Rail, aviation, maritime, and their operating mechanisms.
Connections across modes
A railway turnout changes a train's route by changing the path available to its wheelsets, not by turning the train like a road vehicle. The wheels are guided by rails on both sides; at a branching point, the track components must present one continuous, correctly connected route.
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A port has a limited length of quay, and a ship must occupy one continuous stretch of it for the duration of service. Assigning an arriving vessel to the first apparently open place can block another vessel that needs a different length or arrival window.
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An electric train can return energy to the traction system while braking. Another train can use some of it if that train is accelerating at the same time and the electrical connection can carry the power. Without such a match, the opportunity may be lost even though the braking train still produces energy.
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Quay cranes are shared resources. Splitting them evenly between two ships may seem fair, yet keeping both ships in service longer can delay a third vessel that needs a berth. The time at which a ship leaves can matter more than how busy every crane appears at each instant.
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An inbound flight is late, and some passengers are trying to board a departing connection. Holding that outbound aircraft could save their trip, but it also delays the people already aboard and may cause new missed connections farther down the route.
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Aircraft can wait at a gate or on a crowded airport surface. Pushing them back as soon as they are ready often moves the queue toward the runway, where engines are running while planes creep forward. Metering gate departures can shift some of that wait to a less costly location.
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A ship that reaches port before its berth is ready often spends fuel to arrive quickly and then waits at anchor. Just-in-time arrival asks whether some of that waiting can be moved back to the voyage, where the vessel can sail more slowly instead.
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Airlines expect some booked passengers not to appear. Selling exactly the number of seats on an aircraft can therefore leave capacity unused. Selling more tickets raises the chance of a full flight, but it also risks having more people arrive than can board.
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A tightly packed railway timetable can move many trains when everything runs exactly on schedule. A small delay, however, may force later trains to wait for the same track and spread disruption through the service. Extra time between planned movements can absorb some of that shock.
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