Saturday, November 1, 2014

Reconciling Bridges and Urbanism

Bridges have been a feature of urban design ever since King Nabopolassar spanned the Euphrates River with a causeway around 620 B.C, joining together the two halves of the city of Babylon and much later inspiring the title of a Rolling Stones album.  That this innovation represented a major improvement over the ferry transportation that had formerly prevailed was evident to ancient observers such as the Greek historian Herodotus, who noted that "under the former kings, if a man wanted to pass from one of these halves to the other, he had to cross in a boat; which must, it seems to me, have been very troublesome." 

If the transportation advantages were clear at the time, the design challenges of incorporating bridges into a dense urban fabric presented difficulties that have continued to the present day.  Apart from engineering challenges, the primary contextual concern is that a bridge high enough to avoid obstructing the flow of maritime traffic will typically be higher than the city itself, with the result that approaches to the bridge, if they are to accommodate wheeled traffic, will need to extend deeply into the city.  Long approaches, however, disrupt and divide the urban fabric, undermining the very connectivity that the bridge was intended to provide.

For a well-known example, consider the Brooklyn Bridge, which was built to a height sufficient to accommodate the masts of sailing ships that still plied the East River in the early 1880s, and which, like Nabopolassar's bridge, replaced ferry services.  An engineering marvel, the bridge was nonetheless so massive that its approaches reached deep into the heart of Manhattan, overshadowing many blocks and requiring the demolition of others:

The Brooklyn and Manhattan bridges circa 1916. Source.
Built some years before Robert Moses was even born, the bridge represented the first instance of an elevated roadway carving a swathe through a built-up area of Manhattan and dividing parts of the city from each other.  In the years since the bridge was built, access ramps from the FDR Drive have further expanded the initial scar, leaving a gap of 360 feet in the city's fabric with limited crossing points.  Although the arch spaces under the approach were creatively rented out as storage space for wine merchants (the bricked-in warehouse spaces can still be seen today), the effect on the immediately surrounding neighborhood could hardly have been a great positive.  The area sliced up by the approaches to the Brooklyn, Manhattan and Williamsburg Bridges became notorious as Manhattan's Lower East Side, and was some decades later subjected to some of the most intensive urban renewal in the city.  

In Europe, where watersheds tend to be smaller than those of North America, major rivers narrower and where many bridges had been built long before the advent of suspension or steel-frame technology, a much more complementary design has long prevailed.  Rather than sending approaches deep into the urban fabric, European cities tend to raise masonry embankments directly against the river, allowing a bridge even of substantial height to discharge traffic directly onto riverfront streets.  Bridges were also considered architectural works in their own right intended to be experienced on foot, and incorporated sidewalk lighting, statuary, benches and other pedestrian amenities.

Pont Neuf, Paris. Google Maps.

Bird's eye view of another Pont Neuf, in Toulouse, with its entry point flush with a
 25-foot embankment providing flood protection against the Garonne River. Bing Maps. 
Running along these embankments at just above water level are often found quays, which formerly served the shipping trade but which today have been converted to car expressways or recreational areas for cyclists and pedestrians (a notable conversion from the former to the later has recently taken place in Paris).

In some famous instances, the city itself extended out onto the bridge, turning transportation infrastructure into a bustling city street with shops and homes.  Among the best known of these are the former London Bridge, the Ponte Vecchio and the Rialto Bridge in Venice:

Pont Notre-Dame, Paris, depicted 1756. Source.
Paris seems to have had several such bridges as well, but most had their houses torn down in the late 1700s when the spatial demands of wheeled traffic began to make themselves increasingly apparent in the larger cities of Europe.  The Pont Notre-Dame, above, was scraped clean of its tall dwellings in 1782, and the centuries-old bridge itself was replaced in the 1850s.  London Bridge's houses, apparently allowed onto the bridge as a means of producing rent to offset the cost of bridge construction in the medieval period, were removed in the late 1750s at great expense to improve the bridge's level of service.  The trend toward retrofitting cities around the needs of wheeled traffic would steadily accelerate through the late 20th century.

