By which rule of thumb can you determine from the speed the distance in metres a motor vehicle travels in one second?

The correct rule of thumb to estimate the distance a motor vehicle travels in one second is to take the speed in km/h, divide it by 10, and then multiply by 3. This works because dividing by 10 simplifies the speed scale, and multiplying by 3 roughly converts it to meters per second. For example, at 50 km/h: 50 divided by 10 equals 5, and 5 times 3 equals 15 meters per second, which is a good approximate distance traveled in one second. This quick calculation helps drivers estimate safe following distances and reaction times without needing precise instruments.