Conrad B., from the look of this simplified concept/sketch, I’d guess that the simplist way (at least in terms of design) is that the spring gets “loaded” simply by backpedeling (or at least applying some reverse resistance to the motion) upon decellerating towards a stop sign. This is similar to how riders of fixed-gear bikes stop all the time. And my non-expert understand is that back-pedalling does not feel as taxing on the human muscle as one might expect.

At any rate, the rider could choose when and how much to resist, or how much to use a handbrake instead. Of course, the spring could likely be loaded by some other more-complicated mechanism that does decellerate the bike without any effort, or any need to backpedal.

Bike regen would help a little, but 15mph to 0 won’t take you back to 15, maybe 10mph if it’s a really efficient system.

You’re far better off just riding an efficient lightweight road bike, which will accelerate much better than a typical casual biker’s bike.

`it is sad that people twitter thier farts`

The only way I see urban riding while obeying traffic laws to be practical and safe is to have regenerative breaking allowing me to accelerate quicker off the line and stay out ahead of the wave of angry metal death pressing behind me.

I would absolutely worship regenerative breaking

For those people who do ues it for excercise, having the bike do the work for you would not be an option.