Pray tell me which major canal goes to Birmingham, for one example.
Ok, you found an exception.
But it is pretty much the only exception.
Every other sigificant urban area is considerably closer to a suitable seaway.
And even it is only 80 miles from a major port infrastructure, which is easily within the reach of electric HGVs.
That's probably true, because a Class 66 is over 20 years old and IIRC the original ones weren't subject to any emissions regulations at all and even the later ones had fairly minimal controls. Which does of course mean that rail freight emissions might be higher than otherwise, if uncertainty over decarbonization discourages operators from replacing 66s with newer diesels. A freight train should be able to beat the equivalent number of HGVs in terms of emissions pre unit load.
Unlikely, Class 66s have EMD two strokes that obtain superior fuel consumption to most more "modern" engines that have to comply with emissions regs.
This is why they were so desperate to get around the emissions requirements using that whole prebuilt engine thing.
Unless the state orders them to buy new diesels they simply won't.
They will just scream that their margins are too tight and demand ever greater subsidies.
And demand that the entire network be bent so they can avoid adapting themselves to a changing network.