Grade Separation: The Decadal View

For the last few years of debate around the issue of high-speed rail, grade separating the peninsula rail corridor was often cast as an all-or-nothing proposition.  This extremist view clouded two important facts: first, the corridor is already mostly grade-separated (in 2013, only 40 road crossings out of 104 between San Francisco and San Jose will remain at grade); and second, grade separation is a slow and inexorable process that takes place over many decades.

If we assume the next several decades will be like the last several decades, we can take an educated guess about how and in what order grade separations will be built.  The criteria for prioritizing each project could be:

• creating long, uninterrupted stretches of grade separated right of way to enable higher train speeds without compromising safety
• creating a four-track mid-line overtake facility to increase the capacity of the corridor, to support initial HSR service
• separating crossings that rank highest in the CPUC's Section 190 Grade Separation Priority List
• delaying the most expensive and politically costly projects until last

Phase I is simply the completion of the San Bruno grade separation in 2013.  The San Mateo / San Bruno grade crossing being replaced was once rated #7 statewide on the CPUC's priority list.

Phase I: San Bruno Grade Separation

Phase II consists of four projects in San Mateo County, opening up two long stretches free of crossings by the early 2020s, including 14.8 miles free of crossings north of Burlingame, and 6.5 miles south of San Mateo.  This enables the future construction of the "short" mid-line overtake envisioned in Caltrain's corridor capacity analysis, and leaves only a few dense clusters of crossings within San Mateo County.  The new grade separations, in order of priority, are:

1. 25th Ave in San Mateo, the only grade crossing that remains between San Mateo and Redwood City.  Along with new grade separations already planned at 28th and 31st, this project enables the future 4-track mid-line overtake.
2. Broadway in Burlingame, an extremely congested crossing that has been slated for grade separation since the 1970s.  It rates #11 statewide on the latest CPUC priority list.
3. Linden Ave in South San Francisco, originally planned as part of the San Bruno project, but dropped from the final design in 2007.  Grade-separation at Linden is accompanied by the closure of Scott St, which becomes a pedestrian tunnel.
4. Center Street in Millbrae, a grade separation that will require a U-shaped elevated ramp due to the nearby BART subway tunnel box.  Such are the consequences of bad planning.

Each of these projects is independent and can be negotiated on a case-by-case basis with the four affected cities.  Starting in San Mateo County allows at least another decade for the Pacheco vs. Altamont debate to run its due course, legally and politically; these four projects are useful either way.

Phase II: San Mateo County Grade Separations

Phase III occurs mostly in Santa Clara County, creating a new stretch free of grade crossings from the southern half of Palo Alto all the way to San Jose in the late 2020s, assuming the routing of HSR over Pacheco survives as currently planned.  The last two grade crossings in San Francisco are also eliminated as part of the downtown extension project.  This phase includes the following six discrete projects:

1. Mary Ave in Sunnyvale, the corridor's busiest grade crossing in this county, with more than 25,000 daily vehicles
2. Sunnyvale Ave
3. Rengstorff in Mountain View, with about 18,000 daily vehicles
4. Castro in Mountain View, with about 9,000 daily vehicles
5. Charleston and East Meadow in Palo Alto, with a combined ~30,000 daily vehicles plus numerous pedestrians and bicyclists
6. 16th and Common in San Francisco, as part of the DTX project

Together, these six projects create a new 16-mile stretch of track that is entirely free of grade crossings.  The corridor is now left with just three dense clusters of grade crossings, in San Mateo / Burlingame, Redwood City, and PAMPA (Palo Alto - Menlo Park - Atherton), highlighted in orange in the figure below.  Note that these three dense clusters contain 27 crossings, and that to get this far, only 12 existing crossings were newly separated.

Phase III: Santa Clara County Grade Separations

Phase IV is the Great Redwood City Grade Separation.  This project, potentially for the early 2030s, would prolong the four-track mid-line overtake by three miles, by removing six grade crossings in downtown Redwood City.  Removing this cluster first makes sense from the standpoint of increased corridor capacity, the lowest number of new structures, the short mileage, and the entire project being politically simplified by virtue of its containment within Redwood City limits.

Phase V is the Great San Mateo / Burlingame Grade Separation.   This is a tougher project because it involves some of the most highly constricted portions of the corridor.  It also involves political and technical coordination between two neighboring cities, adding an additional challenge.  The sheer quantity of crossings (13 grade crossings + 4 obsolete grade separations within 2.4 miles) is also a complicating factor.

