There's been some discussion over at the California High Speed Rail Blog about the cost of the system. Basically, a Freakonomics guest blogger threw around the figure of $80b for the system, which is considerably higher than the forecasted $40b. No one really knows how much the high speed rail system will cost, but the numbers everyone quotes need to be contextualized. In other words, much did the Interstate Highway System cost? Per person, and adjusted for inflation? Was it considerably more than high speed rail?
According to the wikipedia site about Intersates, the highway system cost $425b (inflation-adjusted) to build over a period of 35 years. In 1950, the population of the country was 150m, and in 1960 it was 180m. So, in 2007 dollars, the Interstate system cost about $2500 per person alive at its inception (425b/165m, the approximate population when the highway system was funded, in 1956) to build. Per year, it cost about $75 per person.
California has a population of approximately 37m, and we can assume that the final bill for high speed rail would come in somewhere in this $40b to $80b range. Running these numbers, California's HSR system would cost about $1100 to $2200 per person, spread over a period of about twenty years. Per person, it would cost less than the Interstate system—perhaps considerably less. Per year, it would be between $55 and $110—quite comparable to the Interstate system.
There is one minor difference between the Interstates and High Speed Rail. Say what you want about CAHSR's business plan, but as far as I know, the Interstate Highway System never had a business plan which showed the system making a profit.
Sunday, July 26, 2009
Saturday, July 25, 2009
Viaducts: The High Line
After the success of the Viaduc des Arts in Paris, some New Yorkers looked at their community and realized they had a somewhat similar asset, and didn't really know what to do with it. Was the structure a blight—as it was seen by the Giuliani administration, which wanted to tear it down—or something worth saving? Like the Viaduc Des Arts, it was nearly 30 years between the abandonment of rail service and the opening of the structure to the public, but the results, in the month which it has been open, have been similarly positive.
The elevated railroad south from 34th street has an interesting history, following the use of the west side of Manhattan. It was first built, at-grade, in the 1850s. Along the Hudson were dozens of docks, and until the 1960s, New York was one of the busiest ports in the world. By the 1920s, the railroad across surface streets on the west side was the cause of so much congestion that a proposal was made to elevated the tracks south of the yards at Penn Station, and by 1934, the work had been completed: a two-track railroad (which was, in places, wider) extended for a couple of miles along the docks.
The line ended at the Saint John's Park terminal, which was built in the 1860s, and rebuilt once the elevated line was completed. The complex stood near the current Canal Street IRT and IND (1 and ACE) subway stations, a few blocks east of the Hudson. The rebuilt station truncated the line a bit, and it now ended at Spring Street, about a block east of the river—close to the docks—although it retained the name. The facility was impressive, with nearly a million square feet of floor space, eight railroad tracks, dozens of truck bays, customs offices and a connection to the docks. Speed would be improved as well; before the grade separation, trains were limited by law to six miles per hour and had to be preceded by a man on horseback. The New York Central published a pamphlet extolling the virtues of the new line.
In addition to the services to the docks, the line served factories and, especially, the meatpacking district, encompassing more than 250 slaughterhouses. The New York Central touted the relationship of the line to destinations by both ship and railroad (assuredly because they were the only possible provider of service) for factory locations, and, indeed, several were built, some of which straddled the line. During World War II, the line was used heavily to service these various industries. Within 35 years, it would be abandoned.
The decline of the West Side Line was not only attributable to the automobile, although it definitely had an effect. With automobiles and trucks, of course, production no longer needed to be as centralized. In other words, it didn't have to be on the island of Manhattan. In addition, trucks could more easily make deliveries to Manhattan (although it is still notoriously hard to deliver goods to the island, even the milk in The City expires earlier than elsewhere, due, ostensibly, to longer periods when it is out of refrigeration during transport).
But there were other factors at work in the demise of the Line peculiar to it (many railroads in the country saw major declines with the coming of the car and truck). One was the improvements made in refrigeration. In the first half of the 20th century, meat processing was best done as close to the point of consumption as possible, as refrigeration was rather rudimentary. However, major strides were made in refrigerated trucks and rail cars that by the end of the war, it was easier to process meat outside the city and ship the smaller product—just the meat—in. Thus, of the 250 slaughterhouses which once operated in the meatpacking district, only a couple dozen remain.
