Sepulveda Pass and LAX Transit

Since both of these topics have been in the news a lot lately, it’s about time for a look at north-south transit on the Westside.

Sepulveda Pass in Context

Before we start laying out transit lines, we need to understand the urban context of the area in question. This is especially important for rail transit and other high capital cost projects, because bad decisions will haunt us for a really long time. So…

First, in terms of network design, Sepulveda Pass is a world-class bottleneck, right up there with San Francisco Bay and the Hudson & East Rivers. Your reaction to that, might be, “well, duh”, but we need to realize the implications for network design. Jarrett Walker goes into more detail in Chapter 4 of Human Transit but the chief points here are that (a) more deviation from straight routes is acceptable at bottlenecks and (b) bottlenecks are natural locations for transfers between parallel transit lines.

Second, in terms of engineering and cost, Sepulveda Pass is a very challenging and expensive area. We’re looking at a 7-mile tunnel from Westwood to Sherman Oaks, hundreds of feet deep in the middle. Vertical access between the tunnel ends is difficult at best for ventilation, and impossible for a station or emergency exit. This suggests that within the current planning time frame, we’re only going to get one shot at transit through Sepulveda Pass, so we’d better do it right and get a ton of capacity out of it. In 106 years, New York has managed to build only seven crossings of the Hudson, to connect all of Manhattan, the Bronx, Brooklyn, & Queens with all of New Jersey.

Therefore, any tunnel through Sepulveda Pass should serve multiple transit lines on both sides, and provide as much capacity as possible. The stations at each end will be natural transfer points between the lines. It doesn’t make sense to go to the expense of building a tunnel that long if all it’s going to serve in the Valley is one LRT line on Van Nuys. The tunnel should serve at least two lines on both sides, and probably more. We don’t have to actually build all of the lines right away; the important thing is that the piece from Westwood to Sherman Oaks is built properly at the outset. This is probably a great location for one of Alon Levy’s large diameter TBM tunnels, with four tracks running from Westwood to Sherman Oaks, since there won’t be any stops in between.

This also means that the tunnel should serve rail traffic exclusively and have no auto lanes. In addition to having a lower capacity, auto lanes have much heavier requirements for ventilation. There’s also the question of what facilities auto lanes would connect to at each end, since it’s not like there’s a ton of spare capacity kicking around on the 405, the 10, and the 101. (Note: you could argue for a bus tunnel, using dual-mode buses, with exclusive lanes on arterials for the rest of the lines. I’m not going to get into a bus vs. rail analysis here, since the quality of the ROW is more important than the technology.)

Transit Lines Through Sepulveda

Now that we’ve established what the facility through Sepulveda Pass should look like, we can lay out some transit lines to go through it. In my mind, the logical candidates for north-south transit in the Valley are Reseda, Sepulveda (Valley section), Van Nuys, and maybe Balboa. (Anything east of Van Nuys, at least IMHO, is a future north-south line to connect to La Cienega.) There’s also the potential for east-west lines on Venutra, west to Warner Center and east to Burbank. On the Westside, the north-south candidates are Lincoln, Bundy/Centinela, Sawtelle, Sepulveda (Westside section), Westwood/Overland, and maybe, as a stretch, Avenue of the Stars/Jefferson.

Personally, I’d leave Ventura alone as a separate east-west project. Sawtelle is too close to Sepulveda (Westside), so it doesn’t make the cut. The appeal of the Avenue of the Stars/Jefferson route is that it would serve Century City directly from the Valley, but the resulting line has such poor overall geometry that it wouldn’t be very useful for anyone not going to Century City, so I think it’s out as well.

The other intriguing option, which has been suggested by Henry Fung elsewhere, is having the Westside Subway Extension turn north in Westwood and go to the Valley. Assuming the other lines would be LRT, extending the Purple Line would create some technical challenges (including differing vehicle width). I’ll leave that for a future post focusing on that alternative. This option would take care of Century City.

Here’s a rough plot of these options with reasonable stop spacing:

Don’t worry too much about the stop spacing for now; we’ll take a closer look at that in future posts. Remember, the important thing at the outset is to serve the right area and choose logical overall route alignments. You also might guess from this graphic that I’ve got some changes in mind for Metrolink in the Valley. Yet another topic for yet another future post.

