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.

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.

Focus on: Burlingame

Burlingame, a city of trees, is increasingly aware of the impending arrival of high-speed rail. The city has taken a strong pro-tunnel stance in its EIR scoping comments, and is a founding member of the Peninsula Cities Consortium. The peninsula rail corridor in Burlingame could be described as mostly Kansas-flat and Mississippi-wide: an abundance of railroad right-of-way with relatively few constraints contrasts sharply with Burlingame's neighbor to the south, San Mateo.

Downtown Area

The Burlingame station recently underwent a $20M renovation by Caltrain that converted the narrow center platform to outside platforms, to allow two trains to safely occupy the station area at the same time. The new platforms were opened in early 2008, just in time for the city's centennial celebration. The depot was built in 1894 in the Mission Revival style and is listed on the National Register of Historic Places (photo above by Schaffner). Not surprisingly, it is considered one of the architectural jewels of the city, and visions of what might become of it in the age of HSR differ greatly.

In the discussion of visual impacts in the program EIR, the CHSRA happened to have picked North Lane for a before/after comparison of a grade separation. The authority's photo simulation features a vaguely European structure elevated by approximately 10 feet, with electrification poles placed between the tracks--evidently to keep high voltage away from trees.

In another photo simulation that clearly seeks to convey a different message, the pro-tunnel grassroots group Don't Railroad Us! shows the depot building overwhelmed by a fully elevated viaduct executed in the worst freeway-brutalist style, with unsightly high voltage headspans reaching high into the sky.

Existing condition	CHSRA photo simulation	Don't Railroad Us! photo simulation

If the tracks are elevated at North Lane, the result may not look quite as good as the CHSRA photo, but it's also a safe bet that it won't look quite as bad as the Don't Railroad Us! photo.

Broadway Area

Weekday Caltrain service to the Broadway Burlingame station, formerly ranked #23 in ridership, was discontinued in July 2005 to allow express service to be scheduled more effectively--despite objections from city officials who pointed out that a large portion of Burlingame residents lived near that station. Unfortunately, too few of them used the train. Nevertheless, Broadway is a station that could benefit greatly from electrification and HSR. Because of improved train performance, more Caltrain stops can be made in a given trip time, and stations that once fell on the wrong side of the Baby Bullet cut-0ff have an excellent chance of being revived.

The city of Burlingame requested in its scoping comments that the Broadway grade separation project be coordinated with the nearby Broadway interchange with highway 101, where a $73 million reconstruction is planned for traffic congestion relief on what is a primary access route for the city.

Eucalyptus Trees

Burlingame is known for the majestic Eucalyptus trees that line many of its thoroughfares; the tree even appears on the seal of the city. Rows of mature Blue Gums (eucalyptus globulus) line the railroad tracks through most of the city (photo by K. Hecteman). The tree has a long-standing relationship with the railroad: it was reportedly cultivated in California to quickly produce timber for railroad ties. Many of these trees could be affected by the high-speed rail project because E.globulus has a root system that can grow primarily out sideways. Furthermore, this species tends to shed long ribbons of bark, something that may be frowned upon when 25,000 volt overhead wires are strung up nearby. While detailed impacts are still to be evaluated, Caltrain did produce a Tree Survey and Assessment for its own two-track electrification project that considers Burlingame in some detail. The impact of four-track HSR construction will depend on the selected construction method.

Horizontal Alignment

Burlingame is lucky that the right-of-way throughout most of the city is over 100 feet wide, with some stretches over 150 feet wide. The only pinch point is at the southern end of the city, where the tracks are lined by the parking lots of auto dealerships--land that would not be difficult to acquire. For details, consult Caltrain's right-of-way maps for mileposts 13, 14, 15 and 16.

Vertical Profile

Burlingame has six grade crossings and one pedestrian grade crossing, shown in the profile diagram below (created from Caltrain track survey maps). The tracks already form an undivided barrier through half of the town, serving as a buffer between residential and industrial zones. The first thing to notice is just how low the land lies: barely 15 feet above sea level.

