What is Headway? Understanding Train Frequency

Headway is the measurement of the time interval between the tip of one vehicle (train, tram, or bus) and the tip of the next one behind it, passing the same point. It is the key metric for determining the capacity of a transit line.
While passengers often ask about “Frequency” (how many trains per hour), engineers calculate “Headway” (minutes or seconds between trains).

Headway vs. Frequency

They are two sides of the same coin:
Headway: “There is a train every 5 minutes.”
Frequency: “There are 12 trains per hour.”
A shorter headway means higher frequency and greater passenger capacity.

What Limits Minimum Headway?

Why can’t trains run bumper-to-bumper like cars?
Signaling System: The safety distance required between trains. Traditional signaling might limit headway to 3-5 minutes, while modern CBTC systems allow for 90 seconds.
Dwell Time: The time a train spends stopped at a station to let passengers board and alight. A train cannot enter the station until the previous one leaves.
Turnback Time: How fast a train can change direction at the end of the line.

Typical Headway Values

Reducing headway is the most effective way to relieve congestion in crowded cities without building new tunnels.