Round sign telling pedestrians not to cross railroad tracks

Answering the Call: Pedestrian Button Questions

Recently published an article, “Ain’t Too Proud to Beg? Views on Pedestrian Call Buttons,” which posed several questions related to the functionality of these buttons, most notably, “do they actually do anything?” As a collector of traffic signal equipment that has built my own home setup with real retired traffic signal equipment and author on a previous comprehensive series on traffic signals, I want to weigh in on that.

A traffic signal, illuminated red, against a blue sky.
Traffic signals. Author photo.

Fixed Time vs. Actuated Phasing

First, it’s important to understand how traffic signals are controlled and some terminology. “Fixed time” traffic signals run on what are essentially dumb timers, while “actuated” traffic signals respond dynamically to “calls,” a request for service when a pedestrian pushes a button or a car drives over a loop detector or into the field of a video camera. A “phase” is the entire sequence — usually green, yellow, red for a given movement — and an “interval” is each individual indication of a phase. Generally speaking, fixed time signals tend to be used and work better where a number of signals are spaced closer together, like a busy downtown. Actuated signals tend to work better where traffic and signal placement is more sporadic, as in the suburbs.

Actuated signals always require push buttons, and the buttons do have a function; otherwise there would be no way for the signal to know a pedestrian is there. Chances are the light won’t immediately change upon activation, but it does have an effect. At the intersection of a wide suburban street and a strip mall driveway, where traffic is light enough that no cars are on the side street, it could be 5 minutes or more before the main street reaches the “max green time” and the light cycles without input. Or the main street could even be programmed to “rest in green,” and the light will never turn green for the side street absent an input from a car or pedestrian.

Pedestrian Timing

A vehicle-only phase can be as short as 8 seconds if, for example, a single car is waiting to enter a suburban arterial: 3 seconds green, 3 seconds yellow and a few seconds for all-red. By contrast, a phase with a pedestrian call is much longer: 7 seconds for the “walk” interval, and often 30 or more seconds for the change interval. So it’s understandable why engineers don’t want to have an automatic walk signal whenever the light turns green, or to periodically grind all traffic on the main street to a halt every minute or so on the off-chance a pedestrian who’s “too proud to beg” might be there wanting to cross.

So what if the minimum vehicular green time actually is longer than pedestrian time? In that case, the walk sign can be lit without affecting overall operation. Dakota County does this, in fact. Drive down County Road 42 and you’ll see that the walk indications along the main street turn on, while those on the cross streets do not. This is not something I’ve seen other agencies implement, and I have no idea why not.

Pedestrian Timing MUTCD
Pedestrian Timing from the MUTCD (Manual on Uniform Traffic Control Devices)

So Why Might the Buttons Appear to Do Nothing?

In a traditional traffic signal controller, pressing the button momentarily connects a 24-volt power source to a logic input of the controller. There’s no light or haptic feedback to indicate that pressing the button actually did anything. The only thing a controller acknowledges is that the button has been pressed at least once and thus there’s a call for service on that phase. It doesn’t respond any differently if you press and hold the button, or if you press it really hard, or if a kid presses it down 50 times. Typically a phase has a “minimum green time” so if that time has not elapsed, a button press will appear to do nothing until it has, and then it will change the signal at that point. It’s fair that a person will wonder if their button press really did anything.

In cities, where traffic tends to be more balanced and the phases are shorter, the impact of a button push to the timing is more subtle — lengthening a phase from, say, 30 seconds to 35 seconds instead of from 8 seconds to a minute.

Sometimes traffic signals are reprogrammed to convert from actuated to fixed time. As mentioned in the recent article, the City of Minneapolis did this to a number of signals when we thought fomite transmission of COVID was a bigger issue than it turned out to be. In this case the button really doesn’t do anything, but it’s generally not removed; that would mean extra work, and keeping it on hand allows for the possibility of easy re-conversion in the future. Traffic signal techs really dislike having to make hardware modifications to an intersection every time they want to change the programming, and that programming can increasingly be done from a central office without even having to send a truck out to the intersection.

