The Butovskaya line (, ) is a line of the Moscow Metro. The line was an experiment for building rapid-transit in areas where boring or excavation for Metro tunnels is considered expensive and impractical. Previously, attempts had been made to build lines at ground level, like the Filyovskaya line, but harsh Russian winters and the occupation of the large amount of useful land, make such projects impractical. Still, more and more districts emerging on the edge of the city, particularly beyond the Moscow Automobile Ring Road (MKAD), required some kind of rapid-transit connection. In the late 1980s Moscow Metro design bureau, Metrogiprotrans started to develop a set of projects that would bring rapid-transit beyond MKAD, using a system of tracks raised above ground. Yuzhnoye Butovo District was the first district to be connected in such a way. The term light metro () was applied to these new projects, as it would feature a continuous elevated structure. Special rolling stock had to be developed to serve the line, as it would have to be resistant to the harsher climate elements and be able to negotiate sharper curves. For ease of operation, the light metro was integrated into the conventional metro service. The Butovskaya line essentially extends the Serpukhovsko–Timiryazevskaya line beyond the Serpukhovsky terminus. The line was opened on 27 December 2003. The first were bored in a tunnel, which allowed for a convenient transfer connection at the Bulvar Dmitriya Donskogo terminus. For the rest of its length it is elevated, with both single and double tracks protected by a sound barrier. Currently four elevated stations, each of identical design, are in operation. All of them except Ulitsa Starokachalovskaya have a lift for wheelchair users only. The line interchanges with Line 9 at Ulitsa Starokachalovskaya and Line 6 at Bittsevsky Park. Stations Rolling stock The line shares the Varshavskoe depot (№ 8) with the Serpukhovsko–Timiryazevskaya line. Specially built class 81-740/741 (Rusich) trains serve this line. These were designed for outdoor operation. A total of 12 three-car trains are currently assigned. Recent developments and future plans Although the light metro was indeed innovative, it also received its share of criticism from different social groups and the media, which could well affect its future. The main problems arose from finances, as the design was originally planned to be cost-saving; however, the BLLM turned out to be more expensive than conventional Metro lines. Passenger discomfort