All our speed bumps in Kenya are substandard and must be removed!
By MUNGAI KIHANYA
The Sunday Nation
Nairobi,
18 December 2016
A while ago, fellow columnist, Sunny Bindra quipped that Kenya is the
only country in the world where a speed bump is erected on a road to
reduce accidents and then removed a few days later to reduce accidents.
I have also found that this is the only place in the world where a speed
bump will be erected to slow down cars and then a traffic officer is
stationed at that spot to urge drivers to speed up! I see it every
morning on the way to work.
The recent accident at Naivasha has put speed bumps to question on a
national scale. Even the President of the republic has commented on the
matter.
Erecting speed bumps is a science. You dont just go and dump a lump of
tarmac at the selected spot! The Kenya National Bureau of Standards
(KEBS) published the design standard a long time ago (November 2000) but
it has largely been ignored.
The standard KS774:2000 says that the maximum height of a speed bump
is 10cm above the road surface; but, in exceptional circumstances, the
height can be increased to 20cm. In addition, the gradient must not
exceed 1-in-40 (1-in-20 for exceptional cases).
In simple English, 1-in-40 means that for every 40cm travelled
horizontally, the bump rises only one centimetre. So, the highest bump
should ascend over a distance of 400cm and then descend for another
400cm along the direction of the road. In other words, the entire speed
bump should be at least 8m!
Similar calculations reveal that the highest (20cm) and steepest
(1-in-20) bump also straddles over a total of 8m along the road. Even
the very long and very low Mercedes S-Class Pullman (4.315m between
front and rear tyres and 15cm ground clearance) will go over such a bump
without getting scratched underneath.
So far, we have assumed that the speed bump is formed from two inclined
straight surfaces one ascending, the other descending. But, normally,
they are in the shape of an arc of a circle. To stay below the maximum
limit of the gradient, the curved profile requires an additional 2m
along the road bringing the total size to about 10m.
Speed bumps are so-called because they are intended to reduce vehicle
speeds. Can the Kenyan standard do that work effectively? The answer is
yes; research in other countries has shown that the 10cm, 1-in-40 cuts
the average speed to between 50km/h and 60km/h just what we need!
In a nutshell, all the speed bumps in Kenya are substandard. They cause
accidents, they cause traffic jams and they break our cars. They a good
for nothing and they must be removed!
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