Saskatchewan Driver's Handbook


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Time - The key to judgement

It is difficult to judge how far things are ahead of you. It's even more difficult when both your vehicle and the object outside the vehicle are moving. For example, can you judge how far away that approaching car is?

We all have internal clocks. We all have an internal awareness of time. Why not use time to measure how far ahead things are in day-to-day driving? You can do this by counting seconds.

To count time in seconds, say out loud, "Thou - sand and one, Thou - sand and two, Thou - sand and three," at a normal speaking rate without pausing between the numbers. This will give you a reasonably accurate count of three seconds.

Practise checking against your watch; you'll be counting off perfect seconds in no time.

The language of time

The most important skill in driving is being able to use your eyes effectively to seek out the information you need to drive. To use time as the basis for all of your driving, with special emphasis on your eye use, you need to understand the different ways of estimating time.

First, you must be able to estimate, while you are driving, how far stationary objects or fixed distances are from you. For example, the sign is nine seconds away and at 100 km/h the spaces on the broken lines on the highway disappear about 12 seconds ahead.

Estimate distance ahead in the following way:

  1. Pick a stationary object that is on or near the road (for example: a sign, shadow, overpass or pavement patch).
  2. Guess how many seconds the object is ahead.
  3. Then start counting "Thou - sand and one, Thou - sand and two, Thou - sand and three," etc.
  4. When your front bumper is beside the object, stop counting. This will give you the number of seconds between you and the object chosen. If you guessed 15 seconds and the distance ahead is really eight seconds, then guess a lower number next time. Try for longer distance; see if you can guess how far away 40 seconds is. This way you’ll improve your judgment.
  5. Continue practising this exercise until you can judge time accurately.

The relationship between time and distance varies with speed. Therefore, begin by making all your judgments at the same speed. Then, practise at other speeds at which you most commonly drive, say 100, 80 and 50 km/h.

Pick a stationary object. Start counting. Stop counting when the front bumper reaches the stationary object.

Using time to estimate your following distance

When you are driving, estimate the distance between you and the vehicle in front in the following way:

  1. Pick something that is on or near the road and is not moving (for example, a sign, pavement patch, shadow or overpass).
  2. When the back bumper of the vehicle ahead is even with the object you have chosen, start counting - "Thou - sand and one, Thou - sand and two, Thou - sand and three," etc.
  3. When your front bumper is beside the object, stop counting. This will give you the number of seconds between you and the vehicle you are following.
  4. If you are closer than three seconds, drop back and check again until you have achieved a minimum of three-seconds following distance. Any following distance longer than that is safe. However, a longer following distance is recommended when following a motorcycle.
Pick a stationary object. Start counting. Stop counting when the front bumper reaches the stationary object.

You will notice that by keeping a three-second following distance, regardless of your speed, the distance between you and the vehicle in front will automatically lengthen as you go faster. So, for a three-second following distance at 100 km/h, you will be twice as far back as you would be at 50 km/h and four times as far back as you would be at 25 km/h.

There is one situation where a three-second following distance is not enough. If you are following a large truck or van that blocks your view of traffic ahead, drop back to more than three seconds until you can see around the vehicle (as illustrated below).

You may feel that if you try to keep a three-second following distance, other drivers will cut into the space you leave. This will happen sometimes, but less often than you think. To give up your sight distance, your planning and response time and relaxed driving just because you want to save a few seconds and not let other drivers cut in, is a poor bargain. If you let other drivers dictate your driving style, then you are not in control.

The three-second following distance is recommended when driving conditions are ideal. If driving conditions are less than ideal, your following distance should increase accordingly.

Time - Distance relationships

Speed
(KM/H)
Speed
(MPH)
Metres/Second3-Second following distance (in metres)12-Second following distance (in metres)
100622884336
90562575300
80502266264
70431957228
60371751204
50311442168
40251133132

For a three-second following distance at 100 km/h, you will be twice as far back as you would be at 50 km/h.

Followind distance

To understand why, you will need to examine how three seconds would be spent in a situation that could turn into a collision.

First, you will spend some of the three seconds identifying the problem, predicting the outcome and deciding what to do, through the IPDE approach to driving. Then you need some reaction time - to get your foot off the accelerator and apply the brake. If you're reasonably alert, you can do all of this in three seconds and begin braking, too.

Estimate distance

If you stop at the same rate as the vehicle ahead, you will not hit it.

But, if the driver in front hits a fixed object; you are tired and are slower to react than the other driver; the other vehicle has better traction; or, the other driver is more skilled at braking than you are, then you need more than three seconds to avoid a collision.

Estimate distance

However, if you are looking ahead as far as you should, you will see the cause of the problem any time from 12 to 60 seconds ahead - possibly before the driver ahead of you sees it. In this case, you can respond to the problem rather than to the brake lights of the vehicle in front of you.

Estimate distance

Disclaimer

Rev: 2017