I think the theory with HS2 using classic gauge is that having a very high frequency of normal trains is better than having a smaller number of bigger trains on a bigger track. The issue being that double decker trains take longer to load and unload at stations, so you don't really see a benefit in capacity on long distance routes.
I think the theory with HS2 using classic gauge is that having a very high frequency of normal trains is better than having a smaller number of bigger trains on a bigger track. The issue being that double decker trains take longer to load and unload at stations, so you don't really see a benefit in capacity on long distance routes.