What assessment has been made of the effect of the volume of traffic on the structure of the Britannia Bridge?
No additional assessment is required regarding the Britannia Bridge and the volume of traffic currently using it. Bridges are assessed for the worst-case traffic loading, such as fully laden HGVs travelling quickly in close proximity. For a bridge assessment the full width of the carriageway is also used, so if you can physically fit in five lanes of HGVs across the width of the road on a bridge then that is used regardless of what lanes are actually marked out for use.
It is typically only where the carriageway is widened, or otherwise modified or as a result of deterioration that a bridge would have to be reassessed.