Source: Old Urbanist.
Some North American cities have bridges in approximately the European fashion, particularly where the city is located on a bluff overlooking a river or where the river is relatively narrow.  Chicago, Milwaukee and San Antonio, in particular, have numerous such bridges over their relatively narrow rivers, and Austin has partial embankments overlooking a riverside trail.  Des Moines, also, has a series of very European-looking bridges.  Even if geography requires a bridge to enter a city at height, however, that does not mean that integrating it into the city need be impossible.

For instance, even if the ground level cannot be raised to meet the bridge, buildings themselves may be constructed up to the bridge level.  The photo at right shows this approach deployed along a Danube River bridge in Regensburg, Germany (actually, in this case, I believe the bridge may have been constructed to align with the second floors of existing apartments).  With this method, similar to the built-upon bridges described above, the bridge adds a second linear dimension to the city rather than simply being a passive structure accessible only at its endpoints.  

Additionally, the long approaches themselves are demanded only by wheeled traffic.  Where a bridge serves only foot traffic, it is possible to provide high clearance, even with masonry construction, and yet have little or no landward approach.  This method was employed abundantly in the towns and cities of pre-modern China, such as Wuzhen, below, where although the bridge appears to rise very steeply, the grade is quite a bit less than in the standard staircase, and the climb less arduous:

Steep automobile bridges are possible, but rarely seen, as in this example from Matsue, Japan, which fortunately has a fairly mild winter climate:

The American approach, reflective of the era of Heroic Materialism in general, has typically been to see bridges as engineering projects first, architecture second, and an integrated part of the city third, if at all.  Even where existing bridges with lengthy approaches have been converted to pedestrian use, long approaches are typically retained, or in some cases, even rebuilt.  

The Big Four Bridge in Louisville, Kentucky, a rail bridge over the Ohio River which had its long approaches removed in the late 1960s, leaving only the central span, was inexplicably rebuilt with approaches even though it was intended primarily for pedestrians (a much simpler plan requiring no land acquisition which would have involved a ramp directly around the final bridge pier was apparently rejected).  On the Kentucky side, pedestrians must ascend a massive, circuitous and over-engineered ramp to reach the bridge:  

Google Maps/Shawn Conn.

A switchback staircase leading directly to the bridge pier was present during construction for the convenience of workers according to Streetview imagery, but seems to have been removed now that the approach is complete!

Nashville's downtown Shelby Street Bridge, which never had its approaches demolished prior to its pedestrianization in the early 2000s, took a more sensible approach of adding a steel staircase and elevator, thereby taking advantage of the tremendous spatial efficiencies of pedestrianism while allowing people with bicycles, strollers or in wheelchairs to reach the bridge: 

Google Maps.
In a first step toward directly integrating the bridge roadway with the surrounding buildings, the bridge and elevator are attached by an elevated walkway to the office building at the left.  It is difficult to overstate the effect pedestrian infrastructure like this contributes toward making the bridge feel like a place, rather than an obnoxious intrusion into the life of the city.

Turning bridge design away from the Heroic Materialist model of bridge-building toward a more pedestrian and city-oriented perspective is a long-term process that appears to be underway with bridge conversions, but many positive changes can done incrementally.  Providing pedestrians with shortcut access points to bridge approaches, linking the bridge surface directly to surrounding buildings and even considering construction of new buildings flush with or underneath the bridge, can all help turn bridges into more than simply impressive engineering feats.

Related posts: Jarrett Walker has a similar take on urban viaducts here (h/t to commenter Marc), and of course these observations could also be applied to other forms of elevated infrastructure to greater or lesser degrees.


  1. "On the Kentucky side, pedestrians must ascend a massive, circuitous and over-engineered ramp to reach the bridge."

    This example brings to mind several disturbing renderings I've seen in recent years (I don't recall specific examples) in which the designers quite deliberately made the approaches to their bridges circuitous, indirect, and meandering, as if trying to counter the usefulness of the bridges themselves! Perhaps this is a symptom of the muddled Landscape Urbanist thinking currently burning its way through the design professions...

    I've seen a couple straightforward switchback stairs retrofitted into some bridges (or included in some new ones), but I definitely agree they're rarer than they should be. Particularly disturbing is that I've actually run across more abandoned, overgrown, fenced-off, and/or partially-dismantled connectors than I've seen new ones, suggesting that the maintenance of pedestrian connections still doesn't rank high on the list of DOT/DPW priorities.

