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:

Source.

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

Source.

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.

Housing Innovations in Texas

Citylab recently posted an interesting profile of a new development in Harlingen, Texas by Amanda Kolson Hurley.  Having written about this area of the country earlier this year, I was curious to take a closer look at the development, which appeared to take some design cues from the Mexican urbanism that is just a short ride away from this border region.

An aerial view of the development, La Hacienda Casitas, shows it set among mobile home parks that are very common in Harlingen.  These homes, however, are site built, and use lots as small as 1,800 square feet, which is similar to the lots sizes found in the new developments of Matamoros, Mexico.  Streets range from 16 to 22 feet wide, with some on-street parking:

The more I looked around Harlingen, the more this particular development stood out: overwhelmingly, new development in the city consists either of mobile home parks or much larger suburban homes of the type found in sunbelt cities across the United States.  It was a pattern I'd seen before, in Bradenton, Florida, where the city's zoning code divided single-family housing into two types: large lot, site-built suburban and small-lot, manufactured and/or mobile.  Could land use in Harlingen be governed by similar provisions?

Fortunately, the city puts its zoning ordinance and map online in an easy-to-navigate format, so finding residential lot minimums was not difficult:

Here we see that Harlingen, like Bradenton, establishes a minimum lot size for lots in mobile home parks that is less than half that required in the single-family "R1" zone.  In fact, the ratio between the two zoning categories is nearly the same in both cities (Harlingen: 6000/2400 = 2.5 vs. Bradenton: 7200/3000 = 2.4).  Unlike Bradenton, Harlingen does not seem to establish minimum sizes for the dwellings themselves, although setback and lot coverage requirements impose effective maximums that are most restrictive on very small lots.

How well the city holds developers to the limits I cannot say for sure, although most lots in developments platted within the last 20 years appear to be between 6,000 and 7,000 square feet. On first blush the "Planned Development" zone appears to provide some flexibility, but it requires the developer to own a parcel of at least five acres, leaving it unavailable to small-scale builders designing infill projects.  Townhouses are also an option, but are not permitted by right in R1 zones.

In any event, the disparity between zones again appears to create a binary pattern of real estate prices, with new site-built homes on large lots averaging around $145,000, and manufactured homes only $45,000 or so.  Thanks to zoning-abetted filtering*, some site-built homes can be bought for no more than $60,000 to $70,000, but these tend to be of very low quality or on much smaller lots that seem to have been grandfathered in under the present zoning code.  This mandated land consumption obviously contributes to a low-density pattern of urban growth, and also illustrates how zoning's affordability and quality of life impact isn't limited to large coastal metros.  Harlingen's affordability safety valve, the mobile home district, establishes what is in effect a physically segregated zone for low-income, market-rate housing where even the homes themselves are forbidden from being site-built.

Homes in La Hacienda Casitas. Credit: bcWorkshop.

In light of all this, was the La Hasienda Casitas project an attempt to circumvent the code with a development of houses on tiny lots and narrow streets, thereby making occupancy (the homes appear to be rentals, at least for now) of new, freestanding and site-built homes available to low-income families of Harlingen?  Kolson Hurley's article discusses the intensive coordination and grant-seeking between and among architect bcWorkshop and non-profit housing developer Community Development Corporation of Brownsville needed to bring the project to fruition, but I have to wonder whether regulatory barriers, rather than anything inherent in the design and construction of this project, is what is standing in the way of adoption of the style by for-profit developers.


*Zoning-abetted in that the restriction of centrally-located lots to single-family use effectively caps land values, allowing the physical deterioration of the housing stock to play the predominant role in establishing property values.

Related posts:
Mobile Home Impediments and Opportunities
Cross-border Urbanism: From Texas to Tamaulipas

Demise of the Duplex

The New York YIMBY website has complied Census building permit data to reveal how construction of single-family and small multifamily dwellings in New York City's five boroughs has plummeted since reaching a peak in 2004.  Of the potential explanations advanced for this collapse, contextual downzoning appears to the most likely to me, as the decline began four years before the peak permit year of 2008.  In general, however, small multifamily buildings have widely fallen out of favor not only in New York but across the country over the past thirty years and more.

Using the same Census data, this time calculating for all 50 states and the District of Columbia, it can be seen that small multifamily dwellings (those with between two and four units) fell from providing around ten percent of all new residential units in the early 1980s to a low of just under three percent in 2013.  Even as multifamily construction has rebounded since 2009, increasing its share of all units from 21 to 34 percent from 2009 to 2013, these smaller multifamily units have actually continued to decline as a proportion of the total (the chart shows the number of units, not the number of structures):

Triple deckers in Bridgeport, CT.

The permit data only begin to capture what is, I suspect, a much longer-term decline in this housing typology. Anyone familiar even in passing with the larger cities of the Northeast will immediately recognize the heavy predominance of the type in their older neighborhoods, as represented by the wood-framed triple-decker, or three-decker, house.  Whether built up to a flat roof, as in the typical image of the Boston triple-decker, or with the third story sheltered under a pitched roof, these are large and bulky structures that generally provide three spacious units with windows on all sides.  Despite the popular narrative of urban-dwellers fleeing cramped apartments for more spacious suburban homes, these units rivaled or exceeded in size the modest Cape-style single-family homes built in the 1940s and 1950s, were conveniently set on a single floor like the ranch houses that later became popular, and offered gracious architectural features such as bay windows and front porches that were often lacking in the new single-family homes. It would not be until the 1960s that the average new single-family home would significantly exceed the size of the ordinary triple-decker apartment.

