Braking from High Speed – Reaction times

We came across this piece of research from the Transport Research Laboratory which appears to have gone under the radar, which we present on our road training courses. Our previous paper on braking a motorcycle (or car) from high speed used the TRL 0.7 second standard reaction time to hazards, but this research shows how much this can vary on circumstance.

There are two factors as to whether you can avoid a collision or minimise the impact speed:-

a. How quickly you can react

b. How quickly you can stop (which we covered in the earlier post) or swerve.

These figures (see below) were reaction times using a simulator in different scenarios.

1. Cars and pedestrians emerging.

Average reaction time at 0.85 is actually a bit greater than that currently used in Highway Code stopping distances.

2. A vehicle braking ahead.

This at an average 1.3 seconds is nearly twice the figure used in Highway Code stopping distances, and the ‘two second rule’ leaves you with a 0.7 second gap in which to brake (or 70 feet at 70 mph). It is also clear that most driver and riders amazingly don’t expect the vehicle ahead to brake suddenly, as from observation they ride/drive far too close and would often simply hit the vehicle in front without even beginning to brake.

3. A vehicle ahead veering off the road and knocking down an overhead motorway gantry.

This I think we can all agree is ‘unexpected’, but reaction time is surprisingly only slightly longer than a vehicle braking in front.

4. A stationary vehicle in front the centre of the lane

This is the real concern as clearly riders/drivers see a vehicle ahead and don’t realise for some while that it is stationary, taking on average nearly 4 seconds to brake or 5 seconds to swerve. A massive 400-500 feet to react at 70 mph. This can also apply in any situation where you do not immediately recognise a hazardous situation, which is why ‘hazard perception’ is such an issue and part of any licencing test, as is planning ahead.

This is known by the emergency services which is why you will see emergency vehicles now always parked across the road or diagonally, to indicate they are stationary.

Also included is the effects of fatigue on reaction times, which is very noticeable, adding more than a second in all circumstances. So if you’re tired a 2 seconds separation distance from a vehicle ahead is nowhere near enough.

So what are the conclusions?

1. Always leave a good gap ahead – 2 seconds is clearly not enough – particularly at high speed.

2. Pay attention!

3. Don’t drive when tired. Stop and get a coffee – a large cup from Costa (other providers are available) not only kept me wide awake riding home the other day, but for half the night.

Again most braking actually occurs in the last few feet, so the earlier you react has a disproportionate effect on  the lowering the speed of any impact or avoiding one (which is better).

Mike Abbott, British Superbike School 25.11.15

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