With the number of trains using Union Station expanding, the stub-end layout of trackage is limiting the station's capacity. Trains can only enter or exit from the north side of the station. The configuration forces trains without cab-cars to slowly reverse in or out of the station and trains heading to or from the south to make a near-180 degree turn. Compounding the problem, is that while the station has 14 boarding tracks, multiple trains must squeeze onto just 5 tracks (originally, there were more tracks at "the throat", but Metrolink had some removed to allow for faster speeds along the curves in and out of the station to improve efficiency) as they enter or exit the station. This choke-point can delay arriving trains as they are forced to wait outside of the station to allow a departing train to exit the station (departures are usually given priority, to free up platforms and to keep them from experiencing delays along their route).
Generally, the sleepers were laid straight onto the existing ground of London clay, far from ideal for supporting a railway. The passage of trains has, and still does cause the track to very gradually sink due to the clay. The problem sections have been gradually removed & improved. The double track section between the loops at either end of the line was also slewed during this period to allow for multiple train operation in the future, although this was not a possibility until February 1986 with the arrival of a second locomotive in the form of ‘Lady of the Lakes’.