Following a dark lorry on the RN1 at night
At 21:30 you are driving a loaded sedan north on the RN1. Your speed is 80 km/h in a 90 km/h limit. Four passengers and luggage weigh the car down, and the rear tyres have about 2 mm of tread. Ahead, an overloaded lorry crawls at 45 km/h with one dim rear light and no reflective markings. You are 40 m behind it. The road is dry and straight, but there is a crest 150 m ahead and occasional oncoming traffic. Your reaction time is about 1 second. You have been driving for two hours and feel alert. The lorry's load overhangs and sways on the rough shoulder. You want to reach the next town before 23:00. Your headlights are on dipped beam, and dust from the lorry reduces visibility. The centre line is broken where you are, but becomes solid near the crest.
1. Is a 40 m gap adequate at 80 km/h? Show your reasoning.
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No. At 80 km/h you travel about 22.2 m per second. A 40 m gap is therefore only about 1.8 seconds of following time, which is below the 2-second minimum even in good daylight. At night, behind an unlit lorry, you need at least 4 seconds, roughly 89 m.
Stopping distance confirms the problem:
- Reaction distance at 1 second: about 22 m.
- Braking distance on dry tarmac with good tyres: roughly 31–36 m.
- Total: about 53–58 m, before allowing for a loaded car and 2 mm rear tyres. Realistically 65 m or more.
So your stopping distance is greater than your following gap. If the lorry brakes suddenly, you cannot stop behind it. The closing speed is 35 km/h, about 9.7 m per second, so the 40 m gap would be consumed in about 4 seconds if you did nothing.
Either drop to about 60 km/h and increase the gap to at least 60–70 m, or increase the gap to about 90 m at 80 km/h.
2. You decide to overtake. What must you check, and what makes this lorry especially dangerous?
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Checks before committing:
- The centre line is broken now but becomes solid near the crest; a solid line means no overtaking.
- The crest 150 m ahead hides oncoming traffic. At a closing speed of 160 km/h, two vehicles cover 150 m in about 3.4 seconds, far too little to react.
- Check the mirror and blind spot for a motorcycle already overtaking you.
- Confirm the lorry driver has seen you; do not rely on a flash alone.
- Ensure you have enough clear road to complete the overtake and return without forcing anyone to brake.
Dangers specific to this lorry:
- It has one dim light and no reflective markings, so its size and speed are hard to judge.
- The load overhangs and sways; it may shift or the lorry may drift left as you pass.
- Dust reduces your view and can hide a pothole or a pedestrian.
- An overloaded lorry may speed up downhill or slow sharply on an incline, changing the gap unexpectedly.
The safer decision is to wait until after the crest and until the solid line ends, then overtake only with a clear view.
3. Halfway through the overtake, the lorry drifts left into your path. What do you do?
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Abort the overtake immediately. Do not steer right into the lorry, and do not continue alongside hoping the driver will correct.
Options in order:
- Brake hard and drop back if there is room behind the lorry. This is usually the safest because it puts you back in a known space.
- Accelerate clear only if you can already see enough clear road ahead and are far enough past the cab that braking would leave you alongside the trailer.
- Sound the horn and flash to warn the driver, but do not rely on a reaction.
Avoid swerving onto the sandy shoulder at speed: the loaded car with 2 mm rear tyres may lose grip or roll. If an oncoming vehicle appears, braking back behind the lorry is preferable to a head-on impact.
The judgement point is that the overtake was marginal because of the crest and solid line. Once the lorry moves, the correct response is to give up the advantage, not to force it.