The U-Shaped Grade Separation

While some cities and towns on the peninsula are still holding out for trenches or tunnels to bury the railroad tracks out of sight, the astronomical cost and difficulty of constructing such structures below the water table in seismically unstable soils makes it likely that above-ground solutions will ultimately prevail, anywhere rail traffic needs to be separated from road traffic.  An attractive above-ground solution is the U-shaped grade separation.

What is a U-shaped grade separation?

U-shape bridge cross section, showing the benefits of
reduced track elevation

A U-shaped grade separation is a type of railroad bridge used to elevate the tracks above road traffic with as few community impacts as possible; there are no property takes and all road turning movements are preserved.  The bridge structure consists of sections made from two pre-stressed concrete side beams, forming the two sides of a U shape, connected by a flat slab forming the bottom of the U, on which the tracks are laid.  The side beams bear the bending loads from the weight of the bridge and the trains that it carries.  This is not a typical railroad bridge design; it is a specialized configuration used to quickly and efficiently build elevated urban metros in cities where these systems are being built from scratch in a densely built environment.  The concept is further explained in a paper and a patent.

While the peninsula rail corridor is not a new metro system, these U-shaped structures could still prove useful in a major push to grade-separate the 40 grade crossings that remain, enabling higher speeds and more train traffic while relieving road congestion and improving east-west access across the tracks.

What are the advantages of U-shaped grade separations?

U-shaped grade separations combine several attractive features that make them ideally suited for developed areas along the peninsula rail corridor, and certainly much better than the massive hollow core concrete box girder bridges considered standard issue by the HSR project as shown in the graphical comparison above.

• Lower track elevation.  The U shape minimizes the depth of the structure (measured from the underside of the bridge span to the top of the rails) to 3 feet or less.  This allows the standard 16-foot road clearance to be provided by raising the tracks just 19 feet above the road surface, about 8 feet less than the large elevated concrete box-girder viaducts that were proposed during the 2010 Analysis of Alternatives for peninsula HSR.  The rails are lowered thanks to the U shape, which places the structural support of the bridge to the sides, rather than under the trains.
   
• Lower visual impacts.  When the tracks don't need to rise as much, the rail approaches to a grade separation become correspondingly shorter and less obtrusive, impacting fewer views. The structures above rail level, such as overhead electrification poles, are also lowered.  This reduces the so-called "Berlin Wall" effect of a grade separation structure.
   
• Lower train noise.  The side beams function as natural sound walls, trapping rail noise before it has a chance to escape into adjacent neighborhoods.  They are especially effective because they are thick and quite close to the train.  This obviates the need to add sound walls on top of the bridge, making the finished structure less visually obtrusive.
   
• Better earthquake resistance.  The lower profile of the bridge structure reduces bending moments applied to the piers and foundations, whether by earthquake forces or train braking and acceleration or wind loads.  This makes the bridge piers less massive and integrates them better into the built environment.
   
• Better station integration.  Where stations must be located on an elevated section, structures are simplified thanks to the lower profile of the track, which reduces the reach of stairs, ramps, escalators or elevators, making for a more passenger-friendly environment.  The side beams of a U-shaped viaduct have their top flange at the same height as the train floor and form the actual platform interface, 50 inches above the rail and 72 inches from the track center line, allowing the U-shaped structure to continue uninterrupted through the station.
   
• Better safety in case of derailment.  The side beams are close to the train.  In case of a derailment, train cars will be guided by the structure and will not topple off the bridge.  This feature is known as "derailment containment."
   
• Lower construction cost.  U-shaped elements can be prefabricated off-site and assembled with minimal disruption compared to traditional cast-in-place construction methods.  Using standardized elements throughout the corridor, in dozens of locations, provides economies of scale.  The decreased profile changes for both rail and road (whether the U-shaped bridge is elevated or at-grade with the road sunk underneath) require less excavation or fill.

The U-shaped design can minimize property takes, preserve turning movements for cars and trucks, cost much less to build than below-grade solutions, and tread more lightly through built-up neighborhoods than a conventional (box beam) viaduct or split-grade separation.  U-shaped bridges are ideal for grade separation in dense areas like the peninsula.

Alternatives Analysis Analysis, Part 1

This post is the first in an open-ended series, picking through the recently-released preliminary alternatives analysis. The AA is a voluminous document with plenty of material to be dissected over the next several months, in no particular order.

The Station Access Fallacy

Section 4.1.2 of the Alternatives Analysis discusses track and station arrangement options. In particular, it is pointed out that a key consideration in providing good station access for Caltrain passengers is to consider that the majority of Caltrain stations, and the majority of Caltrain ridership, is on the west side of the tracks. That sounds pretty good in theory... but in practice, consider the following:

• The rail corridor must be 100% grade-separated, with no crossings, so passengers may only cross the tracks via pedestrian underpasses or overpasses, never at grade.
  
• To access an island platform, or the platform on the "far" side of the tracks for at least one direction of a passenger's daily commute, every passenger will use underpasses or overpasses at least twice daily regardless of station configuration, and regardless of which side of the tracks they might live or work.
  
