Fog, a broken centre line and an overtaking truck
You are driving on a rural two-way road with a posted limit of 100 km/h. Dense fog has reduced visibility to about 60 metres. The centre line is broken, permitting overtaking where safe. A heavy truck ahead is travelling at 70 km/h and throwing up spray. You have been following it for several minutes and your windscreen is streaking. A sign warns of a winding road for the next three kilometres. Your passenger urges you to overtake because the truck is slow. Your headlights are on low beam, and you can just make out the truck's tail-lights and a faint shape of a vehicle beyond it.
1. Should you overtake? Give your reasoning using the information in the scene.
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No. The broken centre line permits overtaking but does not make it safe. With visibility of about 60 metres, you cannot see far enough ahead to confirm the oncoming lane is clear for the whole manoeuvre, and a 100 km/h road means oncoming traffic can close that gap in seconds. Overtaking a 70 km/h truck requires you to accelerate to well above 70 km/h and hold the opposing lane for several seconds, during which an unseen oncoming vehicle could appear. The winding-road warning means the road geometry will hide oncoming traffic even further. The faint shape beyond the truck may be another vehicle, which would make the overtake impossible. The correct decision is to stay behind the truck, increase your following distance, and wait for visibility to improve.
2. What following distance and lighting should you use, and why?
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In fog, use low beam, not high beam, because high beam reflects off the water droplets and creates glare that reduces visibility. Increase your following distance to at least four seconds, and more if spray is heavy, so you have time to react to the truck braking. Do not use rear fog lights unless visibility is seriously reduced, because they can dazzle following drivers. Keep your windscreen and wipers working to clear the streaking, and avoid sudden lane changes. If the fog thickens so you cannot see far enough to stop safely, reduce speed further and consider pulling off the road at a safe place rather than pressing on.
3. The truck slows to 40 km/h and the fog lifts to about 150 metres. What changes, and what checks must you make before overtaking now?
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With visibility improved to 150 metres and the truck at 40 km/h, an overtake becomes possible but still requires checks. You must confirm: the centre line still permits overtaking; there is no oncoming traffic within the distance you will need; the road ahead is straight enough and not within the winding section; and there is a clear gap to return to the left lane. Check mirrors and blind spots, signal, and accelerate decisively so you spend minimal time in the opposing lane. Because the truck is slow, the speed differential is large, which shortens the time exposed. If any of these conditions is not met, stay behind. The decision is driven by the available sight distance, not by the truck's speed alone.