February Descent Behind a Motorhome
You are westbound on a two-lane mountain highway in central Idaho on a clear, cold February morning. The temperature is 18°F. The road has been plowed, but the pavement is patchy with packed snow, and a bridge 300 feet ahead is shaded by the canyon wall. You are descending a 6 percent grade at the 55 mph limit and come up behind a motorhome doing 25 mph. Four cars are stacked behind it. The center line is a broken yellow that becomes solid about 200 feet ahead at a blind crest. Your tires are all-season, not studded. The motorhome brakes briefly as it approaches the bridge.
1. What following distance should you keep behind the motorhome at 25 mph, and why is the usual rule not enough here?
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At 25 mph a basic 3-second gap is roughly 110 feet. On packed snow and a downhill grade, double it - aim for 6 seconds or more, which is about 220 feet at that speed. The reason is stopping distance: on a low-friction surface, braking distance can be several times the dry-pavement figure, and a 6 percent downgrade adds speed even when you are off the throttle.
The motorhome also blocks your view of the road ahead, so the gap is your sight distance as much as your braking room. If the motorhome brakes hard for a shaded patch, you need that space already established, not created by a panic stop. Keep the gap even when the line of cars behind you pressures you to close up.
2. The broken yellow line ends at a blind crest about 200 feet ahead. Do you pass the motorhome?
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No. The broken yellow permits passing only when it is safe, and here it is not. You would be starting a pass with a blind crest roughly 200 feet away. Closing speed matters: if you accelerate to 55 mph to pass a 25 mph vehicle, you are gaining about 30 mph, or 44 feet per second. That puts you at the crest in a few seconds, with no view of oncoming traffic and a snow-patched surface that limits your ability to abort.
Add the bridge and the grade. The bridge is shaded and likely icier than the plowed approach, and a pass would have you changing lanes or braking on that surface. Wait for a straight, signed passing zone with clear sight distance and no bridge, then commit decisively. Until then, hold the gap and accept the delay.
3. The motorhome brakes as it reaches the shaded bridge. What is the right technique for you at that moment?
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Expect ice. A shaded bridge at 18°F holds cold and moisture long after the sunny pavement has dried, so the bridge deck can be slick even though the road before it looks merely wet or patchy. The motorhome's brake lights are a warning, not a cue to close up.
Get off the throttle early and brake gently and progressively while the car is still straight, before the bridge. Do not use cruise control on this road - it can downshift or apply throttle when you need neither. If you have ABS, apply firm steady pressure and steer where you want to go; do not pump the pedal. If the car begins to slide, look and steer toward your intended path and ease off the brake rather than adding more. Keep both hands on the wheel and avoid any abrupt input on the bridge deck itself.