• Putting Caltrain on the west side of the corridor, rather than in the middle, might save each passenger a grand total of 30 feet of walking distance, far shorter than the stairs or ramps to the platform or the walk to the doors of an 85-foot rail car.
• It takes seven seconds to walk an extra 30 feet. Some hike!
  

In a 100% grade-separated corridor, it is given that station access will be limited to a handful of access points somewhere along the 800-foot length of a Caltrain platform. As long as those are well-planned (e.g. Belmont), that's perfectly acceptable. The station access "advantage" of putting Caltrain on the west side of the corridor is insignificant.

The One Percent Rule

In the AA profile plans of Appendix B, page 3, a design criterion is established: the maximum grade for Caltrain (shared use) tracks with diesel-powered freight trains is 1.0 %. The community impacts of this gentle grade, required exclusively for freight trains, were previously discussed. And yet, Caltrain's own engineering standards state that "maximum design gradient (...) for grades up to two (2)% may be implemented with the approval of the Caltrain Deputy Director of Engineering. (...) Grades exceeding one (1)% shall be limited to tangent length less than 1200 feet." Why is a more stringent standard now being applied? Certainly not for high-speed rail or Caltrain, both of which will easily handle 3% grades.

The results of this conservatism are already apparent. For example, the proposed elevated alignment through downtown San Mateo would require lowering 1st, 2nd, 3rd, 4th, 5th and 9th avenues, with extreme community impact, because (a) the grade is 0.8%, even less than the specification, and (b) there is a requirement to return to grade level before the curve into Hayward Park to avoid having a vertical curve in a horizontal spiral, a track geometry complication exceptionally allowed for (see TM 2.1.2 paragraph 6.1.7) in the CHSRA's own track design guidelines. Let's face it: the age of picks and shovels is over; in the 21st century, computers, lasers and differential GPS should make the construction and maintenance of overlapping vertical and horizontal curves a breeze, without having to demolish half of downtown San Mateo.

With things already tight as they are, the time for making judicious and appropriate design exceptions is now. Using overly-generous specifications will unnecessarily constrict the design space, inflame community opposition, and drive costs through the roof.

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.

Focus on: Atherton

If the term wealthy enclave means anything, Atherton (per capita income about 20 times population) is it.

The leafy town of Atherton abuts a mere 0.8 mile of the peninsula rail corridor, and yet may turn out to be the greatest friction point for HSR on the peninsula--and possibly anywhere in California. This is not because of technical difficulty, but rather because the town is more willing and able than most to employ legal means to get its wishes: as a first priority, a routing of HSR that is not through Atherton (namely, via the Altamont Pass), and as a last resort, the construction of a tunnel to put Caltrain and HSR completely out of sight.

In an 11-page letter sent to the CHSRA in late 2007, the Town of Atherton detailed its concerns about the HSR project. Refer to Chapter 22, p. 101 of the Bay Area to Central Valley Program EIR/EIS. The letter includes the following claims:

1. properties will need to be condemned to build HSR through Atherton;
2. partially condemned properties are subject to remainder damages "easily in excess" of the value of the entire property, to compensate owners for noise and visual impacts in perpetuity;
3. the remainder of the property may not be condemned unless it is actually needed for the project; condemnation to limit remainder damages is not sufficient to support the taking.
   

In short, Atherton warned that running HSR through town would entangle the project in an expensive and drawn-out legal battle. That battle has already begun: Atherton was a co-plaintiff in a partially successful legal challenge brought by environmental and transit activists against the above-mentioned EIR, forcing it to be revised. Doubtless this is only the beginning.

Horizontal Alignment

Despite the controversy around the issue of eminent domain, the Caltrain right of way (see maps for mileposts 27 and 28) is 80 - 85 feet wide and straight as a ruler everywhere along the 0.8 mile section that falls within Atherton town limits. In principle, this is sufficient space to accommodate four tracks, although temporary construction easements may still be required to build the grade separation structures at Atherton's two grade crossings, Fair Oaks Lane and Watkins Avenue.

Trees are highly prized in Atherton, and many large volunteer trees growing on the railroad right of way would have to be removed. Caltrain's electrification EIR identified 80 trees that would need to be removed for a two-track at-grade electrified configuration; a wider four-track arrangement would likely result in even more tree removals.

Vertical Alignment

The existing tracks slope down at a gentle (less than 0.5%) grade to the north, and cross a drainage ditch known as the Atherton Channel at Watkins Ave. The vertical alignment of the tracks through Atherton is intimately linked to the choices made in neighboring Menlo Park, which has several closely-spaced crossings that would require a consistent vertical alignment to be used through both cities. The existing alignment is shown in the figure below, created from Caltrain track survey data.


Even with the program EIR in legal trouble, project-level environmental work is continuing, with the CHSRA's preliminary design alternatives including elevated, at-grade and below-grade variations of the vertical alignment through Atherton.