The vertical axis shows the number of  two  and three-family
structures sold over the past three years within the metro area.

Census data provides housing statistics both by year built and by housing type, but unfortunately does not combine these statistics, making it impossible to determine what proportion of the small multifamily stock was built at what time. A workaround can be had, however, by using year-built information from housing listed on the MLS, which should provide a neutral sampling of the overall housing stock. Performing this exercise for the Bridgeport-Stamford-Norwalk area, an area with housing from all eras of American history and continuing high demand, reveals an exponential increase in the type from the 1860s to the 1900s, then a slower increase to an all-time peak in the 1920s.  Small multifamily construction collapsed during the Great Depression, along with most other housing construction, but unlike single-family construction did not rebound, even though the Bridgeport area experienced a manufacturing boom in the 1940s and early 1950s that attracted many factory workers.  Instead, it continued a gradual descent into irrelevance by the 1980s and 1990s.

The appearance of these structures therefore coincided both with the industrialization of American cities and a wave of immigration from rural America and from foreign countries, with the particular architectural style of multifamily housing in New England perhaps influenced or inspired by the multiplexes common in French-Canadian towns and cities (a building type which Urban Kchoze's Simon Vallee has recently explored).  These buildings had particular appeal to new immigrants, who could with sufficient savings purchase such a building and rent the upper two floors out to other immigrant families (often, members of their own extended family) to defray the cost of housing or perhaps even earn some additional income.

Why these dwellings ceased being built after the 1920s, never to return in any great numbers, is a difficult question, but fortunately it is not one that I need to guess at.  MIT graduate student Jacob Wegmann authored a 115-page thesis entitled What Happened to the Three Decker, supervised by none other than Sam Bass Warner, which explores that very question and offers a series of possible explanations which are equally applicable to other forms of small multifamily structures:

• Above all, exclusionary zoning, particularly in the 1970s and later, that restricted small multifamily housing from being built in those places where it would have been most desirable.
• Concentration of the real estate industry in the mid-20th century, resulting in the production of large-scale tract subdivisions that were able to exclude multifamily housing altogether.
• Federal involvement in mortgage finance starting in the 1930s and an emphasis on homeownership paid for by way of extended mortgage terms rather than over a shorter period with the aid of rental payments from tenants.
• Other regulatory barriers, including parking requirements, disability mandates from the ADA and state laws and enhanced fire safety requirements that have increased the construction cost for small, non single-family structures.
• A negative image of small multifamily dwellings that had always simmered among the native middle-class and which intensified during the 1920s and later, and which contributed to attempts to exclude these dwellings from newer areas of cities.

The last point, although it may seem less important, does indicate to me a genuine underlying problem with the three decker or stacked duplex form.  As an article on Worcester's three-deckers puts it, "to look at a three-decker means ... appreciating the attempts of three-deckers to echo freestanding single-family dwellings even in the midst of an undeniably urban setting and the effort to create an illusion of space for residents."  

Bridgeport, CT rent map showing lowest rents in duplex/
triple decker belt between downtown and outlying
single-family neighborhoods.  From Trulia.

That is, the small multifamily house was apologetically urban, and offered as its apology an attempt to mimic the outward form of the cottage or farmhouse style of housing prevalent in New England prior to the 1870s.  This reticence to adopt an unambiguously urban form left such structures appearing to be second-best, a characteristic that was not shared by rowhouse neighborhoods or those composed of larger apartment buildings.  The attempt to leave small gaps between buildings, rather than using shared walls, only served to emphasize the scarcity of space and lack of light and air as compared to larger lot single-family homes.  The virtues of having natural light on all four sides of a dwelling, however, were very much real and have been appreciated for decades by the residents of these apartments.

The limited appeal of these structures has had the upside of keeping them as relatively affordable housing options down the present day even in otherwise expensive cities.  Neighborhoods composed of them are not immune to gentrification, but their form and physical location -- typically in the inner-ring areas once served by streetcar lines -- combines to keep their rents among the lowest in the metro area.  

Although the building type has not come back into vogue, the notion of using a second residential unit on one's own property to help with mortgage payments has, through the New Urbanist revival of the so-called "granny flat" (a concept which goes by countless names, but never "duplex").  The strategy of appealing to homeowners' financial interests rather than to the need for more low-cost rental apartments is politically astute and has probably helped the idea gain traction.  In the meantime, in areas where demand is high, many single-family houses continue to undergo illegal conversion to multifamily use, indicating how the America of 2014, by banning the construction of small multifamily buildings and the division of homes into multiple units, once a commonplace process, is in some areas and in some respects doing an inferior job of housing the poor and recent immigrants than was the country of a century earlier. 

