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.Melissa Hanson can be reached at firstname.lastname@example.org or on Twitter @Melissa__Hanson.