An elevated alignment, as originally suggested in the program EIR/EIS and as previously studied in neighboring Menlo Park, would raise the tracks about 15 feet and lower the roads by about 5 feet. Pedestrian sidewalks would stay at grade. The tracks would have to be elevated over all six crossings in Menlo / Atherton, as shown in the figure below. Note, the 1% grade specified for freight trains considerably lengthens the northern approach to such an elevated structure.



Putting the tracks in a trench would require lowering the rails by 30 feet, to accommodate tall freight cars under overhead electrification. The solid red line in the figure below shows a trench alignment. The tracks must rise back to grade at the existing Fifth Avenue grade separation to the north, so trains, tracks, poles and overhead wires would be out of sight for only a portion of Atherton. Again, freight-friendly 1% grades are shown.


Atherton's Folly

In the analysis of alternatives process for the San Francisco - San Jose project EIR, the CHSRA requested each city to state its preferred design alternative. Atherton's position is still that the Pacheco Pass HSR routing through Atherton is ill-advised, wasteful, expensive, and adds no transportation value. Should this route be built, however, Atherton proposes a tunnel concept that is ill-advised, wasteful, expensive, and adds no transportation value. An eye for an eye...

A letter from Atherton (see p. 5) states a preference for an unusual two-level stacked tunnel arrangement, with two HSR tracks in a tunnel on the lower level and two Caltrain / UPRR tracks in a trench on the upper level, as diagrammed in the notional cross-section at right. All roads would remain at grade, and the horizontal clearances would "fit well within" the 80 - 85 foot right of way, purportedly allowing trees to be preserved. The vertical alignment for such a tunnel is shown in the vertical profile (above) as a dotted red line. Accounting for the minimum vertical clearances, the HSR tunnel would bottom out about 75 feet below grade, well below sea level. The extensive ventilation head houses, emergency evacuation stairwells and pump houses required to operate such a tunnel are not shown in the diagram.

The claimed benefits of such an arrangement include:

• No property takes and little loss of property value
• No barrier or visual impact, little noise
• Less cost than a twin-bore four-track tunnel
• Upper level usable by diesel freight trains
  

The concept was originally proposed by Redwood City resident James Jonas, who calls it the Hat Trench. Jonas was invited to present the concept to Atherton's rail committee in summer 2009.

It remains unclear who would pay for such a pharaonic tunnel structure. While the price of property in Atherton is high, it remains small in comparison to a tunnel. Less easy to quantify is the price of a view and the price of peace and quiet. Are those truly worth $10,000 per linear inch? Atherton should have plenty of MBA's to figure it out.

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

The Effect Of Heavy Freight

Heavy freight trains operate nightly on the Caltrain corridor. "Heavy freight" is characterized by very high axle loads (up to 30,000 kg or 65,000 lb) and very high mass per unit length (up to 7,500 kg/m or 5,000 lb/ft). Today, they are not much of a nuisance and few people notice them, but what will happen when the high speed rail project is built on the peninsula? HSR will bring a lot of changes, but some of them will be attributable to freight more than high speed rail. This is an attempt to tease out the specific community impacts of heavy freight trains.

The Caltrain corridor has more than 40 grade crossings, every one of which will be eliminated. Grade crossings can be eliminated either by closing them permanently, or by building a grade separation overpass or underpass, similar to the many grade separations that already dot the corridor. Usually, the easiest way to build a grade separation is to keep the railroad tracks at ground level and detour the road over or under the tracks. In some cases, though, detouring the road is not practical because of nearby residential or business frontage, or major roads and intersections.

Those situations are where the railroad tracks must be elevated above or sunk below ground level. Those situations are causing quite a controversy in the communities along the Caltrain corridor, because the HSR project's preference is for cheaper elevated structures.

Getting Trains to Climb

You might think that 125 mph (200 km/h) passenger trains would need very gentle grades and a vertical track profile that is as flat as possible--but you'd be wrong! What determines train safety and comfort is vertical curve radius (at that speed, a minimum of 6 miles or 10 km), and not the steepness of the grade. Powerful high speed passenger trains and modern EMU commuter trains planned by Caltrain can easily climb grades that are very steep by railroad standards, like a whopping 3% (i.e. 3 feet up for every 100 feet along the track). It's the heavy freight trains that have difficulty with those grades, because freight locomotives will start spinning their wheels if they attempt to drag a massive train up such a steep incline. That's why heavy freight trains are typically limited to grades of about 1% (i.e. 1 foot up for every 100 feet along the track). Grades any steeper than that require additional locomotives, shorter trains, and cost more to operate.

Grade Separation: Rail Overpass

When a grade separation is built over a road that cannot be lowered, the railroad tracks must be raised about 20 feet above the level of the road. That includes the clearance for road vehicles, plus the thickness of the bridge deck, plus the height of the rails, as shown in the diagram at right. (Trains go on the top, cars and trucks on the bottom.)

To get the rails up to that height, long sloping approaches are needed on either side of the crossing, forming an elongated hump. If you were to stand close enough to such a hump structure, you would see a retaining wall.

