Ever think about traffic lights? When they started, how they work, and why they are the colors they are? And, why have they stayed exactly the same for nearly a century? Isn’t there any new innovation in the traffic light pipeline? Will there ever be?
We fell into the rabbit hole to get you all the answers. ❤️💛💚
A brief history.
The concept of the traffic light actually dates all the way back to 1868, when the world’s first traffic light was installed in London among the posh streets that lined the Houses of Parliament.
The system was composed of two mobile signs attached to pivoting arms that were manipulated by a lever. Like a prop from a steampunk convention, the post was topped with a gas-lit semaphore to ensure visibility.
Of course, back then, nothing was automated; a police officer would be on standby, monitoring the traffic and manually changing the signal as necessary. Unfortunately, the gas-lit, manually operated signal exploded less than two months later, injuring the police officer who was operating it.
We assume he was well covered through Workman’s Comp.
The world had to wait nearly 46 years until electricity became widespread before the first dual-colored traffic light was installed in Cleveland, Ohio on August 5, 1914.
But still, there were only two lights – red and green.
Until 1920, there were still no yellow lights on traffic signals.
But that year, Detroit police officer William Potts suggested adding a yellow light to warn drivers that the light was about to change to red, thus changing the future of traffic light history forever.
New York quickly adopted the tri-color model, and by 1935, The Federal Highway Administration published “The Manual on Consistent Traffic Control Devices” defining uniform standards for all road signs, pavement markings, and traffic signals, mandating them to all employ red, yellow, and green light colors.
It was then that the traffic lights that we know and love today were born and became the norm throughout the world.
Green means go. But…why?
If we remember our ol’ pal, ROY G. BIV (Red-Orange-Yellow-Green-Blue-Indigo-Violet), we’ll recall that the order of the seven colors specifies each color’s wavelengths in descending order – Red has the longest wavelength, whereas Violet has the shortest.
Longer wavelengths tend to travel larger distances when encountering obstructions. As a result, Red light can travel the greatest distance in rain, fog, and mist, and remains visible the majority of the time, followed by Yellow, and finally Green.
Thus, the three signs of traffic light – Red/Stop, Yellow/Caution, and Green/Go – were assigned in order of priority and wavelength.
How do modern traffic signals work?
Most of the traffic lights installed around the U.S. are suffering from antiquated systems (like much of the nation’s infrastructure), and don't have any modern technology installed at all.
Instead, most traffic lights operate based on internal timers – when the light turns red, an invisible countdown begins before the light eventually turns green.
While it may be functional, the flow of traffic is often impeded by these basic timers. When there's not a lot of traffic in general or from a particular direction, forcing everything to stop at the same interval causes unnecessary stops and slows the entire road down.
In an effort to remedy this problem, some cities began utilizing pressure plates at traffic lights in the 1950s. When a car would stop on this plate, an electric signal would be sent to the light, prompting it to change to accommodate the waiting car.
In an evolution of the pressure plate system, some lights now respond to an induction loop hidden under the road on the stop line which generates a magnetic field that changes due to the presence of objects above and triggers a change in the traffic signal. It's essentially the same concept as the pressure plate but a bit more discrete and tire-friendly.
The only real problem with this approach is that motorcycles often do not generate enough of a field difference to trigger those sensors.
Today, many intersections make use of car sensing technology, whether through infrared sensors, microwave sensors, or cameras. Whichever way they go about doing it, the concept is more or less the same — sensors note both the presence of cars on or near the stop line, as well as the number of cars lined up, and the lights switch to prioritize clearing out that lane.
The future of traffic signals:
Emergency vehicles have long leveraged cutting-edge technology to command traffic lights in order to dramatically reduce response times. But, the horizon of traffic management extends far beyond the realm of emergency services.
Through the integration of advanced sensors and localized Wi-Fi signals, smart traffic lights could soon communicate directly with connected vehicles (particularly EVs) to streamline traffic flow and reduce congestion.
Automotive manufacturers believe that by enabling direct communication between vehicles and traffic infrastructure, the system could optimize the flow of traffic, enhance fuel efficiency, and reduce accidents.
Another major focus has been on AV integration.
If all cars were robots, you likely wouldn't even need traffic lights. Self-driving vehicles would just ping their vectors at each other, and collectively choreograph their passage through intersections in a nimble, methodical ballet.
But, throw a few hot-headed, lead-footed meat-sacks into the mix and the self-driving cars can’t possibly predict what’s coming.
So, transportation engineers at North Carolina State University recently proposed a “white light” be added to traffic signals to enable self-driving vehicles to help control traffic flow and let humanoid drivers know what’s going on.
“This concept we’re proposing for traffic intersections taps into the computing power of autonomous vehicles (AVs) themselves,” says Ali Hajbabaie, an associate professor of civil, construction, and environmental engineering at North Carolina State University.
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Not so fast.
In the same way that buyers are not yet ready to jump all-in on EVs or AVs, researchers acknowledge that traffic signals are not yet ready to adopt a new distributed computing approach tomorrow, nor are governments going to install brand-new traffic lights at every intersection in the immediate future.
They even acknowledge the increasingly sophisticated shields required to protect hackers from exploiting the emerging tech.
But just as it took years to establish the traffic signal standard as we understand it today, It’s to be expected that it will likely take another few decades to evolve.
Fun facts:
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Roses are red,
Violets are blue,
Traffic lights are red, yellow, and green,
Lots of things are colorful.