The Tyne & Wear Metro is an overground and underground light rail rapid transit system serving the metropolitan boroughs of Newcastle upon Tyne, Gateshead, North Tyneside, South Tyneside and the City of Sunderland (together forming Tyne & Wear). The network opened in stages from August 1980 and now serves a total of 60 stations, with two lines covering 48.2 miles (77.6 km) of track. The Metro can be accessed from a mixture of underground and overground stations. It has been described as the "first modern light rail system in the United Kingdom". The system is currently owned and operated by the Tyne & Wear Passenger Transport Executive (branded as Nexus), thus is fully under public ownership and operation. The Tyne & Wear Metro has only two lines. The Green Line runs between South Hylton & Newcastle upon Tyne Airport while the Yellow Line runs between St James & South Shields, with the Yellow Line overlapping at Monument Station. Rollingstock There is only one type of rollingstock that is used on the network and that is the Class 994, they entered service in 1980, and they are going to be replaced by the new Class 555 in the coming years. Tyne & Wear Metrocar (Class 994) New Class 555 Signaling: The Tyne & Wear Metro uses PZB, a signaling system that is found on the German routes in TSW2 like Hauptstrecke Munich - Augsburg & Nahverkehr Dresden, Services: Services commence between 05:00 and 06:00 (between 06:00 and 07:00 on Sunday), with frequent trains running until around midnight. Each line runs up to every 12 minutes during the day (Monday to Saturday), and up to every 15 minutes during the evening and on Sunday. This allows for a combined frequency of up to every six minutes (Monday to Saturday), and up to every seven to eight minutes during the evening and on Sunday, between Pelaw and South Gosforth. Additional trains run during morning and evening peak hours (Monday to Friday) between Pelaw and Regent Centre or Monkseaton. This provides a Metro up to every three minutes between Pelaw and South Gosforth, at peak times. Originally, there was also a Red Line between Heworth (later Pelaw) and Benton and a Blue Line between St James and North Shields. Additional trains ran on these lines during peak hours to increase the frequency at the busier stations. This would be a nice network style route and it would be TSW2s second subway route.