From
http://www.mdta.state.md.us/mdta/servlet/dispatchServlet?url=/TollFacilities/BaltimoreHarborTunnel.jsp:
The 1.4-mile, four-lane tunnel handled its first vehicles in November 1957 and is part of a 20-mile system of approach roadways and ramps. Designated I-895, the facility connects the major north/south highways and many arterial routes in Baltimore City's industrial sections. Traffic at the Harbor Tunnel during the past fiscal year totaled nearly 23.6-million vehicles.