The Overtaking Lane on the South Western Highway
You are driving north on a two-lane-each-direction rural highway in WA at 100 km/h, the posted limit. Rain has been falling for 20 minutes on a road that has not seen rain for six weeks. Your lane is a single lane; the right-hand lane is marked for overtaking only and ends 600 m ahead, where it merges back to one lane. Ahead of you, a road train is travelling at 88 km/h and throwing up spray. A line of four cars sits behind it. You have been following at about 1.5 seconds' gap. Your passenger says to overtake now before the lane ends. In your mirror, a ute is approaching fast in the overtaking lane.
1. Should you begin an overtaking manoeuvre in the next few seconds? Explain your reasoning and state what you would do instead.
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No. Several factors combine against it.
- Following distance is already too short. At 100 km/h a 1.5-second gap is about 42 m. In rain and spray, with oil and rubber residue lifting off a dry road, stopping distances are longer and visibility behind the road train is poor. The safe wet-weather gap is at least 4 seconds, roughly 110 m.
- The overtaking lane is closing. You have 600 m at a 12 km/h speed differential (100 vs 88). That is only about 3.3 m/s of advantage, so passing a long vehicle plus a safe return gap would consume most of the remaining lane, leaving no margin for error.
- The ute is already in the overtaking lane and closing. Entering that lane would force you into a conflict you cannot resolve by braking safely.
- Spray from a road train can hide debris, potholes and oncoming hazards.
Instead: ease off, drop back to a 4-second gap to restore visibility, let the ute pass, and wait for a genuine overtaking opportunity with clear sight distance and a lane that does not end. If you cannot see far enough ahead to complete and exit the manoeuvre with margin, do not start it.
2. The road train's driver flashes the left indicator briefly. What might this mean, and how should it change your plan?
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A brief left indicator from a long vehicle in the left lane usually signals that the driver considers it safe for following traffic to pass, or that the vehicle is moving left to let you see ahead. It is a courtesy signal, not a legal authorisation and not a guarantee.
The driver's mirror view is imperfect and their vehicle may be about to change position. The signal does not override your own obligations: you must still have clear sight distance, a lane that will not end under you, and no conflicting vehicle such as the ute.
Treat it as one piece of information. Check mirrors and blind spot, confirm the overtaking lane is clear behind you, confirm the lane has enough length for the pass plus a safe return, and only then commit. If any of those checks fails, stay back. Do not accelerate into a closing lane because another driver waved you through.