Multiple Depots 1 Line

As of now (and it seems quite likely for a while) no, you can't, but there are things you can do:

-You can make the schedule so that there are enough buses continually running all through the night, so that they don't return and overload the depot.

-You can make a long road to the depot so buses that don't fit in will just sit on the road leading to the depot.

-For Future games, use the custom ruleset feature and increase depot repair capacity.

Full credit goes to C40LFR for his post here.