improved traction

With a little work and conveniently-sized gaps in shoe treads a normal pair of trainers could be cunningly adapted to provide excellent grip on snow and ice simply by levering up one end of all the bits of grit which end up embedded in the sulci after a few minutes' walk along a heavily over-gritted city street. It would probably result in falling over with a nails-down-a-blackboard scraping noise the minute you stepped onto a non-iced bit of pavement but you can't have everything.