Where Zoning Went Wrong

In previous posts on zoning, I’ve been pretty hard on the Supreme Court’s Euclid v. Ambler decision, which upheld the use of single-use, and specifically single family-only, zones.  In doing so, the nation’s highest court gave the formal stamp of approval to exclusionary zoning, holding among other things that cities were justified in excluding so-called “apartment houses” from residential zones.

The fact that this dispute even reached the Supreme Court in the first place, however, indicates underlying policy choices that occurred somewhat earlier. Professor Sonia Hirt, who has done extensive research in the greatly underexplored comparative zoning realm, has shown how in Germany, a limited number of zoning categories are established at the federal level, with specific implementation left to local governments.  Although localities can choose where to place these zones, they cannot create zones of their own.  Simon Vallee (at Urban Kchoze) has described a very similar regulatory regime in Japan, where the national government has established a list of certain permissible zones that cities may use.  Hirt mentions similar but even more permissive zoning arrangements in other countries such as Serbia, Greece and Bulgaria. 

Notably, whether by coincidence or design, it appears that in none of these cases have state or national governments established single-family detached-only residential zones. In general, these countries establish only floor-area limitations, thereby allowing both single-family and multifamily housing in all residential areas, and also permit small offices and neighborhood commercial even in the most restrictive zones. Importantly, lot size and setback requirements appear to be modest or minimal.

In contrast to the experience of most other countries, the United States, right from the start, delegated zoning

Munich zoning map ca. 1900. From Harvard Library.

powers from states to localities in spite of the fact that early 20th century American planners greatly admired the German zoning system.  The best-known instrument of this delegation, although it was not the first, was the Standard State Zoning Enabling Act, a document first devised in the early 1920s by Herbert Hoover’s Commerce Department.

The Act was a curious document: although it spent many pages devoted to the legal proceduralism of planning commissions, it offered little guidance, and contained no requirements, as to how localities should actually zone. This intriguing and highly consequential omission was not due to lack of interest or expertise.  Edward Murray Bassett, a principal author of New York's 1916 Zoning Resolution and of much of the Enabling Act, authored a handbook on zoning (entitled “Zoning,” what else) in which he laid out its purposes and proper role. Bassett’s work, one of many on the topic from that time period by such men as Harland Bartholomew and Herbert Swan, establishes several major themes to distinguish zoning in the United States which were reflected in the enabling act and which have characterized American zoning practice ever since:

• Approval of the exclusion of commercial activity from residential zones. Bassett seems to have assumed, without explaining further, that excluding all commercial uses from residential areas was a desirable and legitimate end of zoning. Furthermore, he casually elided any distinctions between noxious and harmless uses: "[In] a residence district a home owner may try to carry on a sweat shop or a restaurant or a junk yard. How shall he be prevented? ... The ordinance should make such act unlawful and make provision for ousting the unlawful use." (p. 327).
• Failure to disapprove of the exclusion of multifamily from residential zones. Although Bassett struck a cautionary note toward single-family zones, this appears to have been primarily because he feared (mistakenly, it turned out) that courts would strike down such zones as lacking justification (p. 323-324). This, in turn, might have cast doubt on the fledgling enterprise of zoning. Elsewhere, he advocated for such zones as a means creating preserves for wealthy urban homeowners (p. 323). Bassett also suggested the use of maximum lot coverage ratios as an alternative means of discouraging apartment houses, notwithstanding that such coverage ratios would also have the effect of discouraging single-family homes on very small lots.
• Extreme deference to localities. Bassett recommended that enabling acts transfer power to regulate the height, bulk and use of buildings to cities, apparently without any restriction on how these powers might be deployed in various zones. The states were to retain little or no power in the zoning area under his proposed arrangement, nor were they to provide any guidance except for the very vague suggestions within the Enabling Act.  There was no reason presented for this policy choice, and transportation policy was in fact moving in the opposite direction at the same time, with states and the federal government playing larger roles in planning and building highway routes.
• Insistence on a "comprehensive" plan.  Although European zoning is often conducted on a block-by-block basis according to Prof. Hirt, and frequently leaves large central areas exempt from most restrictions, Bassett and other American zoning advocates insisted that courts would not accept such piecemeal or partial zoning, and that cities should therefore zone every inch of ground under their jurisdiction.  Allowing different zones within small and otherwise similar areas was also assumed to be unconstitutional "spot zoning," and was not advised.  Impliedly, these recommendations would intensify the use-segregated character and monotony of American zoning.  Nonetheless, once the initial plan was in place, selective rezonings (almost always downzonings) of politically influential neighborhoods were carried out and continue to be carried out to this day.
• Irreconcilable conflict between planning and zoning. Bassett acknowledged that "[e]very vital growing city must change and the zoning plan must be capable of change," but quickly clarified that "a high degree of permanency or stiffness must be insisted upon." In other words, although zoning was adopted in the name of looking "mainly to the future," in Bassett's words, in practice, it would be highly resistant to alteration. To achieve this, Bassett included a proposal to limit the power of the city council to alter the zoning plan once it had been established by, in essence, subjecting every proposed zoning change to a referendum requiring 80% support of affected owners (see p. 330). What's more, Bassett's logic against zoning changes used only examples of upzoning or increasing permitted uses (see p. 330).  Downzoning was not critiqued.
• Heavy reliance on legal process as a substitute for sound policymaking. Bassett, an attorney, was apparently aware that such permissive zoning powers might result in extremely restrictive regulations: "The letter of the ordinance and maps may be the extreme of hardship," he noted (p. 330). Rather than address this potential problem by advocating limits on zoning's restrictiveness at the start, Bassett suggested a Board of Adjustment with the power to grant variances. The obvious potential for abuse, graft and corruption in such an arrangement was noted by Bassett's contemporary, Lawrence Veiller, but the substance of Bassett's recommendations was included in the Enabling Act. Bassett dismissed these concerns out of hand in his book by noting that "it is the business of the mayor or appointing power to see that the board is made up of impartial and experienced men." (p. 331).
• Rejection of aesthetic concerns. The City Beautiful movement of the late 19th and early 20th century, although it shared certain policy goals with the early zoning advocates, embraced a traditionally European emphasis on the outward appearance of the city. Architecture was considered an integral part of city planning, and planning literature frequently included lavish illustrations setting forth a compelling aesthetic vision for the city (what might be called a form-based vision).  In Bassett's view, however, aesthetics could not even supply a rational basis for zoning regulations: "If [regulations] are employed ... for aesthetics or some sentimental object, courts will not support them," he wrote. In short, despite his professed admiration for European planning methods, Bassett was waving the white flag before a shot had been fired in the legal battle.  Bassett was wrong again about how the courts would respond, but with most codes having been adopted under the erroneous assumption that such concerns were illegitimate, it would take until the mid-1990s, with the rise of the New Urbanism and the development of form-based codes, that architecture, aesthetics and form were given a more conspicuous role in zoning documents.
• Concern with protecting the wealth of well-to-do homeowners.  Although Bassett stated that zoning "endeavors to protect investments" as a general matter, the investments he cites as examples tend to be those of very wealthy individuals seeking to erect expensive houses ("A man who built a $40,000 home ... was considered highly speculative because in a few years he might have an apartment house on one side and a factory on the other" (p. 316); "[A] man might put up a fine residence ... and find that the council had changed it to business and he was likely to have a butcher store on one side and a grocery on the other" (p. 330).  This was largely the extent of Bassett's social concern, such as it was, in his book. The interests of poor and middle-class residents, whether owners or tenants, went unmentioned by Bassett (in fairness, Andrew Wright Crawford, writing in 1920, claimed that zoning was "for the protection of the poor man," although did not address the exclusion of apartments).
• Lack of comparative focus. Although Bassett claimed to have been inspired to become involved in zoning matters after a visit to an urban design conference in Dusseldorf, his treatise dismisses European planning models early on as inapplicable to American constitutional government, thereby depriving readers of the chance to learn from non-American planning precedents. Bassett even goes so far as to claim that zoning New York took as long as it did because "there were almost no precedents to help," which was only true if one completely disregarded decades of European zoning practice.

