Metro’s stainless steel future – Rosslyn

As the construction fencing starts to come down around the second entrance to Rosslyn Station, you can now see the future aesthetic for Metro infrastructure. Lots of steel and glass, but little of Metro’s original materials: concrete, tile, and brass.

Elevator-only second entrace to the Rosslyn Station. Photo by the author.

Elevator-only second entrance to the Rosslyn Station. Photo by the author.

The three elevators descend to a new mezzanine adjacent to the existing mezzanine. More renderings of the project are available at Arlington County’s website.

Cutaway of the Rosslyn Station second entrance. Image from Arlington County.

Above ground, the elevators emerge in a completely different structure across the street from the existing entrance. The separation between the two avoids the discord between Metro’s current embrace of stainless steel and the system’s historic colors and materials. Even though this project represents an addition to an existing station, the construction is almost entirely outside of the existing station shell. Unlike the proposed Bethesda renovation, the Rosslyn project thereby avoids the conflict between the old and new palates.

New Rosslyn Station entrance pavilion. Photo by the author.

As the Metro system has expanded, it’s also picked up architectural variety. Even during the build-out of the original Adopted Regional System, the station architecture varies from station to station, depending on age and the construction methods. All of the ARS stations used the same palate of materials, despite the variety in design. Additions beyond the ARS (NoMa infill station and the Largo Extension) feature a different look than other above-ground stations; the Silver Line to Dulles will feature an entirely different architectural vocabulary.

Speed, urban transportation and geometry heuristics

Following up on this previous post, noting that “transport is mostly a real estate problem” – a few quick heuristics on cities, speed, and space:

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Regarding speed:

Speed requires space; faster travel occupies a larger area than slower travel.

Speed alters our perception of space. Faster travel makes large things seem smaller (hat tip to this post from GGW for the links). The properties of the space affect how we use it and what we percieve it to be; wider roadways within streets get used for faster travel.

Regardless of speed, cars require large spaces relative to their capacity. Even when parked (v = 0), cars require lots of space. By extension, building cities around requires a completely different spatial footprint.

Regarding space:

There is a strong tendency for cities to devote about 25% of their land to streets. Street networks are for mobility, but also for access to land. Devoting too much land to streets is wasteful; too little makes it difficult to unlock the value of the land within a city.

Intersection density correlates with walkability and connectivity; wider instersection spacing correlates with the higher speed travel of cars.

Consider the relationship between the density of the network (intersection density), the tendency to use ~25% of land for streets (regardless of the density of the place), and street width on the kind of transportation.

Simply requiring some minimum intersection density for new developments via a code will still be subject to ‘gaming’ and open to unintended consequences.

Street networks are sticky and tend not to change once established; the cities that grow around them are path-dependent. However, transport networks can be layered – subways travel fast, require space and grade-separation, but deliver passengers to the street grid as pedestrians; just as freeways are layered above/below streets and deliver high volumes of cars to local streets.

While the physical space allocated to streets tends not to change, the use of that space can change a great deal over time.

A visual survey of selected elevated rail viaducts: part 5 – Vancouver and Tysons Corner

Pulling together some suggestions from the comments of the series prologue, part 1, part 2, part 3, and part 4…

Vancouver: Alon Levy reminds us to look at Skytrain’s viaducts in Greater Vancouver. Skytrain represents the kind of future for rapid transit this series means to investigate, baked right into the system’s name: expansion of transit aboveground, rather than under.

Skytrain’s fully automated, fully grade-separated network includes underground transit in dense areas and along narrow streets, but makes extensive use of elevated rail along wide streets and freight rail rights of way (active and dormant). Jarrett Walker discusses the virtues of the Skytrain system, above and beyond that of regular rapid transit – with the automated trains allowing for increased frequencies without increasing the associated operating costs:

Light rail is wonderfully flexible, able to run onstreet with signalized intersections, and across pedestrian zones, as well as in conventional elevated or underground profiles. Driverless metro must be totally grade-separated, which in practice usually means elevated or underground. SkyTrain got its name because the original lines were mostly elevated, though the newest, the Canada Line, has a long underground segment.

The system’s most recent addition, the Canada line, features elevated sections for the two southern branches – one that goes to the airport, and one to redevelopment areas in Richmond.

Skytrain Canada Line viaduct over a sidewalk in Richmond, BC. Image from Google Maps.

By placing the line alongside the roadway when next to surface parking, they’ve managed to expand the sidewalk without imposing too much on the pedestrian environment. The benches and trellises around the columns are a nice touch. The single guideway for both tracks helps minimize the bulk of the guideway. When those parking lots are redeveloped, they can front on the sidewalk without overshadowing it.

Aerial view of Skytrain in Richmond, BC – showing redevelopment of suburban land uses. Image from Google Maps.

Older elevated guideways in the system include center running sections through suburban land uses:

Center running elevated Skytrain line. Image from Google Maps.

Some sections run along alleyways.

Aerial of alley-running aerial alignment. Image from Google Maps.

Other sections combine separate and adjacent right of way with berms and greenery:

Elevated rail shielded by trees. Image from Google Maps.

Center-aligned side-platform station. Image from Google Maps.

