Is it impossible to estimate time between cars when driving?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

16 August 2020

I usually start my time management training seminar by asking participants to observe a minute of silence. I ask them to close their eyes and remain silent for one minute and only open them they feel that 60 seconds are over. Most times, the first person opens their eyes after just 20 seconds! By the end of 40 seconds nearly everyone in the room have opened their eyes.

Test yourself and see how you fair. It turns out that humans are horribly bad at estimating! So, when drivers are told to maintain a three second gap from the car in front, the advice is routinely ignored because people simply can’t measure the duration.

On a few occasions, a participant in my seminar will get it to within 5 seconds. They do it by counting slowly from one to sixty, or by counting 72 heartbeats. These are good tricks but they may not be practical when driving.

In America, children are taught to count seconds this way: “One Mississippi, Two Mississippi, Three Mississippi etc.”. Across the Atlantic, in the UK, they count: “One thousand and one, One thousand and two, One thousand and three etc.”

To maintain three second from the car in front, you need to start your count from the moment it passes a stationary object, say, a street lamp post, and then stop when your car reaches the same place.

In a stream of city traffic flowing smoothly at 50km/h, maintaining a three-second gap translates to keeping a distance of about 40 metres. On a highway where the average speed is about 100km/h, the distance doubles to about 80m.

Under such idealised conditions, the number of cars passing through per minute remains same, whether they are driving at 50km/h or 100km/h or any other speed. Since the separation is three seconds, it means that 20 cars pass by every minute whatever their speed.

This is all nice and neat in an ideal situation. The reality however, is quite different: nobody maintains a three-second gap! At 50km/h, drivers keep about one to two car lengths apart on city streets and about three lengths on the highway.