What will heavy freight trains do to the design of a typical grade separation rail overpass? They make the approach ramps much longer and greatly increase the area of the retaining wall that neighbors would have in their back yard, as shown in the figure at left, with the vertical scale greatly exaggerated. Walls block sight lines, are themselves ugly to look at, reduce property values, and can attract graffiti and neighborhood blight.

Compare and contrast a typical 1% rail overpass with a 2.5% rail overpass:

Parameter	1% Grade	2.5% Grade	Freight Effect
Minimum Vertical Radius	10 km (6 mi)	10 km (6 mi)	0% tighter
Height	6.1 m (20 ft)	6.1 m (20 ft)	0% higher
Length of Wall > .3 m (1 ft) High	1250 m (4100 ft)	870 m (2800 ft)	44% longer
Length of Wall > 2.4 m (8 ft) High	840 m (2750 ft)	550 m (1800 ft)	53% longer
Wall Area	4200 m2 (45,000 sq ft)	3000 m2 (32,000 sq ft)	40% larger
Fill Volume (75 ft Width)	125,000 cubic yards (12,500 truckloads)	90,000 cubic yards (9,000 truckloads)	40% larger

Exact values may vary, but the relative percentages will be very close. Smaller walls mean lessened community impact, but heavy freight trains make the walls significantly bigger.

Grade Separation: Rail Underpasses

The other possible option is to sink the rails under the road. When a grade separation is built under a road that cannot be raised, the railroad tracks must be sunk over 30 feet below the level of the road. That includes clearance for trains, high voltage overhead electrification, and the bridge deck. The resulting trench must be dug even deeper than rail level to account for the foundation of the structure.

Once again, to get the rails down into a trench, long sloping approaches are needed on either side of the crossing, forming an elongated sagging profile. Adding a twist, heavy freight trains can be up to three feet taller than regular trains, which requires digging the trench three feet deeper than would otherwise be needed, as shown in the figure at left. On a structure that's 75 feet wide and well over a mile long, that adds up to a lot of extra dirt to remove.

Compare and contrast a typical 1% rail trench underpass with a 2.5% trench underpass:

Parameter	1% Grade	2.5% Grade	Freight Effect
Minimum Vertical Radius	10 km (6 mi)	10 km (6 mi)	0% tighter
Depth of Trench	9.8 m (32 ft)	8.8 m (29 ft)	10% deeper
Length of Trench > .3 m (1 ft) Deep	1850 m (6100 ft)	1000 m (3400 ft)	80% longer
Trench Wall Area	9300 m2 (100,000 sq ft)	4600 m2 (50,000 sq ft)	100% larger
Excavated Volume (75 ft Width)	280,000 cubic yards (28,000 truckloads)	140,000 cubic yards (14,000 truckloads)	100% larger

Exact values may vary, but the relative percentages will again be very close.

Heavy freight trains double the amount of excavation needed for a railroad trench underpass. That may be fine with neighbors because the trains would stay even more out of sight, but since a trench is more expensive, an elevated solution will be preferred. That's right: where a wall might not have been required, heavy freight trains could tilt the balance in favor of an elevated wall. The Churchill Avenue crossing in Palo Alto is a great example where this trade-off may occur to the detriment of the neighborhood.

Rise and Fall

Heavy and long freight trains perform poorly on a track profile that rises and falls across each road crossing like a roller-coaster. Such undulating profiles complicate train handling and can cause hazardous slack action. That's why the grade separations in Belmont and San Carlos are built on a continuous elevated embankment that stretches for several miles, simplifying the handling of trains using the primitive manually operated air brake.

In contrast, modern, powerful electric passenger trains with advanced automatic train control systems can glide over these ups and downs without causing their passengers any discomfort. In the manner of an airplane's autopilot, the train's control software automatically adjusts throttle and braking in concert with the vertical profile of the track, which is stored in an on-board database. This capability allows considerably more rise and fall in the vertical profile, which minimizes the extent of elevated structures and thus lessens impact on communities.

Heavy freight trains tolerate very little rise and fall and will increase the impact of elevated grade separations because the stretches between grade separations may stay elevated.

Bridge Columns

On sections of track elevated over roads, or open viaducts to allow community access to both sides of the tracks, trains run on what is effectively a bridge. Bridge design depends on the load that will be carried. A good proxy for this load is the linear mass density of the heaviest train, or how much the train weighs per unit of length.

Parameter	Heavy Freight	Passenger	Freight Effect
Linear Mass Density	7,500 kg/m (5,000 lb/ft)	2,500 kg/m (1,700 lb/ft)	200% heavier
Load On a 15 m (50 ft) Span	113,000 kg (250,000 lb)	38,000 kg (85,000 lb)	200% heavier

While these values are approximate and do vary quite a bit, heavy freight trains can be two to four times as heavy as a passenger train! Throw in the usual factors of safety, and you don't have to be a civil engineer to guess what that does to a bridge design:

• Bigger and/or more concrete columns
• Shorter spans with columns spaced closer together
  
• Thicker bridge decks
• Costlier construction
  

These are not characteristics that you might call neighborhood-friendly. Heavy freight trains will make the design of graceful elevated structures nearly impossible. (For a representative attempt, visit San Carlos.)