    There is also the issue of urban viaducts (close relatives of urban bridges), which American cities have historically done a poorer job of integrating into the urban fabric than their European and Asian counterparts, though a few examples survive:

    Columbus, OH, interestingly enough, seems to be reviving the ancient art of bridge lining to fight their barrier effects:

    1. Well, the Louisville bridge seems to have been implicitly conceived by its designers as a recreational in nature rather than as genuine transportation infrastructure. If you imagine people using it simply for a pleasant and scenic walk, you would be unconcerned that your design forces them to take a needless detour, since recreational walkers would be unlikely to slog up four flights of stairs to save time, and an elevator would also seem like a pointless extravagance. Or, perhaps, it was only seen as functional for cyclists, in which case the ramp is intended primarily for them.

      DOTs definitely have a blind spot for pedestrian connections. The South Norwalk train station in Connecticut, which I walked to each morning during my commute a few years ago, had an overpass directly adjacent to the station replaced while I lived there. The old bridge, which must have been from the 1890-1910 period, had stairs running up from street level directly to the platform which I used every day. One day these were roped off, and were eventually demolished and filled in with a blank concrete wall (unfortunately there is no earlier image to compare):,-73.420808,3a,75y,245.62h,80.72t/data=!3m4!1e1!3m2!1s9sNo8PnLjdHzi2DLcK0pYA!2e0

      For those people who, like me, were walking to the far side of the platform, this added about two and a half minutes to the walk, requiring a lengthy and pointless detour around the block through the main station building. A desire path through a wooded patch along the tracks kept it from taking even longer.

      Why were the stairs removed? I never got a good answer. The tracks were not reconfigured, so that was not the issue. As best I could tell, it was simply an oversight. Pedestrian convenience wasn't on the radar. The main concern of the people at CDOT was adequate parking at the station. This general attitude seems to be prevalent among DOTs and similar organizations.

      Thanks for that Jarrett Walker piece -- I've added the link.

    2. Given it's very shallow grade, the circuitous path up the KY bridge seems like regulation for wheelchair access more than anything.

    3. That's possible, but if ADA access really had been an issue, you'd think they might have included an elevator, as the Nashville bridge shows is feasible in these circumstances. Elevators do present their own problems, though -- not only of maintenance, but of hygiene, especially when not well-used. This has apparently been an issue in Nashville.

    4. I'm can imagine the city officials perhaps thought "elevators require electricity and maintenance but a ramp won't, let's do that!", even though the ramp will require maintenance too.

    5. Also, Marc & Zeph -- for an example of a more reasonably-scaled and sensibly-designed ramp, see the Hennepin Ave. Bridge in Minneapolis (on the west bank of the river). That bridge does not have an elevator, but in that case, based on the manner and height of the approach, it does not really need one.

    6. "Well, the Louisville bridge seems to have been implicitly conceived by its designers as a recreational in nature rather than as genuine transportation infrastructure."

      This is a particular annoyance of mine - facilities that are designed for "recreation" in a manner that impedes their use for practical, purposeful travel should that need ever arise. I think it's fine to have things like recreational walks, bridges, and trails, but in the US at least, they're often assumed to have little value for anything else, which invokes a feedback loop in which they're designed *not* to be useful for anything other than recreation!

      Recreational travel and purposeful travel are not inherently mutually-exclusive, but we seem to treat them as such. Contrarily, all the European examples in the above post accommodate both without compromising one at the expense of the other.

    7. Yeah. I don't have direct evidence that this was the deliberate intent of the designers, but I do think it can be inferred from the layout of the plan. Someone wanting to provide pedestrians from the most direct route from A to B would never have conceived of a ramp like that. Nor would ample parking have been provided at the entrance to the ramp. Not to mention that, as I said, the ramps seem to be tremendously over-engineered for their modest purpose of accommodating 150 lb. human beings.

    8. I live in Louisville. I agree with the author. The ramp is not practical.

      What is lost in the post is that that bridge is in a wasteland on the Louisville-side. There is nothing around it, save a large road, highways, and some green space. There's no urban fabric to disturb, since there is none to begin with.

