Passersby on East Liberty Street will have seen construction crews beginning work on a $4 million replacement of the bridge carrying the street over the Mad River. The bridge will close to pedestrians and motorists as work begins in earnest, an event expected to occur in the last week of November or the first week of December, Director of Public Works David Simpson said. Dayton Construction Co. has cleared trees and has begun moving utilities that had been supported by the shabby-looking bridge. City officials have approved a $2.8 million contract with Dayton, as well as a $323,829 contract with AECOM Technical Services to provide engineering and construction oversight.