Zoning didn't remain an entirely localized concern by any means: the federal government would, only a decade or so later, become indirectly involved though FHA lending practices, and several states have since adopted regional plans, though not one of the 50, so far as I know, sets out zoning categories that cities must use. Federal fair housing laws would also become entwined with local zoning practice in the 1960s and later, but only incidentally. These original purposes, however, have endured with relatively little change and virtually no challenge over the following ninety-plus years.  

I've quoted legal criticism of some of these doctrines in the past, but there was scholarly critique at the time, as well, from progressive authors, some of it quite strident, but most of it now forgotten. For instance, the German-born Bruno Lasker, writing in 1920:

"Whence, to ask a very simple question, do so many of the zoning commissions derive their sanction for dividing the physical make-up of the city into use districts that distinguish between the residential needs of different classes? ... Why, in this country of democracy, is a city government, representative of all classes of the community, taking it upon itself to to legislate a majority of citizens -- those who cannot afford to occupy a detached house of their own — out of the best located parts of the city area, practically always the parts with the best aspect, best parks and streets, best supplied with municipal services and best cared for in every way? Why does it deliberately segregate the foreign-born who have not yet become sufficiently prosperous to buy or rent a home under building regulations which preclude the possibility of inexpensive development and construction?"

Social justice inquiries like these evidently didn't keep a legal-minded pragmatist like Bassett or his allies up at night. What's more difficult to tell is whether, had the federal government not taken such an active role in promoting a vision of local government-based planning and zoning, a more European zoning model might have emerged in some states.

Related posts:

• h/t to Daniel Nairn for the link to Bassett's book from his post Edward Murray Bassett and the Origins of Zoning, which inspired this one.
• Did Zoning Ever Conserve Property Values?

Going Driverless, or Not

A heated debate over the significance of Google's so-called driverless car has been raging over the past several weeks. On one side of the aisle are those hailing it as a "revolutionary" technology that will dramatically alter personal mobility to the point of  eliminating private car ownership. On the other side are those who reject the premise that the technology represents a groundbreaking shift, instead characterizing it as merely a "slightly different variation" on current transportation modes that is "so incremental that it epitomizes our national short-sightedness, and failure of imagination, when it comes to improving mobility in America."

It's difficult to imagine two more divergent positions on the significance of a new technology. Although I'm wary of attempting to forecast the future, knowing how likely it is that any predictions are likely to appear foolish or worse some years down the line, there are enough parallels, current and historic, that I think some general observations can be made here without wandering too far off into pointless speculation.

