A quick thought about intersections

Some mornings I find myself at the Summer St. and Atlantic Ave. intersection, crossing from the Dewey Square toward South Station. During rush hour, walking commuters build up on all sides of the four-way intersection, (mostly) waiting for the green lights of the traffic light to give way to the white light of the crosswalk. Pedestrians receive an entire cycle to traverse across the intersection, free of automobiles.

The crossing pattern for this intersection follows something like:

  1. all Atlantic Ave traffic
  2. all Summer Street traffic
  3. finally, all walking traffic

When I find myself waiting for all the traffic signals to cycle through before I can cross over to South Station, I’m reminded of a little note Jeff Speck mentioned in his book Walkable City. The interplay of the traffic and walking signals at intersections like Atlantic and Summer, where the pedestrian receives a dedicated cycle to use the intersection, initially appears to be beneficial to the commuter. It elevates the walker to an equal with the automobile. It gives pedestrains free reign to walk across an area usually reserved for cars and trucks, temporarily turning a paved road into a pedestrian plaza. However, it actually disadvantages the walking commuter. Why?

The dedicated-walking cycle pattern increases travel times for walkers. As there is dedicated cycle for pedestrians, the other cycles in the system don’t include an option for walkers. This leads to a reduced proportion of time when the intersection is crossable. If the intersection is like Atlantic and Summer with three cycles, it’s only crossable for roughly one-third of the time: one third for traffic in each direction, and the final third reserved for pedestrians. This is certainly not the most efficient crossing pattern for pedestrians or for drivers.

In a typical intersection, driving and crossing alternate for each direction. While cars can drive through an intersection in one direction, pedestrians are able to cross the street that runs perpendicular to the traffic flow. When the traffic signals change and the other set of cars is allowed to proceed, pedestrians can cross the street the other way. At all times, pedestrians can cross the street in a parallel direction to traffic flow.

This is extremely useful in an urban setting, where a walk from point A to point B likely involves more than just walking in a straight line. A pedestrian probably needs to travel along both the x and y axis, and can adapt along their course depending on what direction is crossable at every intersection. The pedestrian rarely needs to stop and wait at an intersection, allowing their walk to proceed uninterrupted.

On the surface, dedicated crossing time for pedestrians seem to legitimize the city ambler in a world ruled by automobiles. It’s a nice tip-of-the-cap to commuters who forgo the car and walk. Unfortunately, it makes the course for those of us who walk less efficient.