Page 7 has explained, why a different traffic function results in different infrastructure
Where high superelevation is needed most for fast passenger trains, it is lowest in practice. On curvy, steep track in the USA, it is impossible to reach the same passenger train speeds as in Europe or Japan, due to lower superelevation. Exceptions could be
- dedicated passenger traffic lines.
- lines with a low amount of freight, that does not cause a lot of rail wear (example: Shortlines).
- passenger-priority track, with a minimum speed obligation for freight trains. This might be possible on infrastructure, that is supported by public investment.
In most cases, shortlines are set up in a way, that does not allow to route through traffic. Therefore, the number of possible exceptions is limited. There is only one condition, that could change the current logic on the main network: If a major US railroad would be able to operate a profitable express freight system. For reasons explained on the next page, the author does not expect this to happen.