Track Maintenance

The interaction of wheel and rail is an arcane subject that mixes black art with cutting-edge research. It is the stuff of academic journals, so we won't venture out of our depth here. Wheel and rail profiles are typically engineered as a system, in order to achieve a balance of cost, wear, fatigue, and noise characteristics. In a nutshell, as quoted from a journal article, "Lines that handle high-speed passenger trains during the day and freight traffic at night represent the most challenging conditions under which to properly maintain rail and track."

Loaded to 30,000 kg per axle (65,000 lb), freight cars can operate with wheel flat spots that measure up to 2 inches in length. The resulting thump-thump-thump is not only loud, but it wreaks havoc on tracks that are carefully aligned for passenger trains.

On the peninsula, passenger trains will always outnumber freight trains, and by a vast margin. Is heavy freight worth the extra track maintenance cost, likely to be borne by the taxpayer? Is it worth the additional noise, especially if so much more track will be elevated?

A Foreign Idea: Light Freight

While it may initially read like it, the foregoing is not a manifesto against freight. Rail is an environmentally friendly way to move freight on the peninsula, and removes trucks from highway 101. The problem isn't freight per se, but heavy freight. It is possible to operate freight trains with much lighter loads and more compact loading profiles. In other countries, such trains are routinely and safely mixed in with high speed passenger train traffic. American manufacturers like GM and GE export hundreds of light freight locomotives to those countries, so it isn't like this would require any development effort. You can pick up the phone today and order yourself a JT42CWRM (photo at right by CargoFighter), made right here in the U.S.A., and hook it up with freight cars that maybe aren't loaded quite all the way to the brim to keep the weight down. This would be more expensive to operate, but may be worth the enormous savings in capital cost (big structures, more concrete), and especially--most importantly--improved urban design and quality of life in the communities along the Caltrain corridor.

There are many ideas about how high speed rail on the peninsula should be "Done Right". For the reasons enumerated above, doing it right means heavy freight should be banished from the peninsula. The benefits are probably not worth the additional cost to communities. Such a ban would probably enjoy little support from the Union Pacific Railroad, Caltrain, and even the California High Speed Rail Authority and its coterie of engineering consultants, whose U.S.-centric cultural inertia may exceed that of even the heaviest freight train. Are they capable of thinking outside the boxcar?

Threading the San Mateo Narrows

Downtown San Mateo as previously discussed is one of the most difficult bottlenecks on the peninsula corridor, with some of the narrowest right of way anywhere on the peninsula (see mini map at right, extracted from Milepost 17 map). The following is an expanded discussion of horizontal alignment options in the downtown area.

Assuming one needs to build four tracks through this area (an assumption we will later revisit), the inescapable mathematics of right of way width and track clearances dictates that the railroad will expand significantly beyond its current boundaries. The figure below shows a cross-section elevation at Third Avenue looking "north". The building on the left is the cinema, built partially on former railroad right-of-way and completed in 2003. To the right is Railroad Avenue, providing access to several blocks of downtown business frontage. Railroad Ave becomes a residential street north of the train depot.


The cinema, along with other recently built projects such as the Main Street Parking Garage and the new train depot, have greatly restricted horizontal alignment options for the railroad. While they would only cost a few million to tear down and redevelop, these buildings are the source of considerable civic pride, so it is likely that the city will bend over backwards to preserve them--potentially at many millions of dollars of additional cost to the high speed rail project, and possibly with additional impact to residences in North Central San Mateo. Such is the sad reality of cost-benefit analysis when other people's money is involved.

The figure below shows the city's preferred vertical alignment, with the tracks relocated below grade in a four-track trench, with side clearances appropriate for safe 125 mph (200 km/h) operation. The avenues would cross the tracks on bridges.


As is readily observable, a four-track trench (the narrowest possible below-grade solution) could not be built without impacting structures on one side or the other of the right of way. Constructing the side walls of the trench would require even greater clearances than shown, approximately 110 feet by the city's own estimates--to accommodate wall tie-backs as well as temporary tracks to keep Caltrain operating during construction. More importantly, the trench obliterates Railroad Avenue, the only access to several businesses and residences. Those would have to be acquired under eminent domain.

An outright tunnel would allow continued access to Railroad Avenue, along with exciting new land uses on top of the tunnel. However, a tunnel isn't just a trench with a lid: it requires a vertical divider for fire safety and to support the roof, which further increases the side clearances. (The reasoning behind the resulting dimensions was discussed in the Joy of Tunnels.) Building an underground station would consume even more space for platforms, stairs, escalators and elevators, as will be shown later. The figure below shows how a tunnel compares to the available space: it simply won't fit without causing even greater impact than a trench.


About the only option that is possible to construct (a) without "taking" several buildings and (b) without permanently removing Railroad Avenue and its frontage is an elevated viaduct. The diagram below shows what such an elevated might look like. It could be built in halves, in order to keep Caltrain operating during construction. While an adorable little sketch by city staff (reproduced at right) shows a single concrete column supporting the entire four-track bridge deck, it is likely that seismic codes and the requirement to support massive freight trains would lead to four rows of columns, placed directly under each track. Parking is probably the only reasonable use for the concrete forest resulting underneath. The ambiance would be just like other parking garages in downtown--and might even replace other parking structures entirely, freeing up those locations for redevelopment. Driveway access to Railroad Ave businesses could be preserved.


