headway

Headway is a term used to describe the distance or time between consecutive vehicles moving in the same direction. In public transportation and roadway systems, headway is a metric that helps determine service frequency and capacity. The word is also used metaphorically to denote progress toward a goal or objective.

In transportation planning, headway is typically measured as the time interval between vehicles at a given point on a line, or as the distance between the fronts of successive vehicles. Shorter headways imply more frequent service and greater capacity, while longer headways reduce throughput. Headways are influenced by factors such as timetable, signaling, vehicle performance, and traffic conditions.

Time-based headways are usually expressed in seconds or minutes, whereas distance-based headways are expressed in meters. In rail and bus networks, urban services aim for short headways during peak periods, often ranging from a few minutes to around ten minutes, depending on the route and technology. Road traffic uses following headway to maintain a safe distance, and automated systems or adaptive traffic control seek to optimize headways to improve safety and reliability.

Beyond transportation, headway appears in everyday language to describe progress toward goals. For example, colleagues may speak of making headway in research or negotiations, indicating advancement relative to prior progress.