 Complete the following phrase:  In January 2008, an additional 15 units were ordered by Oslo Municipality, with an option for further orders later. This would allow all the eastern lines to have a 7.5-minute headway on their services into the city center, instead of the current 15-minute headway. Trains would start using the balloon loop located at Stortinget, and the western lines would continue to have a 15-minute headway. Additionally, the trains serving the Ring Line were extended to six cars, with a double train set. The order cost NOK 675 million. In addition, Akershus finalized their order for five units, costing NOK 240 million. Unlike the Oslo-owned units, Akershus five units are owned by the transit authority Ruter. The same year, the city council in Oslo decided to upgrade the Holmenkoll Line to metro standard, to allow six-car MX3000 trains to be the main mode of transport to Holmenkollen during the 