A crossing built generously leaves room for journeys its original planners never took.

Generous dimensions are a bet on people you have not imagined. A crossing wide enough for a wheelchair also serves a delivery trolley, twins in a double pushchair, two friends walking arm in arm, and a market that nobody planned for forty years later. Building only for the expected user produces something that fits today exactly and tomorrow badly. Extra room is not waste; it is the space that future uses will need.

When you are sizing anything, from a doorway to a schedule, ask what it would take to leave room you cannot yet justify. That margin is usually where the later value sits.