Jack Brooksbank, MJLST Staffer
City planners and civil engineers across the country face a little-known, yet extremely important, question when designing road systems: how long should the green lights last? Anyone who has ever had a regular commute probably wishes the answer was simply “longer,” but this seemingly minor detail can get quite complex. Traffic light timing decisions are made by both government officials and specialist consulting firms, based on extensive studies, and supported by academic papers. The practice of traffic light timing is so established that it has its own lingo.
Perhaps the most important part of traffic light timing is coordination. Engineers try to set the cycles of lights on a given route in concert, so that a car passing through one green light finds the next light turning green in time for it to continue. “The intent of coordinating traffic signals is to provide smooth flow of traffic along streets and highways in order to reduce travel times, stops and delay.” When done well, it leads to a phenomenon known in the industry as a “green wave,” where a car hits every green light in a row and never needs to come to a stop.
It’s not just a minor detail, either. Coordination can have some serious benefits for a city. One town revamping its timing scheme estimated it would reduce travel times by as much as 10%. And although making the morning commute go more smoothly is a worthy goal in itself, proper light timing can create other benefits too. Efficient traffic light timing can even help the environment: by reducing the number of stops, and the total time spent driving, coordinated traffic signals reduce the amount of fuel burned, and greenhouse gasses produced, by commuters.
However, timing traffic lights relies in large part on one central assumption: that a car leaving one green light takes a certain amount of time to get to the next one. This raises a potential problem: drivers don’t follow the speed limit. Indeed, one study found that nearly 70% of all drivers regularly speed! When timing traffic lights, then, designers must make a choice: do they time the lights based on the legal speed limit, or based on the speed drivers actually go?
If timing is based on the speed limit, many cars will still arrive at the next light before it has turned green. The coordination of signals won’t have mattered, and the cars will still have to come to a stop. By basing the timing on the wrong speed, the designers have negated the benefit of their careful work, and might as well have saved the time and money needed for figuring out how to coordinate the signals in the first place. But, if instead timing is based on the speed drivers really travel, designers are essentially rewarding illegal behavior—and punishing those drivers who do actually follow the law with extra stops and delays!
Most major cities now rely on actuated controllers, or devices that detect when cars are approaching in order to trigger light changes without human input. Some cities are even experimenting with AI-based systems that take the design out of human hands completely. Advances in technology have thus heavily favored the “actual speed” approach, but is this because a decision was made to accommodate speeding drivers? Or have cities, in their enthusiasm to reduce congestion, simply adopted the latest in technology without considering the policy choice that it entails?
Also, if traffic lights should be timed for the actual speed cars travel, it may raise further implications for other areas of law that rely on questionable assumptions of human behavior. Perhaps most notable is the law of contracts, which generally relies heavily on the assumption that people read contracts before signing them. But as electronic devices, apps, and online content proliferate, this assumption gets farther from the truth. And people can hardly be blamed for agreeing without reading: one investigation in Norway found that people have an average of 33 apps on their smartphones, and that reading the terms and conditions of that many apps would take an average of 31 hours. Another investigation found that simply reading all the website privacy policies an average internet user encounters in a year would require 76 eight-hour days of reading! If we should time traffic lights to account for people being too impatient to follow the legal speed limit, surely we should update the laws of contract to account for such a crushing reading load. Perhaps it is time to reform many areas of law, so that they are no longer grounded on unrealistic expectations of human behavior.
