Streets covered in snow and ice are most dangerous when

Road Icing Danger Zones

During icy road conditions, any road can become dangerous. However, most accidents occur in the following areas:

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  Bridges, overpasses and elevated roadways - Elevated roadways collect snow and ice long before the rest of the roads, catching drivers by surprise. This danger zone is so common, we've devoted an entire page to it.
   
• Steep hills - A more obvious danger zone during road icing is on steep hills. Often, friction forces between tires and the road is not strong enough to overcome gravity to slow or stop a car on an icy hill.
   
• High speed roadways - Slides and loss of control occur much easier at high speeds. As a result, accidents are common on interstates, freeways and turnpikes.
   
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  Curves - The act of steering can easily cause the rear of a vehicle to slide outward on a curve. Contrary to intuition, cars initially tend to fishtail and slide toward the inside of a curve rather than sliding to the outside.
   
• Deceleration spots - Braking is often a major trigger of slides on icy roads. Any part of a roadway that causes a driver to apply the brake is a hotspot for accidents, such as at stop signs, traffic lights, steep hills, construction zones, previous accident sites, sharp curves or highway offramps.
   
• Acceleration spots - Hitting the gas can cause drive wheels to spin on icy roads, which can easily result in loss of control. Acceleration danger zones include uphill grades on interstates and highway on-ramps.
   
• Low-traffic roads - Many times, lesser-traveled roads allow snow and ice to accumulate more easily than in high-traffic areas. Trouble spots to watch for include highway exit ramps, driveways, parking lots and rural roads.
   
• Tunnels - Tunnels often contain continuous groundwater seepage which can coat roadways with ice during subfreezing conditions, even if no precipitation has fallen. Weather conditions can be different on opposite sides of a mountain, surprising drivers who exit a tunnel and encounter roadways suddenly covered in snow and ice.
   
• Groundwater & runoff - Particularly in mountainous regions, groundwater and/or runoff from recent rain can flow or drip down onto roadways from nearby cliffs, hills or ditches. When temperatures drop, this water will freeze into a sheet of ice.
   
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  Mountainous regions - Weather conditions can vary greatly with even small changes in elevation. In most cases, air temperatures will fall and rain will change to snow as you climb in elevation. However, a common meteorological condition called an inversion can result in the exact opposite! When traveling in hilly or mountainous regions, be prepared for rapid changes in road conditions.
   
• Cobblestone and brick pavement - Brick and stone-paved streets are prone to icing up just as fast as bridges and overpasses do, due to the gaps in the road surface that allow cold air to infiltrate downward.

Educational Winter Driving Videos - Watch for Free:

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At what temperature are icy roads most slippery?

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