The human-driven motorized car, itself a recognizable variation on the 5,000 year-old horsecart, must have seemed like a rather mundane idea in the late 19th century — almost a throwback to horse-and-carriage travel that the railroads had put out of business — compared to steam railways, attempts at early aircraft and even the bicycle, which represented the first instance in history of a fast yet human-powered wheeled vehicle. The name for the early cars reflected this mindset, which some have used to argue that driverless cars are also being underestimated, as in this blog post:

"One reason I will eventually move away from my chosen name for the technology — robocar — along with the other popular names like “self-driving car” is that this future vehicle is not a car, not as we know it today. It is no more a “driverless car” than a modern automobile is a horseless carriage. 100 years ago, the only way they could think of the car was not notice there was no horse. Today, all many people notice is that no human is driving. This is the thing that comes after the car."

Could it be that these early observers were right, though? The very early car was slower than the steam trains, and its primary breakthrough was economic: by moving the horse out of the picture, and substituting the combustion of an oil, it became possible to maintain a personal carriage without the the constant care and expense needed for keeping horses. The earliest car ads emphasized the savings in cost, care and anxiety from not having to keep a horse rather than advantages in speed. It took several more decades until the velocities enabled by combustion power and paved highways could be fully realized.

By contrast, the driverless car offers no such economic advantage to the individual driver, since he is already donating his own labor to operate the vehicle. In implicit recognition of this fact, the claim is made that the most significant consequence of this invention will essentially be to reduce the cost of taxis to the point that renting a car on a trip-by-trip basis actually becomes cheaper, and no less convenient, than owning one. In other words, a driverless car network, for all the technology it requires, is really a simple labor saving device, which like the very early car, allows an existing function to be performed more cheaply but otherwise not much better: certainly driverless cars will not enjoy the kind of speed advantages over human-driven cars as the autos of the 1920s gained over horse-drawn carriages. In this sense, it is functionally equivalent to a massively subsidized (or, perhaps, completely unregulated) human-driven taxi service, which, in theory, could be funded for no more than the amounts currently spent on private car ownership, and certainly with less technological difficulty.*

As it happens, non-subsidized transit systems of this sort already exist, and have existed for decades, in many cities of the developing world where labor is cheap, car ownership is low and public transit options are limited.

Auto rickshaw in Bangalore and Xe Nom drivers in Hanoi. Wikipedia and Flickr/Gavin White

These transit systems, based first on human-powered rickshaws and later auto rickshaws, motorbikes and pedicabs, provide both point-to-point and last-mile transport, essentially substituting for private vehicle ownership.  However, the tendency over time, as a country grows wealthier, is not for auto rickshaws to become ubiquitous, but for public transit and private vehicles (motorbikes or cars) ownership to supplant them. This is certainly due in part to the rising cost of labor, but must also be due to the inherent comfort and convenience of owning one's own vehicle in low-density areas and of the geometric efficiencies of transit in a dense city (using Jarrett Walker's terminology). The dense city of taxi-based transport tends to be a traffic nightmare. The low-density city, on the other hand, generally uses taxis in a limited supportive role.

(An exception might be the dense but mid-sized city of the developing world, such as Jaen, in Peru, a country that is notorious for the use of largely unregulated, and therefore quite cheap, taxi and bus systems to supplement inadequate public mass transit systems, such as in the far larger capital of Lima):

Motorbike-taxis on the streets of Jaen, Peru. Exploration of the city on Streetview shows a
largely taxi-based transportation system, supplemented with private motorbikes. There are
only a handful of automobiles visible here and there, mostly utilitarian in nature. A far cry
from the SUVs of American streets, these vehicles actually seem designed around the
size and weight of human beings, and create a steady but by no means congested flow of traffic.

For driverless cars to reverse this durable observed trend, and actually encourage people to dispose of their cars, we'd need to believe that the cost savings of driverless taxis could outweigh the inevitably increased inconvenience of not having personal ownership (including ownership of a driverless car) for most or all people. The problem with this scenario, though, seems to be twofold, as stated before:

• In dense urban areas, very cheap and convenient taxi service may overwhelm highways and city streets, as it does in Hanoi or Mumbai or many other cities of the developing world, negating that same convenience and worsening the quality of urban life (miles driven are expected to increase with a "robotaxi" system, according to one recent study, and this may underestimate the number of transit riders, cyclists and pedestrians who switch to driverless taxis). If the number of taxis is limited, as in most cities in developed countries today, then this will partially negate the cost advantage of lacking a human driver and will certainly hinder convenience, illustrating again that this is as much an issue of restrictive licensing and geometry as it is technology. Arguments on behalf of robotaxis appear to assume that their numbers will not be limited by law.
• In suburban and rural areas, sufficiently frequent robotaxi service may be difficult to provide, yet the cost of storing one's own personal vehicle will continue to be minimal or nonexistent while providing total convenience. Additionally, suburban errands often require multiple stops spread out over a large area due to car-based urban design, which will either require tiresome and inconvenient re-hiring of cars for each leg and practical difficulties with transferring purchased goods, or else cars will need to 1) park at each destination or 2) cruise around aimlessly while waiting, either of which would lessen certain of the the advantages over individually owned vehicles. 

