I checked that right now.
- a construction site for depot
- a highwayman
The car is transfered to the new base after it's finished, without doing anything (in the bottom left corner).
There was a bug with vertibird not showing up in such case but I fixed that long ago.
You should check your base carefully, the car should be there. Also, you should specify more details... type of car, any additional message in log? Were any other cars parked at site?