The Police Department will be stepping up enforcement of crosswalk and speed violations in the town center this summer, according to a posting on its official online blog, www.wrenpd.blogspot.com. The department was awarded a $3,000 grant by the state Executive Office of Public Safety and Security to focus on crosswalk enforcement and bicycle safety. Through the grant, during the months of June, July, and August, police will be checking to ensure drivers are not speeding in town center, and are yielding to pedestrians in the 19 crosswalks there. Posted speed limits change from 40 miles per hour to 20 or 25 miles per hour on South Street, and police say drivers who speed have a difficult time stopping for pedestrians there. Police will also be on the lookout for drivers who violate bicycle safety laws during the Pan-Mass Challenge, which sends riders through town as part of its 192-mile route each summer. The local segment of this year’s fund-raiser for cancer research is slated for Aug. 3.