City officials say Chelsea’s street-sweeping program has been postponed until March 18 due to the amount of snow on the ground. The city normally operates the program from March 1 through Dec. 31, sweeping each street once a week. During those months, parking is restricted on streets scheduled for sweeping. Officials said that because of the postponement, residents can ignore the street signs warning of the once-a-week parking restrictions. No cars will be ticketed for violating the restrictions until March 18. Officials said, however, that more snow could result in an additional postponement of street sweeping beyond March 18.