Black Ice - Bridges

Bridges

Bridges and overpasses can be especially dangerous. Black ice forms first on bridges and overpasses because air can circulate both above and below the surface of the elevated roadway, causing the bridge pavement temperature to drop more rapidly.

In the United States, road warning signs with the advisory "Bridge May Be Icy" indicate potentially dangerous roadways above bridge structures.

The I-35W Mississippi River bridge in Minneapolis, Minnesota, was well known for its black ice before it collapsed in 2007 into the Mississippi River. It had caused several pileups during its 40 year life. On December 19, 1985, the temperature reached -34 °C (-30 °F). Cars crossing the bridge experienced black ice and there was a massive pile up on the bridge on the northbound side. In February and in December 1996, the bridge was identified as the single most treacherous cold-weather spot in the local freeway system, because of the almost frictionless thin layer of black ice that regularly formed when temperatures dropped below freezing. The bridge's proximity to Saint Anthony Falls contributed significantly to the icing problem and the site was noted for frequent spinouts and collisions. It was the only bridge in the United States Interstate system that had its own plumbed saline solution system to address the perpetual icing difficulties. Related corrosion has been cited as a contributing factor to the bridge's catastrophic collapse.