There is one other issue which I raise by way of a insightful quote from Neil Salmond's article on robotaxis: "Once you own a car - and so mentally discount the cost of insuring, maintaining, fuelling the car - then every trip looks free." Although I agree with this, it also suggests a very difficult path toward weaning people off private car ownership. A privately-owned car is immensely versatile. It can handle short trips, medium-length trips and cross-country treks. It is always there and ready to go at a moment's notice, at times of high and low demand alike, with no questions asked. For many it is a personalized space as much as one's own bedroom or office, and doubles as a mobile storage unit. The opportunity cost of giving up all this "free" travel, and its associated comforts and conveniences, may therefore be much higher than might be suggested by a pure dollar-and-cents comparison.  Further, once the car is owned, whether it be human-driven or not, the incentive to use a taxi system at all is much reduced for the very reason Neil describes. No matter how reasonable a robotaxi trip might be, it cannot beat the perception of "free."

Whether or not robotaxis can succeed at large scale in American cities, there are a few areas where a privately-owned driverless car could provide an unmitigated social and economic good. For those unable to drive and without access to reliable transportation, such as young people or very elderly living in car-dependent areas, owning such a car could be a lifeline to mobility and independence. That would have the potential to remedy one of the greatest inequities of a car-based transportation system (though certainly not the only one). It's also tempting to imagine, as Neil suggests, driverless cars ferrying commuters to rail stations, and thereby opening commuter parking lots for redevelopment, and it's certainly possible, or even likely, that driverless cars could become the default ownership option. A cheaper, but non-revolutionary, taxi system might not be such a bad thing, especially for households that need access to a car but only rarely. And what of the implications of driverless buses, and driverless car sharing? As an incremental step that expands transportation options while lowering costs, it has promise.

The vision of a fleet of driverless taxis completely supplanting car ownership, however, seems to encounter significant practical difficulties. Many vehicles on the road must remain individually owned in any event (such as vehicles serving a particular business).  With the abundant free parking already prevalent in the United States, one of the greatest cost benefits of a taxi system — eliminating the need for costly local storage — is greatly lessened. In other countries or in certain US cities, this advantage might be more appreciable, but then, a city that is sufficiently dense will, or eventually will, offer alternative transportation options that do not require storage, either. In the case of this technology, only time will tell.

-----------------------------------------------------------------------------

*Let's consider that for a second. One study has estimated that a fleet of driverless taxis could dramatically reduce car ownership, on the order of one driverless taxi replacing eleven owned vehicles. Given car ownership in the US of 800/1,000 population, this suggests a reduction in car numbers to only 72/1,000, or approximately the same number seen on the roads of Mongolia.

Now, with the savings from not having 728 owned cars, at an average of $8,800 per year per car, a surplus of $6,400,000 per 1,000 population is generated, or approximately $90,000 per remaining car just based on eliminating ownership. Even if we generously assume $30,000 per year per car to account for gas, heavier maintenance and more frequent car replacement, that still leaves $60,000 for driver wages even before accounting for any per trip fees levied on riders. Even a modest fee of, say, $2 average per ride, could generate tens of thousands of additional dollars per year. In other words, replacing private car ownership looks, at least on a back-of-the-envelope calculation, like it would be financially feasible right now, not at some uncertain date in the future.

This still underestimates the savings, however, since by eliminating private car ownership, and turning the task of piloting cars over to professional drivers, we both eliminate the need for expensive parking minimums and may reduce the economic cost of crashes (estimated at $871 billion each year nationwide, or $900/person in economic losses).

Furthermore, such a network would presumably make many local bus systems obsolete or uneconomic (though probably not regional bus or rail systems), so that spending in these areas could be transferred to supporting a public network of taxis, offsetting the additional tax that would need to be levied to fund the system. Although the retention of human drivers creates a major added expense, drivers can be expected to perform some duties (refueling/recharging/basic cleaning and maintenance) that would otherwise need to be done by separate employees, and the human brain offers a proven technological fix to many of the difficulties still encountered by driverless cars.

The Problem with Schools and Housing Supply

In an earlier post, I discussed how the population of young adults and young children is rapidly declining in the wealthy suburbs of New York City, a trend previously noted by the New York Times.  Although I alluded to high housing costs being an important factor in these changing trends, I failed to mention an absolutely crucial element that is driving much of the opposition to increasing housing supply: school funding. This factor is so important that is helps explain not only regional patterns in the New York area, but the NIMBY attitudes prevalent throughout much of the United States that have been so heavily covered in recent books and articles.

While it's often pointed out that the American system for education funding creates great disparities both between states and among school districts within states, what's less often noted is that the same locally-slanted funding system greatly contributes to and reinforces opposition to increasing housing supply. A glance at the particulars of the funding system makes it immediately obvious why this should be the case. Crunching the numbers for the city of Rye, in Westchester County, the Zoning Plan blog estimates that:

"Only a small percentage of households in Rye pay enough school taxes to cover the cost of two children in the RCSD. Even most large new homes do not pay enough taxes to pay for two students."

