Why do Bridges
Freeze Before Roads?
Most
people who live in Indiana have seen signs that say "Bridge Ices Before Road,"
or “Watch for Ice on Bridges”, but do you know why bridges freeze first?
There
are several reasons why bridges freeze before roads. Bridges are subject to
much greater temperature extremes than roads. They get colder (and hotter) than
their earthbound counterparts because they are exposed to the elements on all
sides. A highway's blacktop is insulated by the earth that serves as its foundation,
but a bridge is constantly being hit by the below-freezing air that comes with ice and accumulating snow, increasing the chance that it
will freeze over first.
 Bridges also are
especially susceptible to freezing because of how they're made. Highway pavements
are mostly blacktop asphalt, which is made from crushed stone and
asphalt cement. This helps roads maintain flexibility throughout temperature
extremes and also helps them retain heat well even in winter.
Bridges,
on the other hand, are usually constructed out of concrete and metal materials that
are better than asphalt at supporting heavy loads. These materials tend to
conduct heat out of the bridge and into the ambient air, dropping their
temperature.
The bottom line is that a bridge
will follow the air temperature very closely. If the air temperature falls
below freezing, a bridge's surface will fall below freezing very quickly.
Therefore, rain or snow will freeze and stick to the bridge.
INDOT advises motorists to slow down when approaching
bridges and overpasses while traveling in cold weather. Oftentimes you can't
see the ice on the road, and it may be hidden beneath a thin blanket of snow or
appear as simply a wet surface.
Avoid changing lanes when crossing bridges. Tire
friction helps to warm the pavement and areas outside the wheel tracks may be icy.
If, while traveling over a bridge, your car feels like
it's floating, you should gradually slow down to maintain control of the
vehicle. Never slam on your brakes or
make sudden turn movements. When there is ice and snow take, it slow. Always take heed of the warning
that a bridge ices before a road. Stay safe.
Drivers in Northwest Indiana can monitor road
closures, road conditions, and traffic alerts at any time via the District’s
social media channels: www.Facebook.com/INDOTNorthwest
or Twitter @INDOTNorthwest.
Or visit http://www.trafficwise.in.gov
for INDOT’s TrafficWise Traveler Information Service.
Subscribe to receive text and email alerts about
INDOT projects at https://public.govdelivery.com/accounts/INDOT/subscriber/new
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