Complex sentence: Once the damaged tunnel was repaired by Metronet engineers, the line was reopened, also allowing the Metropolitan line to be fully restored, since the closure had meant all trains had to be terminated two stations early, at Moorgate.
Split into simpler sentences: Once the damaged tunnel was repaired by Metronet engineers, the lines were reopened. This also allowed the Metropolitan line to be fully restored, since the closure had meant all trains had to be terminated two stations early, at Moorgate.