SR 21 is one of three routes, along with Roosevelt Boulevard (US 17) and the First Coast Expressway (SR 23), that connect Jacksonville with its surroundings west of the St. Johns River. Congestion has become a problem over the years as local government works to develop infrastructure for the growing populations of Orange Park, Middleburg and Green Cove Springs with the northern connectivity sought and thought to be achieved by drastic road widening despite the decimation of Lake Shore's prewar scale. Residents of both Clay and St. Johns counties' communities rely on Duval's economy (Jacksonville) for employment. As a result, traffic is heavy during morning and evening rush hour, especially near and on I-295. Such has spurred the creation of the Collins Road / I-295 interchange.