Vancouver provides lessons for rapid transit expansion in that it uses elevated rail through suburban-style rights of way.

Tysons Corner:

The Silver Line extension of Washington’s Metro system to Tysons Corner follows some of same principles as Skytrain, but without the same quality of execution. Part of the challenge is the landscape (Tysons features some wider roads than Richmond), and part is in the transit infrastructure.

View of Tysons guideway along Route 7 in Tysons Corner. Image from the author.

Tysons tunnel proponents claimed that a Spanish-style large-bore TBM could tunnel through Tysons at lower cost than elevated rail. The authorities rejected this argument after some study, and with good reason. It may be true that the Spanish can build transit tunnels extremely cheaply (they can!), but it makes little sense to compare American elevated costs with Spanish tunneling costs.

Instead, it’s illustrative to look at relative costs of construction types. If the contractors could’ve built tunnels at the same cost as the Spaniards, they could’ve built elevated rail for less money, as well.

View of Silver Line Metro, looking back towards Greensboro Station. Image from the author.

Along Route 7, they’re starting to install sidewalks, but the pedestrian environment is still lacking.

View of new sidewalk along Route 7, leading to Greensboro Station. Image from the author.

There are opportunities for infill development along these new sidewalks, but sidewalks adjacent to a high-speed stroads isn’t the most compelling environment. Other new transit-oriented development in Tysons isn’t attempting to turn the existing main stroads (routes 7 and 123) into nice streets, but rather add a pedestrian layer on top of the current auto-centric network.

Image from the author.

Table of contents:

More on the geometry of transportation: “Transport is mostly a real estate problem”

In June, the Urbanization Project at NYU’s Stern Center posted several graphics looking at the space devoted to transportation in our cities. As the author, Alain Bertaud, frames it, “transport is mostly a real estate problem.” That is, different transportation modes require different amounts of space to accomplish the same task.

Comparison of population/employee density and street area per person. Image from NYU Urbanization Project.

Each of the selected examples cluster around the diagonal blue line, representing an average of 25% of a city’s land devoted to streets.

Percent of land use devoted to buildings, streets, etc. Image from NYU Urbanization Project.

Two observations: the 25% pattern is remarkably consistent; as is the geometric relationship between modes of transport and the intensity of land use. The green horizontal lines show how much space a car uses at various speeds – the faster the car goes, the more space it requires. A parked car occupies 14 square meters, while one moving at 30 kph takes up 65 square meters.

The obvious corellation is between a city’s density and its type of transportation network. Cars take up a large amount of space relative to their capacity, and a transport system based on cars alone cannot support a great deal of density.

Alex Tabarrok frames this in terms of “the opportunity cost of streets.” While there is certianly an opportunity cost to various street uses, it’s worth noting that some space must be devoted for streets in order to access property. Charlie Gardner at Old Urbanist takes note that the role of streets is not solely about transportation:

In addition to their transportation function, streets can also be understood as a means of extracting value from underserved parcels of land. The street removes a certain amount of property from tax rolls in exchange for plugging the adjacent land in to the citywide transportation network. Access to the network, in turn, increases the value of the land for almost all uses. For the process to satisfy a cost/benefit analysis, the value added should exceed that lost to the area of the streets plus the cost of maintenance. (This implies rapidly diminishing returns for increasingly wide streets, and helps explain why, in the absence of mandated minimum widths, most streets are made to be fairly narrow.) For many of the gridded American cities of the 19th century, as I’ve written about before, planners failed to meet these objectives, although these decisions have long since been overshadowed by those of their 20th century successors.

Charlie also notes that many great, dense, walkable cities around the world devote about 25% of their land to streets, yet many American downtowns use a much higher percentage of their land to streets.

Some of those numbers might depend on the exact method of accounting. While Charlie’s estimate for downtown DC shows 43% of the land used for streets, DC’s comprehensive plan shows approximately 26% for the city as a whole:

Land Use Distribution in DC, from DC’s 2006 Comprehensive Plan.

The graphic doesn’t specify if the street figure refers to street right of way, or just the carriageway portion of the street, but not the ‘parking area.‘ Seattle’s planning documents also showa similar pattern: 26% of land city-wide used for streets, but also a higher percentage of downtown land devoted to streets.

Seattle land use distribution by neighborhood. Image from Seattle’s 2005 Comprehensive Plan.

The Seattle calculation looks at land devoted to right of way for streets, rather than just impervious surface.

Making better or different use of existing right of way is one thing; however, once that right of way is set, it is very difficult to change. Transportation networks awfully path dependent. Chris Bradford looks at Austin’s post-war planning and the abandonment of the street grid – path dependence in action:

Back then, “planning” chiefly meant “planning streets.” It’s a shame that planning lost that focus. The street grid that permeated Austin in 1940 is of course still with us, and forms the backbone for a number of quite livable neighborhoods.