The elevated option is also likely to be far cheaper to build than a trench or tunnel: it involves about the same amount of concrete, but far less earth moving or road closure logistics. Furthermore, an elevated does not require the permanent closure of several residential cross-streets north of downtown, as contemplated in Focus on San Mateo. Despite the visual blight and noise, look for this alternative to be ultimately favored by the California High Speed Rail Authority... and possibly also by the city, once all the trade-offs are fully understood. While the elevated may not be a desirable solution, on the whole it may be the best solution.

Station Placement

The foregoing musings do not take into account the configuration of the downtown San Mateo train station. By far the most important consideration is the location of Caltrain platforms--both their location with respect to the tracks (outside platforms vs. island platform), as well as their location along the tracks. Recall that the new depot was squirreled away to the north of First Avenue, on the outskirts of downtown, to minimize the impact of lowered grade crossing gates on rush hour traffic. If the tracks are grade-separated and grade crossings are eliminated, this concern evaporates, enabling some options for a more centrally located station closer to 3rd and 4th Avenues, which form the main east-west artery of downtown San Mateo. Such central locations would be far more accessible for both pedestrians and motorists.

In a four-track scenario, the resulting station widths are shown in the diagram below, not including the width of any ramps, stairs or escalators that might be required to access the platforms. These widths bear a direct relationship to the horizontal alignment of the tracks, since the station will be constrained on at least one side by existing structures.

The island platform requires about 6 feet more width than the outside platforms, and the tracks sit 23 feet further apart. The CHSRA might use this as an excuse not to implement island platforms, despite their significant operational advantages.

Let us consider the below-grade option favored by the city, with the station remaining at its current 1st Avenue location. The existing station is shown below in a cross section at 1st Avenue looking "north":

A below-grade station would be built in a trench, with 1st Avenue on an overpass. For all the talk about San Francisco's Transbay "train box", San Mateo's very own train box would be nothing to sneeze at, as readily observed in the following diagram.


Whatever horizontal and vertical location is ultimately selected, none of these four-track station options will fit in downtown San Mateo without very significant property impacts. So you might consider...

Solutions with Three Tracks

So far, we have assumed that four tracks would be absolutely necessary throughout downtown San Mateo, with potential property impacts that go along with that. In practice and with a little bit of creativity, the envisioned levels of Caltrain and HSR service could be achieved on just three tracks, by consolidating the two southbound tracks for a brief stretch through downtown. The goals of such an approach are:

• To reduce the property impacts to downtown businesses and residents by minimizing excursions outside the existing right-of-way
• To increase the range of configuration options for the downtown Caltrain station, for example an island platform that maximizes station access from 3rd and 4th Avenues
• To reduce property impacts along the narrow right of way in the North Central neighborhood, immediately to the north, such that residences do not have their driveway under an elevated.

Naturally, such real-world engineering involves compromise. The drawback is that local and express trains must all share the same southbound track through downtown. Scheduling trains around this operational constraint involves coordinated HSR and Caltrain timetables, which can probably be done reliably because all southbound trains originate from nearby San Francisco and are unlikely to build up significant delays in the space of just 17 miles. (The northbound tracks do not benefit from this proximity to a terminal, and would be difficult if not impossible to schedule reliably; for example, a delay in Bakersfield could later result in a northbound conflict at San Mateo. That's why two northbound tracks are still required.)

Two of the most interesting three-track configuration options are shown in the figure below (linked to annotated PDF file), as designed by Richard Mlynarik. Both assume an elevated, for the reasons described above, and stay confined to the existing right of way between Monte Diablo Ave and the San Mateo Creek to reduce impact to residences along those blocks. There may be more design options with three tracks, but these two convey what is possible.
Option 1 is a three-track station with outside platforms. This can be built either just north of the parking garage and cinema, at the existing location of the San Mateo station, or just south of the offending buildings. The southbound track skirts the cinema as tightly as possible. The northbound platform is built over Railroad Ave, which complicates access by ramps, stairs, escalators or elevators. Railroad Ave would have to be shifted underneath the elevated to free up room under the platform, and station access might interfere with business frontage.

Option 2 is a better three-track station with a central island platform built over Third and Fourth Avenues. The same layout from the PDF file is overlaid on an aerial photo below.


The central island platform enjoys easier access from below, since stairs and elevators would have ample space to touch down under the elevated, with direct pedestrian access from both sidewalks of 3rd and 4th Avenues. It doesn't have to be an oppressive structure: it could look like this amazing photo of Amsterdam's Bijlmer station, a model of pedestrian access.

The difficulties in downtown San Mateo will be great, but so is the potential for an elegant solution that better integrates the station with the city.

