For years, the RER A’s pride was that it was running 30 trains per hour through its central segment in the peak direction (and 24 in the reverse-peak direction). With two branches to the east and three to the west, it would run westbound trains every 2 minutes between 8 and 9 in the morning on the seven-station shared trunk line. Moreover, those trains are massive, unlike the trains that run on the Metro: 224 meters long, and bilevel. To allow fast boarding and alighting at the central stations, those trains were uniquely made with three very wide doors per side, and two bilevel segments per car; usually there are two doors near the ends of the car and a long bilevel segment in between. But now the RER A can no longer run this schedule, and recently announced a cut to 24 peak trains per hour. The failure of the RER A’s bilevel rolling stock, called the MI 2N or MI 09, should make it clear to every transit agency mulling high-throughput urban rail, including RER A-style regional rail, that all trains should be single-level.
On most of the high-traffic regional rail lines of the world, the trains are single-level and not bilevel. The reasoning is that the most important thing is fast egress in the CBD at rush hour. For the same reason, the highest-traffic regional rail lines tend to have multiple CBD stops, to spread the load among several stations. The Chuo Rapid Line squeezes 14 trains in the peak half-hour into Tokyo Station, its only proper CBD station, discharging single-deck trains with four pairs of doors per 20-meter-long car onto a wide island platform with excellent vertical circulation. Bilevels are almost unheard of in Japan, except on Green Cars, first-class cars that are designed to give everyone a seat at a higher price point; on these cars, there aren’t so many passengers, so they can disembark onto the platform with just two doors, one per end of the car.
Outside Japan (and Korea, where the distinction between the subway and regional rail is even fuzzier), the busiest regional rail system is the RER. The RER A runs bilevels, but the most crowded line while the RER A was running 30 tph was the RER B, which runs 20 tph, through a tunnel shared with the RER D, which runs 12 bilevel tph. Outside Paris, the busiest European regional rail systems are in London (where bilevels are impossible because of restricted clearances), and in Berlin, Madrid, and Munich, all of which run single-level trains. Berlin and Munich moreover have three door pairs per 17-to-18-meter car. Munich squeezes 30 tph through its central tunnel, with seven distinct branches. Other than the RER A, it’s the less busy regional services that use bilevels: the RER C, D, and E; the commuter trains in Stockholm; the Zurich S-Bahn and other Swiss trains; Dutch regional trains; and many low-performance French provincial TERs, such as the quarter-hourly trains in the Riviera.
Uniquely among bilevels, the RER A’s MI 2N (and later MI 09) was designed as a compromise between in-vehicle capacity and fast egress. There are three triple-width door pairs per car, allowing three people to enter or exit at once: one to the lower level, one to the upper level, one to the intermediate vestibule. The total number of door pairs per unit of train length is almost as high as on the RER B (30 in 224 meters vs. 32 in 208), and the total width of these doors is much more than on the RER B, whose doors are only double-wide.
Unfortunately, even with the extra doors, the MI 09 has ultimately not offered comparable egress times to single-level trains. Present-day peak dwell times on both the RER A and B are about 50-60 seconds at Les Halles; here, the RER B, with its prominent Gare du Nord-to-Les Halles peak in the morning, is in a more difficult urban geography than the RER A, with four stations that could plausibly lay claim to the CBD (Les Halles, Auber, Etoile, La Defense). The RER B has long had problems with maintaining the schedules, due to the 32 tph segment shared with the RER D, using traditional fixed-block signaling; the RER A in contrast has a moving-block system called SACEM. But now the RER A has problems with schedule reliability too, hence the cut in peak frequency.
The problem is that it’s not just the number of doors that determines how fast people can get in and out. It’s also how quickly passengers can get from the rest of the train’s interior to the doors. Metro systems optimize for this by having longitudinal seats, with their backs to the sides of the train, creating a large, relatively unobstructed interior compartment for people to move in; Japanese regional trains do the same. European regional trains still have transverse seating, facing forward and backward, and sometimes the corridors are so narrow that queues form on the way to the vestibules, where the doors are. The RER A actually has less obstructed corridors than the RER B. The problem is that it’s still a bilevel.
Bilevel design inherently constrains capacity on the way to the door, because the stairs from the two decks to the intermediate level, where the door is, are choke points. They are by definition only half a train wide. They are also slow, especially on the way down, for safety reasons. When the train is very crowded, people can’t just push on the way up or down the way they can on a flat train floor. If passengers get off their seats in the upper and lower levels well in advance and make their way to the intermediate-level vestibules then they can alight more quickly, but on a train as crowded as the RER A, the vestibule is already full, and people resort to sitting on the stairs at rush hour, obstructing passageways even further.
As a result, RATP is now talking about extending peak dwells at the central stations to 105 seconds, to stabilize the schedules. Relative to 60-second dwells, this is 45 seconds of padding per station; with about 3 minutes between successive stations in the central segment, this is around 25% pad (on top of the already-existing pad!), a level worthy of American commuter trains rather than of Europe’s busiest commuter rail line.
