Following Distance and Space Management in Blowing Snow
You are driving a 13,600 kg straight truck with a 9 m box on a two-lane highway at night in blowing snow. Visibility drops to about 150 m in patches. The speed limit is 100 km/h, but traffic is moving at about 85 km/h. A pickup ahead is tailgating a slower car, and a semi is closing behind you. The road surface is partly snow-covered with icy patches in the shaded sections. You are 30 km from your destination and running 20 minutes late. The truck has good winter tires but no chains.
1. What following distance should you maintain, and how does the weather change the normal rule?
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On dry pavement at highway speed, the usual guidance is at least a 3-second gap for a loaded truck, more if heavy. In blowing snow with patchy ice, that baseline is not enough.
Use a minimum 6-second gap, and stretch it to 8 or more where visibility drops. The reasoning:
- Stopping distance grows on ice - braking distance can double or triple.
- Visibility of 150 m means you need to be able to stop within the distance you can see; at 85 km/h you cover about 24 m per second, so 150 m is only about 6 seconds of travel.
- The pickup ahead is tailgating, which means a chain-reaction stop is likely. Your gap protects you from their mistake, not just your own.
Being 20 minutes late is irrelevant to the physics. The correct gap is the one that lets you stop, not the one that gets you there on time.
2. How would you manage the semi closing behind you?
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A tailgating heavy vehicle behind you is a serious hazard because their stopping distance is longer than yours.
- Do not brake-check or speed up beyond conditions. Both increase risk.
- Maintain your own gap ahead so you never have to brake abruptly; a smooth, steady speed gives the driver behind time to react.
- If the semi is too close, create an escape route. Look for a pullout, wide shoulder, or chain-up area and let them pass when it is safe.
- Signal early and brake gently if you must slow, so your intentions are visible.
- Increase your own following distance further, because a rear-end collision from a heavy truck can push you into the vehicle ahead.
You cannot control their following distance, but you can control whether you give them a reason to brake hard. Smooth driving and an early pull-over are the practical tools.
3. What adjustments would you make for the icy shaded sections and the lack of chains?
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Shaded sections hold ice longer because they get no sun, so treat every shaded patch as icy until proven otherwise.
- Slow before the patch, not on it. Braking on ice is where control is lost.
- Use gentle steering and throttle, and avoid cruise control so you retain full control.
- Keep the wheels rolling - a locked wheel on ice has no steering authority.
- Increase the gap further through shaded stretches and reduce speed to a level where you can stop within the visible distance.
On chains: you do not have them, so you must drive to the traction you have. If conditions worsen to the point where chains are required by signage, the correct answer is to stop and chain up or wait, not to proceed without them. A 30 km remaining distance does not justify pushing through ice without the equipment the road may demand.