The difficulties of Sheffield-Rotherham should not and must not be an repeated for future tram-train rollout in UK. If we look at the positives, we now have an approved vehicle from Stadler, much underpinning work on infrastructure requirements, creation of applicable standards and regulations. The same basic vehicle, albeit necessarily modified for classic UK high platforms, is planned for use in South Wales. The big ticket overspend items on Rotherham were the late changes and unanticipated work for 25kV clearances and the renegotiated contracting costs associated with with lost work and delays. With a technical spec much better tied down as should now be expected this should not recur. That said, for East Didsbury - Stockport I'm surprised a dedicated light rail line throughout is not the best solution. For Airport - Stockport, some heavy rail sharing might be of benefit, although at the Stockport end such tram trains need not share any of the East Didsbury line tram infrastructure. I suppose the argument is if you need the tram train link into Stockport station via Edgeley for the airport line, you might as well use it for the Didsburys as well, but it means the Didsbury/Stockport line needs to be operated by specialist tram-train vehicles throughout, or at least those services running the whole distance to Stockport.