So what happened? Developers building large, planned subdivisions (Allandale, Barton Hills) continued to add decent street networks after 1940. But the City itself appears to have gotten out of the grid-planning business not long after this map was made…

Collectively, these could and should have been platted into 40 or so city blocks. Instead, they remain two big blobs of land. The lack of connectivity funnels traffic onto South Lamar and Manchaca; impedes east-west mobility, dividing eastern and western neighborhoods; forces people to make circuitous trips to run even simple errands; and forecloses any sort of low-intensity, mixed-use development in the area. Then there’s the sheer loss of public space: South Austin should have a few more miles more of public, connected streets than it has today.

Once the street grid is set, it is very difficult to change.

A visual survey of selected elevated rail viaducts: part 4 – monorails, active uses under viaducts, and precast concrete in Puerto Rico

Pulling together some suggestions from the comments of the series prologue, part 1, part 2, and part 3…

Monorails: Always popular as a technology that can reduce the visual bulk of elevated rail, Alon Levy collected some comparisons showing that purported monorail cost benefits to be mostly illusory. But what about visual bulk? Alon makes a note of the smaller required structure:

It includes a diagram of monorail structures, which can be seen to be quite light and thin. The width of the structure from guideway to guideway is 4.5 meters including both guideway widths, and including the outside appears to raise it to 5.5. Two-track elevated conventional rail structures typically range from 7 to 10.5 meters wide.

Mumbai has monorail under construction:

Mumbai monorail, under construction. CC image from Wiki.

One long-standing example is Seattle’s monorail:

Seattle Monorail, as seen from a neighboring downtown building. CC image from Bala Mainymaran

Seattle Monorail from street level. CC image from The West End.

New York: Commenter Matthew (of Walking Bostonian) offered two photos from New York of mainline rail infrastructure. The approach for the Hell Gate bridge towers over parts of Queens:

Hell Gate bridge approach. CC image from Matthew in Boston.

Another example is from the Long Island Railroad, with retail spaces crammed underneath a viaduct in Flushing, Queens:

LIRR viaduct, Flushing. CC image from Matthew in Boston.

The LIRR shows an example of re-using the space beneath a vaiduct with retail; perhaps without the architectural glamor of the archways in Berlin or Vienna. Nevertheless, it shows the potential for re-using some of the space beneath elevated rail.

Vienna: Neil Flannagan (after looking at Berlin examples) suggested Vienna:

The Queens Boulevard and Berlin examples really seem like missed opportunities we could have had in Tysons: cheap infill retail using the bridge structure as a roof. It would reduce the barrier effect of the median, focus activity near the stations, and set an example of urban form.

This was the solution nobody was looking for because we were so set on fighting out the tunnel-versus- overground plan and trying to keep the project afloat. I certainly was guilty of believing that no viaduct could be attractive, and kept arguing for a tunnel. I was looking at the types without considering design. It’s the same trap that NIMBYs do, wanting to minimize the impact by making a building smaller, rather than better. Damn. Looking outside of the box is why Jarrett Walker is so great.

I would really take a look at Otto Wagner’s Wiener Stadtbahn. The infrastructure is pretty street-friendly. It’s also very well designed, particularly the bridge over the Wienzeile.

Some images from Vienna:

Vienna viaduct and bridge structures, with retail spaces beneath. CC image from Wiki.

Retail beneath a viaduct in Vienna. CC image from Wiki.

San Juan, Puerto Rico: San Juan’s Tren Urbano was also mentioned in the comments. Google does not have streetview images in San Juan, but a brief Flickr search for CC images turns up the following examples of the system’s elevated structures:

Tren Urbano. CC image from I Am Rob.

Panorama of the Torrimar Tren Urbano station. CC image from davsot.

Tren Urbano. CC image from Paul Sableman.

Table of contents:

A visual survey of selected elevated rail viaducts: part 3 – Els that gave Els a bad name

For more, see the series prologue, part 1, and part 2…

A look at some of the Els that gave Els a bad name:

Chicago: The city’s rapid transit system’s elevated lines are ubiquitous; the system is named for them. In the Loop, the Els run above city streets. In other parts, some Els run above alleyways or private rights of way, away from streets:

Chicago El over an alley. Photo by author.

Under the Chicago El. Photo by the author.

Intersection of Wells and Lake in Chicago. Image from Google Streetview.

Owing to both the size of the structure, the relatively narrow streets, and the enclosure provided by the buildings, the Els loom over Chicago’s streets.

Adams/Wabash Station. Image from Google Streetview.

To be fair, most of these Streetview images are from directly under the structures, while many of the others are views from the side. Part of this is due to the street width, and part due to the buildings fronting the street. If you were looking for examples of suitable elevated viaducts for retrofitting suburbia, or for less dense urban neighborhoods, this isn’t a great example. Nonetheless, as noisy and obstructive as the Els can be, you can still find light and air above the sidewalks:

Intersection of Monroe and Wabash, Chicago IL. Image from Google Streetview.

Philadelphia: The number of American cities with legacy heavy rail transit systems (meaning pre-war) is fairly limited (Boston, New York, Chicago, and Philadelphia). Over the last decade, Philadelphia reconstructed most of the Market St elevated, replacing Chicago-style structures with a single pier supporting a steel structure:

Market St El, prior to reconstruction, CC image from connery.cepeda

Market El, reconstructed:

Finishing work on the reconstructed El. Image from Google Streetview.

