian pushbuttons for each pedestrian phase.  These two inputs are wired in parallel to a single input.  The two buttons for phase 2 are wired in series to the input for ped phase 2.  This means that with most signals, the 8 pedestrian inputs are wired in pairs, to inputs 2, 4, 6 and 8.

Modern traffic signal controllers are capable of at least 8 pedestrian inputs.  Many are capable of 16 pedestrian inputs.  Traffic signal cabinets can be configured to include at least 8 pedestrian inputs.  Modern traffic signal controllers allow for mapping of any ped wire input to any controller ped input.  This can be done in two different places, one is in the mapping of the specific pins / BIU designation in the controller, and another in a pedestrian detection input screen.

Since normally the two pedestrian pushbuttons for any specific phase are wired in parallel to a single input, any problem on the parallel circuit will register in the pedestrian detection diagnostics as a failure on the ped phase input.  The parallel circuits for the two buttons creates a situation where the technician needs to spend extra time and effort to isolate which particular button / wire combination in the parallel circuit is failing.

Since multiple inputs can be mapped, the signal can be rewired to have each specific button / field wire set come into a unique input.  This would mean that when a failure occurred, the technician would have immediate knowledge of which particular button circuit was problematic.

A standard approach would need to be figured out.  A potential standard for the wiring could be:

Detection            Mapped               Near/Far
Input                     Phase
1                                 2                           Near
2                                 2                           Far
3                                 4                           Near
4                                 4                           Far
5                                 6                           Near
6                                 6                            Far
7                                 8                           Near
8                                 8                           Far

Where “Near” is the button closest to the approaching traffic on that that phase’s approach, and "Far" is on the opposite corner for the same phase.

This type of wiring, along with pedestrian detection diagnostics would allow for the central system to report the specific button that was failing.

This is important, as when ped detectors become stuck on, this causes added delay to the drivers waiting for pedestrians that don’t exist. 

Special consideration will need to be provided where there are more than 4 phases with pedestrian movements.  While most modern signal controllers include 16 ped inputs, not all modern signal controllers actually include data entry screens to map ped inputs 9 through 16 to anything, nor data entry screens to apply detection diagnostics to the ped inputs 9 through 16.

This type of approach will need to be clearly documented, and most importantly agreed to by the field technicians who will be implementing and using this type of approach.