the City of Toronto. An access road branches off from the westbound on-ramp and travels downward to the valley below and ends in a cul-de-sac just south of the eastbound collector lanes. It is closed to regular vehicular traffic and used by Ontario Ministry of Transportation maintenance crews (and their contractors) as well as housing the Macdonald-Cartier Emergency Service building of the Toronto Transit Commission used for both emergency access to/from track level of the subway but also as an access point for maintenance crews. The bridges can be clearly seen from Yonge Street looking northwest and north of York Mills Road and Wilson Avenue. History The inner under deck truss bridge was constructed beginning in early 1928, and opened on January 5, 1929, providing a much needed bypass of the deep ravine. It also provided a path between Wilson Avenue and York Mills Road. Wilson Avenue's eastern limit was just east of Yonge Boulevard (it was extended to meet York Mills at Yonge St. after 1972). The collector road merged traffic from both Avenue Road and Yonge Boulevard to the bridge to Yonge Street. The Toronto Bypass, today's Highway 401, was routed over the bridge (with an additional south truss bridge added) in December 1952. The collector (outermost) spans are steel girder bridges, and were opened in December 1965 during the widening of Highway 401 to a collector-express system. The older inner bridge's balustrade railing was replaced with retaining walls (since replaced with tall walls). A conventional lighting system with truss-neck poles was added to the bridges (and the rest of the widened 401) around this time. Bridge rehabilitation Hoggs Hollow Bridge is situated on what is considered to be the most sensitive segment of Highway 401, averaging around 400,000 vehicles a day on weekdays. Given the importance of this segment of Highway 401 through the GTA, the Ministry of Transportation was particularly concerned with the development of construction staging plans and the mitigation of traffic during the rehabilitation of the Hoggs Hollow Bridge. "The impact of delays on passenger and commercial traffic resulting from construction activities on this section of highway were an important consideration," says Ron Klatt, Department Manager, Contract Administration Group with Morrison Hershfield Ltd., the engineering and management company that designed the project. In 2008, Morrison Hershfield was retained by the Ministry of Transportation of Ontario (MTO) as the lead consultant for a Total Project