Ask A Scientist© Engineering Archive

Index Key:   ENG035
Author:      patrick t seeman
Subject:     Highway vehicle weight.
Is there a formula for how the weight of motor vehicles effect highways?

Response #:  1 of 
Author:      david r munoz
It is probably not just the weight of the vehicle that is important but the
weight, number of tires supporting that weight and their total surface area
exposed to the pavement.  Therefore, I think that the pressure exerted by
the tires on the road should be compared with the yield strength of the
asphalt.  You could probably find info on the strength of the road in a
Civil Engineering Handbook.  Check the reference section of your local
library.
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Response:  May, 2001

Damage done by a given vehicle increases roughly with the fourth
power of its weight.  Put another way, if you double the weight of a
vehicle, then the damage it does gets doubled four times.  This means that
double the weight causes 16 times the damage.


Spreading the weight over many wheels and many axles greatly reduces the
damage caused per pound of vehicle weight.  Also, axles spaced just a few
feet apart do less damage than axles located individually when used on
asphalt pavement.  On concrete pavement, the damage is independent of the
axle spacing.


Cars do little or no pavement damage in comparison to large trucks.
It takes approximately 12,000 cars to do the same damage as a single 80,000
pound 18-wheel truck.  Engineers who design pavement typically ignore the
number of cars and only concern themselves about the number of trucks.

Andrew Johnson
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