What’s more, this unique design cost the region a lot of money: Wikipedia says the MI 09’s base order was €3.06 million per 22.5-meter car, and the option went up to €4.81 million per car. In contrast, German operators have purchased the high-performance single-level Coradia Continental and Talent 2 for €1.25-1.5 million euros per 18-meter car (see orders in 2014, 2016, and 2017); these trains have a top speed of 160 km/h and the power-to-weight ratio of a high-speed train, necessary for fast acceleration on regional lines with many stops. Even vanilla bilevel trains, with two end-car door pairs, are often more expensive: at the low end the Regio 2N is €7.06 million per 94-meter trainset, at the higher end the high-performance KISS is around €3 million per 25-meter car (about 2.7 in Sweden, 3-3.5 in Azerbaijan), and the Siemens Desiro Double Deck produced for the Zurich S-Bahn in 2003 was around €3 million per 25-meter car as well.
High-traffic regional railroads that wish to improve capacity can buy bilevel trains if they’d like, but need to understand the real tradeoffs. Average bilevel trains, with a serious decrease in capacity coming from having long upper- and lower-level corridors far from the doors, can cost 50-100% more than single-level trains. They offer much more capacity within each train (the KISS offers about 30% more seats per meter of train length, with a small first-class section, than the FLIRT), but the reduction in capacity measured in trains per hour cancels most of the benefits, except in cases where peak dwells don’t matter as much, as in Zurich with its two platform tracks per approach track. In terms of capacity per unit cost, they remain deficient.
The MI 09 was supposed to offer slightly less seated capacity per unit of train length and equivalent egress capacity to single-level trains, but in practice it offers much less egress capacity, at much higher cost, around 2.5-3 times as high as single-level trains. If RATP had bought single-level trains instead of the MI 09, optimized for fast egress via less obstructed passageways, it would have had about €2.5 billion more. Since the cost of extending the RER E from Saint-Lazare to La Defense and beyond is about that high, the region would have had money to obtain far more capacity for east-west regional travel already.
The American or Canadian reader may think that this analysis is less relevant to the United States and Canada, where the entire commuter rail ridership in all cities combined is about the same as that of just the RER A and B. Moreover, with higher US construction costs, the idea of saving money on trains and then diverting it to tunnels is less applicable than in Paris. However, two important American factors make the need to stop running bilevels even more pertinent than in Europe: CBD layout, and station construction costs.
North American CBDs are higher-rise than European ones – even monocentric cities like Stockholm have few city center skyscrapers. The job density in Paris’s job-densest arrondissement (the 2nd) is about 50,000/km^2, and it’s higher in its western end but still only about comparable to Philadelphia’s job density around Suburban Station. Philadelphia has three central stations in the SEPTA commuter rail tunnel, but only Suburban is really in the middle of peak job density; Market East is just outside the highest-intensity zone, and 30th Street Station is well outside it. In Boston, only two proper CBD stations are feasible in the North-South Rail Link, South Station and Aquarium. In New York, Penn Station isn’t even in the CBD (forcing everyone to get off and connect to the subway), and only 1-2 Midtown stations are feasible in regional rail proposals, Penn and Grand Central. Some of these stations, especially Penn and Grand Central, benefit from multiple platform tracks per approach track in any plan, but in Boston this is not feasible.
The other issue is station construction costs. High construction costs in the US mean that spending more money on trains to avoid spending money on infrastructure is more economic, but conversely they also make it harder to build anything as station-rich as the RER A, the Munich S-Bahn tunnel, or Crossrail. They also make stations with multiple platform tracks harder to excavate; this is impossible to do in a large-diameter TBM. This makes getting egress capacity right even more important than in Europe.
New York and Philadelphia meandered into the correct rolling stock, because of clearance restrictions in New York and the lack of a domestic manufacturing base for bilevel EMUs. Unfortunately, they still try to get it wrong: New Jersey Transit is buying bilevel EMUs (the first FRA-compliant ones). Railroads that aren’t electrified instead got used to bilevel unpowered coaches, and get bilevel EMUs: Caltrain is getting premium-price KISSes (about the only place where this is justifiable, since there are sharp capacity limits on the line, coming from mixing local and express trains on two tracks), and the Toronto RER (with only one CBD station at Union Station) is also planning to buy bilevel EMUs once electrification is complete.
Paris’s MI 09 mistake is not deadly. The RER E extension to the west will open in a few years and relieve the RER A either way. Being large and rich can paper over a lot of problems. North American cities are much poorer than Paris when wages are deflated to tunnel construction costs, and this means that one mistake in choice of alignment or rolling stock can have long-lasting consequences for service quality. Learning from the most forward-thinking and successful public transit operators means not just imitating their successes but identifying and avoiding their failures.