The Overtake Behind a Slow Truck
You are riding on a single-carriageway rural road with one lane in each direction and a broken white centre line. Ahead of you is a prime mover with a dog trailer travelling at about 80 km/h in a 100 km/h zone. You have followed it for several kilometres. The road ahead curves gently to the right and rises over a crest about 400 metres away. There is a dashed line marking a short overtaking opportunity, but you cannot see beyond the crest. An oncoming car was visible a moment ago and has just passed. Your bike accelerates strongly from 80 km/h. You have been riding for about three hours.
1. Should you begin the overtake now? Justify your answer using what you can and cannot see.
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No. The decisive factor is the crest roughly 400 m ahead: you cannot see whether a vehicle is approaching beyond it, and an overtake at a closing speed of 20 km/h plus the oncoming vehicle's speed can take far longer than the visible clear distance suggests. The broken centre line permits overtaking where safe, but permission is not an instruction. The fact that one oncoming car has just passed does not mean the road beyond the crest is clear - another may be following. Wait until you have a clear view past the crest and can confirm the oncoming lane is empty for the full distance you need.
2. Estimate what you need to check before committing, and explain why the closing speed matters.
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You need enough clear oncoming lane to complete the pass and return to your lane with a safety margin. At 80 km/h you are doing about 22 m/s; to pass a long rig you must accelerate, draw alongside, and clear its length plus a buffer. If an oncoming vehicle is doing 100 km/h (about 28 m/s), the two of you close at roughly 50 m/s - about 50 metres every second. A gap that looks generous at a glance can vanish in a few seconds. Long vehicles also take longer to pass than cars, so the exposure time is greater. That is why you only commit with a clear, long sight line, not a short dashed-line window.
3. What role does your three hours of riding play in this decision?
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Fatigue degrades hazard perception, reaction time and judgement - precisely the skills an overtake demands. After three hours, your ability to judge closing speed and distance accurately is reduced, and you may be more inclined to take a marginal gap. The safe choice is to recognise the fatigue, delay the overtake, and plan a break rather than use a short opportunity. A rider who is fresh might consider an overtake with a clear sight line; a tired rider should build in more margin, not less.