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Going 5 km/h faster? How much time are you actually saving?

Published November 22, 2012
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Most motorists don’t think that going a little faster really makes much difference to their safety. What’s another 5 or 10 km/h? It’s not like we’re breaking the sound barrier!

I would bet most drivers though feel that extra 5 or 10 km/h makes a huge difference in their driving time.

Statistics Canada pegs the average commute by car in the GTA at around 30 minutes. The average speed a commuting driver could hope for in rush hour might be 60 km/h with part highway and part city driving. That would make the average distance travelled about a 30 km drive.

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If it was possible to average 65 km/h instead of 60 km/h, that would only cut around 2 minutes off the commuting time. It would not be easy to average that extra 5 km/h in rush hour. That two-minute gain could easily be wiped out by getting two or three more red lights instead of green lights. Many motorists spend much longer than that sitting in a Tim Hortons drive through each morning.

Let’s put that two minute gain in perspective. If you live to a modest age of 80 years, you will have enjoyed about 42,048,000 minutes of life. Trying to save a measly two minutes works out to a mere 0.000000024% of your life time.

But what does that extra 5 km/h mean for your safety?

Let’s look at it this way:

We have two identical vehicles travelling the same section of road with one travelling at 60 km/h and the other at 65 km/h when an emergency situation presented itself to the two drivers. The vehicle travelling at 65 km/h has just come along side to pass the vehicle doing 60 km/h when they encounter the emergency situation directly in front of them. They are side by side when they hit the brakes.

With both drivers being of equal skill etc. they both would react at the same time and apply the brakes equally at the same instant.

Now things get very interesting and you will be amazed at the results.

According to the experts at Monash University Accident Research Centre in Australia, in this situation during the last five metres or braking, your vehicle loses half of its speed.

In other words, when our two “test” vehicles mentioned previously finally reach the “emergency”, the vehicle that was moving at 60 km/h will hit the obstacle at only 5 km/h but the vehicle that was travelling at 65 km/h, initially only 5 km/h faster, will collide with the obstacle at a whopping 32 km/h. That is a huge difference.

That 5 km/h difference before the braking translates into a massive 27 km/h difference at the impact point.

You are probably wondering how only 5 km/h difference on speed can make such an impressive difference in braking.

I urge you to watch this video produced by the Monash University Accident Research Centre to see for yourself.

This short video demonstrates it well.

Motorists and truckers are bound by the Laws of Physics and as such our vehicles’ braking distances increase as a square of the speed. In other words, if you double the speed of your vehicle, its braking distance won’t just double, it will quadruple the stopping length.

This is why slowing down when progressing through an intersection is such a good idea.

According to safety.transportation.org about 20 per cent of traffic crashes happen at road intersections (which make up much less than 1 per cent of all roads). It is obvious that intersections need extra care. Collisions in intersections are often fatal due to the nature of the collision. T-bone collisions are very serious.

When approaching any intersection, even with the green light, it is always wise to take your foot off the gas and cover the brake pedal in the event emergency braking is required. Slowing by only 5 km/h through an intersection can make a very large difference in your braking distance and the force of any collision should there be one. For example, if the speed limit is 60 km/h and you cross through an intersection at 55 km/h instead of 60, it will make a big difference in your safety.

Every time you encounter any intersection remember these safe driving hints:

1. Never assume crossing traffic will stop. Red lights and stop signs do not stop cars and trucks. People do and they are notoriously unreliable.

2. Slow slightly when approaching the intersection by taking your foot off the accelerator and covering the brake pedal for an emergency.

3. Think back to that Monash University video and how important going slower through the intersection by only 5 km/h is.

4. Look both ways to check if crossing traffic has or is stopping. A simple glance to the left, right and left, right again can give you a sense of crossing traffic speed. Then look where you want to go.

5. Being distracted while driving is dangerous, Being distracted while driving through an intersection is doubly dangerous. Stay focused on your driving.

The bottom line – that extra 5 km/h most motorists think will save them tons of time really is insignificant in the overall big picture. However that 5 km/h can reduce your stopping distance and increase the force of a crash in a big way.

It is much better in some cases to slow by 5 km/h than to speed up by 5 km/h (unless you’re racing in the Daytona 500).

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