15 A joint report published in February 2004 by LUL and Infraco JNP's owners Tube Lines found that the likely primary cause of the derailment was a weakness in the design of the switchblade of the points (in use without incident since 1968), combined with a number of other factors such that wheels tended to over-climb a new switchblade, an anomalous (but within standard) train bogie adjustment and recently re-profiled train wheels. Tube Lines staff, experienced and all formerly employed by LUL, replaced the switchblade the night before the incident. The lack of wear, together with other specific factors including the sharpness of the curve before the point and the high levels of friction between the wheels and the rails, is likely to have caused the train to derail.
16 Most switchblades are not of this design, which are only used on tight curves and are avoided wherever possible. LUL has prohibited, on all three Infracos, the replacement of switchblades with this type, unless special precautions are agreed with LUL in advance where replacement is essential. Tube Lines has produced a new design of switchblade. A switchblade to this new design has been installed and commissioned at Camden Town and is subject to detailed performance monitoring. So far the switchblade is performing well. Assuming it achieves the wear and performance characteristics required over time, the design will be accepted for wider use.