Safety margin Lessons Note

Always maintain a safety margin around the vehicle by keeping distances and by driving at appropriate speeds. Having a sufficient safety margin could mean the difference between safely avoiding a collision and being involved in a fatal crash.

Rear-end collisions are almost exclusively caused by one vehicle tailgating another, and not being able to stop in time as a consequence.

Create a ‘buffer’

Give yourself time to react by creating a ‘buffer’ between yourself and potential hazards. For example:

  • keep a safe distance from parked cars to avoid pedestrians and/or doors opening
  • before changing lanes, make sure that you have enough space around you

If something moves into your safety margin - slow down to maintain your buffer.

Following too closely (A) dramatically increases the risk of rear - end collisions (B)

When you spot a potential hazard, you should prepare to stop by smoothly slowing down while kee

When being tailgated

If you feel that a vehicle behind you is too close, gently slow down if safe. A lower speed will give you more time to respond to possible hazards and prevent sudden braking, which may cause a collision with the vehicle behind you.

How much safety margin do you need?

Ask yourself if you can stop in time if the vehicle in front has to brake hard

How much safety margin you need is determined by a combination of the time you need to react and the time you need to respond.

You should have a sufficient distance to the vehicle in front so that you have time to react and safely stop or steer away to avoid a collision.

The 3-second rule

A general rule is to have at the very least a 3-second gap to the car in front of you, called the ‘3-second rule’.

You can measure this by a simple test:

  • Note when the vehicle in front of you passes an object (a road sign, building etc.) and count the seconds until you pass the same object
  • If less than 3 seconds, slow down!
  • If just above 3 seconds, it’s still safer if you slow down additionally

Reaction and response time

Think of reaction time as the time needed to:

  1. See the potential hazard
  2. Understand what it means
  3. Decide what to do
  4. Initiate a response
You, or the car in front, may have to brake for a pedestrian crossing the road unexpectedly

Think of response time as the time needed to respond. Braking is often the only appropriate response to avoid a severe crash, as swerving may result in a more severe crash (e.g. a head-on collision).

A fit and alert driver requires about 1.5 seconds to react to a hazard and responding also takes time. That's why you should keep a following distance of at least 3 seconds.

A 3-second gap leaves no room for error

Keep in mind that a 3-second gap leaves no room for error, so it's often a safer option to have 4 seconds or more. Conditions are rarely perfect, and you might need a much longer time to react and respond safely.

You should always drive at a speed suitable to the conditions - slow down and increase your following distance when:

  • road conditions are bad (e.g. wet, icy or gravel roads)
  • driving in low visibility situations.
Increase your safety margin when it's raining

Additionally, increase the following distance and be extra careful:

  • When driving with a heavy load
  • When driving on a gravel road
  • When following large vehicles. If you're too close behind a truck, it will block your view of oncoming traffic, and the driver won't see you
Increase the following distance when driving behind large vehicles

Always be extra careful around heavy vehicles as they take longer to change direction and stop. Stay out of their safety margin.

Safety margins for long vehicles

Vehicles with a combined length of at least 7.5m (including a trailer) are considered 'long'.

A long vehicle following another long vehicle must drive at least 60m away from it. However, there are two exceptions to this rule:

  • In a built-up area (street lights or buildings next to the road)
  • On a multi-lane road
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