      The bridge is indeed purely for recreational purposes. It is very popular, actually. It is a true destination. People drive here from all over the city for a walk or a jog or a bike ride.

      It's not great, I would have liked the ramp to be more compact, but it is better than it used to be. there used to be nothing. baby steps here in Louisville, but steps nonetheless.

  2. Oh, and here's an interesting example of a dual-level building in Philadelphia's stairmaster Manayunk neighborhood:

    I suspect that, in the US at least, stringent contemporary DOT regulations and engineering practices would restrict or prohibit the ability of private buildings to connect to bridges like this. (The above example is perhaps revealing: you'll note that the contemporary townhouses catty-corner from the older house made no effort to connect to the upper bridge, though it's unclear whether this was prohibited by design or simply out of the developer's range of imagination.)

    1. There's actually a building under construction in Boston that appears to be connecting to a bridge, specifically the Charlestown Ave/Gilmore Bridge over the railroad tracks between Lechmere and Charlestown. You can only see the foundation of the building on Google Maps (N/NW corner of Charlestown Ave and North St), but when I passed by, it very much looked like they were building an outdoor deck at the level of the bridge for a connection to a staircase down to ground level. So, this sort of thing is not impossible even in the US.

  3. (Note: the second image in the article, after the Brooklyn Bridge and before the Pont Neuf at eye-level photo, appears to be broken or at least not allowing access)

    1. Thanks, it seems to be a ghost of an image that was deleted. It was the same Pont Neuf image in a format that didn't display properly, and which for whatever reason is continuing to appear. I'm not able to delete it.

  4. Two other potential work-arounds:

    - bridges that run diagonally to a river, such that the length of the bridge is increased, its maximum height kept the same but it's actual grade decreased. This also allows oncoming traffic to drive alongside the river coming up to the bridge without plowing though city centers.

    - similarly, bridges built with semi-circular paths, so that again the length is increased and the grade is lower, and the riverbank traffic runs parallel to the river before merging onto the bridge. This is similar concept to the Millennium Bridge, but not meant to be an over-engineered monstrosity:

    1. Here is a hastily photoshopped example of what I'm talking about:

    2. Very creative ideas -- thanks! Bridges do seem to almost always be built perpendicular to the course of rivers even though, when you count the approaches, this does not really save them much if any length. The Tappan Zee Bridge has a modified version of your suggestion, with a main span perpendicular to the river, but the approaches curving sharply northwards, at the west bank, and southwards at the east bank. This type of design, closer to your second suggestion, might be more feasible for denser urban areas with multiple bridges. Here is another variant, with a bridge approaching perpendicularly but curving the roadways over the river so as to be parallel to the opposite bank (from Sao Paolo):

      Another one from Norway:

  5. Thanks for making me think about bridges in a new way. Here's an example of a steep pedestrian bridge in Xochimilco, Mexico City. The district is full of these, especially in the island districts and ped-only islands. The less dense islands are still gondola-only.

  6. Are there actually truly tall bridges in Europe that don't have long approaches (and where the valley is not steep)? I think most rivers in Europe are shallow so they used barges on the rivers instead of sailing ships with keels, so you didn't have to build particularly tall bridges.

    And what exactly is the problem with long approaches? I think the main negative effect is when you have gloomy spaces below and noisy traffic above, both of which deter pedestrians from those areas.

    Building under the bridges, like the viaduct examples Marc gave helps with the gloominess, as well as potentially lighting for wider bridges/viaducts and a more attractive underbelly.

    But scale is an important factor too I think. I find this section under the Gardiner expressway,-79.3832554,3a,75y,270h,90t/data=!3m4!1e1!3m2!1sfqRbwa8XtxvZHZDmr6NJZw!2e0!4m2!3m1!1s0x882b34d557417d69:0xf061b87b440506e0
    Than this section which is narrower and taller,-79.4003214,3a,75y,163.66h,84.91t/data=!3m4!1e1!3m2!1saGu7gmCLTSXj7Ndosnf4_g!2e0

    With the Brooklyn Bridge I think all the affiliated infrastructure, like the FDR ramps made it far worse. You now have to cross these at street, and there's several of them. The Brooklyn Bridge overpass doesn't pose a danger or delay, the issue with it is only aesthetic. The same goes for the Gardiner Expressway in Toronto, it's not just the overpass, I would say that Lakeshore Boulevard and the access ramps are far worse in terms of being a barrier. You have to wait for a long signal cycle to cross one direction of traffic, then wait in a small often fairly overcrowded island for almost a minute with cars passing you at 45mph before crossing the other half.

