Scraping ice from a car's windscreen is no-one's idea of fun first thing in a morning. I suggest that if the temperature is detected as below 0 degrees C, then the wipers periodically give a wipe to keep the ice at bay before it has a chance to harden. I'd imagine that temperature and humidity would be used as the algorithm to calculate the dwell.
Obviously, the usual safeguards of manual deactivation, battery low detection, car parked up for a long time detection, and overload so the wipers don't try and clear a tonne of snow.
Oh, and breaking an unsuspecting traffic warden's fingers can't be a bad thing either.-- paraffin power, Jan 24 2005random, halfbakery