Ever wondered whether a suspiciously long (or short) traffic signal change, combined with a police cruiser hiding nearby, was an attempt to boost tickets? Could police be changing signal timing? In theory, sure. In reality, not so much. Here's why.


Earlier this week, a poster on Reddit got suspicious about an abnormal traffic light and a strategically placed police cruiser:

I have been going through this same 3 way intersection at around 4-5 am for several years now and up until a few weeks ago there was no problem. There are usually only a couple of cars in sight at this hour and if the light isn't green already when I approach it, it usually only takes 10 seconds to change.

Then, a couple of weeks ago I came to a stop at a red where another car in the opposite direction had been waiting. I waited there for a good 4-5 minutes (literally) and was about to turn when the light finally changed for the other car, then shortly after, for me. I'm glad I waited because a quarter block up hidden behind some bushes was a cop...Over the past couple of weeks it has happened 2 more times, coincidentally with the cop there (hiding in different locations each time).


Let's walk through the questions from easy to hard:

How do traffic lights get set in the first place?

Not by accident. There are some 300,000 traffic lights in the United States, and about as many laws and regulations that govern how they work. Older models are not much more complicated than a string of Christmas lights on a timer; others have a bevy of wired and wireless sensors. All have manual overrides, so that police can control unusual traffic following big events.

There's a whole set of national guidelines and recommendations, overseen by the U.S. Department of Transportation and the Institute of Transportation Engineers. Those rules take traffic flow, time of day and other factors into deciding the quickest and safest way to shuttle vehicles through an intersection. State laws also vary about who has control over timings leading into state-owned roads.

While there are several ways to make traffic signals respond to traffic flow, with sensors buried in the pavement or nearby, such systems tend to be too rich for most towns; the U.S. Department of Transportation estimates only 1% of traffic signals have those sensors.


Can the lights be changed remotely?

Yes, and frequently are. Back in the 1970s, 3M invented a system that put special light sensors into the traffic light frame. When a strobe flashing at a certain frequency was picked up by the sensor, the light would switch to green.


Originally a way to let emergency vehicles move faster and safer through traffic, such systems were prone to hackers or people who figured out the strobe controls. While some locations still have infrared systems, the more modern systems use encoded cellular transponders and more advanced sensing inside the traffic lights that have two stages — an immediate change for ambulances and firetrucks, and a less-urgent code for mass transit vehicles, letting them save fuel by avoiding stop-and-go driving. (It's kin to the tracking system that allows large cities to tell riders when the next bus will arrive at any given stop).

Occasionally someone will pop up claiming to sell a device that changes traffic lights which is usually an infrared beacon that a fire or police department has lost track of, for systems that are not in use anymore.


Have police messed with timings to boost tickets?

There have been dozens of cases where cities altered their traffic signals to increase citations — all of which involve red-light cameras. The standard yellow light in the United States lasts about four seconds; but as red-light cameras became popular over the past several years, cities found that cutting even a half-second off that yellow-light time could double their haul from tickets.


But those changes were made by engineers across an entire system of traffic lights, not one at a time by traffic cops. Gary Biller, executive director of the National Motorists Association, says while cities frequently mess with traffic light timing for cameras, he's never heard of a case where an individual officer was accused of changing lights at a single intersection to trap red-light runners.

What's more likely, given the time of day posted by the Reddit questioner, is that with little else around 4 a.m. on the graveyard shift, a patrolman found an ill-timed light and camped out for the inevitable driver who didn't feel like waiting in the middle of the night. If authorities want to mess with traffic signals to boost tickets, they'll wait to do it in broad daylight.


Photos: AP, U.S. DOT

Hat tip to Jason!