Eli5 Why do race tracks have rough sides?

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Especially f1 or carting tracks

In: 4

Nearly everything you see next to a race track serves two purposes,

a) create respect for the track. It should cost more to go astray than staying on

b) create a passive slow-down-scheme for all vehicles that go outside of the track. In case the driver is incapacitated and the vehicle is running astray with no-one to control it. It saves lives.

Gravel absorbs energy as is “pushed in” or pushed away by wheels or a vehicle that’s out of control, and serves to brake the vehicle to a stop. They use it for [emergency stop off-ramps](https://aws1.discourse-cdn.com/boingboing/original/4X/3/0/8/308b04d49adda76a80dea8113ddbdb59601e21a6.jpeg) for trucks too.

It is hard to find a good surface for the areas outside of the track. It should be slower to drive off-track then on-track so that drivers do not take advantage of this and start cutting corners. It is better for the racing when they get punished for their mistakes right away then for some judge to issue a punishment some time later. But the areas where drivers often make mistakes can see quite a lot of traffic during a weekend and therefore needs to be sturdy to not get damaged. It is never popular when the race have to be stopped to have the track repaired. In addition to this you need to get good traction on the surface so that the car may be able to stop in an emergency.

So although it is far from perfect making the edge of the track rough asphalt or concrete does achieve much of this. Every time the wheel hit the surface on a bounce it gets pushed back slowing the car down. And while the wheel is in the air there is no traction so no acceleration or turning. This punishes the driver for going over the white line while they can still do it thousands of times over the course of a race without damaging the curbs.

The stripped curbing gives you obvious course limits and sometimes has rumble strips. The kitty litter is an attempt at avoiding major wrecks by getting cars slowed down or stopped before they can hit hard objects.

If you’re talking about the stripes that circuits such as Paul Riccard uses in its run-off areas, it’s an safety improvement of gravel traps: it’s hard to control a car that goes through gravel, it may end up leaving gravel in the track itself, and sometimes it may flip a car over.

They started to use asphalt run-off areas because it turns out that the best way of slowing down a car is by using its brakes (who knew!), and in the rare instances where a car goes straight through a corner, there’s not much difference between a gravel trap and an asphalt run-off (this is why they use all kinds of protections for the walls, from tire walls to Tecpro barriers).

Now, if the run-off surface is asphalt, drivers are tempted to use it to gain an advantage (something that, with a gravel trap, doesn’t happen). Well, they experimented with “sausage kerbs”, but they were kinda dangerous, being able to launch cars into the air. But they still use rough surfaces so going off track has some kind of “automatic penalty”.

If you want to know more, [there’s a video made by Chain Bear about run-off areas](https://www.youtube.com/watch?v=5N06z6VHXGA), and other ones about [barriers](https://www.youtube.com/watch?v=FkpvPWB3jMk), and [helmets](https://www.youtube.com/watch?v=wdwyP2UcCf8).