I can't vouch for the accuracy of these particular estimates, but there's no doubt that the typical state's funding system, which places around 44% of the cost of funding local schools directly onto homeowners through local property taxes, punishes those jurisdictions that choose to increase their residential housing supply, and in particular the type of housing supply that is aimed at families with children.* The town that adds additional homes of this type has two basic options: either increase the tax burden on existing residents, with no improvement in the quality of education, or keep taxes constant while letting school quality decline.

The quoted blog is particularly interesting in how it illustrates how opposition to demolition of smaller homes, and their replacement with so-called McMansions, is linked to concerns about school-related property taxes. The site puts its bluntly: "We don’t want to be told we can’t replace a three bedroom, senior-friendly ranch, with a five bedroom, family-friendly colonial, but then, why should neighbors pay more school taxes and endure class-overcrowding when [school] enrollment increases?"

The blog suggests the common-sense solution of increasing the proportion of child-free households by constructing much smaller single-family homes to retain empty-nesters, something I've advocated previously.  In most American towns, however, and certainly in the elite suburbs of Westchester and Fairfield County, such a recommendation is likely to be met with intense hostility. Multifamily residential is even less welcome, and non-residential uses are feared as nuisances and traffic generators. Faced with the threat of larger homes bringing increased taxes and smaller homes portending decreased property values, the shrill NIMBY voice is raised against any project, large or small.* 

The typical American system of local school funding appears to be unique in the world, or nearly so. As psychologist Robert Slavin wrote in 1999:

"To my knowledge, the U.S. is the only nation to fund elementary and secondary education based on local wealth. Other developed countries either equalize funding or provide extra funding for individuals or groups felt to need it. In the Netherlands, for example, national funding is provided to all schools based on the number of pupils enrolled ... ."

Canada's provinces maintained a roughly analogous funding system in the not-too-distant past, but educational reforms in several provinces in the 1990s — notably in Ontario, British Columbia and Alberta — brought about a transition from joint local-provincial school funding systems to provincial-level systems. These changes also seem to have involved a shift in funding sources away from local property taxes and toward general tax revenue. In the case of Alberta, these reforms are reported to have enabled a reduction in residential education property taxes of 65%.

The heavily localized school system in the United States long predated Brown v. Board of Education and school desegregation, but incentives for localization were greatly increased with the Milliken v. Bradley decision from 1974, which endorsed political balkanization of urban areas as a means of evading desegregation mandates. In combination with exclusionary zoning codes, which the court had approved nearly 50 years earlier, self-governing municipalities were given almost every imaginable enticement and ability to restrict increases in housing supply. Since good schools, no matter what their enrollment, are associated with higher property values, the incentive is to create the best possible schools for the fewest possible students.

At worst, the result is an urban area composed of petty fiefdoms, each groaning under the weight of local property taxes and thus resistant to the arrival of any new families, but equally resistant to conceding any revenue or authority to higher-level governments. A handful of jurisdictions with legacy stocks of time-worn apartment rentals are made to absorb most of the region's low-income students, and with correspondingly lower levels of per-student funding. Is it any surprise that young families are deserting these areas in large numbers, as I showed was the case in Fairfield and Westchester Counties?

Not every state has so localized a school system, however. In Fairfax County, Virginia (a state that doesn't lack for its own school funding problems and controversies), where schools are run at the county level, property taxes are half the level of Westchester, achievement is comparable or higher, and the under-5 demographic, which is in freefall in Fairfield and Westchester despite overall population increase, is growing rapidly. Similarly, in Davidson County, TN, which merged with the city of Nashville 50 years ago, the 25-35 and under-5 populations have surged.

Westchester County school administrators object that the high cost of housing in the county requires higher teacher and staff salaries, but this too is partly a consequence of restricted residential supply. The attempt to exclude families in an effort to limit property taxes increase ends up inflating housing costs, and these increased costs are shifted back onto property taxes in the form of the increased employee salaries needed to account for the cost of living. Lately, cities have attempted to shift even this consequence onto the private sector by mandating inclusionary zoning for new development to provide for city employees (typically, law enforcement, firefighters and educators) unable to afford market prices, and doing so for purportedly altruistic reasons. However, when Darien, CT, attempted to limit its own inclusionary zoning program to so-called priority populations, including town employees, it drew attention from the Department of Justice.

Policymakers haven't been blind to the perverse incentives created by localized school funding. Massachusetts' Chapter 40R, which creates incentives for towns to upzone residential land, has companion legislation providing for additional funds for cities and towns that establish such upzoned districts to cover the costs of educating children who move into those same areas. Not that it has been successful in this end, at least as of a few years ago: according to a 2009 study, "[v]ery few districts approved to date allow construction of the type of housing (modest single family "starter" homes) that would be expected to trigger payments under [the law]."  In addition, the charter school phenomenon, although far too complex a topic to delve into in any detail here, frequently involves direct state-level funding of charter schools.

Even in Connecticut, the problem has long been known and obvious solutions proposed: a report from back in 2003 observed that the state was "badly in need of regional and statewide revenue raising and land-use planning for long-term development." In Connecticut's case, as is the case for many states, this is a solution that is easier said than implemented.

