The rail advocate Shaul Picker has uploaded a fascinating potpourri of studies regarding commuter rail operations. Among them, two deserve highlight, because they cover the invention of bad timetable practices in New York, and, unfortunately, not only think those practices are good, but also view their goodness as self-evident. They are both by Donald Eisele, who was working for the New York Central and implemented this system on the lines that are now Metro-North, first introducing the concept to the literature in 1968, and then in 1978 asserting, on flimsy evidence, that it worked. Having implemented it in 1964 based on a similar implementation a few years earlier in the Bay Area, Eisele must be viewed as one of the people most responsible for the poor quality of American mainline service, and his idea of zone theory or zonal operations must be discarded in favor of the S-Bahn takt.
Eisele’s starting point is that commuter rail service should be exclusively about connecting the suburbs with city center. He contrasts his approach with urban transit, which is about service from everywhere to everywhere; trips short of Manhattan were 20% of single-trip ticket revenue for New York Central suburban operations and 5% of multi-ride pass revenue, and the railroad wanted to eliminate this traffic and focus on suburb-to-city commuters. From this inauspicious starting point, he implemented a timetable in which suburban stations are grouped into zones of a few contiguous stations each, typically 2-4 stations. At rush hour, a train only stops within one zone, and then expresses to city center, which in the original case means Grand Central.
The idea behind zone theory is that, since all that matters is a rapid connection to city center, trains should make as few stops as possible. Instead of trying to run frequently, it’s sufficient to run every 20 or 30 minutes, and then once a train fills with seats it should run express. This is accompanied by a view that longer-haul commuters are more important because they pay higher fares, and therefore their trips should not be slowed by the addition of stops closer in.
It’s important to note that what zone theory replaced was not an S-Bahn-style schedule in which all trains make all stops, and if there’s more demand in the inner area than the outer area then some trains should short-turn at a major station in the middle. American railroads had accumulated a cruft of timetables; Eisele goes over how haphazard the traditional schedules were, with short but irregular rush-hour intervals as some trains skipped some stations, never in any systematic way.
The first paper goes over various implementation details. For example, ideally a major station should be the innermost station within its zone, to guarantee passengers there a nonstop trip to city center. Moreover, considerable attention goes to fare collection: fares are realigned away from a purely distance-based system to one in which all stations in a zone have the same fare to city center, simplifying the conductors’ job. The followup paper speaks of the success of this realignment in reducing fare collection mistakes.
The failure of zone theory
We can see today that zone theory is a complete failure. Trains do not meaningfully serve anyone except 9-to-5 suburban commuters to the city, a class that is steadily shrinking due to job sprawl and a change in middle-class working hours. Ridership is horrendous: all three New York commuter railroads combined have less ridership than the Munich S-Bahn, a single-trunk, seven-branch system in a metropolitan area of 3 million. Metro-North would brag about having an 80% market share among rush hour commuters from its suburban shed to Manhattan, but that only amounts to about 90 million annual riders. In contrast, the modal split of rail at major suburban job centers, even ones that are adjacent to the train station like White Plains and Stamford, is single-digit percent – and Metro-North is the least bad of New York’s three railroads in this category.
Even on the original idea of providing fast service from the suburbs to city center, zone theory is a failure. The timetables are not robust to small disturbances, and once the line gets busy enough, the schedules have to be padded considerably. I do not have precise present-day speed zones for Metro-North, but I do have them for the LIRR courtesy of Patrick O’Hara, and LIRR Main Line service is padded 30% over the technical travel time of present-day equipment on present-day tracks. A textbook I have recently read about scheduling best practices cites a range of different padding factors, all single-digit percent; Switzerland uses 7%, on a complex, interlined network where reliability matters above all other concerns. With 30% padding, the LIRR’s nonstop trains between Ronkonkoma and Penn Station, a distance of 80 km, take about as long as local trains would with 7% padding.
Eisele is right in the papers when he complains about the institutional inertia leading to haphazard schedules. But his solution was destructive, especially in contrast with contemporary advances in scheduling in Europe, which implemented the all-day clockface schedule, starting with Spoorslag ’70 and then the Munich S-Bahn takt in 1972.
Zone theory and reliability
The first paper claims as self-evident that zonal timetables are reliable. The argument offered is that if there is a short delay, it only affects trains within that zone, and thus only affects the stations within the zone and does not propagate further. There is no attempt at modeling this, just claims based on common sense – and transport is a field where intuition often fails and scientific analysis is required.
The problem is that zone theory does not actually make trains in different zones independent of one another. The second paper has a sample timetable on PDF-p. 4 for the evening rush hour, and this can also be reversed for the morning. In the morning, trains from outer zones arrive in city center just after trains from inner zones; in the afternoon, trains serving outer zone stations depart city center first, always with a gap of just a few minutes between successive trains. In the morning, a delay in a suburban zone means that the trains in the zones behind it are delayed as well, because otherwise they would clash and arrive city center at literally the same minute, which is impossible.
This isn’t purely an artifact of short headways between running trains. Subway systems routinely have to deal with this issue. The key is that on a subway system, trains do not have much of their own identity; if a train is delayed, the next train can perfectly substitute for it, and cascading delays just mean that trains run slightly slower and (because the equipment pool is fixed) are slightly more crowded. The principle that individual suburban stations should only be served every 20-30 minutes means no such substitution is possible. S-Bahn trains are not as interchangeable as subway trains, which is why they cannot run as frequently, but they still manage to run every 2-3 minutes with 7% padding, even if they can’t reach the limit values of a train very roughly 1.5 minutes achieved by some big city subways.
Eisele did not think this through and therefore made an assertion based on intuition that failed: reliability did not improve, and with long-term deterioration of speed and lack of reduction in operating expenses, the express timetables at this point are slower than an all-stops S-Bahn would be.