Be Careful On The Road, 80km/h is Not A Safe Speed
By MUNGAI KIHANYA
The Sunday Nation
Nairobi,
06 February 2005
Thanks to transport Minister John Michuki, buses,
Matatus and other commercial vehicles will never exceed 80
kilometres per hour. But is this a very safe speed? Should we throw all
other caution to the wind since the vehicles are now moving slowly? What
would happen if two vehicles collided headon at 80km/h?
Suppose you are in a car moving at 90km/h and you
approach a “Michukicompliant” bus travelling at 80km/h. As you
overtake, you will notice that you pass the bus very slowly even though
your speed is quite fast. Indeed, to the passengers in the bus, your car
will seem to be cruising at 10km/h only!
On the other hand, if the bus were approaching from
the opposite direction, it would appear to you to pass extremely fast.
If you had a speed gun in your car, you would record that the bus was
moving at 170km/h (the bus’s 80km/h plus your car’s 90km/h).
Therefore, if two buses moving at 80km/h collided
headon, the combined impact velocity would be 160km/h. That is, the
collision would be equivalent to ONE vehicle hitting a concrete wall at
a speed 160km/h. Would any passenger would survive?
Let’s put this in proper perspective by comparing it
to a falling object. The velocity of a falling object depends on the
height from where it is released. If a stone were released from a height
of 5 metres it would hit the ground at about 10 metres per second
(36km/h). At 10m high, the landing speed increases to about 50km/h.
The next question is: from what height would an
object need to be dropped for it to hit the ground at 160km/h? The
answer is 99 metres. That is approximately the height of the Kenyatta
International Conference Centre (KICC). In other words, the impact of a
headon collision between two vehicles travelling at 80km/h is the same
as that of a car dropping from the top of the KICC – head first! Can
anyone survive such a drop?
Furthermore, if a bus collided with a car, the impact
on the car is much greater than that on the bus. This is because of the
difference in the mass of the two vehicles. A bus weighs about ten
tonnes while a car is only one tonne in weight. Therefore, the momentum
of the bus is ten times that of the car.
At 80km/h, the impact from a bus is equivalent to
that of a car moving at 800km/h! Now imagine the effect of a 40tonne
trailer… It is no wonder that, even at the reduced speeds, buses and
Matatus still killing people, albeit in fewer numbers. So, even
though Michuki has done his part, we must do ours and exercise extreme
care on the road.