Since all tracks must be grade-separated for HSR, the tracks must either go over or under the roads--keeping in mind that roads are difficult to raise or lower without big impacts to properties along each side. The basic vertical alignment options for Burlingame were first revealed in the CHSRA's preliminary alternatives analysis; the tracks will run at grade until just before Broadway, and continue along one of three possible alignments: above, at, or below grade. That doesn't narrow things down very much.

Despite the city's stated wishes, it's probably safe to rule out a deep bored tunnel that goes far below sea level--that sort of structure is better suited to crossing bodies of water or mountain ranges, not suburban neighborhoods with 100-foot right-of-way and flat topography. That's why the next diagram shows only a 30-foot deep trench.


More than one mile of this trench would dip below the water table (which lies ~10 feet below the surface in this area), and it would likely require constant pumping. The Sanchez creek would need to be "grade-separated," as would the other minor aquifers that run through a half-dozen culverts alongside and under the tracks in this area. This trench might be expensive and challenging not only to build, but also operate and maintain.

Those challenges will inexorably lead back to the much-reviled elevated track solution. The diagram below shows split grade separations, with the tracks elevated by ~16 feet and the roads depressed by a low-impact ~5 feet.

While the elevated solution will not impede physical access from one side of the tracks to the other, it is perceived as a community divider, especially for the one-quarter of Burlingame's population that resides east of the tracks on the other side of Burlingame High School and Washington Park. Elevated tracks promise to be highly controversial, and will have to be weighed against the far greater property impacts of sinking the roads underneath the tracks, in a sort of pick-your-poison situation.

Ultimately, Burlingame will not entirely control its own fate. From a technical point of view, what happens immediately south of Peninsula Ave as the tracks enter downtown San Mateo will have (literally) far-reaching implications for Burlingame, because the tracks cannot rise or fall quickly--thereby forcing the solutions to match up on each side of the border. Because San Mateo is a far more difficult problem to solve, Burlingame will have to build a close collaboration with its larger neighbor to obtain a solution that suits both cities.

NOTE: This post will be updated continuously, as warranted by additional information or new events relating to Burlingame.

Headspans and Poles, Oh My!

The High Speed Rail and Caltrain electrification projects converge on one requirement: electrification with 25 kV overhead wires. This is a standard choice around the world, easy to implement, compatible with most train types, commercial off-the-shelf, and able to handle the high power loads (many megawatts) drawn by fast trains. The photo at right is a typical sample. (credit: Vitó) Electrification is a no-brainer, so you wouldn't think it could be screwed up.

Documents from the California High Speed Rail Authority and Caltrain show one particular way to electrify a four-track railroad. As Richard M. pointed out in a comment in another post, it is not the only way and it is certainly not the best way for the local conditions on the peninsula. Read on to understand why. (Warning: train geek alert. Proceed with caution.)

Supporting the overhead wires (also known as catenary) on a 4-track electrified railroad can be done with poles, headspans or gantries. The three options are described below.

• Poles (a.k.a stanchions in British parlance) are placed between pairs of tracks, and have support brackets on each side to support the catenary wires. In a four-track arrangement, the poles are placed between the inside and outside pair of tracks.
  
• Headspans are networks of steel cables hung across all four tracks, rigged from a tall pole on each side of the outside tracks. Mechanically speaking, this is somewhat analogous to a suspension bridge across the tracks. The catenary wires for each track are hung from the headspan wiring.
  
• Gantries are rigid metallic portals that span across all four tracks. Brackets are hung from the horizontal member to support the catenary wires.

Each of these options has pros and cons. We'll discuss headspans first, since that is the option seemingly favored in the California High Speed Rail Authority's Bay Area EIR/EIS cross sections (Volume 2, Appendix E, Figure CC-8), as well as in the Caltrain electrification EA/Draft EIR (Chapter 2, Figure 2.3-3).

Headspans

A headspan is shown in the diagram at right. The dimensions shown reflect the narrowest practical 4-track headspan arrangement that complies with Federal Railroad Administration and California Public Utilities Commission requirements (assuming those requirements will not be waived). While their thin cables are somewhat easier on the eyes than other options, headspans also have several significant drawbacks.

