end in 1956. 1950s to 1960s After the Second World War, train tracks in Finland were generally in a very bad shape. Massive war reparations for the Soviet Union meant that the Finnish state was left with little to no resources for even regular maintenance of the country's railway lines. Thus, the Main Line and the beginning section of the Coastal Line had to keep accommodating long-distance and freight trains alongside a growing need for new local services and new diesel trains such as the Class Dm7. The age of the modern Finnish commuter train began in 1969 as the first stretch of the Coastal Line up to Kirkkonummi station was electrified. With electrification came a significant drop in journey times – while the Class Dm7 railbus took an hour to reach Kirkkonummi after stopping at all stations, the electric Class Sm1 did the same in 45 minutes. 1970s to 1980s The 1970s marked many firsts for urban rail transport in southern Finland. Early in the decade, the term commuter train () was first adopted into official use. Letters of the alphabet were introduced as service identifiers in 1972, as inspired by the Copenhagen S-train network. The initial letters A, H, K, L, N, P, R, S and T were chosen deliberately to function as mnemonic devices and to minimize the risk of ambiguity between each other. Somewhat confusingly, certain letters were also taken to use as identifiers for travel zones in the commuter train system. Work began on the first purpose-built commuter rail lines in the country. The Martinlaakso Line, opened four years later, was the first rail branch in Finland meant exclusively for commuter trains and has been a backbone for urbanization of the city of Vantaa. The Kerava Urban Line was initially an additional third track for commuter services running on the newly electrified Main Line, first being built up to Hiekkaharju station in 1972 and reaching Kerava station in 1981. 1990s With the 1990s, the first common transport ticket system came to use in Greater Helsinki. YTV – the capital region commission for transport and environment, a partial precursor of HSL – took over ticket sales and inspections in the four capital region municipalities, former VR zones A and B. In 1991, the Martinlaakso Line became the Vantaankoski Line after being extended one station further to Vantaankoski station. The Coastal Line was electrified up to Karis