Episode 4 - S1.E4

Signal problems lead to a restricted service during rush hour, which causes severe congestion at the station and the same equipment causes more grief 24 hours later - leading to the complete suspension of the line. Jonny and his team of engineers are replacing a 60ft section of rail as one of the clamps holding it in place has weakened, but they have just four hours to complete the complex task before the morning rush begins.