Phase VI is the Great PAMPA Grade Separation.  This project is left for last because it lies in the most expensive real estate on the corridor, involves coordination between three different cities, and is liable to cause the fiercest political and legal backlash anywhere on the peninsula.  Delaying it until last, perhaps into the late 2030s, allows the customarily long planning process to run its course without undue haste in all three affected communities.

We didn't arrive at today's state of grade separation (more than half) overnight.  It resulted from a slow and steady process that began in earnest in the 1940s.  The future is likely to be similar, and the peninsula rail corridor can reach a far improved state by separating just 12 more crossings over the next couple of decades, as described in Phases II and III.  This dozen should be prioritized for construction, before any of the crossings in the remaining dense clusters are touched.

Millbrae, Half a Billion Cheaper

The powers that be have determined that the Millbrae intermodal station does not have sufficient right-of-way width to accommodate four tracks of Caltrain and HSR, in addition to BART. That is why the Supplemental Alternatives Analysis from last August and the Millbrae preliminary station footprint from October consider only one solution: three tracks at grade and the fourth track sent down into a trench and covered tunnel, along the profile shown below:


This 2.5-mile trench and covered tunnel facility would dive up to 60 feet below grade, passing below the Hillcrest Blvd underpass (itself passing under the at-grade tracks) and nearby storm drains, as well as under the Mills Creek to the south. It would also pass directly under the existing Millbrae station, requiring the excavation of an underground cut-and-cover "train box" as shown in the section drawing at right. If the cost estimates are to be believed, this one-track trench and tunnel facility would cost about $500 million more than at-grade tracks.

There may be legitimate reasons why a four-track at-grade arrangement can't fit in the existing Millbrae station. But are they half billion dollar reasons? For that kind of money, you'd imagine there would be some serious pencil-sharpening going on.

Shoehorning It In

One of the very first issues covered in these pages, way back in 2008, was the amazing lack of foresight embodied in the design of the Millbrae station. The structural grid of the station mezzanine was laid out so narrowly, and so far to the west of the sprawling BART facilities, that it now precludes four tracks from being built through the Caltrain side of the station without major impacts to the structure itself and to residential areas adjacent to the west.

If the going-in assumption is that BART facilities cannot be impacted by HSR construction, no matter what the resulting cost, then we do indeed end up with the solution proposed by the CHSRA.

But we live in a world where cost matters.

That's why it's worth exploring a significantly cheaper option: converting one BART platform track (of three) for use by Caltrain and/or high-speed rail. The diagram at right shows what the Millbrae might look like under such a scenario. The structural grid is preserved, and no encroachments occur outside the right of way to the west of the station (to the top in the diagram.)

The diagram below shows the wider context of the track layout, including station approaches and tail tracks. (Warning: 2.1 MB image)

What are the pros and cons?

1 TRACK BELOW GRADE	ALL TRACKS AT GRADE
Impact to existing Millbrae station structure
Extensive, with cut-and-cover excavation below existing tracks and below foundations and support columns of existing mezzanine.	None.
Impact to BART operations
None.	Removes one BART platform track and one tail track, leaving two platform tracks and three tail tracks. This facility should be perfectly adequate, considering its similarity to other BART terminals at Pittsburg, Dublin/Pleasanton and Fremont.
Impact to BART tunnel box
None.	Portal of BART tunnel must be modified and additional reinforcement provided to support loads from adjacent track and freight trains.
Impact to passenger convenience
Forces Caltrain passengers to use additional vertical circulation to reach underground southbound platform track. Preserves northbound cross-platform transfer between Caltrain and BART, but removes at-grade Caltrain access from west side, where TOD is planned.	Removes northbound cross-platform access between Caltrain and BART, but creates two new bi-direction cross-platform transfers between Caltrain and HSR. Preserves Caltrain access from west side, where TOD is planned.
Impact to residential areas
None.	None.
Regulatory challenges
None.	Requires Caltrain and possibly freight trains to occupy a track immediately adjacent to BART trains, with no room for a traditional separation wall. Violates CPUC GO-26D side clearances. This could realistically be mitigated by passive and active safety measures, such as a thin but strong steel crash barrier and a permanent speed restriction on that track. This PTC-enforced speed restriction would be about 20 mph for freight and 40 mph for Caltrain, with no impact to Caltrain trip times since all trains stop at Millbrae. Additionally, sensors could be provided to detect shifted loads on freight trains before they pass through the Millbrae station.
Cost to taxpayers
About $500,000,000 (for example, the entire amount of the funding shortfall for the Caltrain electrification project, if it were spent instead to dig a hole in the ground)	Minimal, although some expense in the tens of millions would be incurred for modifications to BART facilities.
Profit to engineering & construction firms
A cut of $500,000,000.	A cut of nothing.