    The bridge in Nashville looks like a great way to bring more pedestrians to the areas the bridge passes over, and also shorten trips for pedestrians headed that way.

    Also not that related but on the topic of buildings brought up to the road level, this is a triple decker road that appears to be designed to bring goods to the upper floors of warehouses in Singapore.,103.8056974,3a,75y,79.44h,120.93t/data=!3m4!1e1!3m2!1sqsq2zja6_WKyYzMvp8EanQ!2e0

    1. Nick – remains of ancient Roman ships found near the Rhine are shallow-keeled or flat-bottomed with oarlocks but also have masts which could be taken down and stowed:

      So I think you are exactly right about the design of the hulls, but most of these ships did have masts and sails as well. I cannot find any direct confirmation one way or the other, but it would make sense that the masts were made to be removable in order to pass under fairly low bridges. Barges do not necessarily need to have low profiles above the waterline, either. The design of most contemporary Danube/Rhine river barges and cruise ships seems to be limited by bridge clearances:

      As for the long approaches, the issues are the same as for any highway viaduct. The typical American post-1920 experience with such structures is overwhelmingly negative. Since the roadway is grade separated and concentrates the flow of traffic, it tends to be very noisy and obtrusive. Building under the viaduct is a theoretical possibility, but in practice rarely happens as the land values in its vicinity are very low. Much more often, it simply becomes surplus parking space or is even left abandoned. Something that looks like this:,-73.9209517,3a,75y,253.59h,88.49t/data=!3m4!1e1!3m2!1sUdlAjIAaqFFZxpFsJhOfLw!2e0

      Also, while the Brooklyn Bridge was built some 15 years before the first car appeared on the streets of the city, older bridges often get retrofitted with additional approach ramps and roadways which are not compatible with a pedestrian-oriented city. Bridges with high approaches tend to be more susceptible to this type of treatment.

      If a bridge is pedestrianized and therefore returned to something closer to the pre-1900 state, without the constant roar of traffic and stink of exhaust fumes, possibilities are suddenly opened again for a more sympathetic integration into the city fabric. This is exactly what Nashville has been doing with the Shelby Street Bridge. A truly pedestrianized bridge, however, does not need long, low-grade approaches as I mentioned – I can’t think of any European examples, but the typical highway pedestrian overpass is a pure example of the type, with a single horizontal span flanked by two stairways running perpendicular to the span:,-73.9631228,3a,75y,196.9h,85.86t/data=!3m4!1e1!3m2!1sGjlg9mMsF11bLMknNBfGCg!2e0

    2. "Building under the viaduct is a theoretical possibility, but in practice rarely happens as the land values in its vicinity are very low. Much more often, it simply becomes surplus parking space or is even left abandoned."

      Yes, definitely! I wonder who should take the first step to break this chicken-egg scenario, though: should a municipality/transportation department incorporate (i.e. subsidize) commercial and mixed-use spaces under a bridge or viaduct to fight their barrier effects and therefore boost land values (or at least prevent them from dropping)? Or should we wait for surrounding neighborhoods to improve until they expand into the dead zones, as they sometimes did in the 19th century? Jacobs suggested deploying "extraordinarily strong counterforces" to fight these kinds of barriers, but I still found the recommendation rather vague.

      The link to Columbus' bridge liner in my first post suggests that, if the publicly-provided infrastructure that supports the infill tissue under a bridge or viaduct is designed to boost cross-use between two or more strong neighborhoods (downtown Columbus and the Short North as referenced in that article), then the public expense of providing a bridge liner/filler on marginal land can eventually be recouped by property taxes from the businesses that move in to connect the neighborhoods (theoretically). Of course, in many cities there are already too many vacant buildings in neighborhoods with "good bones," so it may seem rather foolish and ultimately unrealistic to inject more mixed-use space under bridges/viaducts when there is already an oversupply of said space in any other given area (you'd just end up with more empty storefronts).

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