A new bike-share program in New York City, starting this month, has an official numbers cruncher worried. The city comptroller thinks the city is unprepared for the liability blowback when rented Citi Bikes are involved in car accidents.

Ten thousand bikes that aren't already weaving through New York could be added to city streets by this time next year. The plan allows people to rent bikes in one part of the city and drop them off at one of more than 400 proposed locations in Manhattan, Brooklyn and Queens.