The other factor at work was containerized shipping. In "The Box" Marc Levinson details how shipping was extremely inefficient and costly after World War II, especially in major break-in-bulk points like New York City. Shipments would arrive on trains and have to be unloaded, sorted and then reapportioned in to ships for overseas travel. Improvements in efficiency were frowned upon, especially if they would cost the union jobs. New York still accounted for a good deal of shipping until the advent of the container. Within 20 years, the New York docks were moribund, as shipping had shifted to locations which could process metal containers, which were easily lifted from trains and truck to ships. The Saint John's Park Terminal, at the cutting edge of integrated shipping little more than a generation before, had outlived its usefulness. Factories closed up shop, and the meatpacking district became a den for prostitution, transvestites and others seen as socially undesirable.
It was about the same time that the railroad ceased to be used—the last three carloads were delivered in 1980 and it fell in to disuse. Local residents lobbied for it to be torn down in the 1980s, and it may well have been, had the city not been in such dire financial straits that a demolition and environmental cleanup were not in the cards. By the time the city was solvent enough to tear down the structure, in the 1990s, a small group of devotees and urban explorers—loosely organized as The Friends of the High Line lobbied against its demolition. Thus, while portions were torn down, it was kept intact north of Gansevoort Street. Some of the explorers of the structure, such as Joel Sternfeld (whose book of images from the line is now out of print and fetches high sums on the open market) introduced the structure to the masses, and Giuliani was unable to knock it down. Michael Bloomberg was more supportive of the project, the neighborhood through which the line runs had transformed from a den of vice to one of the trendiest parts of town, and fundraising began to open the structure to the public. The Design Build Network has a good history and description of this time frame of the structure.
Reaction to the project has generally been quite positive. The main detractors have not been those who wish it away, but those who lament the loss of the frontier aspect of the previously wild viaduct. Before it was completed, the High Line was open to a select few who climbed atop it, and wandered through a veritable prairie that was growing up in the middle of Manhattan. The current design tries to incorporate such aspects, keeping some of these plants and portions of the abandoned track, but with demarcated walkways and thousands of visitors, it is a different space entirely. Still, it was not feasible to let the structure rust in to oblivion, and keeping it as a public space is surely preferable to tearing it down, and having the landscape become a sea of condos like any other in New York.
The High Line opened to the public last month. I have not been in New York City since, but it is most definitely a destination the next time I am there. It seems to be similar, at least in the above, to the Viaduc des Arts, although more minimalist in design. How it will continue to interface with the city in the future will be interesting: it is one of the less-developed parts of Manhattan, and still has a few undeveloped parcels facing the High Line. Whether these will ever open out on to the structure is questionable: it's a rather controlled space (one that is closed at night, for example). Also interesting will be what happens underneath it. Still, it is one of the most exciting new public spaces in New York in some time.
(Part of an occasional series.)
The elevated railroad south from 34th street has an interesting history, following the use of the west side of Manhattan. It was first built, at-grade, in the 1850s. Along the Hudson were dozens of docks, and until the 1960s, New York was one of the busiest ports in the world. By the 1920s, the railroad across surface streets on the west side was the cause of so much congestion that a proposal was made to elevated the tracks south of the yards at Penn Station, and by 1934, the work had been completed: a two-track railroad (which was, in places, wider) extended for a couple of miles along the docks.
The line ended at the Saint John's Park terminal, which was built in the 1860s, and rebuilt once the elevated line was completed. The complex stood near the current Canal Street IRT and IND (1 and ACE) subway stations, a few blocks east of the Hudson. The rebuilt station truncated the line a bit, and it now ended at Spring Street, about a block east of the river—close to the docks—although it retained the name. The facility was impressive, with nearly a million square feet of floor space, eight railroad tracks, dozens of truck bays, customs offices and a connection to the docks. Speed would be improved as well; before the grade separation, trains were limited by law to six miles per hour and had to be preceded by a man on horseback. The New York Central published a pamphlet extolling the virtues of the new line.
In addition to the services to the docks, the line served factories and, especially, the meatpacking district, encompassing more than 250 slaughterhouses. The New York Central touted the relationship of the line to destinations by both ship and railroad (assuredly because they were the only possible provider of service) for factory locations, and, indeed, several were built, some of which straddled the line. During World War II, the line was used heavily to service these various industries. Within 35 years, it would be abandoned.
The decline of the West Side Line was not only attributable to the automobile, although it definitely had an effect. With automobiles and trucks, of course, production no longer needed to be as centralized. In other words, it didn't have to be on the island of Manhattan. In addition, trucks could more easily make deliveries to Manhattan (although it is still notoriously hard to deliver goods to the island, even the milk in The City expires earlier than elsewhere, due, ostensibly, to longer periods when it is out of refrigeration during transport).
