Lots of cities are starting bike-sharing programs or thinking of doing so. But in Vancouver, British Columbia, a decision to subsidize a new bike-share system has sparked debate over whether the program can thrive if the province retains its 1996 law requiring cyclists to wear a helmet when riding on a road or bikeway. Daniel Fontaine, a columnist for Vancouver 24 Hours, says debate has been intense. Bike advocates have suggested that if cyclists are forced to wear helmets, so too should car and truck drivers. Fontaine will host a live discussion about it on Twitter next week.