In order to ensure trains would be able to run on the new line at full speed without the risk of getting too close to the infrastructure, a dedicated structure gauge mounted on a flat wagon was fabricated.
The gauge represents the dynamic envelope of a train running in the worst case conditions (speed, cant, etc...). The structure was then circulated at very low speed on every route and junctions and measurements were taken at each ‘hot spots’ to ensure no pieces of infrastructure would ever get into contact with a running train.
These verifications occurred late in the construction programme at a time where most if not all of the infrastructure had been installed.
During the Dynamic testing that saw the extensive use of Eurostar test trains, the structure gauge was circulated on a secured Test Track before the runs could commence to ensure nothing would infringe with the safe corridor of the train during the tests.