On the other side of Center City, the El above Front Street almost reaches from building face to building face along Philadelphia’s narrow streets:

Elevated rail above Front St. Image from Google Streetview.

Boston: Much of the post-war transit investment in Boston focused on re-arranging infrastructure, tearing down Els and replacing those lines with subways. Few elevated sections remain, such as this portion of the Green line near Lechmere Station:

Green Line El near Lechmere Station. Image from Google Streetview.

Perhaps the only reason this portion survives is because it’s directly attached to a river crossing:

Aerial view of Boston from Google Maps.

Table of contents:

A visual survey of selected elevated rail viaducts: part 2 – best practices of integrating viaducts into urban designs

Continued from the prologue and part 1… A look at legacy examples of older elevated construction precedents. Some examples drawn from this post and this thread on the archBoston forums.

Berlin: As a part of his writing about elevated rail, Jarrett Walker takes note of Berlin’s elevated rail, and the use of space beneath them:

But the Stadtbahn is something else. Completed in 1882, it runs east-west right through the middle of the city, with all kinds of urban land uses right next to it. It’s a major visual presence in many of Berlin’s iconic sites, from affluent Charlottenberg to the Frederichstrasse shopping core to the “downtown of East Berlin,” Alexanderplatz. It even skirts Berlin’s great central park, the Tiergarten, and looks down into the zoo. If you were proposing to build it today, virtually every urbanist I’ve ever met would instinctively hate the idea, and if the idea somehow got past them, the NIMBYs would devour it.

…

Yet much of it is beautiful. Most of the viaduct is built as a series of brick arches. Each arch is large enough to contain rooms, and today many of these are retail space, most commonly restaurants. These restaurants put their tables outside, sometimes facing a park but still, unavoidably, right next to the viaduct, and they’re very pleasant places to be. A train clatters overhead every minute or two, but it’s not dramatically louder than the other sounds of urban life, so it’s a comfortable part of the urban experience, devoid of menace. I could sit in such a place for hours.

Indeed, the four-track Stadtbahn cuts through Berlin on its own right of way, not in adjacent to or in the median of another street. Many streets run tangent to the elevated railway for segments, but much of the city directly abuts the railway.

Berlin Stadtbahn aerial image from Bing Maps.

By cutting through the city on a separate level and without directly mirroring the street grid, the transit network adds another layer to the cityscape. The city, both old and new (and yet to be built), has grown around the elevated rail:

Berlin Stadtbahn aerial from Bing Maps.

At the street, many of the viaduct’s archways have been turned over to retail uses, activating what would otherwise be a barrier of dead space:

View of the same viaduct from street level. Image from Google Streetview.

Jarrett’s post features a number of other images from Berlin, showing the various types of spaces the Stadtbahn creates. He closes asking if we might learn from these legacy examples in building new transit infrastructure:

Europe has some really beautiful transit viaducts, including some in the dense centres of cities. Most of them are a century old, so the city has partly grown around them. But the effect is sometimes so successful that I wonder if we shouldn’t be looking more closely at them, asking why they work, and whether they still have something to teach us about how to build great transit infrastructure.

Paris: Metro Line 6:

Paris Metro Line 6. Image from Google Streetview.

Line 6 runs down the middle of several wide streets, providing enough room for bike and pedestrian pathways beneath the viaduct, while also leaving enough space alongside for trees and landscaping. The aesthetic elements of the rail infrastructure (stone piers, steel spans) echo the architecture of the city as a whole.

Paris also has examples of old, now un-used vaiducts re-purposed as part of a vibrant cityscape:

Viaduc des Arts, Paris. Image from Google Streetview.

Above the viaduct is now an elevated linear park.

New York: In the comments of Part 1, Charlie asked about New York’s High Line. I did not initially include it, but I do think it offers an intersting example. The High Line (or what remains of it), like Berlin’s Stadtbahn, does not run directly above many streets. Also, the city grew around the infrastructure – in the High Line’s case of delivering freight to adjacent factories, that direct interaction was the very point of building the line.

Aerial view of the High Line weaving between and through buildings. Image from Google Maps.

Southern end ot the High Line, running adjacent to Washington St. Image from Google Streetview.

One particular example of elevated rail in New York both looks to the past (we don’t build ’em like we used to) but could also learn from the repurposing of the spaces created under viaducts for uses other than storage. The Queens Boulevard elevated rail line runs down the middle of a wide street, with large archways beneath the tracks – currently used for parking.

Queens Boulevard elevated rail. Image from Google Streetview.

Consider that when the line was built, the surrounding area was completely undeveloped. The city (and the roadway) emerged around the rail line, rather than cutting the rail line through an existing urban evironment (I don’t know that any single image better conveys the links between transportation, land use, and development). Meshing transit expansion into low-density areas is not just about transportation, but about re-shaping the city. Under the right conditions, it can work well.

New York has other examples of repurposing space beneath viaducts. While not specifically a transit example, the re-use of space under the Queensboro Bridge approaches in Manhattan is an example of what’s possible with some of these rail viaducts:

Queensboro bridge approach, New York. Image from Google Streetview.

