I had a Schwinn folding bike with similar rear band brake as yours, with the stopping power of a sponge. I had a similar incident having to do a Flintstone foot stop to keep me from running into cross traffic. The photos of your bikes doesn't show any bosses for vbrakes. You could try putting on a set of caliper brakes, but you might have to lose that rear fender. You could probably also install a set of caliper brakes on the front as well for extra safety.