the metro. Similarly, the Østensjø Line would also be converted to metro. To ease the conversion, the Lambertseter Line was built for wide trains, lean curves and no level crossings. At the time it was presumed that the metro would be built with overhead wires, the same as the Oslo Tramway. Between Munkelia and Bergkrystallen, the Rabben Tunnel was built, and a branch line to the brick factory at Høyenhall. The station at Høyenhall was built with the high platforms that would be used on the metro; therefore the tram platforms were built as a low-entry expansion of metro platform. Ryan and Brattlikollen received turning loops with radius . Construction cost 20.1 million Norwegian krone. From Helsfyr the line continued to the city center via the Vålerenga Line and the Gamlebyen Line. The Lambertseter Line was the first suburban line operated by Oslo Sporveier, and therefore the company copied the security procedures of Bærumsbanen, that operated the Kolsås Line and the Østensjø Line. The first operation on the Lambertseter Line with the SM53 trams was on 10 April 1957, after technical trials had been conducted with the Gullfisk trams. Travel time from Jernbanetorget to Bergkrystallen was 28 minutes. The official opening took place on 28 April. The lines were trafficked with SM53-trams that had been in service up to five years with the company, and were bought specifically in mind to be able to operate the suburban line, in addition to street lines. In addition, school trams were operated with Gullfisk. At first, the Lambertseter Line was made part of Line 4, that connected onwards along the Kolsås Line. This was later changed so it only operated to Vognmannsgata from 19 June 1960. From 24 June 1963, the trams terminated at Jernbanetorget. Starting in September 1960, the loop at Ryan was taken out of service, and a depot for the metro was started built at the site. Metro operations Conversion to metro started in September 1962. Building the new stations commenced in October 1963 and were completed by the end of 1965. The upgrades cost 11 million kroner, excluding third rail. Originally the Groroud Line was to be the first line of the metro to open. However, lack of rolling stock and other technical problems caused Oslo Sporveier to alter the plans on 16 March 1966, and instead opted to open the Lambertseter Line first. The last trams operated during