Night overtake on a two-lane mountain road
You are driving a loaded car at 22:40 on a dry two-lane road outside a settlement. The road runs along a mountainside: on your side there is a rock wall, on the opposite side a low guardrail with a drop beyond it. The posted limit is 90 km/h and you are doing 75 km/h. Ahead, a lorry with a trailer is doing 40 km/h, and its rear marker lights are partly obscured by mud. The road curves gently to the left about 120 m ahead, and the curve is hidden behind the rock wall. Your headlights are on dipped beam. You have already closed to about 25 m behind the lorry and the driver ahead has not signalled. There is no traffic visible in your mirror and no oncoming headlights at the moment. Your passenger urges you to pass before the curve.
1. Using the visible geometry and speeds, decide whether an overtake should be started now. Show the arithmetic you rely on.
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No - do not start the overtake.
Two independent checks both fail:
Sight distance. The curve is ~120 m ahead and its far side is hidden by the rock wall. An overtake needs the whole manoeuvre plus a safety margin to be visible. Closing speed against the lorry is 75 − 40 = 35 km/h ≈ 9.7 m/s. Even a modest 8-second exposure covers ~78 m, and you would begin the manoeuvre only ~120 m from a blind bend - the margin collapses the moment the lorry accelerates slightly or you need to abort.
Abort path. To abandon an overtake you must return to the right. Your right side is a rock wall; the opposite side is a guardrail over a drop. There is no escape lane, so a misjudged abort means a head-on or a barrier impact.
The absence of oncoming headlights proves nothing: a vehicle can appear from behind the rock wall with only 2–3 seconds of warning at combined closing speeds near 130 km/h. Wait for a section with a clear, uninterrupted view (typically a straight with no crest or bend for several hundred metres), then pass decisively.
2. Your passenger says the mud-covered marker lights make it safe to follow closer so you can 'see the gap'. Explain why closing to 15 m at 75 km/h is unsafe and what following position you should take instead.
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Why 15 m is unsafe. At 75 km/h you travel 75 ÷ 3.6 ≈ 20.8 m every second. At 15 m gap you have well under one second of reaction room - less than the distance covered while your foot moves from accelerator to brake. The lorry's obscured lights also mean you may perceive its braking later than normal, so the effective reaction time is worse than the standard assumption.
Correct position. Hold back so that you can see past the lorry's left side and read the road ahead, and so that a following vehicle can see your lights. A practical rule at this speed is a gap of at least 2 seconds in good conditions - about 42 m at 75 km/h - and more at night with a partially lit vehicle ahead. A larger gap also gives you the run-up needed to complete a pass quickly once a genuinely safe straight arrives, rather than crawling alongside the lorry in the curve.
3. Halfway through a later, properly sighted overtake, the lorry's driver accelerates and an oncoming car's headlights appear. State the correct sequence of actions.
Read the worked answer
Abort immediately; do not 'win' the race.
- Brake firmly but progressively and drop back behind the lorry - braking shortens the time you spend in the oncoming lane. Do not swerve right into the lorry's path.
- Signal right to show your intention to return, and only move back once you can see the lorry's front in your mirror or over your shoulder.
- Do not flash or gesture at the oncoming driver; keep both hands on the wheel and your lights on dipped beam so you do not dazzle them.
- If the gap has closed so far that returning behind is impossible, the least-bad option is to brake hard and move as far right as the road edge allows while the oncoming vehicle passes - but this situation only arises because the overtake was started without enough margin, which is why the earlier decision matters.
After aborting, re-establish a 2-second-plus gap and wait for the next clear straight. An aborted overtake costs seconds; a head-on at combined closing speed does not.