I think there is a real concern about who is expected to cope with the reimbursement calculations. That's why I suspect that the option of inventing their own method has not been adopted anywhere. Big cities might be able to do that, and I could believe that London would (but of course its buses are different anyway). Big companies maybe could too, but have a lot of
TCAs▸ to deal with.
For small companies and TCAs, finding someone suitable even to follow the
DfT» 's formulas could be a problem.