----------------------

*It's an easy task to find quotes from city and state officials raising concerns with affordable housing programs on the basis that they attract young families with children, typically prefaced with the caveat that the legislator in question doesn't disapprove of children per se. A state representative from the town of Trumbull, in Connecticut:, reacting to the effects of the state's affordable housing law (the notorious Section 8-30g): "The [affordable] developments tend to have children, and children are great. But the fiscal reality is that our schools have grown considerably. We've had to build a new school in part because of our increasing population. We would have had to have built it eventually, but that [affordable housing] sped that along."

*This paranoid mindset, especially when paired with other latent biases and prejudices, can result in what I would term "NIMBY derangement syndrome," where otherwise reasonable and mild-mannered homeowners make shocking, hysterical and/or outrageous claims and allegations, usually against so-called "greedy" developers.

Mobile Home Impediments and Opportunities

A few days after the recent post on American and Mexican housing, the New York Times Magazine ran a lengthy article, which I was alerted to thanks to Brandon Donnelly's blog, profiling America's mobile home industry. Brandon considers the ethical issues raised by the apparently considerable profits to be made in this area of real estate, such that there are now entire courses offered by successful investors in making one's fortune, or at least living, owning and operating mobile home communities.

The article serves as a nice jumping off point from the earlier post, as it deals with what is, in much of the United States, nearly the only type of single-family detached housing that is allowed to be both very small and built on very small lots. Much of the affordability of this housing type, it seems, is attributable not only to the efficiencies of mass production or the frequent separation of the cost of land from the cost of ownership, but the common exemption of areas zoned for mobile homes (setting aside for now the curiosity of why there should even be such zones) from the standard restrictions of single family zoning, including minimum lot sizes, front and side setbacks, parking requirements and even minimum street widths.

Consider, for instance, the zoning code of Bradenton, Florida, which like many Florida cities has a large number of so-called mobile home communities (though in the majority of cases, these homes are never moved after being sited):

City of Bradenton.

In the above chart, admirably simple for an American zoning code, R-1 is single-family, R-2 is two-family, R-3 multifamily, and R-4 "Mobile Home" (UV is a special "urban village" district that covers very little of the city). Note that in the mobile home district, minimum lot sizes are less than half that required in the single-family district, even though both only permit single-family homes! The comparative minimum dwelling sizes are a strikingly divergent 1,500 sq. ft. and 400 sq. ft. The mobile home zone is allowed to be built so densely, in fact, that its maximum permitted units/acre is equivalent to the multifamily zone. Not shown here are the parking tables, which require only one space for mobile homes, yet two for single-family homes, regardless of square footage.

The resulting streetscapes in the mobile home zones are completely different from almost anything else in American suburbia, featuring extremely narrow streets without on-street parking, very modest setbacks and tiny lots either with pocket backyards or none at all (from Bradenton):

Some are so tightly packed that streets can barely accommodate a single car (again from Bradenton):

The separate standards for site-built and mobile homes probably arise from the fact that the latter homes were initially presumed to be transient, and that the sites designated to host them were therefore viewed more as parking lots than as a formal arrangement of streets and building lots. As one study puts it, many of the complex issues surrounding mobile homes "arise, in part, from the mobile home's historical classification as a travel trailer, the vestiges of which persist even though mobile homes have become a more permanent housing solution." Although city planners, such as those in Bradenton, appear to be gradually imposing more conventional siting requirements on mobile homes, this statutory inertia continues to manifest itself in more permissive square footage and lot sizing requirements as well as the separate zoning designation itself.

The existence of dueling single family zones with such disparate requirements produces some striking visual contrasts, as below, where R-4 adjoins R-1:

The relaxed requirements for mobile home zones may help explain their proliferation in Florida, particularly in permissively-zoned unincorporated areas of surrounding counties such as Manatee. The looser regulations serve as a major subsidy on top of manufactured homes' significantly cheaper construction costs. A resultant surge in construction of such neighborhoods in Florida, where trailers have probably always been subject to less zoning ostracism due to the need to accommodate RV-driving and trailer-bearing seasonal visitors, appears to have normalized the type.

It may seem strange to discuss how mobile homes occupy a privileged position in many zoning codes, given that literature on mobile home areas tends to focus on the regulatory impediments to their construction. However, these impediments tend to take the form of limited areas actually zoned for mobile homes, rather than the restrictions within these zones. The money to be made in operating mobile home communities appears to be a form of regulatory arbitrage that takes advantage of the much smaller lots, home sizes and generally cheaper infrastructure permitted within mobile homes zones as compared to those for single-family zones. This permissiveness has not escaped notice of the tiny house proponents, who have sought to use existing RV park designations to accommodate tiny house communities.

Although Bradenton actually bans site-built homes within its mobile home district, a few cities are gradually coming around toward embracing by-right smaller lots for site-built homes in existing suburban neighborhoods. Portland's (Oregon) infill regulations permit lots as little as 2500 square feet in some instances, though not without predictable hysterical reactions. Had such small lots been permitted as of right in a city like Bradenton for site-built homes, it seems plausible that trailer homes would be less common. When small lots are combined with attractive homes on narrow streets, the result doesn't have to be so terrifying after all.

Key West, Florida.