Short of re-purposing the space beneath the tracks, the Queens Boulevard elevated rail allows for a perfectly acceptable kind of rail, without shadowing the streets or sidewalks below, making use of the street’s wide right of way. Alon Levy takes note:

But when there is an el about Queens Boulevard, everything works out: the street is broken into two narrower halves, with the el acting as a street wall and helping produce human scale; the el is also farther from the buildings and uses an arched concrete structure, both of which mitigate its impact.

Any other examples of older elevated infrastructure we can learn from?

Table of contents:

A visual survey of selected elevated rail viaducts: part 1 – the universe of post-tensioned pre-cast concrete

For background, see the prologue for this series.

With phase I of WMATA’s Silver Line through Tysons Corner nearing completion, we now have a better sense of the visual impact of the elevated guideways on the cityscape of Tysons Corner. Elevated rail in Tysons, given the widths of the roads it runs over/along, makes perfect sense. However, there are other examples of urban rail viaducts with more visual appeal and urban design sense than the Silver Line guideways.

Tunnels, all else being equal, would be preferable. Given the costs of tunneling (even with the promise of large diameter TBMs, Spanish-level construction costs, and other tunneling practices that could get American subway costs under control) and the reality of costs and land values means that most potential Metro expansions outside of the core will need to consider elevated rail.

Like the roads in Tysons, many potential rights of way feature plenty of room for elevated rail – if it is done well. While elevated rail in Tysons makes sense, the execution of the guideways could’ve featured better design with less visual obstruction. Jarrett Walker discusses the pro/con of elevated rail here, noting that rapid transit requires full grade separation.

For comprehensive visual documentation of the Phase I construction, I recommend Sand Box John Cambron’s blog.

Through Tysons, the elevated guideway is aligned in the center of the Route 7 roadway and alongside the Route 123 roadway. The guideways use segmented pre-cast post-tensioned box girder spans, with one box girder for each track supported by a variety of piers. Large portions of the guideway use a single pier with a large hammerhead cap to support both tracks.

Metro guideway in Tysons Corner, VA. Image from John Cambron.

Center-running guideway with hammerhead pier caps in Tysons Corner. Image from John Cambron.

Center-running guideway showing single pier supporting both tracks. Image from John Cambron.

Center-running elevated rail guideway in Tysons Corner. Image from John Cambron.

Using hammerhead pier caps increases the visual bulk of the elevated structure. A few columns integrate the pier into the guideway’s structure, providing a slimmer profile for the guideway:

Support piers integrated into guideway, reducing bulk in Tysons Corner, intersection of Route 7 and Westpark Dr. Image from John Cambron

Other aerial examples: This isn’t meant to be an exhaustive survey, but a look at a few illustrative examples of what aesthetic alternatives are available for elevated rail.

These examples are primarly from light rail and rapid transit systems relatively recently constructed; they do not represent the legacy elevated systems of Chicago, New York, and so on.

WMATA examples: Green Line, southern extension to Branch Ave. This extension of the Green line makes use of several segmented pre-cast concrete elevated structures, similar to the kind of guideway used through Tysons Corner. While the majority of the guideway crosses the green environment of Suitland Parkway, this concrete guideway has the advantage of carrying both tracks in a single structure, both minimizing the bulk of the guideway and the support piers.

WMATA Green Line guideway over Suitland Parkway. Image from Google Streetview.

Near the Branch Avenue station, as the tracks separate for the station’s island platform, each track with its own structure. North of the Branch Ave station, the two guideways are able to share a common pier without a large hammerhead cap.

WMATA guideways near Branch Ave station. Image from Google Streetview.

South of the Branch Ave station, each of the guideways feature their own piers.

WMATA Branch Ave station, looking towards Southern Ave station. Image from Google Streetview.

Seattle Link light rail: Sound Transit’s Link light rail could be called a pre-metro, thanks to extensive grade separation combined with the repurposing of Seattle’s downtown bus tunnel. It features a large amount of elevated rail (with the requisite views along the way) also making use of pre-cast concrete segmental bridges used in Tysons.

Sound Transit elevated rail. Image from Google Streetview.

Support piers feature more detailing than in other examples, with the shape of the pier caps matching the profile of the pre-cast box girder segments. Longer spans introduce subtle arches to the guideway, adding a bit of elegance to the concrete structures. The guideway also makes use of metal railings rather than soundwalls next to the track, reducing the visual bulk of the structure.

Sound Transit elevated rail over Duwamish Waterway. Image from Google Streetview.

View of elevated guideway along arterial street. Image from Google Streetview.

Seattle’s light rail pier in roadway. Image from Google Streetview.

On lower traffic roads, Seattle’s light rail includes several examples of dropping a pier in the middle of a roadway, rather than using a bigger straddle bent.

Bay Area: BART’s elevated guideways don’t appear to use the same construction methods as WMATA, but have the same concrete aesthetic. In this case, the guideway runs adjacent to a residential street, while the area under the guideway is used for greenspace and a biking/walking trail.

BART viaduct, with greenway underneath. Image from Google Streetview.