1. Headspans are more complicated to maintain, since the headspan cables mechanically link the overhead contact system for all four tracks. Tweaking one cable may knock another cable out of alignment; replacing an electrical isolator on one track also affects other tracks, which may need to be taken out of service. On a busy 4-track railroad, this is not desirable.
   
   
2. Headspans are more vulnerable to pantograph failures. Rarely, pantographs (the spring-loaded metal frames on top of trains that pick up electricity from the overhead wire) fail or snag on the wiring. While there are safeguards to limit the damage from such an occurrence, the damage can be quite extensive. With a headspan configuration, a failed pantograph can damage all four tracks at once, shutting down service entirely; with a bracket support, the damage is contained on one track. This video, showing a spectacular pantograph failure, illustrates the potential problem.
   
   
   
   
3. Headspans require very tall poles located on the outside edge of the right of way. Not only is this ugly because taller poles dwarf surrounding structures and vegetation, but it requires trees to be trimmed back further from the tracks.
   
   
4. High voltage (50 kV) feeder wires, strung from the top of those poles, are required by the CPUC to have a minimum of 4 feet of radial clearance (General Order 95, Rule 35, Appendix E). This 4-foot high voltage keep-out zone is shaded in pink in the diagram above. On the peninsula, in places like Atherton, Burlingame or Palo Alto where large trees sometimes grow near the tracks, the outside poles and feeders that come with headspans might require more heritage trees to be cut down to build HSR.
   
   
5. Headspans are not easily reconfigured to add tracks. They need to be built to their full width from the get-go.
   

Given that headspans have these drawbacks, it's worth looking at the other options.

Gantries

Gantry frames are aesthetically the most upsetting, as the photo at right shows. (credit: polandeze) This photo is sure to be a hit with detractors of HSR on the peninsula. Gantries are not just uglier than poles because of their massive horizontal beams, but they are structural overkill in the benign conditions of the Bay Area. Gantries are typically used in situations were mechanical loads on the wires are high, horizontal spans are very wide, or vertical clearances are limited. This is exemplified by some areas of Amtrak's Northeast Corridor between New Haven, CT and Boston, MA, where the relatively recent overhead electrification is overbuilt to withstand large forces from hurricane winds and the heavy buildup of ice during winter storms. Obviously, we don't need to worry about ice storms or hurricanes here on the peninsula, and we hope the HSR and Caltrain folks won't unquestioningly emulate Amtrak.

Poles

Poles located between the inner and outer pair of tracks, as shown in the diagram at right, have many advantages:

1. Poles and brackets are easier to maintain without affecting multiple tracks
   
   
2. Poles and brackets are mechanically robust to pantograph failures, containing damage to the affected track (as seen in the video above)
   
   
3. Poles are much lower than headspans (32 ft above rail versus 43 ft, according to Caltrain engineering drawings) and therefore less visually obtrusive
   
   
4. Poles keep high voltage away from the edges of the right of way, where they might interfere with surrounding objects and vegetation. The 50kV feeders are now hung above the tracks. As before, the diagram shows a pink 4-foot voltage keep-out zone, which is smaller and concentrated over the tracks, unlike headspans.
   
   
5. Poles make it easier to build two tracks first, then add another set of outside brackets (but no additional poles) to accommodate four tracks without tearing out any of the existing electrification. This would add flexibility to the construction phasing between HSR and Caltrain electrification, enabling Caltrain to future-proof anything they might build before HSR.
   

Poles do have one slight downside: the California Public Utilities Commission, which issued the existing clearance standards for rail infrastructure in California in 1948 (that's right, nineteen forty-eight!), requires 8'3" clearance (2.51 m) between a pole and the center line of the track. Including 1'6" for the tensioner assemblies that hang from certain poles, that puts the minimum track spacing at 18 feet, about 3 feet more than without the poles. Nevertheless, overall width of the right of way may not increase that much because less clearance is required along the edges, where poles are not present.

For either poles or headspans, the four-track electrified right of way running at ground level can fit within 70 feet (21.3 m), in a pinch. While the foregoing discussion is somewhat arcane, it will be quite relevant in those situations along the peninsula where the Caltrain right of way is narrowest, where HSR may cause greater community impacts and possibly eminent domain takes.