Night Rain Behind a Mud-Covered Flatbed
You are driving north on the Desert Highway at night in light rain. The posted limit is 100 km/h and your speedometer reads 100. Ahead, a flatbed truck is doing about 70 km/h. Its rear reflectors are caked with mud, and a length of steel pipe projects about 0.5 m beyond the tailgate on the left side. You have been driving for three hours and have 90 km still to go. The centre line is broken for the next 300 m, then becomes solid. Oncoming headlights are continuous, and spray reduces visibility. Your passenger is asleep. You have been closing on the truck for the last kilometre and are now about 40 m behind it. The hard shoulder is narrow and unlit. Your headlights are on dip because of oncoming traffic.
1. Calculate whether 40 m is an acceptable following gap at 100 km/h in these conditions, and state what you should do.
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At 100 km/h you travel about 27.8 m every second. A 40 m gap is therefore only about 1.4 seconds - less than the bare minimum dry-weather gap and far too short in rain, spray and darkness. Use at least four seconds when the road is wet: about 111 m at 100 km/h. The truck is also a special hazard because its reflectors are muddy and a pipe protrudes on the left. Reduce speed to about 70 km/h to match the truck; at that speed a four-second gap is about 78 m. Drop back gradually rather than braking late, and use the broken-line section only for a planned overtake, not to sit alongside the truck.
2. Should you overtake the truck in the next 300 m? Give your reasoning.
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Probably not. The broken line allows overtaking in principle, but the decision depends on visibility and a safe gap, not just the marking. Oncoming headlights are continuous, spray is reducing visibility, and the truck has a pipe projecting on its left side, so you would need extra lateral clearance. A 300 m broken section at a closing speed of about 30 km/h gives roughly 36 seconds of legal overtaking opportunity, but you cannot see far enough to guarantee the oncoming lane stays clear. The safe choice is to hold back, keep the four-second gap, and wait for a dual carriageway or a clearly visible straight section. If you ever start an overtake and doubt it, abort it by dropping back, not by speeding up.
3. You have been driving for three hours and still have 90 km to go. How should fatigue affect your plan?
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Fatigue raises reaction time and makes gap judgment unreliable, so it changes the plan even if the road looks clear. Do not use the overtake as a way to 'get it over with'. Take the next safe rest area or lit fuel station, stop, and rest; a short sleep is more effective than caffeine or open windows. If no rest area is near, reduce speed, increase the gap further, and stop at the first safe place rather than pressing on. The passenger being asleep removes a useful second pair of eyes, so do not rely on them to keep you alert.