Blog Post #4: EOTO — Traffic Signals

Everytime I'm stuck at a traffic light for longer than a minute, I get curious. A swarm of questions hits me: How do they work? At complex intersections with turn signals, what if there's no one in the turn lane? Would the signal still go off? And if it doesn't, how did it know? Or pedestrian lights that don't have a button but work anyway— what IS their secret?

Everytime I say: ‘when I get to my destination, I’ll look up the answer and solve the mystery once and for all’. Which as you may have already inferred: that’s never happened. The good news is that the cycle has ended!

Before diving into mechanics, consider the classic 1900s movie scene where someone runs into the road: there’s some yelling (maybe cursing) as the horses pulling the cart rear up along with the typical ‘whoa’. Traffic gets disrupted due to instinct, a horse reacts to the obstacles in the way.

Motorized vehicles changed everything. A car didn't have survival instincts and certainly wouldn't voice protest over an obstacle. Traffic control wasn't invented simultaneously with cars, but safety became vital as vehicles flooded the streets.

The history of traffic lights spans over 150 years of trial and error. The world’s first traffic signal was installed in London (1868). It was adapted from railway signals by John Peake Knight, using pivoting arms by day and red/green gas lamps by night. That design was quickly shelved after a gas leak resulted in an explosion, injuring the police officer operating it. 

As cars became more common in the 1900s, road safety became an urgent problem. America led the charge starting with Lester Farnsworth Wire. He created a two color electric light in 1912 but it only signaled ‘stop’ and ‘go’, resulting in frequent crashes.

Enter Garrett Morgan: an inventor who witnessed a severe crash between an automobile and a horse drawn carriage. In 1923, Morgan presented the three position traffic signal.

With a ‘caution’ stage, he gave drivers time to clear intersections safely (so yes— technically yellow means clear the road, not slow down, but don’t quote me in court). By the 1930s, international treaties standardized the colors worldwide so drivers everywhere could navigate safely.

So, still waiting at that light— what’s happening? Well Traffic Signals don’t function as isolated machines, but part of a larger system managed by Traffic Engineers. Before a signal is even put in place, they evaluate an area to see what the road needs to manage the flow of traffic and safety. 

It could be a 4-way stop sign, a rotary, a merging road— often, traffic signals are best used where multiple roads overlap.

Consider Car B turning left, right, or going straight while opposing Car A approaches. A 4-way stop works fine for low traffic, but in a dense city during rush hour? That’s just a nightmare.

Traffic engineers would assess a road like this and come up with a plan, usually programmed into the traffic signal. The flow of traffic is divided into phases of movement that enables the most amount of cars to move without any collisions.

The wires you see on traffic signals tend to lead underground to discrete boxes that allow for changes when necessary. If  there's construction or the traffic flow of the road has changed.

While often set on timers, there are even additions such as cameras to check if there are cars in the lane or pressure plates underneath the road to fire off when it senses the weight of a car.

Now that Traffic Signals have lost their mystery I can spend my time waiting at the light questioning other parts of life: like what’s the process of getting electricity from there to a home? How do power grids actually work— what's THEIR secret?