But there were other factors at work in the demise of the Line peculiar to it (many railroads in the country saw major declines with the coming of the car and truck). One was the improvements made in refrigeration. In the first half of the 20th century, meat processing was best done as close to the point of consumption as possible, as refrigeration was rather rudimentary. However, major strides were made in refrigerated trucks and rail cars that by the end of the war, it was easier to process meat outside the city and ship the smaller product—just the meat—in. Thus, of the 250 slaughterhouses which once operated in the meatpacking district, only a couple dozen remain.
The other factor at work was containerized shipping. In "The Box" Marc Levinson details how shipping was extremely inefficient and costly after World War II, especially in major break-in-bulk points like New York City. Shipments would arrive on trains and have to be unloaded, sorted and then reapportioned in to ships for overseas travel. Improvements in efficiency were frowned upon, especially if they would cost the union jobs. New York still accounted for a good deal of shipping until the advent of the container. Within 20 years, the New York docks were moribund, as shipping had shifted to locations which could process metal containers, which were easily lifted from trains and truck to ships. The Saint John's Park Terminal, at the cutting edge of integrated shipping little more than a generation before, had outlived its usefulness. Factories closed up shop, and the meatpacking district became a den for prostitution, transvestites and others seen as socially undesirable.
It was about the same time that the railroad ceased to be used—the last three carloads were delivered in 1980 and it fell in to disuse. Local residents lobbied for it to be torn down in the 1980s, and it may well have been, had the city not been in such dire financial straits that a demolition and environmental cleanup were not in the cards. By the time the city was solvent enough to tear down the structure, in the 1990s, a small group of devotees and urban explorers—loosely organized as The Friends of the High Line lobbied against its demolition. Thus, while portions were torn down, it was kept intact north of Gansevoort Street. Some of the explorers of the structure, such as Joel Sternfeld (whose book of images from the line is now out of print and fetches high sums on the open market) introduced the structure to the masses, and Giuliani was unable to knock it down. Michael Bloomberg was more supportive of the project, the neighborhood through which the line runs had transformed from a den of vice to one of the trendiest parts of town, and fundraising began to open the structure to the public. The Design Build Network has a good history and description of this time frame of the structure.
Reaction to the project has generally been quite positive. The main detractors have not been those who wish it away, but those who lament the loss of the frontier aspect of the previously wild viaduct. Before it was completed, the High Line was open to a select few who climbed atop it, and wandered through a veritable prairie that was growing up in the middle of Manhattan. The current design tries to incorporate such aspects, keeping some of these plants and portions of the abandoned track, but with demarcated walkways and thousands of visitors, it is a different space entirely. Still, it was not feasible to let the structure rust in to oblivion, and keeping it as a public space is surely preferable to tearing it down, and having the landscape become a sea of condos like any other in New York.
The High Line opened to the public last month. I have not been in New York City since, but it is most definitely a destination the next time I am there. It seems to be similar, at least in the above, to the Viaduc des Arts, although more minimalist in design. How it will continue to interface with the city in the future will be interesting: it is one of the less-developed parts of Manhattan, and still has a few undeveloped parcels facing the High Line. Whether these will ever open out on to the structure is questionable: it's a rather controlled space (one that is closed at night, for example). Also interesting will be what happens underneath it. Still, it is one of the most exciting new public spaces in New York in some time.
(Part of an occasional series.)
Viaducts: The Viaduc des Arts
In Paris, the Viaduc des Arts is impressive in various dimensions. From the street, its stately arches stand out from the city—not in a bad way, but they provide a different streetscape than the prototypical Parisian boulevard. Above, the viaduct carries a tree-path. You never forget you are in one of the largest cities in the world, but it is a very unique space, and quite different than the various Places and Gardens of the city.
The Viaduc is rather transparent—underpasses are wide and high enough that they stay rather bright. The arches themselves are even translucent; in some you can look in one window and out the other.
The Viaduc des Arts was originally built during the Hausmannian period of Parisian redevelopment in the 1800s, as the innermost link of a Paris-Strasbourg railroad (which, several iterations later, is now served by a superfast TGV line). Using techniques of the mid-1800s, the viaduct was built with dozens of handsome arches along Avenue Daumesnil east of Place de la Bastille. As Paris grew, many railroad stations were built, most of them with multi-track mainlines serving them. The station at the end of the viaduct, however, only had the two tracks on the viaduct, and, since it was across the street from the monstrous Gare de Lyon. With the coming of the RER, suburban services were shifted such that the viaduct no longer served passengers (and it never really served freight), and service was abandoned.