In terms of sequencing, the consensus is that Van Nuys is the top priority in the Valley. On the Westside, Sepulveda (Westside) and Westwood/Overland are only ½ to ¾ of a mile apart, so whichever of the two is built first, the other should be built last. I’d do Sepulveda (Westside) first, if only because it’s more centrally located and spreads the wealth. It’d be useful to some future users of the Bundy/Centinela and Westwood/Overland lines, whereas those two lines wouldn’t help each other’s riders much. The argument for Westwood/Overland first is that it’s closer to Palms and Culver City, which are denser than Mar Vista, and it’s a good enough argument that you could probably talk me into it.

I’d sequence the lines as follows:

• Van Nuys and Sepulveda (Westside)
• Reseda and Lincoln
• Sepulveda (Valley) and Bundy/Centinela
• Balboa and Westwood/Overland (no Westwood/Overland if Purple Line is extended)

The benefits start immediately with the first line completed, and are amplified as additional lines are finished. To the south, future phases could extend the lines out Florence, Manchester, Century, Hawthorne, Sepulveda/PCH… more than enough possibilities to leave for a future post.

LAX Transit

Note that all these lines naturally converge near Sepulveda & Century, right at LAX’s front door, and would serve far more people than any LAX rail transit proposal on the board now. So in addition to serving LAX, basically at the future Terminal 0, this project would directly serve a couple million other people who might or might not be going to LAX. In other words, this plan would follow one of Jarrett Walker’s main principles: be on the way!

You might have noticed in the first graphic that I didn’t show any connection from the new lines to the Green Line & Crenshaw Line. Clearly, you’d want to provide that link somehow.

Here’s one option for an initial build with two lines. In this scenario, the Crenshaw Line would take over the Green Line’s route south of Aviation/Imperial, and the Green Line would be extended a mile west to meet up with the new Reseda-Lincoln Line. This gives the combined Reseda-Lincoln-Green Line and the Van Nuys-Sepulveda (Westside) Line front door access to LAX, with decent geometry and without making any through passengers go out of their way.

I’ve violated my own rules on stop spacing in El Segundo, going to half a mile to provide a Green Line stop at Maple and a Sepulveda Line stop at Mariposa. With this level of transit service, easy access to LAX, the 105, and the 405, there’s no reason El Segundo’s business district couldn’t become LA’s third downtown.

Here’s an option for full build with four lines.

In this case, I’ve routed Balboa and Bundy/Centinela together, and the line could be extended out Florence towards South LA, HP, Bell, Cudahy, Bell Gardens, and Downey – all dense cities that should get good transit use. I’ve also shown the Purple Line being extended to the Valley and up Sepulveda.

Again, don’t worry too much about the specific stations and routings – we’ll go into more detail on each option in the future.

To Bore or Not to Bore

The decision to tunnel is one of the biggest ones that must be made. Tunneling results in faster speeds and more reliable operations, but the higher cost can push project completion further into the future. Obviously, we’re tunneling through Sepulveda Pass, but on either side, it would be possible to do full tunnels, surface running with selected grade separations (like Expo Line and Crenshaw Line), or full surface running.

Any surface running segments are dependent on the ROW of the arterial roads. Contrary to popular conceptions of LA, the north-south arterials on the Westside are somewhat underpowered. Lincoln and Sepulveda (Westside) are two lanes each way with a center turn lane. Bundy/Centinela and Westwood/Overland are cobbled together, with pieces where the second travel lane is only provided during peak periods by sacrificing on-street parking (always a sign of desperation).

The situation is much the same on Reseda and Balboa, which have the same basic configuration as Sepulveda (Westside), but with more generous proportions. On Balboa, there are three lanes each way with no parking. Sepulveda (Valley) and Van Nuys are wider, at least three lanes each way with a center turn lane plus parking. In many places they’re even wider (presumably where there used to be transit ROW in the middle).

I was going to go into detail and compare grade separation options for each branch, but that would make this post much too long. Now that we’ve got the basic framework set up, we can come back and give each branch the attention it deserves in future posts.