Some interesting facts and a bit of conjecture to mull over
passengers journeys carried per year (2013) UK 1,610 million USA 476 million
Modal ratio of railway transport compared to other modes UK 5.9% USA 0.3%
Freight by million-ton UK 104 million USA 1,820
The figures make interesting reading, especially when you consider that the size of the UK is 1/36 the size of the USA and has a 1/6th population.
If you multiplied the above UK figures to equal the size of the USA for size and also by population then then figures at the top become even more significant.
The new stats are only for fun and do not constitute any reality due to lots of factors which are probably too in depth to scope in for this topic.