At Arlington’s “intersection of doom,” the traffic signals are so complicated they’re nearly impossible to follow. Photo by author.

To make streets walkable, we need to re-think the basic principles of how people on foot and people in cars share the roadway. This is the third post in a multi-part opinion series.

Walk signals are not only unsafe and inconvenient, they’re also incapable of making pedestrian travel efficient. Engineers simply don’t have the time or resources to correctly configure every traffic light for pedestrians.

Traffic lights and signs are not police officers standing in the intersection. When engineers use them to direct traffic as if they were, they impose on themselves a task they cannot carry out.  In real-world practice, it is simply not possible to program the lights and place the signs in a way that moves people efficiently.  The engineers are short of information, time, and money.

Highway departments don’t even have the resources to fully optimize traffic controls for drivers.  They traditionally simplify their work by planning for the busiest time of day.  But traffic, especially foot traffic, flows all day.  Outside rush hour, both drivers and pedestrians find themselves standing and watching empty streets, waiting for slow lights timed to minimize rush-hour backups.

It is possible, as New York and a few other cities have shown, for complex signals to make walking easier.  Pedestrians get a few seconds to enter a crosswalk before cars can turn.  Or turns are banned while people are crossing.

But if you try to orchestrate movement on foot in this way at every streetcorner, the traffic engineers’ job becomes entirely unmanageable. They cannot possibly find the time to adjust every walk signal for the proper balance between walking and driving.

And even when walk signals are properly adjusted, the engineer still knows less than the person walking on the street.  Anyone standing on the corner can see whether cars are coming.  The pedestrian knows best when it will be safer to cross immediately than to wait for the green light and dodge turning vehicles.

In any case, highway agencies rarely give foot travel much attention outside big-city downtowns.  At best, they make a half-hearted effort to meet federal minimums.  By-the-book engineering creates hazards in the form of disappearing sidewalks, badly timed lights, and inscrutable signage.

Walk signals are expensive

Not only are walk signals costly in staff time and information, they are a financial burden.  Highway agencies say that the cost of installing a full-featured traffic signal is a quarter to half a million dollars, and sometimes more.

There are thought to be more than 300,000 signalized intersections in the United States.  (No one really knows the exact number.)  Retrofitting all of them with walk signals to current standards would run up a bill in the ballpark of $100 billion.

Incremental fixes just create new problems

The rules for crossing streets grow ever more complex, and they have come to resemble the Gordian knot that the ancient Greeks were unable to untie.  Straightening one piece out only creates new tangles.

Rosslyn’s “Intersection of Doom,” where drivers turn right across a bike path, shows this dynamic at work.  After much public agitation, the walk signal on the bike path was set to begin before the green light. But drivers still came through the busy crosswalk when turning right on red.  So a flashing don’t walk signal went in. Now drivers need eyes on three sides of their heads to comply with the signals.

Signals for the blind have undergone a similar evolution. When walking is controlled by a traffic light, those who can’t see use traffic noise to tell whether it’s green.  But if there’s a walk signal, they don’t know whether it’s lit.  So crosswalks with walk signals need pushbutton-operated beepers for handicapped access.  More expense, more confusion, and more obstruction of the sidewalk.

The complexity has gotten so bad that FHWA can’t even keep its rulebook straight.  It required beepers for the blind in 2009, but did not authorize a sign that says what the button is for.  Rule-bound engineers are now blanketing streets with signs that comply with the rulebook but misinform their readers.

These miscues are not happenstance.  According to the branch of mathematics known as control theory, they are the inevitable consequence of too much complexity.  Beyond a certain point, increasing the number of signals sent by an automatic controller creates more error than it prevents.

Alexander the Great is said to have cut through the Gordian knot with his sword.  We need similar boldness to make our streets walkable.  My next post suggests how that might be possible.