San Jose: VTA light rail features several grade separations. VTA isn’t exactly the kind of agency you’d want to emulate (good discussion here from Cap’n Transit). However, the basic geometry of their elevated track segments shows what kind of visual impact you can have with center-running elevated rail along wide roads. In this example, center-running light rail turns into an elevated alignment down the center of a wide arterial street:

VTA light rail elevated track above the center of an arterial street. Image from Google Streetview.

VTA light rail aerial station in the center of the roadway, with pedestrian access via normal sidewalk and crosswalk. Image from Google Streetview.

Since VTA uses proof of payment, faregates aren’t necessary and allows for a minimal ‘mezzanine’ area for fare control. Contrast that to the visual bulk of the rather large mezzanines in the Tysons Corner WMATA stations.

Aerial view of the same VTA station. Image from Google Maps.

Any other examples to consider?

Table of contents:

A visual survey of selected elevated rail viaducts: prologue and index

Under the Chicago El. Photo by the author.

Elevated rail has a bad name; urban rapid transit requires full grade separation. These two facts are inconveniently opposed to one another. Is there a future for elevated rail in urban and suburban areas? Cheaper elevated construction opens the door for more rapid transit expansion in our regions, but only if the real negatives of elevated structures can be overcome.

Some background reading:

Grade separation is the critical element for rapid transit. Jarrett Walker highlights the technical reasons and advantages to full grade separation: speed, frequency, and reliability.
Richard Layman presumes urban elevated rail isn’t workable in this post title, asking us to remember why we build transit underground. He notes that the real value for transit is in the grade separation.
Jarrett Walker again writes about the tensions and interaction between good transit (speed, frequency, reliability), good urbanism and urban design (streetscapes, aesthetics, design), and the demand for cost-effective infrastructure, using Honolulu’s planned rapid transit project as an example.
Yonah Freemark looks at the same case of Honolulu here – construction is currently stalled as legal battles play out.
Discussion at archBoston on how we’ve done better with integrating elevated structures into the cityscape in the past; a similar survey from the CA HSR blog.
Alon Levy on conditions to make elevated rail work: branding it as something new to avoid the visual associations with Chicago-like structures; ensuring that new structures are aesthetically pleasing; and focusing on wide rights-of-way with room to build without overshadowing the street.
Keep Houston Houston on the “limits of cute transportation.”

In addition to mitigating the negatives from elevated structures, there’s also the matter of emphasizing the positives of transit. Considering that a great deal of the public opposition to elevated structures is likely now framed by thinking of freeway overpasses and flyovers rather than Chicago-style Els, it’s worth considering the relative capacities of each. Market Urbanism writes about benefits vs costs, citing Robert Fogelson’s Downtown:

Elevated rail lines are far smaller in footprint than elevated highways, and although highways may have been quieter than rail lines a century ago (though I’m not sure if this is even true), the technology has surely shifted in rail’s favor with regards to noise. And even if the technologies were equally obtrusive on a per-mile basis, you much fewer less elevated rail miles to transport the same amount of people as with an elevated highway – perhaps even almost an order of magnitude less.

From Downtown:

John A. Miller was one of the few Americans who was puzzled by the construction of elevated highways. “Elevated railways with a capacity of 40,000 persons per hour in one direction are [being] torn down,” he wrote in amazement in 1935, “while elevated highways with a capacity of 6,000 persons per hour are being erected.”

Thankfully, we appear to no longer be considering urban highway expansion. Urban rail expansion shouldn’t be off the table, however, thanks to the ill-advised highway expansions of the past.

In a brief series of posts, I wanted to take a visual survey of elevated rail precedents around the world. My work here is by no means exhaustive; I welcome any feedback you might have.

Index of posts in the series:

Prologue
Part 1 – The universe of post-tensioned pre-cast concrete
Part 2 – Best practices of integrating viaducts into urban designs
Part 3 – Els that gave Els a bad name
Part 4 – Monorails, active uses under viaducts, and precast concrete in Puerto Rico
Part 5 – Vancouver and Tysons Corner
Part 6 – Hong Kong

Hyperloop: lots of hype for something that doesn’t yet exist

The last few days have seen lots of pixels spent on Elon Musk’s Hyperloop concept – and I couldn’t resist chiming in. It’s a fascinating idea, but far from an actionable one. Musk seems to have put a lot of thought into dealing with some of the technical hurdles of previous vac-train ideas, but rather than put these forward in the marketplace of ideas, he has taken to bashing California’s high-speed rail project instead.

Musk’s supporters take his endorsement seriously, with many openly hoping that the Hyperloop will kill off high speed rail, even though high speed rail is a proven technology operating around the world, while the Hyperloop exists nowhere but as a sketch on the back of a cocktail napkin. It’s a testament to the power of an idea, but it also shows how easily we can fall for bad ones.

A few base criticisms of the idea come to mind: the Hyperloop is not necessarily a superior technology for the problem it seeks to solve (travel between SF and LA); technology does not change the basic geometry of a transport system (and it must respect the basic tolerances of the human body); a fancy new technology is not necessary for innovation and improvement; and every strain of common sense indicates that the cost projections for this thing are pulled out of thin air (where else would they be pulled from?)

