Yup, the roads wearing down and crumbling is a constant, expensive
irritation. Congress just passed an approximately 290 billion dollar
highway spending bill for fixing worn-out roads and building new ones.
One might imagine that schemes designed to reduce the rate of road
failure might be welcome.
Driving down most roads and looking at the pattern of wear on the
pavement does indicate that a good fraction of the pavement rarely
comes in contact with tires, and that most of the contact is restricted
to wheel paths.
I must confess, though, that I am not convinced that a scheme of
evening this out would either work or be cost effective or safe. Road
failure comes in a great variety of forms -- potholes form not only in
the places where the wheels come in contact but also in places where
the cars don't press down so much. Part of the reason for that is that
cracks may form in the part of the lane between the wheel paths which
allows water in, which melts and freezes. Freezing water expands,
cracking the pavement further. Evening out the wear might push cracks
back together again, but I wouldn't be too optimistic.
High-traffic, hard-to-maintain roadways are built with better
methods and materials than small roads and many city streets. A good,
high-quality roadway is built with concrete which has reinforcing steel
bars inside. This prevents cracks before they get started. It is also
important to build a road on a stable foundation -- shifting earth can
cause more problems than the traffic wear. Maintenance can help --
sealing the cracks with tar is a common way to extend the life of a
road. A road which is poorly designed or constructed on weak soil which
washes away in the rain (some roads in mountainous regions of
California where mudslides are common come to mind) will fail
regardless of wear schemes.
That said, there are additional problems with evening out the
wear. A simple scheme may simply guide traffic to shift over by half a
lane so the wheel paths run over previously unworn pavement. But roads
are constructed so that cars which follow the normal wheel paths pass
oncoming cars at a safe distance. You'd have to arrange so that the
oncoming traffic shifts in the same direction, and make the roads
clearly marked enough that people won't follow the old wheel paths but
the new ones. Sometimes paint on the road isn't enough -- people also
use roadside markers and the shoulder to calibrate where they should be
driving. I've noticed this in construction zones where the lanes are
shifted, sometimes by partial amounts, and sometimes it can be
confusing to tell just where the right place to drive is.
You'd probably have to build a half-lane on the side to shift
everyone over. Perhaps new roads can be built extra-wide for this (but
then the temptation to just add another half-lane may be overwhelming).
(republished on 07/17/06)