It's not possible, we'll consider it as a possible update, but I'm a bit worried it would make the editor a bit too complex.
Is your issue is just "barriers blocking vehicles", you options are:
- Adjust the vehicle starting positions not to get in the way of the waypoints.
- Adjust the walk waypoints no to get in the way of the vehicles. The two are of course interdependent so, you might have to adjust both.
- Disable all barriers.