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?

Bridges Freeze Before RoadsThere 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.

Bridge_1Bridges 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.

Bridge_2Bridges, 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.

Bridge_3The 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: or Twitter @INDOTNorthwest. Or visit for INDOT’s TrafficWise Traveler Information Service.