Travel time

Travel time is how long it takes to get from one place to another by a particular mode of transport. It sounds simple, and it is the single most useful measure in accessibility work, because it is what people actually experience. Nobody plans their week around distance.

Measuring it properly means following the network. A walking travel time uses paths, crossings and steps. A cycling travel time can account for gradient and for whether the route uses a protected lane or a main road. A public transport travel time has to include the walk to the stop, the wait, the ride, any transfer and the walk at the other end, which is why it depends on the departure time and why an average across the day can hide a service that only runs twice.

Because travel time is comparable across places and modes, it is the natural unit for questions about fairness. Two neighbourhoods the same distance from a hospital can be twenty minutes apart in travel time, and the travel time is the number that matters.