We tried this with our fleet of landrovers. Each one has a waterproof interior and is plumbed with sprinkler pipe with hoze-lock connectors on the back of the vehicle so it can be plugged in to the water supply.

It doesn't work, the water spray is not strong enough, or directed enough to remove the mud and sand. We still have to have people going round with water jets to spot clean. A have my doubts a fully automatic system could ever work effectively.

If you are competing on price for commuters the obvious thing is a waterproof interior and some high pressure nozzles in the ceiling. Car drives up to machine with hose, hose attaches, water sprays.

The obvious thing is to pay a couple of people minimum wage to sit in a parking lot and clean cars when they arrive.

A car with a waterproof interior would be miserable and cheap feeling. No one wants to sit in a humid, rubber car.

Having a few people waiting in a parking lot to clean cars is a far more cost-effective strategy. There's no need for complex automation on this.