Heathrow Express was planned as a joint venture between BAA and British Rail, but was taken over fully by the former following the privatisation of British Rail. Construction began in 1993. The principal works were two 5-mile single-bore tunnels (including eight escape shafts) and underground stations at and Terminal 4. Electrification of the Great Western Main Line (GWML) between Paddington and Airport Junction, where the new line diverged from the GWML, was also required. A flying junction known as "Stockley Flyover" was constructed to connect the tunnel to the GWML fast lines. Beginning in January 1998, an interim service called Heathrow FastTrain ran to a temporary station called Heathrow Junction, where a coach took passengers the rest of the way.