Not only did the tunnel through the city centre have to be built, the full railway infrastructure had to be expanded. The network of suburban lines had to be changed over and modernized. A large number of stations had to be upgraded; platforms were extended to a length of to allow for three-unit trains, and the platform height was raised to . However, the floor height of trains used then and now is at approximately , which makes boarding difficult for people with wheelchairs or prams. Tunnel stations and platforms updated recently where no freight trains run do feature a height of , however.