Solving SF to LA: Musk’s proposal does not actually serve either Los Angeles or San Francisco. The ‘last mile’ problem in any urban transportation system can be really challenging and really expensive. Musk simply avoids the problem by terminating in Sylmar and the East Bay. The hyperloop’s faster speed is irrelevant to the real question: travel time. Maximum speed alone tells you little about travel time, just as the Acela Express (as limited as it is) easily takes the majority of air/rail traffic between DC and New York, despite slower vehicles and longer trip times – the benefits of easy boarding (Penn Station be damned), downtown station locations, and relatively low security requirements make for a better overall value.

Musk didn’t just pitch the hyperloop as a way to make evacuated tube trains feasible, he pitched it as a way to make SF-LA travel work better than the CHSRA can. His pitch is part technical concept and part policy proposal, and the policy elements fall short.

Technology does not change geometry: This is true for driverless cars and for hyperloops. The type of technology used doesn’t change the technology’s purpose – moving people from place to place. Since the hyperloop is essentially a transit service, it still must obey the same geometric rules as all other modes, the ones that govern capacity, headway, throughput, etc. Musk ups the speed for his concept, but his own proposals show a very low overall capacity – and even those estimates seem optimistic given his assumptions on safety margins and safe distances between pods. At GGW, Matt Johnson compares capacities of different modes of transport:

According to Musk, pods would depart LA and San Francisco every 30 seconds during peak periods. Each pod can carry 28 passengers. That means that under the maximum throughput, the Hyperloop is capable of carrying 3,360 passengers each hour in each direction.

For context, a freeway lane can carry 2,000 cars per hour. A subway running at 3 minute headways (like the WMATA Red Line) can carry 36,000 passengers per hour. The California High Speed Rail, which this project is supposed to replace, will have a capacity of 12,000 passengers per hour.

Technology also does not magically change the tolerances of the human body (save for science fiction inventions like inertial dampers). Musk is selling speed, and his assumptions on acceleration are more akin to a roller coaster than rapid transit. From The Verge:

According to Powell, that’s a problem: “In all our tests, we found people started to feel nauseous when you went above 0.2 lateral Gs.” The closest comparison would be roller coasters, which usually top out around half a G — but the Hyperloop wouldn’t just peak at 0.5; it would stay there for the duration of the curve. The result would be well short of blackout, which most studies peg around 4.7 lateral Gs, but it would make the Hyperloop challenging for the faint of stomach.

Others have noted the lack of bathrooms in the Hyperloop pods. It would seem that the roller-coaster analogy is apt, as roller-coaster operators don’t want you leaving your seat in the middle of the ride, either. It’s not safe.

Other opportunities for innovation: Much of the praise for the Hyperloop seems to be based solely because it’s something new and exciting (and people take Musk’s cost claims at face value); part of it also seems to be a lack of faith in high speed rail. The desire for something new ignores the reality that most innovation is incremental; it also ignores the power of transportation networks and the value of connecting to something that already exists.

Matt Yglesias looks at alternative transportation improvements that would seek to solve the same problem (decreasing LA-SF travel time) by tackling some low-hanging fruit, rather than inventing new technology. Yet, people don’t want boring improvements in processes. Molly Wood at CNet just wants to believe in technology, noting that practicality is for cynics:

I refuse to keep accepting that until our cynically imagined dystopian future comes to pass. As justone alternative to the essentially already-failed high speed rail project, we now have a detailed plan for a high-speed transit system that could cost as little as $6 billion to build and, by the way, would be solar powered and infinitely more environmentally friendly than the dirty, diesel-powered rail project. It seems obvious that Musk is unveiling this plan ahead of the ground-breaking for the rail project in what is hopefully a successful attempt to stop the monster from ever being born. So get over the sunk cost fallacyof the California “high speed rail” and move on to a better solution.

All we citizens of California, and the Internet, and the world, have to do is believe that this technology is possible. Then those of us with the lucky happenstance of representative government should use it like it’s supposed to be used, and demand better. Instead we tend to give up and talk about great ideas that will never happen — or worse, tear those ideas down as silly, unrealistic, or impossible.

Leaving aside Wood’s unquestioning acceptance of Musk’s cost estimates f0r a technology that doesn’t exist (even in prototype!), and the obvious mis-information about HSR’s power source, this kind of technological evangelism is fine for entrepreneurs (as Alon Levy’s post title argues), but it makes for bad public policy. If Wood had the same faith in HSR, and was willing to look over HSR’s faults with the same starry-eyed gaze, then HSR wouldn’t have the PR headaches that it does.

Slate’s Will Oremus is similarly infatuated with the concept, but at least he realizes the steps required for the Hyperloop to prove itself worthy:

Wise or not, California is unlikely to drop its plans just because one rich guy has a light bulb over his head. On the other hand, if Musk does build a demonstration line, and it’s faster, cheaper, more energy-efficient, and requires seizing less private property than laying down train tracks, a change of plans might start to sound pretty appealing. That’s a lot of ifs—but so is every big idea, in the beginning.

Indeed, that is quite a few ‘ifs.‘

The odd thing is, despite all of the references to Musk as a master innovator, it’s worth noting that all of Musk’s companies and products, as daring and inventive as they are, still are just incremental improvements over existing technology. Tesla did not invent the electric car and certianly did not build the massive network of auto-centric transport. SpaceX did not invent rockets. SolarCity did not invent solar power. Each company offer incremental (though meaningful) improvements on existing concepts and products.

