Because sidewalks are sloped for rain, one arm may tire before the other when pushing a stroller or wheelchair because it constantly requires more force from one hand to offset gravity in order to go straight. A slip clutch to couple/uncouple the rear wheels acts like AUTOPILOT STEERING, and that makes pushing more efficient, easier/less strain, on any surface. The slip clutch automatically couples/uncouples the wheels depending on the force difference applied by the hands pushing. When the force difference is moderate, the combined force will 100% efficiently propel straight! Without a slip clutch, even a moderate difference in force will cause some zigzagging which is less efficient and takes more energy than going straight. To turn, the force difference is intentionally greater to automatically uncouple the two wheels to allow turning. Turning requires more energy—that's the tradeoff. However, conveyances are pushed straight most of the time.