Yes, there are difficult design constraints. Yes, this proposed design violates a few engineering specifications and even some regulations. Yes, it will be politically challenging to infringe on BART. But when a half billion dollars hangs in the balance, it's time to work smarter and not harder. It would be reckless and irresponsible not to explore a compromise solution, through a carefully considered combination of design exceptions, regulatory waivers, and inter-agency agreements. Taxpayers should demand it.

And if that doesn't work out, stop everything, tear down the whole station and start over from scratch with a proper track layout. The entire Millbrae Intermodal station complex, including 3,000 parking spaces, cost $75 million to build ten years ago. In today's dollars, it would be about $100 million, ONE FIFTH of the cost of the below-grade "solution".

Roller Coaster Physics

Roller coaster rides, and avoiding them on the peninsula rail corridor, is a recurrent concern that recently came up in a discussion of tunnels. Millbrae councilwoman Gina Papan claimed that an underground station in Millbrae would cinch a tunnel through Burlingame because "you can't have a roller coaster from Millbrae to Burlingame."

Let's bust this myth with a quick look at the physics and specifications of HSR track alignment.

Discomfort arises when there is a curve in the tracks, because passengers conform to Newton's first law: they tend to keep going straight. The centripetal force imparted by the train causes them to follow the curve, and sometimes to spill their drink. In horizontal curves (left or right), engineers can use superelevation, a simple trick that harnesses gravity to provide the centripetal force and smooth the ride. Vertical curves (up and down) are a different matter: passengers must bear the full brunt of the centripetal force.

The centripetal force is perceived as a vertical acceleration, such as you might feel when riding an elevator, and goes as velocity squared divided by radius.

The recently published HSR design standards (specifically, TM 2.1.2 section 6.1.6.2 and TM 1.1.6 section 6.1.7, which trace to the AREMA manual, Chapter 5, Part 3.6) describe the design limits placed on vertical acceleration: typically just 2 to 3 percent of gravity, obviously much less than would ever be experienced on a roller coaster. Given this acceleration limit and the planned operating speed of 200 km/h (125 mph), the references above contain the following constraints:

Parameter	Desired	Limit	Exceptional
Passenger-Only 125 mph Vertical Curve Length*	840 ft	650 ft	420 ft
Freight 75 mph Vertical Curve Length* (sag)	2000 ft	1200 ft	1200 ft
Freight 75 mph Vertical Curve Length* (crest)	1500 ft	1200 ft	1200 ft
Passenger-Only Maximum Grade	1.0 %	1.7 %	3.0 %
Freight Maximum Grade	1.0 %	1.0 %	2.0 %

* per percent of grade change

What do these mean? To find out, it's helpful to look at a picture of what a vertical track profile looks like when you need to transition from one elevation (or depth) to another. The figure at right shows the basic anatomy of a vertical transition. Passenger discomfort (if any) occurs only in the curved portions at the beginning and end of the transition; the straight ramp in between is not perceived as having any less comfort than flat and straight track. Simply lengthening this ramp will increase the overall height of the transition. Assembling the above specifications into actual ramp lengths, we can calculate a useful metric: the total length of a vertical transition, depending on how much rise is required.

Transition Rise	Train Type	Desired	Limit	Exceptional
15 ft (Ground Level to Elevated)	Passenger Only	2340 ft	2140 ft	1830 ft
	Passenger + Freight	2830 ft	2600 ft	2600 ft
30 ft (Trench to Ground Level)	Passenger Only	3840 ft	3300 ft	2750 ft
	Passenger + Freight	4730 ft	4200 ft	4170 ft
45 ft (Trench to Elevated)	Passenger Only	5340 ft	4200 ft	3470 ft
	Passenger + Freight	6250 ft	5700 ft	5370 ft
90 ft (Tunnel to Ground Level)	Passenger Only	9840 ft	6850 ft	5100 ft
	Passenger + Freight	10750 ft	10200 ft	8100 ft
105 ft (Tunnel to Elevated)	Passenger Only	11340 ft	7740 ft	5600 ft
	Passenger + Freight	12250 ft	11700 ft	8850 ft

Keep in mind that even the "exceptional" values would not be anywhere close to a roller coaster ride: the acceleration would be only about 4% of gravity. Roller coasters routinely exceed 100% of gravity.

