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I keep thinking this during my daily commute along a 3 lane freeway. If a bus/truck overtakes another bus/truck (often), it basically becomes a single lane freeway. And during peak, that little manoeuvre is going to cost you and hundreds of cars behind you, probably for a long time.
My small city's main suburb to centre link is a 100km/h, two lane each way parkway, until it merges with a similar road from a different centre, grows to 3 lanes each way, and slows down sharply as it gets close to the centre
Between the last traffic lights and the spaghetti junction that merges it with a similar road it's free flowing and fine. The slow lane goes about 95, the fast lane about 100 to 110, with occasional slight slowdowns when a 95km/h car catches up with a slower one
But on that stretch there's about 300 metres of slow traffic due to a fixed speed camera. People going 95 who think their speedometer might be wrong the opposite way to which it is slow to 80; people doing 110 slow to well below 100, people following too close brake heavily, the fast lane ends up with a standing wave with a peak (or is it a trough?) of 60km/h
Then as you get past the camera it gets loud with even the slow cars rebelling against the slowdown give much throttle. That camera must cost so much CO2. I doubt it catches anyone except during the lightest traffic times. In even medium traffic you couldn't speed through that bit of road if you tried