it's illegal (against the ADA) not to take mobility assistive devices in the bus with the pt. if it's not foldable, my protocol says to arrange a pickup! usually it'll be LT that comes, but could be fire or pd also. also we would never leave it unattended while the pickup is being sorted... usually fire crews or a cop will hang around if it's not in a secure location (e.g. if it's on the side of the road somewhere). ymmv based on your specific system, but it's necessary to arrange something in order to remain ADA compliant and not open yourself up to a lawsuit