What immediately jumps out from the table is that the trickle of peninsula freight trains make these transitions much longer and potentially much more community-disruptive than passenger-only infrastructure.

As for Gina Papan's notion of Burlingame getting a tunnel as a consequence of a hypothetical underground Millbrae HSR station: it would take less than a mile for tracks to rise up to an elevated structure that clears Broadway in Burlingame, with the utmost passenger comfort.

Myth Busted.

Lemonade from a Lemon: Millbrae Take 2

The comments in response to Focus on: Millbrae were quite thoughtful and identified another couple of reasonable options for reconfiguring the station for the arrival of HSR. They are labeled Option C and Option D in the expanded diagram below.

(click to enlarge-- and yes, this figure is getting too big...)

After some consideration, Option D stood out to me as the least-terrible way of making lemonade out of the existing Millbrae lemon.

Option D pro:

• 4 platform tracks for HSR / Caltrain
  
• Cross-platform transfers between Caltrain Express / HSR and Caltrain local, in both directions
  
• No demolition and reconstruction of the existing station mezzanine
• Platforms stay pretty much where they are
• "Site One" transit-oriented development to the west is minimally impacted
• Keeps It Simple, Stupid (compared to nearly every other solution)
  

Option D con:

• Loss of northbound cross-platform transfer between BART and Caltrain
• Non-stop HSR passes platforms at ~125 mph
• Need to establish physical separation of BART and Caltrain on adjacent tracks

While this is probably the best technical solution, it remains to be seen whether it is politically workable, especially because it destroys the BART cross-platform transfer, which was a huge selling point for the existing station. Then again, follow the money... the smaller station footprint and lesser impact to the neighboring development may favor Option D.

Focus on: Millbrae

Millbrae, by virtue of its proximity to SFO and its connection with BART, is planned as an intermediate HSR stop. The existing BART / Caltrain station is to be expanded, and is naturally the focus of the HSR project in Millbrae.

Millbrae Station

Plans for the Millbrae HSR station, described in the CHSRA's environmental impact documents, call for four tracks to pass through, with two outside platforms. This is shown as Option A in Figure 1 below.

Unfortunately, the incompetent design of the existing Millbrae station (opened in 2003 and billed as the largest multi-model station west of the Mississippi) has squandered much of the space available within the Caltrain right of way. Massive support columns for the expansive station mezzanine have been placed right where you'd want to run extra tracks, and a third platform track at the south end of the station (presumptuously built to terminate some Caltrain services, assuming everyone would want to ride BART into San Francisco) sits unused, with no possibility of continuing north through the station. The photo at right, taken in 2000 during construction, illustrates how a forest of concrete pillars now constrains the right of way.

The total lack of foresight in this design is breathtaking.

To make room for four tracks, the existing southbound platform and part of the mezzanine that it supports (including the ill-placed pillars) may have to be demolished and rebuilt a few dozen feet further to the west.


View Larger Map

Millbrae is an important stop for Caltrain, ranking 5th in ridership, and even higher when counting BART. As a measure of its importance, every Baby Bullet stops there. Assuming one wanted to make Millbrae an important interchange point with HSR, it would make sense to maximize the opportunities for cross-platform transfers. Cross-platform transfers require an island platform between two tracks, allowing passengers to quickly and easily change trains on the same platform. For example, a much-touted cross-platform transfer is already possible between Caltrain and BART in the northbound direction.

With four tracks through the station, a solution that maximizes cross-platform transfers would consist of two island platforms flanking the center pair of express tracks. The existing northbound island platform shared with BART would be preserved. Advantages:

• 4 trains can occupy the station at once (not counting BART)
• Cross-platform transfers between HSR and Caltrain
  
• Cross-platform transfers between Caltrain local and Caltrain express
• Flexible routing through station under perturbed schedule, which minimizes cascading delays

There are also some disadvantages. Non-stop HSR trains pass platforms at 125 mph, likely requiring a physical safety barrier. Other disadvantages depend on how this configuration is built. Two possibilities are labeled Option B and Option D, in Figure 1 below.

