Fixed-route buses avoid repeated detours, but in a thinly populated corridor they may require many passengers to walk far from their doors. A flexible service can keep a general travel direction while deviating sideways to reach scattered requests. Which design works better depends on how many requests appear.
A flexible vehicle first sweeps through the long service area. At low demand, door-to-door access can outweigh the cost of occasional deviations. At high demand, serving every individual request makes the flexible route increasingly circuitous, and the fixed service gains an advantage. The final act keeps the high demand but lets passengers walk a limited distance to selected meeting points, reducing the number of vehicle detours. The insight is a design spectrum, not a fixed-versus-flexible winner: pooling pickup locations can preserve much of the access benefit while controlling the operational burden of flexibility.
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.
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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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