The city of Ann Arbor has been installing some new traffic lights around town. Traditional signals display a “Walk” light for as long as 25 seconds. This new type of signal displays a “Walk” light for only four seconds, out of a total cycle of up to 90 seconds. One example of such a signal is the crossing of State Street at Liberty Street downtown.
The cars at these signals get up to a minute of green light. The rationale for the short “Walk” signal is that it includes a staggered timing that allows pedestrians to get into the crosswalk and be more visible to turning motor traffic, thus making their crossing safer. But this staggered timing could also be achieved even while giving pedestrians far more than 4 seconds to start crossing. The extra time would come from the green time for cars. So the four-second “Walk” timing represents a choice to move cars more quickly through the intersection by imposing a waiting penalty on pedestrians.
I became curious as to how much of a penalty this really is. What if we accepted as a matter of course these short “Walk” lights at all of our street crossings? Rather than make many walking trips with a stopwatch, I wrote a simple pedestrian simulator computer program, and sent it on hundreds of simulated walking trips across town on Liberty Street, between the State Theater at State and the Fleetwood Diner at Ashley. This is a distance of 2,500 feet with seven traffic lights.
I used five feet per second as my walking speed. That’s the average for men under 60 in the U.S., according to a Portland State University study, and agrees closely with my own walking speed. At this speed, if there were no cars or signals, it would take a little over 8 minutes to cross town.
Note that the amount of time it takes to cross town depends only on the “Walk” light timing, and not on the flashing “Don’t Walk” timing. Legally and practically, there is no difference between flashing and continuous “Don’t Walk.” Both indicate that the pedestrian should continue crossing if already in the crosswalk, and to stay on the curb if not.
Other than the walking speed, I had to make one important assumption. I assume the timing of the different lights is uncorrelated, that is, the phase of any one light at the time a pedestrian arrives is random. This is in fact not the case. Many of the lights are timed for the benefit of cars, so that someone driving at a constant speed through town will only have to wait for the first light, then will be able to breeze through the rest of them without stopping as each light turns green. I don’t know how this timing affects pedestrians, but since it’s done for the benefit of motor vehicles, I doubt that it helps people on foot.
There are two questions about the new signals I wanted to answer. One is how long it takes to get across town. From a practical point of view this is the question that matters. The other question is how many lights I have to wait for. Waiting for lights is often strictly a nuisance factor, but an important one when considering the walkability of a place. Waiting for lights in the wintertime probably qualifies as more than a nuisance.
Armed with my pedestrian simulator, I made 700 simulated trips across town for each of two scenarios, first with the old, longer “Walk” timing (25 seconds), then with the new (4 seconds). With the old signal timing I made it across town in an average of 10.5 minutes and waited for 4.8 red lights. With the new timings, it took an extra 2 minutes for a total of 12.5 minutes, and I had to wait for 6.6 lights.
This may not seem like a huge penalty. Two minutes isn’t all that long – less time than most of you will take to read this column. What if drivers had to pay a similar penalty? Ann Arbor has recently announced plans to make Fifth and Division streets more pedestrian friendly by adding bumpouts and other calming measures that could delay drivers by up to 20 seconds. This prompted several angry letters to the local newspaper from drivers who felt this was an unreasonable penalty. Yet the new signals impose a pedestrian penalty six times greater.
And what about having to wait for an average of 6.6 red lights, on a trip that only has seven lights? This means that on most trips, pedestrians will have to wait at every light. They will go all the way from Ashley to State, a distance of almost half a mile, without encountering a single green light. My guess is that if people on foot have to start waiting up to a minute and and fifteen seconds at each intersection while the cars go right through, they may be tempted to start crossing against the light.
As far as I can tell, these new signals are being deployed without any public notice or hearings. At a time of increased road congestion, high fuel costs, and global warming, I’m not convinced it’s good public policy to sacrifice pedestrian convenience for the benefit of motorists, especially in the downtown area. Changes in public policy deserve public debate.
Note: Jim Rees is a staff research programmer at the University of Michigan.