Originally Posted by JohnDThompson

Plan ahead at stoplights; reach down when your pedal is coming to the top position and swipe your hand across the strap. The flange on the buckle will catch on your hand as it moves across and will loosen the strap. It helps to use good quality straps (i.e. Alfredo Binda) that have buckles with rollers so they loosen smoothly.

Put end buttons on the straps so you have something to grab when you tighten the straps up again; the sooner after you start moving you can do this, the better as the faster your pedals are moving the harder it will be to grab the button as it goes by.