Night Rain Behind a Dimly Lit Cargo Truck
It is 8:40 p.m. and you are driving a lightly loaded delivery pickup northbound on a two-lane provincial highway. Light rain has been falling for an hour; the asphalt is wet and reflective and your wipers are on intermittent. You are doing 60 km/h. Ahead, about 45 metres away, is a cargo truck moving at roughly 40 km/h. Its tail lamps are dim and it has no reflective tape, and it is throwing up a fine spray. Oncoming vehicles pass every 20 to 30 seconds and their headlights wash out your view of the road ahead. The centre line is double solid for the next 300 metres, then becomes broken. Your passenger is awake and talking to you.
1. What is wrong with your present following distance, and what should you change? Support your answer with numbers.
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Current gap is a dry-weather gap, not a wet-night gap.
- A 2-second gap at 60 km/h = 60 ÷ 3.6 × 2 ≈ 33 m. You are at 45 m, so you technically clear the dry-road minimum - which is exactly the trap.
- Wet-road stopping distance at 60 km/h, assuming a 1.5 s perception-reaction and a wet friction coefficient of about 0.4: reaction 16.7 m/s × 1.5 = 25 m; braking 60² ÷ (254 × 0.4) ≈ 35 m. Total ≈ 60 m before any margin.
- At 45 m you would be into the truck before you stopped.
What to do:
- Ease off the throttle - do not brake sharply with a following car behind you - until you have at least a 4-second gap (≈ 67 m).
- Bring your speed down to about 50 km/h. At 50 km/h the wet stopping distance falls to roughly 21 m + 25 m ≈ 46 m, so the same gap buys you far more margin.
- The truck's dim lamps and the spray mean you will detect any change in its speed late, so the gap must cover detection time, not just braking time.
2. The double solid line ends and the broken line begins. Do you overtake? Explain the criteria you would use.
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A broken line permits overtaking; it does not require it and it does not make it safe.
Test the manoeuvre against these conditions before moving out:
- Speed differential. You would need to accelerate to roughly 70 km/h to pass a 40 km/h truck, a closing rate of about 20 km/h ≈ 5.6 m/s. Clearing roughly 150–180 m of lane plus returning safely takes around 30 seconds of clear oncoming lane.
- Sight distance. Oncoming headlights arrive every 20 to 30 seconds. You cannot guarantee 30 seconds of clear lane, so the sight distance is not there.
- Being seen. Pulling out into the oncoming lane puts you in the glare path of the next vehicle; the truck's spray will also blind you exactly when you need to judge the gap.
- The truck's own signals. If it is slowing, indicating left, or drifting near the centre line, abort.
Decision: stay behind and wait for a straight section with a genuinely clear oncoming lane, no crest or curve, and no spray. Overtaking on a broken line into glare is one of the classic night-time head-on collisions.
3. Oncoming high beams blind you and the truck's spray gets worse. Where do your eyes go and what do you do with speed and lights?
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Eyes: do not stare at the oncoming lights. Shift your gaze down and to the right edge line and use it to hold your lane position until the vehicle passes. Peripheral vision will still register the oncoming car.
Speed: slow to the speed at which you can stop within the distance you can actually see. On low beam in rain that may be only 30–40 m, which at a wet friction of 0.4 corresponds to roughly 45–50 km/h or less. If you cannot see far enough to stop, you are overdriving your lights.
Lights: keep your own headlamps on low beam so you do not blind the truck driver through his mirrors; do not retaliate by flashing high beams, which destroys his night vision and yours.
Visibility housekeeping: defogger on, washers and wipers on a faster setting, clean the inside of the windscreen when you stop.
If it becomes unmanageable: find a wide, firm shoulder or a lit establishment and pull over completely until conditions ease. Arriving late is cheaper than a head-on.