In this world a nation has built 2 railway networks, a smaller 3'6" gauge network & a heavier 4'8" railway network. The 4'8" network connects most of the major cities & has very high American level axle loadings. It is built to enable up to 250kph running of ~40 meter long 4-6-4-4 locomotives with axle loadings of 33 tonnes & 5 cylinders, although they only do 230kph in regular operation. Think Pennsylvania Railroad class T1 with valves actually built for the speeds it can operate at & an extra driving axle.
Now at this point it's roughly the ~1960s-70s technology wise. Proper high speed rail is on it's way in with trains like the 0 Series Shinkansen & Intercity 125. This country now wants to convert it's 4'8" heavy axle loading railways towards more conventional HSR away from the old steam haulage.
But most HSR trains have relatively low axle loadings, however that's mostly to reduce infrastructure requirements. But in this case the infrastructure was already built for very very heavy axle loadings at the same time as high speed operation.
So the question is here, within the limitations of 1960s-170s technology, what could be done to take advantage of very heavy axle loadings on HSR lines?
- There's about ~800km of track in this network.
- The government is willing to pour a lot of money into this
- Increasing track speeds beyond about ~250kph isn't an option, they don't want to do significant track work beyond electrification & would like to avoid even that if possible.
- Due to the network being being built for extremely long locomotives bogies aren't 100% needed but preferred
- The network is all 3 track lines aside from lower speed branches
- Freight trains do share the tracks & vary in speed significantly