Patrick, thank you. Your screen shot helped. It was as simple as inputting the xml file as the “dtm surface or roadway model” and it converts it to .pro format. No need for additional strings / surfaces or messing around.
I ended up with the design centreline which I could check offsets to at any chainage.
Alan, thank you also for your reply.
TBC wouldn’t allow me to import the alignment, or even the surface model with alignment centreline I had created. Very strange but something I can look at at a later date!