GAs, ACO, and Traffic Lights

Posted on July 15, 2013


Red, yellow, green. Where did traffic lights come from, and how do they work? From distributed intelligence to heuristic optimization by simulation, these guardians of auto safety are secret marvels of modern scientific mentality.

Each year that goes by adds more new humans to our population, and within them, more drivers. Congestion has grown to the point that our saturated highways resemble the in-line marching of ant colonies. The analogy may not be new, but engineers are seeing new ways of applying ant colony behavior to rush-hour traffic patterns, employing distributed intelligence and heuristic optimization by stimulation. That’s quite a mouthful compared to “red, yellow, green,” so let’s take it back to the simple days and work our way up from there.

The first patented hand-operated traffic signal was designed in 1868 by railroad signal engineer JP Knight. This signal used red and green gas lamps and two semaphore arms, to tell road travelers when to wait and when to proceed. The railways already used red for danger and green for go; the subtleties of semaphore involved changing the angle of inclination of wooden arms on pivots. Knight’s signals were first installed in a carriage-dense metropolitan area in London near the Houses of Parliament.

Some time later, across the pond in Detroit, Michigan, Henry Ford produced his first Model A automobile. By 1913, he had cars rolling off his first assembly line and in 1914 he added two more assembly lines. Each one put out an automobile every six hours. High consumer demand placed more and more automobiles on the roads, and with two more automotive companies, Dodge and Chrysler, opening up shop, traffic congestion was only going to increase. These early adopters were paving the way (so to speak) for the immense tangle of freeways, highways, and roads now often controlled using computers, algorithms–sometimes borrowing concepts from artificial intelligence.

But back then? Things were just getting rolling. A policeman on traffic duty in Detroit, Michigan noticed that it was becoming necessary to control traffic at more and more intersections. It was officer William Potts who invented and installed the first automatic, electric, red-amber-green four-way traffic light that we are so familiar with today, though the patent credit went to an inventor named Garrett Morgan. Prior to Potts’ invention, there were other electric signals patented which excluded the amber light, but had additional elements that alerted drivers to upcoming light changes, like emitting a buzzing noise. This signal was unidirectional, and required the use of four signals per intersection, which may have been difficult to coordinate.

Other earlier signal models included the aforementioned gaslight, but after one exploded, killing the police officer who was operating the device, engineers felt the need to go back to the lab. Once the familiar red-yellow/amber-green style was adopted, the exterior of US and other Western countries’ traffic lights didn’t change much. But big technological changed occurred under the hood when Yalie Harry Haugh designed the traffic-actuated pressure sensing signal switch. You can thank him when you’re at a four-way stop at three in the morning, and your light almost immediately turns green. (One traffic-actuated switch that fortunately did not catch on was the horn-activated switch. It’s this reporter’s guess that it didn’t take long from installation to removal.)

Nowadays, law-enforcing traffic cameras use artificial intelligence to control and time traffic signals. We also currently utilize ACO, or Ant Colony Optimization. This mind-boggling concept was born out of necessity, due to the over-saturation of roadways that receive traffic from feeder streets. Engineers looked to nature to come up with a way to alleviate some of the congestion. By studying ant colonies’ behavior of convergence upon one home base from several food sources, and applying genetic algorithms (GA) and intelligent distribution of signals within a network, they realized that their efforts were best focused on regulating the flow into the arteries.

This is easily illustrated with the insertion of entrance ramp lights. The lights are fitted with computerized technology that tracks traffic flow patterns during all times of the day, and communicate with other signals in their network in order to adjust the timing of the lights to traffic need. It’s a little Big Brotherish, but this type of smart design allows traffic flow to be orderly. It’s also been shown to curb aggressive driving.

Transportation and traffic control have evolved significantly to include integrated computer chips and solar panels over the years, while clinging to the old railway system of lights. And we keep driving the routes like ants in a colony.

Kiped from the archives of the SyFy channel’s IdeaLab Blog for the TV show Eureka. Well kinda kiped, since I wrote it to begin with. Edited by Tiffany Lee Brown, without whom I’d be stuck in the land of curly quotes.