Slow near people

The United Kingdom’s Highway Code, first published in 1931, now prints a table of typical stopping distances for a car. At 20 mph it is about 12 metres; at 40 mph about 36 metres. The braking part alone goes from about 6 metres to about 24: twice the speed, four times as far.

One thing to hold: The stopping-distance table in the Highway Code, with thinking distance and braking distance side by side.

Why it matters: That square law is why streets near schools have low speed limits, and why robots that drive around warehouses are built to slow down or stop when a person comes close: a robot that is going slowly can stop in time.

What we don’t know: The table is a rough guide for a dry road and an alert driver. Real stopping distances change with the weather, the tyres and the vehicle, and the rules for speed limits near schools are different from place to place.

Sources: Department for Transport, The Highway Code, rule 126 (“Typical stopping distances”) · ISO 3691-4:2020, Industrial trucks — Safety requirements and verification — Part 4: Driverless industrial trucks and their systems · Wikipedia, “Braking distance”