Focus on: San Mateo

The city of San Mateo was incorporated in 1894, 30 years after the railroad began operating. Along the 4.5 miles of rail through the city, there are today three Caltrain stations, two of which (Hillsdale and San Mateo) are Baby Bullet stops. The three stations in San Mateo generate greater combined Caltrain ridership than San Jose, a city with ten times San Mateo's population.

San Mateo is among the most treacherous areas on the peninsula to expand to four tracks for high speed rail because the existing Caltrain tracks run through dense residential neighborhoods and downtown blocks where the available right of way width is significantly less than 100 feet. The city is a "ground zero" of future grade separations: it is home to one-fifth of the grade crossings on the entire peninsula rail corridor (9 out of 46). To improve safety and traffic circulation, the city has long had plans to grade-separate all of its rail crossings; high speed rail will only hasten this process. The San Mateo County Transportation Authority has been carrying out a series of preliminary grade separation footprint studies in support of these plans.

San Mateo finalized a Rail Corridor Transit-Oriented Development Plan in April 2008, covering the vicinity of the Hillsdale and Hayward Park Caltrain stations and including the re-development of the Bay Meadows racetrack site.

Station Area and Downtown

The San Mateo Caltrain station was rebuilt in 1999-2000 to alleviate auto traffic congestion. The new $11 million station with underground parking (photo above by ibison4) replaced a sparse older station a few blocks to the south. Every time a train stopped at the old station's center boarding platform between 3rd and 4th Avenues, auto traffic on 2nd through 5th Avenues was paralyzed, exacerbating rush hour congestion.

With some foresight, albeit a bit fuzzy, the new station's underground garage and surrounding structures were reportedly built so as to allow the tracks to be relocated underground. This would not only grade-separate the tracks through town, but also accommodate a future BART subway, as was envisioned in the late 1990s while construction of the SFO extension was underway.

Plans change.

The problem is now this: the new station building and underground parking encroach on the railroad right of way and do not leave the necessary clearance for four tracks, as likely required for Caltrain and HSR, whether at, above, or below grade. Worse, a couple of blocks south of the station, San Mateo's new downtown cinema and Main Street parking garage were completed in 2003 and encroach on what was once railroad right of way, leaving just 50 - 60 feet for the tracks (see Caltrain right of way map).

There will be no easy or cheap solutions to these constraints. In discussions about a preliminary grade separation footprint study for downtown, city staff makes the following key observations:

• The vertical alignment of all the downtown rail crossings must be consistent, since their close spacing does not allow sufficient space for rail grade changes;
• Any grade separation alternatives with the tracks at grade or near grade is infeasible because of the need to lower or raise downtown streets in a manner that severely impacts frontage on both sides of these streets;
  
• The two remaining vertical alignment alternatives leave the streets at grade, with the rails either fully elevated or underground--the latter being the city's stated preference;
• The right of way required to build a four-track underground trench is 110 feet wide, far more than the 50 - 60 ft available;
  
• Moving the horizontal alignment of the tracks to the east (with impact to Railroad Ave and frontage) is preferable to impacting the new train station, Main Street parking garage and downtown cinema;
• The underground alignment presents significant technical complications, with residential property impacts just north of downtown where the tracks would ramp down, possible street closures, as well as the technical difficulty of crossing San Mateo Creek underground.

While no decisions have yet been made, and despite the city's stated preference for a depressed alignment, the elevated alignment may present the least physical impact to property adjoining the tracks, although the visual impacts are worst. The city is considering options to mitigate the Berlin Wall effect, including building the track on a viaduct instead of retained fill. Contrary to San Mateo's official preference, the California High Speed Rail Authority shows an elevated track profile with 15-foot embankments through San Mateo in their program EIR/EIS; this may or may not be the preferred alternative once they complete the project EIR/EIS.

The issue of track alignment through downtown San Mateo is discussed in much greater detail in Threading the San Mateo Narrows. That discussion includes diagrams showing various track configuration options such as the elevated shown below.
For more details, read all about Threading the San Mateo Narrows.

North Central San Mateo

North of downtown, the tracks curve through dense residential blocks on right of way that ranges from 60 to 90 feet wide, less than the ~75 feet required to run four tracks on a retained embankment, and certainly less than the ~110 feet required to excavate a trench or tunnel. The tracks cross four residential streets (Poplar, Santa Inez, Monte Diablo and Tilton avenues) on low-clearance bridges that have long been slated for refurbishment.

The key question for downtown and the North Central neighborhood will concern the vertical alignment of the tracks. The close proximity of these residential blocks to downtown, combined with the gentle track gradients required for freight trains (yes, freight trains), will require that these areas be considered as one.

Vertical Alignment Considerations

The vertical profile of the existing tracks in San Mateo is shown in the figure below. This figure was created from Caltrain track survey data, with the vertical scale greatly exaggerated. The grade level of cross streets is estimated from the known vertical clearance at each location; the level of creeks is likewise estimated.


