How long the stop really is

1Look

Two pairs of cones

Same rider, same machine, same brakes, same day. The only thing that changed between the near pair and the far pair is how fast the machine was going when the levers were squeezed.

2The idea

A stop has three parts and only one of them is braking

First you see it. Then you decide. Then you brake. For the whole of the first two parts the machine is still travelling at whatever speed it was doing, and you are not slowing down at all, because nothing has happened yet.

Anything that stretches the middle part stretches the stop. Massachusetts Safe Routes to School names three: phones, music and being tired all delay your response time. None of those change the braking. They change how much road has gone by before the braking starts.

3The idea

Speed is the part that multiplies

Double your speed and your stopping distance goes up around four times. That is the relationship taught in the Massachusetts flyer and it is ordinary physics: the energy the brakes have to get rid of climbs with the square of the speed.

And it shows up in what happens to people. In a study of paediatric e-bike patients, the crashes flagged as speed-related had a head, neck or facial injury 49.1 per cent of the time against 28.7 per cent for the rest. The threshold that study identified was speeds higher than 20 mph.

4Your turn

Mark your own stop

It does not print a number anywhere. It just leaves the cones, which is the only honest way to show you this.

5The idea

The gap in front of you is the same distance

On a road you do not get to choose how suddenly the thing in front of you stops. The one thing you do choose is how much room is between you and it, and that room has to be at least as long as the gap between your own two cones.

So the gap is not a feeling, it is a measurement you have already taken. And because the cones move apart as the speed goes up, the faster you are going the further back you have to sit. Most riders do the opposite without noticing.

6Decide

You are behind a car on a residential street, close enough to read the writing on the back of it.

7The idea

Both numbers in your head came from somewhere else

You have a feel for stopping from two places: being a passenger in a car, and riding a pedal bike. The car’s stopping distance belongs to the car, and it is not something you can borrow by riding close behind one.

The pedal bike number is the more dangerous of the two, because it feels like yours. The mass of an e-bike and the speed it holds both lengthen the stop, and the machine gives you no signal that they have. The cones are the only thing that will tell you.

8Find them

Which of these steal the deciding part?

Tap the ones that count.

9Say it

The question for the gap

Ask it behind cars, behind other riders, and coming up to anything you would have to go round. If the answer is no, the only thing you can change is the room.

10Do it

Before you leave this page