Winter Weather Travel Safety - Bridges and Overpasses

We're a couple weeks away from the start of the busy holiday travel season, and winter weather will be arriving just in time for many parts of the U.S. This weekend, parts of the Midwest are experiencing their first cold snap and measurable snowfall.

With millions of travelers getting ready to hit the road for Thanksgiving, it's time to start thinking about winter driving safety. In this blog, I'll discuss bridges and overpasses, and why they can be particularly hazardous spots when winter weather hits.

We've all seen the yellow warning signs approaching bridges and overpasses that scream out "Watch for Ice on Bridge," or with similar language, depending on where you are. During my time as a Forensic Meteorologist, a number of cases I investigated involved fatalities and personal injuries stemming from major crashes and pileups on icy bridges.

Graphic Source: National Weather Service, Sioux Falls, SD.

While travel during any winter weather event can be hazardous, the most dangerous scenario occurs when with the onset of a winter storm with temperature above freezing, but then temperatures drop below freezing as the storm continues. In this instance, precipitation will initially fall as rain or wet snow that melts on contact with the surface. As the air temperature drops below freezing, paved surfaces on ground may take longer for their temperature to fall below freezing. Meanwhile, the temperature of bridge surfaces will tend to drop below freezing more rapidly as cold air passes above and beneath the bridge deck, dissipating heat from the bridge surface and lowering its temperature as a faster rate than the surrounding ground. As a result, one can be driving on roads that are wet, but then encounter a bridge that is completely covered with ice and snow. A motorist who is not prepared for the slick bridge surface can lose control of their vehicle and crash.

How icy bridge conditions are mitigated

In areas prone to winter weather, road crews typically treat bridges and overpasses with de-icing chemicals, rock salt, or sand before and during a winter storm. Snowplows are used to clear ice and snow from icy bridges to enable safe passage of vehicular traffic. Some bridges, mainly in northern-tier states may be equipped with de-icing systems that either release de-icing chemicals onto the bridge deck, or use heating elements to warm the bridge deck during a winter storm. However, these de-icing systems are not in widespread use due to their high cost of installation and maintenance. In severe icing conditions, the bridge may be closed to traffic until conditions improve.

What to do when you encounter an icy bridge

• Slow down! While the posted speed limit might be 75 mph, never drive at a speed greater than what is safe for the weather and road conditions you're driving through.

• When you encounter the icy bridge and the vehicle feels like it's floating, gradually let your foot off the gas pedal, but don't slam on the brakes. Keep the vehicle pointing straight ahead and avoid making any sudden turns.

• If you start to slide, steer into the direction of the slide. For example, if the rear of your vehicle starts sliding to the right, turn your steering wheel to the right, but be careful not to over-correct.

• Check the weather before you depart. If winter weather is expected, consider taking an alternate route that avoids the hazardous weather conditions, or delaying your travel until conditions improve.

While winter storms and icy bridges are a common concern during the holiday travel season, staying alert for changing road conditions and using sound judgment will ensure you make it safely to your destination.