interval between train

Hello can you clarify this for me please?

If everything is actually on track with your train you might still end up waiting in stops to "even the gaps" between trains in the service. Does 'wait in stops' mean anything to you? Have you ever heard 'even the gaps' Would you say that in your country?

Do they keep the subway waiting so that the interval between trains is equal and that the trains aren't too close to one another.

Is it correct to say 'interval between trains is equal'? Would you say something else? Would you tell me please if you could say 'interval between trains is equal' ?

Is this natural?
The trains run at equal intervals. Would this make any sense?
The trains run at shorter intervals. Would this make any sense?
The trains run at regular intervals. You said this was natural.

I don't understand the use of interval here?
Heretofore railways of this kind have provided a single service, with all trains stopping at all stations, a limited express service being sometimes obtained by a third track, on which trains could run in the direction of the heaviest travel, and stop at longer intervals than the others. What does it mean to stop at longer interval. I thought interval meant 'a gap'?

Thanks