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.
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.
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.