The Avenue Daumesnil, along the Viaduc, has one of many segregated bike lanes in Paris. The eastern end of the Viaduc is much more modern, and this building was built to interface with the space.
For twenty years, the viaduct sat. Weeds grew on top and the structure became dilapidated, but by all accounts was rather sound. There were plans to demolish the structure, but they were never carried forth. The viaduct, built of red brick and yellow stone, is quite attractive, and the arches allow though significant light, so it is seen as neither a major barrier or a cause for blight (at least, other than the "weed infested" former track bed). In the 1990s, its potential was foreseen, and by the end of the decade, it had been transformed in to the Viaduc des Arts.
Believe it or not, this watery, green scene is thirty feet above the streets of Paris, almost adjacent to the busy Gare de LyonThe amazing part of the viaduc is that it has been rehabilitated on two levels. In many cases, the areas below elevated structures are used for parking—there are few other uses for the small plots of land below noisy and/or ugly railroad lines. In the case of the Viaduc des Arts, approximately one sixty-fourth of the structure is still used in this manner—albeit as an entrance to an underground parking garage. The rest of the arches have been transformed in to mostly art studios, although there are some cafes and other stores. Considering the popularity of loft spaces with the artistically-inclined, the bare-brick arches offer such airy confines in a unique setting. In fact, the "arts" portion of the viaduct generally refers only to the street-level portion of the structure.
From several gaps along the viaduct, it is possible to look towards he Seine, across the apartment blocks and railroad yards of the city.However, the top of the viaduc was not ignored. A series of staircases were built from street level up approximately thirty feet, and the top of the structure is now known as the "Promenade Plantee." From weeds, the structure has been changed to a linear park above street level, with a narrow path and surprisingly dense foliage. This does not mean that it is disconnect from the city; the landscape seems to alternate from views of the greenery to views of the buildings and courtyards on either side (and even a few across the nearby railroad station towards the Seine). From the street below, the top of the viaduc is all but invisible—you have to move further away to realize that it is landscaped. Thus, it is possible to walk the length of the structure on the street, and then retrace your steps parallel to, and thirty feet above, the street, albeit in a completely different setting with completely different scenery.
The views from the atop the viaduct, along one axis, a of a green pathway, and along a perpendicular axis they interface with the courtyards and small streets of Paris.
By all accounts, the Viaduc des Arts and Promenade Plantee has been a resounding success at reusing an elevated structure. The arches have been inhabited, humanizing the structure, and it provides a green space in a very dense city. (Inside the peripherique, Paris is nearly as dense as Manhattan; or to put it another way, it is as large as San Francisco with three times the people.) Parisians, and tourists, have embraced the Viaduc, and it is now a lovely place for a quiet stroll in an otherwise harried city (aside, of course, from the ubiquitous cafes). Here's a lovely video of a Frenchwoman touring the Viaduc. Beyond the old viaduct, the linear park continues towards gardens built on old railroad yards, but it is generally at grade, and a bit less interesting.
(Part of an occasional series.)
Thursday, July 23, 2009
Viaducts: in with the old
Recent travels have taken me to Chicago, San Francisco and Paris (and explain the lack of activity on this page). It is the latter of these cities which I am going to use to explore the above-city landscape.
What is the above-city landscape? Well, in the late 1800s and through much of the 1900s, cities realized that it was generally quite easy to build transportation networks above street level. The first of these took the form of steam-powered, elevated railroads. In most cases, these were built on metal structures above the street, but in a few, they were built as stone or masonry structures instead. The next generation were electrically-powered elevated railroads, which were mostly built in the early 1900s and, in many cases, torn down during the latter half of the 20th century, which were followed by, after 1950, mostly concrete elevated road structures.
Most of these structures, especially the narrower, non-road ones, were built over existing roads. (Road structures are often several lanes wide and required significant property takings, as there were no existing rights of way wide enough to carry them.) Thus, when they fell in to disuse or when they were made redundant by paralleling surface or underground routes, most were seen as a blight to the landscape and torn down. Metal, over-street elevateds are easy targets: they are ugly, they block light, they generally carry noisy traffic and their supports impede the flow of traffic. If they no longer serve a purpose (such as carrying passengers) there is usually little debate as to their fate. Abandoned elevateds are a rare sight indeed.
