Lyft and GM are expanding their car rental program into three more cities

Conversations about General Motors’ partnership with and $500 million strategic investment in Lyft largely center around the two companies’ future plans for an on-demand network of self-driving cars.

But a huge part of that partnership, and one that still factors in Lyft’s pool of drivers today, is the recently launched Express Drive program.

Express Drive, which the companies first launched in Chicago in March, is a car rental program through which Lyft drivers can rent a GM vehicle to drive on the platform. Today, the two companies launched the program in three more cities: Baltimore, Boston and Washington, D.C.

The expansion of the program is not just important because it gives potential Lyft drivers without cars, or who don’t want to use their personal vehicles, access to a car (thus helping Lyft scale its driver base), but also because it’s setting up the foundation for Lyft and GM’s network of self-driving cars.

These Express Drive hubs, where the GM cars are now stored, will likely serve as the hubs where GM’s self-driving cars will be stored as they wait to be summoned by a Lyft passenger. The ownership model also mirrors closely what many predict the car ownership model will look like when self-driving cars hit the road.

“Many of the operational details of where the cars are stored, how are they maintained, how are they paid for — all of that is very applicable in the autonomous world,” David Rust, Lyft’s director of operations strategy, told Recode. “Things like how to enable drivers to get quick access to cars without owning them.”

The way the program works is that drivers gain access to a car that is ready to be driven on the platform — the rental fee includes the appropriate commercial insurance and standard maintenance fees. But the key benefit for drivers is the company’s tier system.

In Chicago (the rates vary by city), renting a car costs $99 a week and you pay $.20 per mile to use it for things other than driving for Lyft. But if you give 40 or more rides a week, you don’t have to pay the per-mile rate, and if you drive 65 or more rides a week, the rental is free. That’s all on top of getting approximately 80 percent of the fare for each of those rides before expenses.

Completing 65 rides a week or more is no small feat. Both Lyft and Uber increasingly pitch their platform as an easy way to gain access to part-time employment opportunities, but 65 rides during a five-day week amounts to at least 13 rides a day — so drivers looking to give enough rides to cover the cost of rent will likely be working full-time. (Uber has a similar car rental program called Xchange.)

But according to Rust, 65 percent of drivers who rented cars through Express Drive in Chicago were earning a reward each week. That means they gave at least 40 rides a week which in turn means the majority of Express Drive drivers are full-time. It’s a stark contrast from the casual driver model both Lyft and Uber say they are seeing more and more of across the country.

There’s apparently a huge demand for a ready-to-drive rental car among Lyft drivers. In the eight weeks since the launch of the program, there have been close to one million miles driven in Express Drive vehicles in Chicago alone. And in these four cities, Chicago included, there were 160,000 people who applied to Lyft who needed a car.

The company expects to expand the program rapidly throughout the country (to as many markets as they can this year, Rust said) but will first launch in markets where there is high demand for a car rental program like Express Drive.

“In Washington, D.C., we’ve seen strong interest from drivers,” he said. “Twenty percent of applicants weren’t able to sign up with Lyft because they didn’t have a car.”

This article originally appeared on Recode.net.