An electric and driverless transportation system could improve livability and eventually save trillions of dollars a year, but University of California at Davis researchers say it won’t happen without shared mobility.

A UC-Davis report, prepared with the New York-based Institute for Transportation & Development Policy, says a shared, electric and driverless transportation system could reduce urban transportation carbon-dioxide emissions by 80% or more worldwide by 2050.

Compared to a business-as-usual case in 2050, such a system could reduce the costs of vehicles, infrastructure and transportation-system operations more than 40%.

The report delves into three urban travel scenarios surrounding three transportation revolutions –  vehicle electrification, automation and widespread shared mobility – which moves beyond single-occupant ride-hailing.

The report says shared mobility is the vital piece that could move global transportation into a future that not only saves energy and emissions, but also decongests highways, frees up parking lots for other urban uses, cuts transportation costs and improves walkability and livability.

“When it comes to cars, what we learned early in life still holds true – sharing makes everything better,” says lead author Lewis Fulton, a co-director at the Sustainable Transportation Energy Pathways program of the UC-Davis Institute of Transportation Studies.

“All the futuristic automotive technology being developed could make our cities more livable and the air more breathable – but only if we take sharing seriously,” Fulton says in a statement.

Shared mobility includes ride-hailing services carrying multiple occupants and new forms of on-demand public transportation, such as small commuter buses with flexible routes, as well as active transportation such as cycling.

The report spans eight global regions including five major markets – the U.S., Europe, China, India and Brazil.

The global regions vary considerably in their starting points. For example, the U.S. is highly car-dependent, whereas India’s challenge will be to preserve and enhance the shared-mobility options already there.

But worldwide, the researchers found without a concurrent shift away from private-vehicle ownership and toward ride sharing, the potential for electric and autonomous vehicles to reduce traffic and sprawl are severely limited, and CO2 reductions will be significantly less.

The report says electrified, driverless vehicles alone actually could increase traffic congestion as people spend even more time in their cars. It also raises the possibility of zero-occupant, driverless vehicles continuously circling the streets rather than parking.

Electrification also is important; the report estimates an autonomous-vehicle world without electrification or ride-sharing would not cut CO2 emissions at all, and might increase vehicle travel 15% to 20%.

Jacob Mason, manager-transport research and evaluation for IDTP, says the findings show urban transportation must evolve beyond single-occupancy vehicles and single high-occupancy-vehicle lanes.

“If passenger vehicles do not become predominantly shared by 2050, our cities will continue to be choked by congestion, and defined by sprawling land development and the massive emissions this system generates,” Mason says. “Instead, the urban residents of tomorrow should ride electric, automated and shared vehicles into a cleaner and healthier future.”

The authors say they recognize bringing about the sharing scenario won’t be easy. Their report says unprecedented levels of policy support and coordination are needed at the local, state and national levels.

It says policies could include fees tied to vehicle CO2 emissions, vehicle occupancy and possible restrictions or heavy charges on private ownership of autonomous vehicles, along with strong disincentives for zero-occupant trips.