Forty bicycle riders were cited for infractions, including red light violations, illegal turns, and failure to signal, when police conducted a bicycle safety and enforcement operation near Commonwealth and Massachusetts avenues. Boston, Brookline, State, Transit, and Boston University police staked out the area at 8 a.m. Thursday. Police chose the location because of its history of bicycle-related incidents and collisions. Police also conducted an operation along Commonwealth Avenue at 4 p.m. Results of that operation were not immediately available, police said. During the two operations, police also gave riders dozens of free helmets and bicycle lights donated by the university.