It looks like they're juuuuuuuuuust the right length so they perfectly match up to pedal stroke. i.e. - Your push stroke unwinds the string to its max extensio

It looks like they're juuuuuuuuuust the right length so they perfectly match up to pedal stroke. i.e. - Your push stroke unwinds the string to its max extension length, and then the rotational inertia of the wheel does the job of winding the string up again. EDIT: Scratch that, disregard the above. Looks like they're using a spring to wind up one side while it freewheels. As for assholes? Yeah, they're going to be able to slice those with a pocket knife in a few seconds. Even Dyneema and the like would likely be quickly frayed with a few good knife swipes to the point of being in danger of snapping from a hard pedal push when taking off from a stoplight.