> Although according to Google Washington DC has 700,000 people and Baltimore 600,000. Probably a more realistic comparison would be Bristol and Southampton/Portsmouth where there is realistically 1 train an hour (technically 2, but the second one has a change and runs 8 minutes after the first one).

OTOH between Macon (pop 34000) and Lyon (pop 500000) there is up to 4 trains / hour at commute times (1 an hour otherwise), over a slightly longer distance.