In a some cases, however, elevated railroads were not built over a street, but next to it, or in between streets. Examples of this type of construction include some active lines, such as the Park Avenue Viaduct in New York, the Reading Viaduct in Philadelphia and various elevated lines in Chicago (the Red Line north of the Loop and the Blue Line east of Logan Square). Quite often, however, segments of urban, elevated lines have been abandoned, for various reasons: a new at-grade or (more often) underground segment opened, their need was made redundant by a parallel line, or the need they served ceased to exist. Once this occurs, cities are left with long, grade separated rights-of-way, and no clear procedure for what to do with them.
Urban viaducts are often seen as a blight, and while they do represent significant infrastructure, there is often pressure to tear them down. In Boston, no one could wait to get rid of the Central Artery—there was almost no discussion of keeping it for any reason. Although it could have been used as an elevated park or a means to connect North and South Stations, consensus was to remove it and reconnect the city to the waterfront. This was likely the correct approach; the structure was close to 100 feet wide and ran between the city and the harbor, casting an ominous shadow.
In some cases, however, disused structures are less abhorred and there is not such swift pressure to demolish them. This, in particular, is the case with railroad structures. Few, if any, highway structures in cities are less than six lanes wide—if you are going to bother building an elevated highway and the various accoutrements which go with it (exits, entrances, underpasses, and such), it makes little sense to build it as a two-lane roadway. A two lane roadway can not handle much traffic, and the marginal cost of adding a few extra lanes is relatively small. Thus, highway bridges tend to be at least six lanes wide, and with shoulders, barriers and supports, they are often 100 feet wide (add a couple of exit ramps and they are even more intrusive). Furthermore, because the roadways need to be accessed from below, these structures are usually built at a minimum height above other streets, often providing less than 20 feet of clearance. Thus, highway structures tend to create large and dark spaces underneath, which are almost universally disliked.
Railroad structures, however, often are built differently. Height is less of a consideration, although elevated structures are usually not built any higher than necessary. However, width is much less of an issue. Highways need to be built to a considerable width because the capacity of a highway lane is only about 2000 persons per hour. One railroad track, however, can carry ten times that many people (trains carrying 1000 passengers and operating at three minute headways are commonplace), so in most cases, no more than two tracks are needed. In a few cases, three tracks are built to allow for extra capacity, and sometimes even four—although since the entirety of Grand Central Station can be served by four tracks, wider structures are rarely necessary. And since railroads don't need breakdown lanes, exit ramps or barriers, elevated railroad structures are rarely wider than about 40 feet, and often only 20 feet from side to side. These structures are not as often seen as the "Chinese Walls" that highways (or railroads built entirely on fill) are compared to, and therefore not universally torn down when they are no longer in use.
While aerial structures have been abandoned for some time, there is not yet a definitive protocol for what to do with them. Some, of course, are torn down and, often, the rights of way are used for new structures, all but obliterating the previous use (except to the well-honed eye). For instance, the CTA in Chicago demolished several short elevated segments, such as the Humbolt Park Line (the only visible traces of which lie in buildings which end suspiciously short of nearby alleys) and the north end of the Paulina Connector (redundant once the State Street Subway was built), which is only visible where the structure is still used for railroad signals.
More recent closures, however, have not necessarily been followed with demolition. As cities have transformed, planners and residents have realized that there is potential to use old viaducts to create unique urban spaces. Demolishing such structures often leave narrow and sometimes-bizarre plots of land which are not conducive to new development (especially when they are less than two dozen feet wide), so the land does not have much intrinsic value. However, the structures are often quite sound (having often been overbuilt) and seen as opportunities to bring green space in to the city—without demolishing the structure. The two most significant examples of this type of reuse are the Viaduc des Arts / Promenade Plantee in Paris and the High Line, which very recently opened in New York City. We'll explore both of these in an occasional series.
What is the above-city landscape? Well, in the late 1800s and through much of the 1900s, cities realized that it was generally quite easy to build transportation networks above street level. The first of these took the form of steam-powered, elevated railroads. In most cases, these were built on metal structures above the street, but in a few, they were built as stone or masonry structures instead. The next generation were electrically-powered elevated railroads, which were mostly built in the early 1900s and, in many cases, torn down during the latter half of the 20th century, which were followed by, after 1950, mostly concrete elevated road structures.
