How Do Traffic Signals Work?

Traffic management in dense urban areas is an extremely complex problem with a host of conflicting goals and challenges. One of the most fundamental of those challenges happens at an intersection, where multiple streams of traffic - including vehicles, bikes and pedestrians - need to safely, and with any luck, efficiently, cross each others’ paths. However we accommodate it now or in future, traffic will continue to be one of the biggest challenges in our urban areas and traffic signals will continue to be one of its solutions.

Writing/Editing/Production: Grady Hillhouse
Animation: Stephanie White, Connor Claver, Dayan D’Aniello

This video is sponsored by Squarespace.

[stephen_l]

Simple!
They show red light when I am near, they show green when I am not.

[Raaaahhhhbbbie]

When I was a kid I thought traffic lights were operated by people in offices under the intersection

[Ian-jqzg]

Light: *turns yellow to warn drivers to slow down because it's turning red*

Drivers: *speeds up because it's turning red*

[byronrideaux]

If roadways ways are like veins, then Los Angeles has a bad heart and has daily heart attacks

[Kezenmacher]

Here in germany the amber light also turns on for a brief moment, when it goes from red to green. This allows the drivers to engage the clutch early, and start driving as soon as the light turns green.

[grindarius]

Thailand's traffic light.
Green : go
Amber : go faster
Red : go when nobody is around
I'm sick of it lol

[albertbatfinder]

Many countries have a countdown indicating the number of seconds to green. It’s good for stress. If you just miss the green light and immediately the red light starts counting down from 45 or whatever, it doesn’t seem so bad. Red light wait time is often perceived to be three or four times longer than it really is. There’s also a sense that the light has made a “contract” with the driver.

[el.blanco]

There's a light near where I live where for a busy intersection that literally gives 3 seconds of green light and causes the most frustrating traffic imaginable

[TheAssassin]

As a Traffic Engineer, I think he did a good job with this video.

[lovelybooff]

In my home town, the timing between several lights (roughly a mile apart) is set up so if you were to drive the speed limit, you could hit all green lights. Only when you would go over or under the speed limit would you have to brake for a light.

[you_just]

“You can’t put a high-five interchange on every block”
My cities in Cities: Skylines would beg to differ

[billrussell]

I have a 52 year career involving design, fabrication, installation, timing and manufacturing vehicle traffic control systems. I applaud you for an excellent summary of these very complex systems. You even got then lingo correct that, in my experience, is rare except for actual practitioners of the art.

[robhelenflaherty]

You took a mundane topic like traffic signals and made it interesting! Some of the photography was spectacular, all in all a very slick production.

[philipberthiaume]

Where I am from in Canada, we are beginning to use roundabouts more and more, even in residential areas. These permit a continual flow of traffic, even at the heaviest part of rush hour while naturally slowing traffic down through intersections. The stats show a significant decrease in vehicle to vehicle and vehicle to pedestrian collisions.

[avaaznfan]

I'm a traffic engineer and I do a lot of work with traffic signals from design, programming, and retiming. Very challenging but enjoyable work. This video is very well explained

[bololollek]

The best solution we have right here and now is basically public transport. There is nothing in traffic that is as inefficient as 1 person in a car.

[FlymanMS]

Good but not perfect, needs more pretty colored flowing water.

[kwayy]

Engineers: Traffic management is hard

Cities Skylines players: Watch this bish

[DBR]

I’m watching this video while waiting for a light to turn green.

[seagie]

WHEN YOU STOP BEFORE THE SENSOR AND WONDER WHY EVERYONE BEHIND YOU IS ANNOYED AND THE RED IS TAKING TOO LONG,