Figure 1: Millbrae station configuration options

Option B, to construct new island platforms and preserve the existing BART cross-platform access, increases the station footprint the most. The westernmost track is shifted ~60 feet to the west (vs. ~30 feet for thru configuration), with possible impact to private residences to the north and Millbrae Ave overpass to the south. As in the CHSRA's Option A, most of the station mezzanine and support columns must be reconfigured.

Option D (raised in the very thoughtful comments to this post) calls for converting the westernmost BART track to use by Caltrain / HSR. The way BART is operated, with half the trains terminating at SFO, the Millbrae station is underused. The eastern BART island platform is usually closed to service. With the expected HSR and Caltrain improvements, BART has no chance of being extended past Millbrae. All of these factors support the notion of cutting the BART portion of the Millbrae station from three platform tracks to a more reasonable two.

The biggest advantage of this approach is to preserve the existing mezzanine and platform configuration, without the need for large-scale demolition. The cross-platform transfer to BART (the cherry on the cake!) would be lost, in favor of better cross-platform options between HSR, Caltrain express and Caltrain local services. Option D also has the least encroachment on land to the west of the station, which may ultimately seal the deal.

Constructing Option D would require some reconfiguration of the existing station, such as removing the eastern Caltrain siding track, removing the western BART tail track, reworking the BART subway portal, and probably constructing a physical barrier to separate BART from Caltrain/HSR on the adjacent track.

Another possibility that preserves the existing mezzanine structure is Option C, although it only provides three platform faces for HSR and Caltrain. This option involves routing two new tracks to the west of the existing station, with some of the disadvantages mentioned above.

None of the options discussed here is perfect; all of them have drawbacks because of the suboptimal way the station was originally built. If the city of Millbrae, Caltrain, and the CHSRA are serious about making the Millbrae station live up to its intermodal billing, they should opt for the lesser of all evils (Figure 1 Option D), and not the design currently described in the EIS/EIR documents. While the BART cross-platform transfer (the station's political selling point) would be lost, other advantages far outweigh this loss.

Station Area Development

Whatever the final station configuration, adding two tracks to the Millbrae station will expand its footprint to the west, encroaching on an area locally known as 'Site One,' where the city of Millbrae and private developers desire to build a Transit Oriented Development. Ironically, the developers have claimed that HSR threatens to derail their TOD plans, quite shamelessly undermining their claim to be "Transit Oriented." The people who run Caltrain appear to have capitulated prematurely by promising the developers that HSR can be accommodated within the existing station footprint, an option that even the CHSRA doesn't try to pass off as feasible.

The CHSRA has also penciled in another parking structure for 230-400 cars to the west of the station on Site One, apparently without regard to the existing under-utilized 3,000 space BART parking structure, which has plenty of surrounding land for expansion.

Grade Separations

Most road crossings in Millbrae are already grade separated. A separation at Center St, at the entrance to Marina Vista, remains to be built. This is a constrained location where the BART tunnel box runs immediately to the east of the crossing, which prevents lowering the road.

BART Tracks

The BART to SFO project (which, as built, is much better described as BART to Millbrae) was brought to you by Quentin Kopp, who is now chairman of the High Speed Rail Authority. While Kopp has clearly established a track record in bringing large transportation projects to fruition, his BART extension shows all the signs of having satisfied not just a transportation need, but the raw urge to pour way more concrete than strictly necessary.

A lot of this concrete was poured on, under, and around the Caltrain right of way, constraining it in various unpleasant ways that will come back to bite us (the taxpayer) as HSR is built. The botched Millbrae station discussed above is only the tip of the iceberg. The construction companies won't mind: there's real money to be made in jackhammering old concrete to make room for new concrete.

According to the CHSRA's environmental impact report Appendix 2D for the Caltrain Corridor, the HSR tracks will run through Millbrae at grade, right next to the BART tracks. But after BART was built so expansively into the Caltrain right of way, there isn't a lot of room left to build another pair of tracks. For example, take a look here and here, and think about how to fit in the planned 100-foot, 4-track right of way as shown at left.

NOTE: This post will be updated continuously, as warranted by additional information or new events relating to Millbrae. Last updated 09 December 2008.