Express Drive, the car-rental service that is jointly run by GM and Lyft, is coming to California and Colorado. Since launching in Chicago in March, the car-rental program aimed at Lyft drivers, has expanded to Baltimore, Washington, DC, and Boston. Now it will launch in San Francisco sometime this summer, and then Los Angeles and Denver later this fall.

Drivers have earned $2 million since the program’s launch

Express Drive is not your typical car-rental program: the more trips drivers complete for Lyft, the less they pay in rental fees. And those who finish 65 trips or more per week will pay for nothing but gas. Vehicles that can be rented through the service include the soon-to-be-released 2017 Chevrolet Bolt EV and the extended-range electric 2016 Chevrolet Volt. GM president Dan Ammann called the electric vehicles “a perfect fit for ridesharing.”

The companies, which announced a partnership last December to develop a fleet of on-demand, driverless cars, lauded the success of Express Drive. They say Lyft drivers using Express Drive vehicles have earned $2 million since the program’s launch. And that 30 percent of new Lyft drivers in Chicago requested Express Drive vehicles.

Meanwhile, Lyft is pursuing creative car-rental programs on multiple fronts. Last month the ride-hailing company announced a partnership with Hertz to supply Lyft drivers with vehicles “rotating” out of Hertz’s fleet.