Most of these structures, especially the narrower, non-road ones, were built over existing roads. (Road structures are often several lanes wide and required significant property takings, as there were no existing rights of way wide enough to carry them.) Thus, when they fell in to disuse or when they were made redundant by paralleling surface or underground routes, most were seen as a blight to the landscape and torn down. Metal, over-street elevateds are easy targets: they are ugly, they block light, they generally carry noisy traffic and their supports impede the flow of traffic. If they no longer serve a purpose (such as carrying passengers) there is usually little debate as to their fate. Abandoned elevateds are a rare sight indeed.
In a some cases, however, elevated railroads were not built over a street, but next to it, or in between streets. Examples of this type of construction include some active lines, such as the Park Avenue Viaduct in New York, the Reading Viaduct in Philadelphia and various elevated lines in Chicago (the Red Line north of the Loop and the Blue Line east of Logan Square). Quite often, however, segments of urban, elevated lines have been abandoned, for various reasons: a new at-grade or (more often) underground segment opened, their need was made redundant by a parallel line, or the need they served ceased to exist. Once this occurs, cities are left with long, grade separated rights-of-way, and no clear procedure for what to do with them.
Urban viaducts are often seen as a blight, and while they do represent significant infrastructure, there is often pressure to tear them down. In Boston, no one could wait to get rid of the Central Artery—there was almost no discussion of keeping it for any reason. Although it could have been used as an elevated park or a means to connect North and South Stations, consensus was to remove it and reconnect the city to the waterfront. This was likely the correct approach; the structure was close to 100 feet wide and ran between the city and the harbor, casting an ominous shadow.
In some cases, however, disused structures are less abhorred and there is not such swift pressure to demolish them. This, in particular, is the case with railroad structures. Few, if any, highway structures in cities are less than six lanes wide—if you are going to bother building an elevated highway and the various accoutrements which go with it (exits, entrances, underpasses, and such), it makes little sense to build it as a two-lane roadway. A two lane roadway can not handle much traffic, and the marginal cost of adding a few extra lanes is relatively small. Thus, highway bridges tend to be at least six lanes wide, and with shoulders, barriers and supports, they are often 100 feet wide (add a couple of exit ramps and they are even more intrusive). Furthermore, because the roadways need to be accessed from below, these structures are usually built at a minimum height above other streets, often providing less than 20 feet of clearance. Thus, highway structures tend to create large and dark spaces underneath, which are almost universally disliked.
Railroad structures, however, often are built differently. Height is less of a consideration, although elevated structures are usually not built any higher than necessary. However, width is much less of an issue. Highways need to be built to a considerable width because the capacity of a highway lane is only about 2000 persons per hour. One railroad track, however, can carry ten times that many people (trains carrying 1000 passengers and operating at three minute headways are commonplace), so in most cases, no more than two tracks are needed. In a few cases, three tracks are built to allow for extra capacity, and sometimes even four—although since the entirety of Grand Central Station can be served by four tracks, wider structures are rarely necessary. And since railroads don't need breakdown lanes, exit ramps or barriers, elevated railroad structures are rarely wider than about 40 feet, and often only 20 feet from side to side. These structures are not as often seen as the "Chinese Walls" that highways (or railroads built entirely on fill) are compared to, and therefore not universally torn down when they are no longer in use.
While aerial structures have been abandoned for some time, there is not yet a definitive protocol for what to do with them. Some, of course, are torn down and, often, the rights of way are used for new structures, all but obliterating the previous use (except to the well-honed eye). For instance, the CTA in Chicago demolished several short elevated segments, such as the Humbolt Park Line (the only visible traces of which lie in buildings which end suspiciously short of nearby alleys) and the north end of the Paulina Connector (redundant once the State Street Subway was built), which is only visible where the structure is still used for railroad signals.
More recent closures, however, have not necessarily been followed with demolition. As cities have transformed, planners and residents have realized that there is potential to use old viaducts to create unique urban spaces. Demolishing such structures often leave narrow and sometimes-bizarre plots of land which are not conducive to new development (especially when they are less than two dozen feet wide), so the land does not have much intrinsic value. However, the structures are often quite sound (having often been overbuilt) and seen as opportunities to bring green space in to the city—without demolishing the structure. The two most significant examples of this type of reuse are the Viaduc des Arts / Promenade Plantee in Paris and the High Line, which very recently opened in New York City. We'll explore both of these in an occasional series.