Bus bunching can begin with a very small delay. A bus that reaches a stop late finds more passengers waiting, spends longer boarding them, and falls farther behind. The following bus encounters fewer waiting passengers and catches up. The original even spacing can collapse into a pair of buses followed by a long gap.
The first act isolates the dwell-time mechanism by comparing a lightly loaded stop with a busier one. The second places several buses on a loop so the feedback can repeat from stop to stop. Passengers accumulate during long gaps, which makes the late bus slower still; short gaps give the next bus an easier stop. The important lesson is that bunching is self-reinforcing, not merely a consequence of a bad initial timetable. Reliable service requires attention to how passenger arrivals and boarding time interact with the spacing between vehicles.
Widening a road may shorten car trips at first. But if some bus passengers respond by driving, bus ridership falls. A transit agency trying to balance its budget may then run fewer buses, making transit less attractive and sending still more travelers to cars.
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A longer urban train could carry more passengers, but extending every platform is costly. The front-and-rear operating idea uses a train longer than its platforms while controlling where it stops and which doors open, so travelers can still reach the correct station safely.
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A trunk bus line can move people efficiently along a corridor, yet passengers living far from its stops may face a long walk at both ends of the trip. That access burden can make an otherwise fast line unattractive.
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