Saturday, April 25, 2015

HAWK Signal

The city of Tucson, AZ, developed the High intensity Activated crossWalK (HAWK) pedestrian crossing beacon in the late 1990s to assist in pedestrian crossings, especially for major arterials at minor street intersections.

When I first moved to Tucson, I had never seen this signal before.  In fact, based on my limited knowledge of the Manual on Uniform Traffic Control Devices (MUTCD), I thought the signal was likely illegal.  Traffic Signals are not allowed to remain "dark" unless they are bagged.

But my biggest concern was in what to do while this intersection is flashing red.  My interpretation of this signal indication is that the crosswalk should be treated as a stop sign control.  However, all of the motorists treat it as yield control - initially stopping but then cautiously entering the crosswalk without stopping after the pedestrian passes.  But over time, I respect the signal and my guess is that it is extremely effective.

Traffic Signal Engineers are faced with a dilemma when it comes to pedestrian crossings.

 According to the Model Traffic Code (adopted by most agencies), a pedestrian has the right-of-way at any intersection - whether it is striped with a crosswalk or not.  But pedestrian behavior is erratic.  When there is no crosswalk, the pedestrian takes extreme care when crossing a road.  But when there is a crosswalk, most pedestrians believe that the white stripe on the ground will protect them.  It won't.

So the HAWK signal is a great tool for the toolbox.  It creates a safe pedestrian crossing that is only activated when needed.

What most people don't see, however, are the trade-offs.  When the crossing is activated, it creates huge motorist delay.  This delay isn't just because the motorist must stop at the HAWK crossing, but also because they will then become "out-of-sync" with the queue.  If the road is timed for optimal progression - it could actually cause two additional stops.  It is the stop that really annoys motorists.  It also creates a huge roadway user cost.  If a benefit/cost analysis were done of this traffic signal control, I am sure it would not be positive.

The Federal Highway Administration has been in review of this concept for some time.  They just recently released a Safety Effectiveness of the HAWK Pedestrian Crossing Treatment. The report documents the experience in the Tucson area.  I plan to read it and give further thoughts.