At the risk of stating the obvious: Hyperloop is not an incremental improvement for an existing technology. Existing technologies have the benefit of linking into existing networks. Tesla’s cars can use regular roads and charge through regular outlets. High speed rail can use existing tracks and rights of way to get into city centers.

This is not a serious cost estimate: Musk is not just proposing a new technology, he is also offering an explicit critique of high speed rail. Plenty of observers have critiqued the CHSRA’s track record to date; comparisons to HSR best practices in planning, construction, and operation from around the world are not favorable. Nevertheless, this does not make the Hyperloop’s assumptions any more realistic. And, if the state were to buy the hype, the Hyperloop would likely see even wilder cost overruns – putting it on the same trajectory as Seattle’s failed monorail transit system.

Alon Levy takes a closer look at some of Musk’s cost estimates, and finds that most don’t even pass the smell test:

This alone suggests that the real cost of constructing civil infrastructure for Hyperloop is ten times as high as advertised, to say nothing of the Bay crossing. So it’s the same cost as standard HSR. It’s supposedly faster, but since it doesn’t go all the way to Downtown Los Angeles it doesn’t actually provide faster door-to-door trip times.

At a broader level, consider what Musk is claiming: that a system of precisely aligned and machined de-pressurized tubes could be built for a fraction of the cost of infrastructure with a similar footprint. Musk is proposing that the pods would clear the tube walls by fractions of an inch, compared to much larger machined tolerances for lower-speed modes of travel:

The biggest question mark is the tube itself, which has emerged as the most genuinely unprecedented part of the plan. By enclosing the track, the Hyperloop is able to sidestep worries about air friction and noise that usually limit the speed of trains to under 400mph, but the tube also presents a unique set of challenges. James Powell PhD, co-inventor of the maglev train, is particularly concerned about the smoothness of the inside of the tube. As Powell points out, the current design allows for just three hundredths of an inch between the tube wall and the skis encircling the pod. “Getting it that smooth won’t be easy,” says Powell, and might require a more expensive production process than the plans envision.

The small gap is crucial to the system’s overall design, allowing for a stable air cushion that keeps the pod hovering frictionlessly in the tube. But the small gap also requires great precision in tube construction. Powell thinks that a single bump, just three-quarters of a millimeter high, would trigger catastrophic damages, possibly even ripping the ski from the pod at top speed. Keeping the tubes straight can be done, but it won’t be cheap. “It’s going to be an arduous process,” says Vinod Badani, an engineering consultant at E2 Consulting. “Quality control and measurement have to be very accurate.” Musk’s plans envision a specially designed device to smooth out the inside of the tube, but it presents a serious engineering problem for anyone thinking of building a prototype.

Musk proposed using I-5’s right of way as a way to keep land costs down. However, I-5 has trucks. If one semi truck jack-knifes on the road, ramming into one of Musk’s cheaply-built pylons, how will his tube maintain that level of precision required for safe operation? Musk asserts his system is safer than HSR during earthquakes (nevermind the safe operation of Japanese HSR during major earthquakes) without any evidence, yet the basic physics of what he is proposing demand a high level of precision on a massive scale.

The real question should be if it’s even possible, not asserting that it will be cheap.

In the New Yorker, Tad Friend takes note of Musk’s propensity for exaggeration:

The bad news is that there’s no conceivable way that the system would cost just six billion dollars, or that one-way tickets would cost twenty dollars. Overpromise disease is endemic to Silicon Valley, but Musk has an aggravated case. When I wrote a Profile of him, in 2009, he told me that a third-generation Tesla would be selling for less than thirty thousand dollars in 2014, the same year that he expected SpaceX’s Falcon 9 to begin ferrying tourists around the moon. Well, no and hell no. More worrisomely, he promised that you could start driving the Model S in western California “at breakfast and be halfway across the country by dinnertime.” Musk is a lot better at math than I am, but he eventually acknowledged that by “dinnertime” he really meant “the following morning’s breakfast”—if, again, you didn’t stop to go to the bathroom.

This isn’t to argue that exploring these ideas shouldn’t happen. It is, however, an argument that a concept like the hyperloop shouldn’t be used to bring down high speed rail. If the Hyperloop is nothing more than a device to force better results out of the CHSRA, that would be a welcome result. However, if that is to happen, it won’t be because the Hyperloop is a realistic (or event a plausible) alternative.

Two weeks ago, Eric Jaffe editorialized that we should stop obsessing about the “next great thing” in urban transportation. There’s thinking big, and then there is fantasy. It’s worth noting that a project like California High Speed Rail is plenty ambitious – it’s certainly thinking ‘big.’ It’s also achievable, but is facing real-world constraints (economic, political, physical, institutional, procedural, regulatory, etc) and is in need of some practical planning.

The Hyperloop may seem like an attractive end-run around these constraints, but such benefits are illusory. The real benefit is in reforming the institutions to reduce the constraints.

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Hyperloop: lots of hype for something that doesn’t yet exist