1/ In 1923 the Board of Scientific & Industrial Research set up a "Bridge Stress Committee" to assess whether ageing bridges could withstand the increasing train weights. Particularly, there were fears that a phenomenon called the 'hammer-blow' would imperil structural integrity.

2/ The investigators, drawn largely from the Big 4 companies, stood on a platform by the bridge, and using extensometers and deflectometers measured its oscillation as specially assigned locomotives passed over at varying speeds. Fifty-two bridges in the North East were tested.

3/ Issuing its report in 1929, the committee found that the largest locomotives - which had caused the most anxiety - would not cause problems if they were designed to be perfectly balanced. They also found that many old structures were stronger than they had previously believed.

4/ More broadly, it was proclaimed that the findings constituted major steps forward in engineering knowledge and theory, and that the experiments contributed to the advancement of research practice generally.

5/ "The Sphere" 06 Apr 1929. ©Illustrated London News Group https://www.britishnewspaperarchive.co.uk/