and hourly weekend service in both directions The Richmond Hill and Milton lines continue to operate during rush hours only, although there has been an increasing number of trips on these lines in recent years. As part of the Regional Express Rail plan, there are plans to eventually offer two-way, all-day 15-minute or better service on the central sections of the remaining five lines. Nevertheless, rush-hour service accounts for over 90 per cent of GO Train ridership. Rolling stock GO Transit's rolling stock uses push-pull equipment. Its passenger car fleet is composed entirely of Bombardier BiLevel Coaches built in Thunder Bay, Ontario. These double-decker coaches, which have an elongated-octagon shape, were designed in the mid-1970s for GO Transit by Hawker Siddeley Canada as a more efficient replacement for GO's original single-deck coaches, built by the same company. Later coaches were manufactured by Can-Car/UTDC and the most recent coaches are produced by Bombardier Transportation, who now owns the designs and manufacturing facilities. GO Transit owns 979 BiLevel Coaches, which are also used by a number of other commuter railways across North America. They have a seating capacity of 162 and a standing capacity of 248 per coach, or 5,256 per train (maximum crush load). All upper levels of the coaches on rush hour trains are designated "Quiet Zones". The coaches are primarily hauled by MPI MPXpress series locomotives. The current model, the 4000-horsepower MP40PH-3C, is more powerful than their predecessors, the EMD F59PH. They are capable of pulling or pushing trains of 12 coaches instead of 10. More than 60 of these locomotives have been ordered since their introduction in 2006, with a further 16 types of an even more powerful model, the 5400-horsepower MP54AC, which can pull a full 12 car train more efficiently. Opposite the locomotive, trains are bookended by cab cars, which are coaches with driver controls incorporated into them. GO Transit upgraded their entire cab car rail fleet with newly designed, more crashworthy cab cars in the summer of 2015, incorporating an improved visibility, safety features and comfort for train crews. Rolling stock is maintained at the Willowbrook Rail Maintenance Facility, located west of Mimico station in Toronto and also at the newer Whitby Rail Maintenance Facility. The Willowbrook facility occupies the Willowbrook Yard, a historical freight yard established by Grand Trunk Railway in 1910. GO Transit acquired the Willowbrook Yard from Canadian National sometime after its