People in my comments and on social media are taking it for granted that investments into modernizing commuter rail predominantly benefit the suburbs. Against that, I’d like to point out how on the modern commuter rail systems I know best – the RER and the Berlin S-Bahn – ridership is predominantly urban. Whereas the typical American commuter rail use case is a suburban resident commuting to a central business district job at rush hour, the typical use case on the commuter trains here is an urban resident going to work or a social outing in or near city center. Suburban ridership is strong by American standards, benefiting from being able to piggyback on the high frequency and levels of physical investment produced by the urban ridership.
Here’s Berlin’s passenger traffic density on the U- and S-Bahn, as of 2016 (source, p. 6):
The busiest section of the S-Bahn is the Stadtbahn from Ostkreuz to Hauptbahnhof, with about 160,000 passengers per weekday through each interstation. The eastern sections of both the north and the south arms of the Ringbahn are close, with about 150,000 each, and the North-South Tunnel has 100,000. These traffic density levels extend into outer urban neighborhoods outside the ring – ridership on the Stadtbahn trunk remains high well into Lichtenberg – but by the time the trains cross city limits, ridership is rather low. All tails crossing city limits combined have 150,000 riders/day, so a little more than a quarter of the ridership density on the city center segments. Of those tails, the busiest, with a traffic density of 24,000/day, is to Potsdam, which is a suburb but is an independent job center rather than a pure commuter suburb like the rest of the towns in Brandenburg adjacent to Berlin.
https://pedestrianobservations.com/2025/05/30/s-bahn-and-rer-ridership-is-urban/
