Lyft and GM have announced the next big phase of their partnership, unveiling Monday a plan to rent GM cars to Lyft drivers for the low cost of nothing — with a few stipulations and provisos, of course. Called "Express Drive," the idea is to make cars available to people who want to drive for the ride-hail company but presumably neither own their own car nor are inclined to take on an onerous lease offered through a third party company.

The program, according to a press release, will start later this month in Chicago and will roll out to other cities later this year.

And while intuitively appealing on its face, the details of Express Drive suggest that in this particular case "free" could end up costing drivers quite a bit. For example, to get that zero dollar weekly rental rate a driver must log at least 65 rides a week — and according to the terms of service "all miles driven while not in 'driver mode' within the Lyft app" will cost the driver $0.20 per mile.

If a driver logs less than 65 rides, the cost jumps to $99 per week (still paying that $0.20 per mile for non-driver mode time). If the driver logs less than 40 rides per week, than he or she will pay the $99-a-week rental fee, plus $0.20 per mile even when driving passengers.

Also, although not exactly clear as to what they may be, the TOS states that Express Drive "does not cover any applicable rental fees that may apply." So, you know, caveat emptor and all that.

The program will only allow a driver to rent a car for a maximum of eight weeks, suggesting this is intended for drivers who just want to briefly hop into the ride-hail game. Besides, as the GM and Lyft partnership progresses, ride-hail drivers are likely to be replaced by self-driving cars anyway. According to Lyft, give it about ten years.

Previously: Lyft Scores $500 Million General Motors Investment, Plans Autonomous Cars