Is there a word for the round-trip time of a train line?

Question

On a subway line, trains go from the starting terminus to the other terminus, and then back to the starting terminus. Is there a word that is usually used to refer to the time it takes for a train to travel as described?

"Round-trip time" seems to be mainly used when referring to packets on the Internet.

This is the context in which I want to use this word: "The blue line has a shorter _______ than the green line, so fewer trains are required."

EDIT: I would like to specifically refer to the time taken, not the distance covered (since the time taken could depend on lots of other things, like the waiting time at each station and the speed at which trains travel). For example, the word "headway" specifically refers to the time interval between consecutive trains, instead of the distance between them. (The distance between them changes as they travel on the subway line, but the headway never changes (assuming an ideal situation where each station has a fixed duration for which every train must wait, and each track has a fixed speed at which every train must travel).) I am hoping that there is a similar train-specific term for the duration that I am describing.

Answer 1

It’s not clear if question is for

• linear track e.g. A-> B -> C -> B -> A or
• a ring track e.g. A -> B -> C -> D -> A.

For a ring track consider circuit:

The blue line has a shorter circuit than the green line, so fewer trains are required.

... or perhaps for a either ring or line a shorter (or faster) route works.

If your prefer to focus on time not distance and track is a a ring then lap time may work:

The blue line has a shorter lap time than the green line, so fewer trains are required.

Or if there is variance, you could say average lap time.

Answer 2

What you are looking for is a cycle.

"The blue line has a shorter cycle than the green line, so fewer trains are required."

MW:

cycle

 noun

2a: a course or series of events or operations that recur regularly and usually lead back to the starting point

Answer 3

A word often used in this (and broader) sense is turnaround (also turnaround time).

"The blue line has a shorter (quicker) turnaround than the green line, so fewer trains are required."

Collins:

turnaround 

noun

2. 

the total time taken by a ship, aircraft, or other vehicle in a round trip

Collins English Dictionary. Copyright © HarperCollins Publishers

Answer 4

You could use the notion of period or frequency here.

The blue line has a shorter period than the green line, so fewer trains are required.

The blue line returns more frequently than the green line, so fewer trains are required.