Commuter rail systems with high bidirectional frequency succeed in monocentric cities. This can look weird from the perspective of rail advocacy: American rail advocates who call for better off- and reverse-peak frequency argue that it is necessary for reverse-commuters. The present-day American commuter rail model, which centers suburban commuters who work in city center between 9 am and 5 pm, doesn’t work for other workers and for non-work trips, and so advocates for modernization bring up these other trips. And yet, the best examples of modern commuter rail networks with high frequency are in cities with much job centralization within the inner areas and relatively little suburbanization of jobs. What gives?
The ultimate issue here is that S-Bahn-style operations are not exactly about the suburbs or about reverse-commutes. They’re about the following kinds of trips, in roughly descending order of importance:
- Urban commuter trips to city center
- Commuter trips to a near-center destination, which may not be right at the one train station of traditional operations
- Urban non-work trips, of the same kind as subway ridership
- Middle-class suburban commutes to city center at traditional midcentury work hours, the only market the American commuter rail model serves today
- Working-class reverse-commutes, not to any visible office site (which would tilt middle-class) but to diffuse retail, care, and service work
- Suburban work and non-work trips to city center that are not at traditional midcentury hours
- Middle-class reverse-commutes and cross-city commutes
The best example of a frequent S-Bahn in a monocentric city is Munich. The suburbs of Munich have a strong anti-city political identity, rooted in the pattern in which the suburbs vote CSU and the city votes SPD and Green and, increasingly, in white flight from the diverse city. But the jobs are in the city, so the suburbanites ride the commuter trains there, just as their counterparts in American cities like New York do. The difference is that the same trains are also useful for urban trips.
I don’t know the ridership by segment in Munich, but I do know it in Berlin, as of 2016 (source, p. 6):
Between Ostkreuz and Hauptbahnhof, just west of the meeting point with the North-South Tunnel, the east-west Stadtbahn has 160,000 daily riders. The proper suburbs are mostly less than 10,000 each, and even the more suburban neighborhoods of the city, like Wannsee, don’t contribute much. Overall, the majority of S-Bahn traffic is urban, consisting of trips taken either within the Ring or in the more urban outside-the-Ring areas, like Pankow, Steglitz, and especially Lichtenberg.
The high-frequency model of the S-Bahn works not because there is a mass of people who work in these outer areas. I don’t know the proportion of jobs in the Berlin region that are within the Ring, but I doubt it’s low. For reference, about 35% of Ile-de-France jobs are in a 100 km^2 blob (about the same area enclosed by the Ring) consisting of Paris, La Défense, and the suburbs in between. New York likewise has about 35% of metro area jobs in a 100 km^2 blob chosen to include Manhattan and the major non-Manhattan job centers like Downtown Brooklyn, Long Island City, and the Jersey City waterfront. I imagine Berlin should be the same or even somewhat higher (this proportion is inversely correlated with city population all else being equal) – Berlin is polycentric but all of its centers are on or within the Ring.
Rather, the reason the high-frequency model works is that there is a lot more ridership in urban areas than in low-density suburbs generating strictly unidirectional trips. The main users of the S-Bahn are city residents, or maybe residents of dense inner suburbs in regions with unusually tightly drawn city limits like Paris. If the highest demand is by people whose trip is 20 minutes and not 90 minutes, then the trains must run very frequently, or else they won’t ride. And if the highest demand is by people who are traveling all over the urban core, even if they travel to the central business district more than to other inner neighborhoods, then the trains must have good connections to the subway and buses and many urban stops.
In this schema, the suburbs still get good service because the S-Bahn model, unlike the traditional metro model (but like the newer but more expensive suburban metro), is designed to be fast enough that suburb-to-city trips are still viable. This way, middle-class suburbanites benefit from service whose core constituency is urban, and can enjoy relatively fast, frequent trips to the city and other suburbs all day.
I emphasize middle-class because lower-income jobs are noticeably less centralized. I don’t have any European data on this, but I do have American data. In New York, as of 2015, 57% of $40,000-a-year-and-up workers worked in Manhattan south of 60th Street, but only 37% of under-$40,000-a-year workers did. Moreover, income is probably a better way of conceptualizing this than the sociological concept of class – the better-off blue-collar workers tend to be centralized at industrial sites or they’re owner-operators with their own vans and tools and in either case they have very low mass transit ridership. The sort of non-middle-class workers who high-frequency suburban transit appeals to are more often pink-collar workers cleaning the houses of the middle class, or sometimes blue-collar workers with unpredictable work assignments, who might need cross-city transit.
In contrast, the sort of middle-class ridership that is sociologically the same as the remnants of the midcentury 9-to-5 suburban commuters but reverse-commutes to the suburbs is small. American commuter rail does take it into account: Metro-North has some reverse-peak trains for city-to-White Plains and city-to-Stamford commuters, and Caltrain runs symmetric peak service for the benefit of city-to-Silicon Valley commuters. And yet, even on Caltrain ridership is much more traditional- than reverse-peak; on Metro-North, the traditional peak remains dominant. There just isn’t enough transit-serviceable ridership in a place like Stamford the way it looks today.
So the upshot of commuter rail modernization is that it completely decenters the suburban middle class with its midcentury aspirations of living apart from the city. It does serve this class, because the S-Bahn model is good at serving many kinds of trips at once. But the primary users are urban and inner-suburban. I would even venture and presume that if, on the LIRR, the only options were business-as-usual and ceasing all service to Long Island while providing modern S-Bahn service within city limits, Long Island should be cut off and ridership would increase while operating expenses would plummet. The S-Bahn model does not force such a choice – it can serve the suburbs too, on local trains making some additional city stops at frequencies and fares that are relevant to city residents – but the primacy of city ridership means that the system must be planned from the inside out and not from the outside in.