Freezing Drizzle on the Bridge Deck
At 7:05 a.m. in February, Grace is driving a four-wheel-drive pickup east on U.S. 20 near Fort Dodge. The temperature is 28°F, and freezing drizzle has been falling for 20 minutes. The road looks wet, but the bridge deck ahead has a dull, slick sheen. Grace has the cruise control set at 65 mph, the posted limit, and is following a minivan about two seconds behind. The pickup has all-season tires with good tread. Traffic is moderate, and a salt truck is spreading ahead but is not yet over the bridge. Grace's phone alerts her to a text, and she glances down for a second. She is on her way to work and is not late. She has driven this route many times.
1. What should Grace do in the next few seconds about speed, cruise control, and following distance?
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Grace should immediately turn off cruise control, reduce speed well below 65 mph before she reaches the bridge, and increase her following distance to at least eight to ten seconds. Cruise control is a bad idea on ice because it can apply throttle when a wheel slips, causing a loss of control; she needs manual control. Two seconds behind the minivan is far too close for freezing drizzle. She should also turn on her headlights, avoid sudden braking or steering on the bridge deck, and keep both hands on the wheel. The salt truck ahead is not a guarantee that the bridge is treated, and bridges cool faster than pavement on solid ground.
2. Does four-wheel drive make Grace safer here? Explain what it does and does not do.
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No. Four-wheel drive helps a vehicle accelerate and can improve traction on loose or slippery surfaces, but it does not shorten braking distance and does not give the truck extra grip for steering. All four wheels can still slide on ice. The danger is that four-wheel drive can create false confidence, leading a driver to maintain speed or follow too closely. Grace's all-season tires and good tread help, but they are not winter tires, and tread does not equal ice traction. She should drive for the conditions, not for the badge on the fender.
3. What should Grace do if the pickup begins to slide on the bridge?
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If the pickup begins to slide, Grace should ease off the accelerator and steer gently in the direction she wants the front of the truck to go, while looking at her intended path. She should not slam the brakes, because locked or abruptly applied brakes can make the slide worse. If the truck has anti-lock brakes, she can brake firmly once she has straightened out, but on ice the first priority is to avoid sudden inputs. She should avoid overcorrecting; a small steering correction is better than a big swing that starts a spin. After the slide, she should slow further and consider leaving the highway at the next safe exit.