Hi Julie
This was discussed quite a bit at the consultation stage, and several respondents pointed out the difficulty of enforcement for limits that don’t correspond to a ‘plated’ vehicle weight. But DfT receive quite a lot of requests for authorisation for non-standard limits and wanted to avoid this workload.

I think TSM Chapter 3 will continue to recommend using 3.5t, 7.5t or 18t, and anything else will be at the authority’s own risk regarding enforceability.