The Board of Trade investigation report on the Inverythan accident had commented on the problem of latent defects, but had concentrated attention in the first instance on composite girders, bolted together mid-span, and those of over 25 feet (7.6 m) span.
(The failed girder in the Carlisle incident was non-composite, with a 25 foot (7.6 m) span and had a major hidden casting defect.
It had been built before the 1847 Dee bridge disaster[2] and the consequent specification by the Board of Trade of required wide safety margins on cast-iron structures; even if perfect it would have not have met them.
The task fell to Sir John Fowler, who recommended that many be replaced by wrought iron (or preferably steel) structures, commenting that the result of my investigation does not indicate any peculiar weakness in the Brighton bridges which are neither better nor worse in that respect than those on similar lines of railway at home or abroadThe accident led the Board of Trade to issue a circular requesting details of all cast-iron underbridges on the UK network.
There were thousands of them, and most were gradually replaced, but as of 2007 Network Rail stated that there are still many hundreds of cast-iron beam overbridges remaining, many with very low weight restrictions.