Following distance on a wet highway at night
Kai is driving a 22-tonne rigid truck on a rural highway at 100 km/h. It has been raining for an hour, the road surface is wet, and visibility is reduced by spray from a B-double ahead. Kai's headlights are on low beam. The truck is loaded to its legal maximum and the tyres are at the minimum legal tread depth. A car overtakes Kai and pulls into the gap ahead, leaving only about 30 metres between Kai's truck and the car. Kai's reaction time is average, and the truck's brakes are in good condition but the load increases stopping distance. Kai considers flashing high beam to move the car along.
1. Evaluate whether 30 metres is a safe following distance in these conditions. Show your reasoning using a time-based gap.
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At 100 km/h a vehicle travels about 27.8 metres per second. A 30-metre gap is therefore roughly 1.1 seconds of following distance. The general dry-weather minimum for heavy vehicles is at least 3 seconds, and in wet conditions with reduced visibility and a loaded truck, 4 seconds or more is appropriate. That means a gap of roughly 110 metres at 100 km/h, far more than 30 metres. The car has cut in too close, but responsibility for the gap still rests with Kai: he must back off, not maintain the position. The load, wet surface, and minimum tread depth all lengthen stopping distance, so the safe response is to ease off the accelerator and rebuild the gap to at least four seconds before anything else.
2. Should Kai flash his high beam at the car? What is the safer course of action, and why?
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No. Flashing high beam at a driver directly ahead at night, in rain, with spray reducing visibility, can dazzle the other driver through their mirrors and provoke an unpredictable reaction. It does not create space and may escalate the situation. The safer course is to reduce speed, increase the gap to at least four seconds, and keep low beam on so Kai remains visible without blinding others. If the car continues to sit too close, Kai should increase the gap further and consider whether it is safe to continue at 100 km/h; dropping to 90 km/h in wet conditions is reasonable and reduces both stopping distance and spray. Only if the car's behaviour becomes dangerous should Kai consider pulling over at the next safe opportunity.