We make a few assumptions (for more background on where these came from, read about The Shape of Palo Alto):

• Vertical track radius is constrained to a minimum of 10 km
• Gradient limit of 1 to 1.5% for freight trains, 2.5% for passenger trains
• 20-foot clearance from underpass road surface to top-of-rail (to clear trucks)
  
• 30-foot clearance from overpass road surface to top-of-rail (to clear freight trains)
  
• Tracks must be close to level for 750 feet north of First Ave, for Caltrain platforms
• Tracks are elevated at Peninsula Ave., an area with adequate clearances and commercial frontage that would favor this minimum-cost solution.
  

Scenario #1: track elevated throughout. With a 1% gradient limit and a 10 kilometer vertical radius constraint, this is what San Mateo would look like. We assume each road is depressed by 5 feet (something that can be done with little impact to adjoining frontage), with the rails raised by 15 feet. It is likely that a viaduct structure would replace the existing embankments, possibly making room for a rebuilt Railroad Ave. All vehicle height restrictions in North Central would be removed. Worth noting, the elevated alternative does not require the closure of any crossings, unlike depressed alternatives.


Scenario #2: trench through downtown. To shorten the sloping approaches and reduce the depth of the trench, we assume each road is raised by 5 feet (something that can be done with little impact to adjoining frontage), with rails depressed by 25 feet. Even this 25-foot trench penetrates below the water table and will require constant pumping to keep dry. With the 1% gradient limit desirable for freight trains, this design would require the closure of Villa Terrace, Bellevue, Poplar, Santa Inez, Monte Diablo and Tilton avenues, unless those streets were either raised or depressed with considerable impact to frontage on either side of the tracks.


Scenario #3: trench through downtown, with steep approaches. With a less stringent gradient limit just a shade over 2%, difficult for freight trains but easily handled by high speed trains and Caltrain, the approaches to the trench are much shorter. This allows underpasses at Villa Terrace, Bellevue and Poplar and reduces the need to close cross-streets. Santa Inez, Monte Diablo and Tilton would likely still be closed.


Scenario #4: tunnels. While this alternative will no doubt be studied by the CHSRA, it is unlikely to be implemented due to a host of disadvantages, not the least of which is the astronomical cost. The sloping approaches to a tunnel diving under downtown are likely to present even greater interference with cross-streets than the depressed trenches described above.

Whatever alternative is ultimately favored, one must keep in mind that the biggest constraints on the vertical alignment of the tracks come from freight trains, which don't handle steep grades well and require very high vertical clearances. The more nimble electric trains used by HSR and Caltrain would easily handle steep gradients up to 2.5%, and would require about 3 feet less vertical clearance. In short, freight trains may have a direct impact on San Mateo neighborhoods.

Southern San Mateo

The southern half of San Mateo is an area currently slated for extensive re-development. It does not have nearly as much access across the tracks as northern San Mateo, and the available right of way is far less constrained, generally greater than 100 feet (see maps for mileposts 18, 19 and 20). The area encompassing the Hayward Park and Hillsdale Caltrain stations (and the former Bay Meadows race track) is slated for redevelopment as described in San Mateo's Rail Corridor Transit-Oriented Development Plan.

Hayward Park includes a reverse curve in the tracks (curving right, then left). The northern curve at milepost 18.8 has a radius of just 1100 meters, good for about 95 mph. This curve made #5 on our list of Top Ten Worst Curves on the peninsula. While it was already flattened by shifting the tracks 20 feet westwards in the year 2000, this curve may need to be straightened some more so that high speed trains don't need to slow down as much in this area. This may not please residents of South Boulevard.

The Hayward Park Caltrain station was rebuilt in 2000 and moved slightly to the south of its former location. The original station provided convenient pedestrian access across the tracks at 16th Ave; the City is now considering a new pedestrian underpass at this location to restore the access that was lost after the move. The new Hayward Park station was built for three tracks, although it currently has only two tracks. The southbound platform already includes a cut (see photo at right) allowing it to be trimmed back to make room for a third passing track. Whatever the original intent of this configuration, the station will likely be entirely rebuilt when high speed rail comes through town.

The Route 92 overpass (actually two side-by-side bridges, seen in the background of the photo) provides ample clearance for four tracks.

The Hillsdale Caltrain station is already planned for relocation to the site of the former Bay Meadows station, and will be located between newly constructed grade separations at 28th and 31st avenues, connecting the west side of El Camino to the newly developed Bay Meadows area. The tracks will be elevated over 25th, 28th and 31st, linking up to the existing grade separation at Hillsdale Ave. These long-standing plans by the Caltrain JPB and the City are unlikely to be altered by the HSR project, except for quadruple tracking; for a detailed description, refer to Chapter 4 of San Mateo's Rail Corridor Plan. The resulting vertical profile is shown in the diagrams above.

South of Hillsdale, the frontage along the east side of El Camino Real is already owned by Caltrain, Samtrans or Union Pacific; while businesses on that narrow strip of land will likely be displaced, plenty of land is available for expansion of the tracks.

San Mateo promises to be one of the biggest design challenges on the peninsula. The CHSRA certainly has its work cut out for it, with a 50-foot right of way threaded through dense city blocks surrounded with residential neighborhoods, with a creek thrown in for good measure.

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