As it says on the tin.
With any non-ASB PoD, maximise the portion of railroads in total transportation and/or maximise the length and traffic frequency of railroads and/or the importance of railroads in urban and rural geography, culture etc., in short: go total railroad bonkers!
All and any fuel types and adhesion systems are equally OK.
The only condition is that railroad transportation needs to be, like OTL, a predominantly public form of transportation, so finding some clever solution of how to organise individual automobile traffic on rails does not count.
I´m looking forward to both knowledgeable PoDs and imaginative outcome scenarios.