Rain, an Unsecured Load and 4 Seconds
11.20 pm on the PIE, three lanes, speed limit 90 km/h. You are in the centre lane at 80 km/h with two sleeping passengers, heading for Jurong. Light rain has left the surface shiny. Ahead of you in the same lane is a flatbed lorry doing a steady 75 km/h. Its load of scaffolding poles is unsecured and overhangs the tailgate, the left tail lamp is dead, and the rear of the lorry is caked in mud. The left lane is carrying traffic at about 70 km/h. The right lane is clear behind you for 200 m, but you cannot see the road past the lorry's cab.
1. Calculate the minimum gap you should hold at 80 km/h, and justify the wet-road adjustment rather than simply asserting it.
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The arithmetic:
- 80 km/h = 80,000 m ÷ 3,600 s = 22.2 m per second.
- Dry 2-second rule: 2 × 22.2 = about 44 m.
- Wet: at minimum double it → 4 seconds = about 89 m. Round it to 90 m.
Why doubling is not over-cautious:
- Thinking distance alone is 22 m if you take a full second to react - and at night, in rain, behind a mud-caked lorry with a dead lamp, a second is optimistic.
- Braking distance roughly doubles on a wet surface because available grip roughly halves. From 80 km/h the full stopping distance in the wet is in the region of 85–90 m - which is the same figure as the 4-second gap. So the 4-second gap is not a generous margin; it is the distance at which you can just about stop if the lorry's brakes lock up in front of you.
- You cannot see past the cab. Normally the vehicle ahead is your early warning of a hazard. Here it is a blind wall, and the gap is your only source of information and reaction time.
- The load is an unsecured hazard and the dead tail lamp means drivers behind may not register the lorry's actual width or speed at all.
Conclusion: hold about 90 m - four seconds measured against a fixed object such as a lamp post - and treat that as the floor, not the target.
2. Decide between holding position, dropping back further, and overtaking. Set out the conditions that would have to be met before an overtake is safe here.
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Hold at 90 m; do not close up. Do not sit at 75 km/h a car length behind the lorry for the next 20 km either - that is the classic position for a load strike.
Overtaking is the reasonable long-term answer, but only on conditions:
- The passing lane must be clear for a long distance, behind and ahead. It is clear behind for 200 m; that is enough to begin, not enough on its own.
- You must be able to see far enough past the cab to know you are not moving into a hazard - a stationary queue, a works zone, a weaving motorcycle. You cannot see that from behind. So you build speed in your own lane first, and accept that the decision is completed as you come alongside.
- You must have an abort plan. If a hazard appears as you draw level, you brake and drop back behind the lorry - you do not force your way through.
- No need to exceed 90 km/h. If passing requires breaking the limit, the gap is not there.
- Signal early and repeatedly. At night, in rain, with a driver whose mirrors are probably as filthy as his tailgate, assume he has not seen you.
Never pass on the left here: the left lane is running at 70 km/h, it is the slower lane, and undertaking across it at a 10 km/h speed differential is exactly how cars end up under trailers.
Judgement point: the safest driver in this scenario is the one who is content to sit 90 m back until the pass is genuinely clean, even if that costs two minutes. The crash risk is concentrated in the moment you commit, so you buy certainty first.
3. A pole slides off the lorry and lands across your lane about 40 m ahead. What do you do in the next two seconds?
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Brake, do not swerve.
The arithmetic of the decision: the pole stops dead; you do not. At 22.2 m/s, 40 m is 1.8 seconds to the obstacle. Doing nothing for even half a second to see where it lands costs you a quarter of your remaining distance.
The stop: from 80 km/h, stopping inside 40 m requires roughly 6 m/s² - hard, threshold braking, at the limit of a wet road. So it is a maximum-effort stop from the instant the pole moves, with both hands on the wheel, straight line, ABS doing its job.
Why not swerve:
- Into the left lane, into traffic running at 70 km/h, at night, in rain - a side impact at a 10 km/h closing speed difference is survivable; a side impact at a steep angle into a live lane at 80 km/h is not.
- Into the right lane, into road you cannot see. You would be trading a visible object for an unknown one.
- A hard swerve at 80 km/h on a wet surface invites a spin, and a spun car across three expressway lanes at 11.20 pm is the worst outcome available.
After you stop:
- Hazard lights on immediately. Keep the passengers belted in the car if you are still in a live lane and the car is intact - a car with its hazards on is more visible than three people standing in lane 2.
- Once it is safe to move, get everyone out on the side away from traffic and behind the barrier.
- Call 999 - a pole across a live expressway lane is an immediate danger to life.
- Do not attempt to drag the pole yourself while traffic is still running.