Freezing Drizzle, a Wing Plow, and a Bridge Deck at 6 a.m.
At 6:05 a.m. in mid-January the outside temperature reads 12 degrees F, and fine freezing drizzle has been falling for an hour. You are eastbound on a two-lane US highway posted 65 mph with the cruise control set at 62. Ahead of you, a plow truck running amber lights and a right-side wing plow is spreading sand at about 30 mph. About 400 feet beyond the truck is a bridge deck over a coulee; the pavement before the bridge looks merely wet. Your tires are all-season with roughly 5/32 inch of tread remaining. A deer stands at the treeline about 200 feet off the right shoulder, head up. There is no traffic behind you for a quarter mile, and you are 25 minutes into a 90-minute commute.
1. Evaluate the speed and the cruise control setting. What should change before you reach the bridge?
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Twelve degrees with drizzle means the pavement is at or below freezing, so anything that looks wet can be a sheet of clear ice. At 62 mph on 5/32-inch all-season tires, you are too fast for conditions regardless of the 65 mph sign - posted limits describe ideal conditions, and a driver can be cited for speed too fast for conditions while still under the limit.
Turn the cruise control off, for three reasons:
- It holds throttle to maintain a set speed, so if the tires lose grip the system keeps feeding power instead of letting the car slow.
- It keeps your feet away from the pedals, costing you reaction time when something happens quickly.
- It encourages a fixed speed when what you need is a speed matched to the worst patch ahead, not the average.
Slow to a speed where your total stopping distance fits inside what you can see and stop for. On ice that distance can be several times the dry-pavement figure, and 5/32 inch of tread is already marginal for slush and standing water. The bridge is 400 feet out; make the adjustment now, not on the deck.
2. How should you handle the plow truck - following distance, and the conditions under which passing is acceptable?
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Stay behind the plow, and stay well back. The truck is doing you a favor: it is laying sand and pushing slush out of the lane, so the surface directly behind it is likely the best you will see for miles.
Following:
- Back off to at least 200 feet - four or more seconds at 30 mph. That keeps you out of the spray, keeps sand off your windshield, and gives you room if the operator slows to adjust the wing.
- Keep your headlights on low beam so the operator can see you in the mirrors.
Passing:
- Never pass on the right. The wing plow extends several feet beyond the truck and is easy to lose against the slush, and the shoulder is not a lane.
- Pass only when the operator pulls aside or clearly waves you by, when you have a legal passing zone and a clear view of oncoming traffic, and when you can get by decisively.
- At 12 degrees, do not linger alongside. Spray refreezes on glass quickly, and an aborted pass leaves you in the worst possible position.
If you cannot pass safely, the correct answer is to settle in behind the plow and accept the delay.
3. What do you expect from the bridge deck, what do you do if the rear of the car steps out on it, and how does the deer change your plan?
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Bridge decks freeze first and thaw last, because cold air moves under the deck as well as over it. The 400 feet of wet-looking approach tells you nothing about the surface on the bridge; assume it is glazed.
On the deck:
- Be off the throttle before you get there, with straight-line steering and no braking on the ice if you can avoid it.
- If you must slow, brake gently in a straight line before the bridge, not on it.
- If the rear steps out, ease off the throttle smoothly, look and steer where you want the front of the car to go, and do not stab the brakes. Locked wheels take away the steering you need to catch the slide.
The deer:
- It is 200 feet off the shoulder now, but deer move unpredictably and usually travel in groups. Cover the brake and reduce speed.
- If it bolts, brake in your lane. Do not swerve into the oncoming lane; a controlled impact at reduced speed is survivable, while a swerve into oncoming traffic at highway speed usually is not.
- Scan the treeline for a second and third animal before you accelerate back to speed.