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).

Comparing trains from London is not really fair because virtually every train in the south ends up in London eventually. Somewhat tragically, I once tried to take a train from Watford to visit Hatfield House, some 14 miles away. I think it took me 3 hours getting in and out of London :-)