With the entire automotive industry looking toward a future of driverless mobility, commercially owned self-driving taxis seem poised to be on the frontline of tomorrow. However, nobody seemed to realize that these vehicles will eventually become little more than mobile toilets.

Animals are universally disgusting and humans are no exception. While we’ve mastered land, air, and sea, consider the spaces we occupy while we traverse those expanses. Rental cars are returned filled with candy wrappers, spilt soda, and human hair. Uber vehicles are routinely vomited in. The subway is a haven for disease. Airplane interiors experience havoc within the first hour of a flight as the worst of us begin defecating into the seats, too lazy and weak to control ourselves.

Autonomous taxis aren’t likely to endure better treatment. Without a driver present, the urge to have drunken sex will be far too strong — and those odds only increase when you add a second occupant to the equation. With nobody watching, we’ll leave half-consumed hamburgers and cans of sweetened tea on their floors that will roll around and turn the carpet into a sticky magnet for larger pieces of garbage.

Bloomberg speculates the never-ending process of cleaning other people’s filth will cost large firms with autonomous fleets tens of millions of dollars annually. That number swells into the billions when you account for insurance, maintenance, storage, and the accelerated devaluation of such vehicles.

Uber is desperate to make the switch to driverless vehicles as soon as technology allows it, but abandoning the vehicle’s owner could result in unforeseen costs. Since drivers are responsible for their own cars, Uber’s policy is to force passengers who make a mess to foot the cleaning bill. This often results in drivers paying it themselves, especially when there isn’t a standout vomiting incident allowing for easy finger pointing. However, even when there is, it’s notoriously difficult to actually force someone to pay and often times not worth pursuing.

Other firms, like Avis’ ZipCar, have seen their fleets used and abused to a point where it has become difficult to keep up with the necessary cleaning. Its vehicles are stored in various locations throughout multiple cities and can change hands hourly. Finding someone to routinely assure they’re clean inside is next to impossible.

Traditional rental companies spend anywhere from $100 to $300 per vehicle each month while maintaining their fleet. For hourly rentals, that fee is much less predictable.

General Motors’ Maven arm, which competes with Zipcar and leases vehicles to both Uber and Lyft drivers, has begun studying how much abuse ride-share vehicles take. In addition to the wear, tear, and grime left in the wake of inconsiderate customers, the costs for parking and insurance will be significant — especially in the major metropolitan areas where such services are more popular.

Peter Kosak, GM’s executive director of urban mobility, has said that Maven’s goal is to provide consumers access to a diverse lineup of vehicles while still making sure it feels akin to ownership. That illusion is tainted the second someone finds another person’s greasy fingerprints on the steering wheel. That’s a new problem, one which will proliferate as community cars become more popular.

Lyft’s co-founder John Zimmer recently referred to personal vehicle ownership as “a ball and chain that gets dragged through our daily life.” He believes car ownership will be all but abandoned in major U.S. cities by 2025. While few are willing to plot a timeline quite so ambitious as Zimmer’s, ride-sharing has become more common. However, it won’t become ubiquitous until manufacturers can make the numbers work and drivers/riders can be assured a sanitary experience. Likewise, a plan has to be put in place to keep autonomous vehicles, with nobody to look out for them, from becoming roving toxic waste dumps.

“Lyft and Uber don’t care about managing the fleet,” said Kosak. “Down the road, you’ll need to dictate who does all of that.”