same time the Kolsås Line was closed for upgrade to metro standard. In 2003 the section of the Kolsås Line in Bærum closed due to budget disagreements between the two counties; after a year of unpopular replacement buses, the line was reopened, only to close again in 2006 for upgrade to metro standard. Disagreements between the two counties meant the upgrade would be done separately on the two sides of the municipal boundary, with the Oslo side opening first. In 2006 the replacement of existing rolling stock with new MX3000 units commenced. The history of the metro and public transport in Oslo is celebrated at the Oslo Tramway Museum in Majorstuen. Network The current route network was introduced on 3 April 2016, with the opening of the connection tunnel from Økern to Sinsen and the new Løren station. The Oslo Metro operates in all fifteen boroughs of Oslo, as well as reaching a bit inside the neighbouring municipality of Bærum. There are five lines, numbered 1 to 5, each colour-coded. They all pass through the Common Tunnel, serving eight branch lines. In addition two lines operate to the Ring Line. Two branches are served by two lines each: the Grorud branch is served by both lines 4 and 5, while the Lambertseter branch has full-time service by line 4 and limited service by line 1. The Grorud and Furuset Line head northeast into Groruddalen, while the other two eastern branches head south into Nordstrand. On the west side, the Holmenkoll and Sognsvann Line cover the northern boroughs of Oslo, along with the Ring Line that connects the northeastern and northwestern parts of town. The Kolsås and Røa Line reach deep into the neighbouring municipality of Bærum. All the lines run through the Common Tunnel before reaching out to different lines, or into the Ring. All lines have a base service of four trains per hour while line 2 and the eastern section of line 3 have eight trains per hour weekdays 07:00–19:00. The eastern section of line 2 also has eight trains per hour Saturdays 10:00–19:00. A reduced half-hourly service operates on all lines during early weekend mornings. Trains run from about 05:00 (06:00 at weekends) to 01:00 the next morning. Lines Line T1 Line T2 Line T3 Line T4 Line T5 Line T6 (under construction) A new metro line that will extend from Majorstuen to Fornebu is under construction