Finally, Minnesota’s interpretation of the ADA requires that “Accessible Pedestrian Signal” (APS) stations be installed in specified places at all new traffic signal installations, even if they’re fixed time. Although they have absolutely no impact to the operation of a fixed-time signal if pushed, they tell visually impaired people where the crosswalk is and what the status of the signal is. As such, they can’t be turned off at night to reduce noise since that would be an ADA violation whether or not the button itself has an effect on signal operation.

Two traffic signals of 1950s vintage, shown against a blue sky.
Eaglelux Signals at Grand Avenue and 34th Street, a model from the 1950s. Author photo.

Why Can’t We Do More Neato Stuff?

Until about a decade ago, traffic signal controllers hadn’t really changed much since the Jimmy Carter era. Instead of a PC like you might imagine, they’re usually simple breadbox-sized devices running a basic program from the factory. Below is a photo of my Eagle EPAC controller. Although our area used other brands, this typifies what’s in the field. Notice there’s no mouse, keyboard, computer display or USB ports, just a few buttons and an LCD screen for selecting basic options that come with it from the factory. A bunch of bundled low-voltage wires to “go” sensors and buttons and load switches to drive main voltage indications.

Eagle EPAC Controller
Eagle EPAC Controller from the author’s personal collection. Author photo.

Behavior based on inputs is limited to things like “is at least one car waiting over a loop sensor?” and “has the button been activated?” There’s simply no capability to behave differently if 20 cars are waiting, or if 20 pedestrians have pressed the button (or a kid has pressed it 20 times), or if the button is pressed down and held. Any video detection equipment is just converted to the same on or off logic input into the controller. Firmware updates have allowed things like leading pedestrian intervals and flashing yellow arrows, but this software/hardware configuration still has a lot of limitations.

The previous article suggested that a status light could indicate there’s a call on the phase — whether from a button, a vehicle or because the signal is on fixed time so the controller is itself generating the call. There is an output on the controller for this, but it is usually not hooked up to anything and generally used only for testing purposes. Although this has been done in other areas, notably southern California, presumably the effort to string additional wires to a light by the button and another load switch (controller outputs have too little current to drive any significant kind of lamp directly) and the maintenance of status lamps in the pre-LED era discouraged wider adoption. Nowadays APS buttons have intelligent communication between the supplemental APS controller in the cabinet and the individual buttons instead of just DC power, so they can do status lights, speakers and whatnot even with legacy controllers and existing wiring.

Newer controllers are much more flexible and are capable of running custom programs, often Android based. An available feature on some newer controllers extends the walk time if the button is depressed for 4 seconds. With video detection, increasingly they’re able to know and respond differently to “a bunch of cars” at an intersection — even if those cars are at an intersection a mile away — by communicating with the controller at that intersection.

The City of Bloomington has implemented one such custom feature (now also used at selected Hennepin County signals), which disallows conflicts between a pedestrian phase and a permissive interval. If a pedestrian presses the button, left-turning vehicles will get a red arrow instead of a flashing yellow arrow.

Old neon "don't walk" sign in red and green
Old neon walk sign from the author’s collection. Author photo.

The first video detection equipment back in the 1990s used analog standard definition video and primitive processors and had difficulty even determining if a car was there. Nowadays experiments with video detection detect pedestrians and respond differently — say, calling a pedestrian phase automatically if it senses pedestrians waiting at the crosswalk, not terminating a phase until all the pedestrians have made it across. Let’s hope this will put an end to the “beg button” controversy with a win for both sides.

About Monte Castleman

Monte is a long time "roadgeek" who lives in Bloomington. He's interested in all aspects of roads and design, but particularly traffic signals, major bridges, and lighting. He works as an insurance adjuster, and likes to collect maps and traffic signals, travel, recreational bicycling, and visiting amusement parks.