Missing the point with a second tube

I figured I’d talk about BART some more because they’ve made it into the news recently. They’re currently fighting a lot of issues, and people are understandably mad, but I don’t think the absurd set of constraints the agency has to operate under gets enough airtime. It’s made even worse by the fact that people are demanding more and more of them as time goes on. Please be patient with them!

As I wrote about last time, talk of running BART around the clock seems to be reaching a fever pitch. One of the big topics here has been the second Transbay Tube, and it seems like people believe that this is necessary and sufficient for 24-hour BART. I think we badly need the second tube, but for completely different reasons. It also seems unlikely to me that this is all we’d have to do to get the trains running all night and we’ll be sorely disappointed if we use this as a justification.

The second tube is an absolutely necessary capacity upgrade, and we can see why from BART’s planning documents. Right now, the Transbay Tube carries 24 trains per hour during peak commute time. This means we can put about 23,000 people across the Bay in one direction in an hour. Unfortunately, it seems like we’re coming close to hitting this number already! This is a huge problem, because we won’t be laying another tube for decades. In the meantime, BART has some ideas to squeeze a little extra capacity out of the current tube. One is to make all Transbay trains 10 cars long. They currently don’t have enough train cars for this one, but the Fleet of the Future promises a massive expansion. They’ll also have to work out those crazy voltage spikes and power issues. When all is said and done, it’ll allow a modest capacity increase to 25,000 or 26,000 people per hour. Another relies on signal upgrades which should be included in the next BART bond. The benefits include an increase in frequency from 24 trains per hour to 30, pushing the capacity further up to around 32,000 people per hour. This is a big help, and is definitely the best short-term strategy, but the Bay Area is expanding so quickly that this will only help for so long.

Enter the second tube: BART projects we’ll be approaching the 32,000 passenger per hour limit in about 35 years, so we should probably begin planning this tube now. It will roughly double Transbay capacity and keep BART humming along even if it surpasses 1 million daily riders. It would also provide some badly-needed redundancy in case something goes wrong with the current tube or a station approaching it. Because of the improvements to capacity and robustness of the whole system, it’s definitely a worthy investment.

The redundancy aspect has people setting their sights on 24-hour BART. After all, if you can run the trains in one tube, you can close the other one for maintenance. If you switch off between the tubes on consecutive days, you should always be able to keep one of the tubes open, and we can run trains all night, every night!

There are a number of problems with this line of thought. For example, just because we have four tracks crossing the Bay doesn’t mean we have four tracks anywhere else in the system (save MacArthur, but that’s not really useful for this aspect). The new tube could play out in one of two ways. One is that it crosses the Bay, connecting up to the existing Market Street Subway in San Francisco. Another is that it creates a new BART line within SF city limits with some connection to the current subway. The most popular formulation of this concept has the connection at Montgomery and the new line running down Post or Geary.

Both of these plans have choke points that aren’t the tube itself—namely, they dump out into two-track subways, and if you close those down, you still won’t be able to run trains. While studying the New York City Subway, I realized that the decision to quadruple-track the trunk lines was one of the most brilliant decisions they made, as it allowed them to run trains along those lines no matter what happened. Unless we have quadruple-track subways, we’ll never reach that same level of availability.

Of course, New York City runs the trains all night on every line, not just the ones with four tracks. Plenty of lines run on two tracks when they leave Manhattan. Some lines, such as the L, have only two tracks the whole way through! I wasn’t sure what to make of this, so I asked my dad (an ex-MTA employee) how it was possible. He gave me two answers: Bus substitution, and the dreaded Planned Service Changes.

Anyone who has been in a subway station in New York has likely seen the enormous boards detailing all of the ways in which service will deviate from the official patterns in the near future. Trains might skip particular stops or there might be breaks in service along the line, requiring free bus bridges along the gap, or transferring to other trains. Trains from one line might use tracks from another line for some duration of their trip to allow maintenance on their own tracks. These service changes allow the trains to run all night, every night, but they have some cost. First, they rely on the network’s massive amounts of redundancy to continue functioning. Second, they make everything really complicated. The NYC Subway is already this huge, complex system with many lines and hundreds of miles of track, and remembering the standard service pattern is hard enough. It must be impossible to keep up if they have to change it all the time!

In either of the scenarios for the second tube, this same strategy of service changes to avoid maintenance areas isn’t going to cut it. The system simply doesn’t have enough redundancy to support the kind of service changes the MTA can pull off, and building that infrastructure now would require many billions of dollars. Let’s look at what we’d have to do even if we only built extra tracks between MacArthur and 24th St Mission, which is basically the smallest area for which it makes sense. We’d be paying for an extra 3 miles of two-track subway on the SF side and 2 miles of one-track subway on the Oakland side, and we’d have to rework the wacky subway-to-elevated transition as the C tracks move into the 980 median. This would add at least $4 billion to the total, and that’s in the absolute best case scenario. Reworking the transition and construction in the stations would probably cause service outages. It would also only grant us 24-hour service on a very limited section of BART. (This isn’t necessarily a bad thing, since we may only want to run trains all night in the areas dense enough with the kind of activity to support them. I assume demand for all-night BART to Pittsburg-Bay Point is pretty low. It is meant to highlight the immense expense of adding this infrastructure.)

What can we do? I know I was something of a killjoy last time when talking about the problems with running BART all night on weekends, but I think the conclusions there are valid here as well. If we can’t rely on service changes and we don’t have the infrastructure to do maintenance concurrently with service, then we’re going to have to turn to our old friend, bus substitution. As I stated before, even the NYC Subway resorts to this, so it shouldn’t feel like a cop-out. Bus substitution isn’t ideal because it drops capacity and doesn’t provide service as rapid as with trains. If we’re going to provide 24/7 service, we might need to do bus substitution at any hour, even during the commute rush. This could be really painful for a lot of people, especially while BART is already having capacity issues! We can do a little damage control by adding more switches in between stops so we’ll only have to substitute over one station, but this requires some extra infrastructure and is probably a ways off if so. We can see examples of this in the wild, though: Chicago’s L has switches between most stations on the two-track segments of its Red and Blue lines, and this is no doubt an integral component to their ability to run trains all night on those lines.

I think the new tube and 24-hour service are often tied together needlessly in discussions about the future of BART in a way that makes it hard to talk about what the former is actually necessary for, and what is actually necessary for the latter. My position on it is:

  1. If we want to be running trains all night, every night, then we do need to wait for the second tube, but that’s not even close to everything we need. Miles of extra subway and lots of new infrastructure will need to be built. Whether or not that’s a worthy investment is beyond the scope of this post, but we shouldn’t make the mistake of thinking we can build the extra tube and be done with it.
  2. If we’re comfortable with bus substitution, then we can mostly already get 24-hour service, if we are willing to tolerate substitution across arbitrary segments of lines and possibly at arbitrary times. This is, again, a value judgement, but given the outcry over the recent issues on the PBP line, I think this would be unpopular.

It’s great to see the Bay Area taking aim at New York here, but we do have to realize that their system is much better suited to 24-hour service than ours is, and we have a lot of work to do if that’s something we want as well. Either way, we are going to need the new tube. We simply shouldn’t delude ourselves into believing it will solve our 24-hour issue as well.

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