This study was inspired by the proposed Thames Gateway Bridge between Beckton and Woolwich and addresses the problem of calculating the long term economic impact of major capital projects, such as bridges. The study of medieval crossings of the Thames reveals that of 18 medieval bridges, only one was allowed to fall into neglect and disappear; the others, once built, remained, and were improved and enlarged and in most cases they or their successors are still present. The conclusion is that in the long term, perhaps the very long term, such capital projects rarely fail to be economically advantageous
