How traffic lights help us exercise judgement and make ethical decisions that impact ourselves and others (in case you were wondering, yes this is a metaphor).

Traffic lights. We all see them, every day, and we understand what they mean. Red means stop, green means go.

But how do they work?

…technically

When you see a traffic light at an intersection, that means there are metal detector wires installed under the surface of the road in each lane. The wires detect vehicles, so that the traffic signal system can identify when a car is waiting to cross the intersection.

This way, the system can determine how much traffic is coming up in either direction, whether the light signals need to change to let it through, and how long to leave the green light on in each direction.

It’s a nifty little system that’s been in continuous use all over the world for about the past 150 years.

…legally

When a traffic light is installed in public by a local government, it’s enforceable by law. That means if a driver doesn’t stop for a red light, or go for a green light, they’re breaking the law and can be penalised. Yellow lights are fiddlier, but there’s still a legal case if the driver’s choice is unexpected.

But most traffic lights aren’t equipped with surveillance equipment. Which means that traffic lights aren’t actually set up to enforce the laws they signal. So how do we know who to fine? By watching. Usually, there are red light cameras somewhere. Sometimes fixed ones, sometimes temporary ones, or sometimes a police car is around and will just snap your registration and send you a fine in the post. The penalty depends on the jurisdiction, and can go from fines to suspended licences to jail time.

However, the wires and the lights don’t make it impossible for a car to stop on a green light, or go on a red. They are only messages — messages and warnings.

…culturally

A traffic light is familiar sign of civilised life in societies across the world. It tells you not only what you must do, but what to expect from others around you: the norms of behaviour on the road. If your light is green, you can comfortably assume that the light for cars perpendicular to yours is red. Which means it’s safe for you to go without crashing into them, because they will stop.

Traffic lights create a shared language, a shared understanding between users of the road. They create comfort, a heuristic for trust between people who have not met and likely never will. They support a legal system, but more pressingly, they support the immediate safety of all users of the road.

Even when we know there are no cameras to catch us, we rarely run a red light because it could kill us — or we could kill someone else.

And how does the yellow light work?

Ultimately, traffic lights are a simple, unambiguous form of communicating a social norm. That norm is linked to law, to individual and collective safety, to good manners. To a sense of trust between us all, that I know what you’ll do and you know what I’ll do.

But most social norms are far, far more nuanced than go or stop. Even traffic lights aren’t that simple: the yellow light is a space for deep nuance and legal debate.

At its simplest, the yellow light means stop.

But it also means traffic in your lane is still moving through the intersection. It also means that stopping could be unsafe. Stopping could cause a collision, either with the car behind you that doesn’t stop, or with the car going the other way through the intersection whose light is about to be green.

And so, for legality, for safety, and for manners, the yellow light means use your judgement about when is safe to stop.

We must never, never forget that all human systems rely on human judgement.

If we don’t trust each other’s judgement any more, norms will collapse. People will die. Society will break down. Trust is hard, and it’s contingent, and — yes — it’s illogical. But it is a part of the shared sociological imagination that makes education possible. If we feel we must rely on our absolute power to enforce the rules of engagement, then trust — and with it, education — and with it, society — is already lost.

But do remember this, if you remember nothing else:

The yellow light
means stop — safely.