At some driving ranges (golf) the grounds have been landscaped to incorporate contours, slopes, high spots etc, that channel all the golf balls to central gathering points, like a drain, where they collect and are mechanically delievered back to the pro shop, similar to bowling bowls. Railroad switching yards use the same principal to marshall empty box cars. A parking lot could be designed to incorporate gravity in the same fashion, using a slight grade and sweeping channels the carts will do the slow mosey to gathering points, where a conveyor belt will hook onto them and bring them back to shopping cart central.-- ty6, Sep 23 2002 Now if we can just keep any customers from parking in the way, this should work!-- lurch, Sep 23 2002 Like it.-- FarmerJohn, Sep 23 2002 Inventive and bakeable I'd think. Plus the kiddies will love it, "can I 'take' the trolly back?, can I? Please!?"-- Zircon, Sep 23 2002 Sponsored by Dave's Wile-U-Wate Paintjob Palace (right next door!).-- General Washington, Sep 23 2002 unfortunately, the guy who used to take the carts back is out of a job. still a bun, though, just because it's neat.-- fischerman, May 17 2011 The trolley guy could make a fortune pretending to be able to use The Force.-- marklar, May 17 2011 This is a nice old idea, but reading the title, about parking lots (car parks I presume), and then the comparison with railway marshalling yards, made me think that it would be for your car - you drive up to the supermarket door, get out of your car, leave the handbrake off and give it a push. Gravity parks it neatly for you.-- pocmloc, May 17 2011 random, halfbakery