Friday, August 3, 2012

Friday Read: Residential Streets and America's Hidden Parking Policy

With discussions about on-street parking tending to focus on high-demand metered spaces in retail districts, the fact can get lost that the overwhelming majority of on-street parking in a given city serves exclusively residential areas.  We tend to take these spaces for granted: in a low-density area, they typically have very low occupancy rates, making them almost invisible.

These spaces are the subject of a new study, Amenity or Necessity? Street Standards as Parking Policy, which examines the "hidden parking policy" implicit in the standards for street width established by many cities.  The study calculates that these standards have produced somewhere between 740 million and 1.5 billion parking spaces along American residential streets enough to host all of the passenger vehicles in the world the vast majority of which are unmarked, unmetered and indeed unused. The authors estimate that the cost of construction of these spaces is in the trillions of dollars, with an annual maintenance cost in the tens of billions. These costs, the authors note, amount to approximately $1,000 annually per home.

Murfreesboro, TN street, 36 ft. wide, built circa 2005.
This parking provision is the result of minimum width requirements which, by their dimensions, automatically prescribe parking lanes (a 36-foot minimum, for instance, effectively provides two parking lanes).  Noting that a requirement for wide streets is equivalent to a requirement for on-street parking in most cases, the authors interviewed a series of city transportation planners to ask a) the basis for mandating street parking and b) the basis for minimum street widths.

Interestingly, although the resulting streets often look the same under both objectives, planners claimed that the purpose of providing on-street parking is to serve as an amenity for residents and visitors, whereas minimum street widths are justified for safety reasons.  As the authors note:
"[Most] respondents believed that the purpose of mandating parking was to provide extra parking, which was accomplished through the minimum street width requirement under the guise of traffic safety (rather than parking demand). In other words, street parking is an amenity, but it is provided in the name of necessity. Such 'flip flop' reasoning reflects local decision makers’ ambiguous understanding of the basis for mandating parking in street standards."

Stranger still, the authors found that width requirements for private streets are generally narrower than those for public streets, which calls into question the safety justifications behind mandated public street widths as well as undermining the amenity argument.  In Las Vegas, for instance, public streets are required to be 37 feet wide, while private streets need only be 28 feet.  Of the many traffic planners surveyed, none were apparently able to convincingly explain the discrepancy between the public and private standards in their cities.  In light of the substantial costs associated with street construction and maintenance, however, these differential street mandates effectively serve as a subsidy for private neighborhoods.

Looking at the issue as a whole, the authors further explain:

"The key problem for the parking mandate implicit in street standards is its hidden nature. ... Street parking policy has typically been buried in street width requirements, which are supposedly based on safety concerns rather than parking demand. Many street standards do not even mention parking in descriptions of the minimum width requirement, creating the impression that these requirements solely address street needs and technical issues.

"This "camouflage" makes parking policy invisible to the public and precludes public oversight. In sharp contrast to minimum off-street parking requirements, the street parking mandate has rarely been publicly discussed or debated in the United States. Even New Urbanism supporters do not oppose street parking but allow it on narrow residential streets ... The hidden nature of this parking policy grants it legitimacy because providing streets has been widely acknowledged as a key government function. The issue could become more controversial if this function of providing streets was modified to include "providing parking..."
 The study closes with two recommendations:
  • Unmask the hidden parking policy and subject it to public debate.
  • Eliminate the double standard between public and private streets, and make parking optional for residential streets.
Although the authors don't delve further into the issue in this study, I think there may be a simpler explanation for the emergence of on-street parking. A study by Michael Southworth and Eran Ben-Joseph suggests that the trend toward requiring wider and wider streets in the first half of the 20th century was in part driven by a conflict between the of the intent of the transportation engineering profession to allow unobstructed, free flowing two-way traffic on all streets and the reality that, once streets were made sufficiently wide for this purpose, drivers would, out of convenience if not necessity, simply park along the curbs, narrowing the street back down again.

With planners' recommendations that travel lanes be 11 feet in residential areas, and the minimum of seven feet occupied by a parked car, this implied roadbed widths of at least 36 feet - precisely what planning commissions and highway engineers had begun advocating for by the 1950s.  In this view, on-street parking was merely a incidental effect of designing for unobstructed movement, which would help explain the confusion current planners have in accounting for the existence of both on-street parking and street width minimums, as well as the identification of speeding as the greatest problem facing residential streets.

This feedback loop of increasing required minimums proceeded in spite of the growing adoption of off-street parking minimums in the 1950s, although these produced little change in form for very low-density suburban areas.  In combination with the higher density suburbs of the more recent past, however, these regulations created something that was the worst of both worlds: very wide streets so riddled with curb cuts that on-street parking was hardly available anyways (see above image). 

This approach was not shared by other countries: Japan, as Paul Barter describes, adopted proof-of-parking requirements for car buyers and helped enforce the policy by continuing to build residential streets so narrow that on-street parking was essentially impossible.  It may not necessarily be the best or most appropriate policy for other cities or countries, but it at least shows a logically consistent approach to the issue.

The question of how street standards and parking supply interact, though, is a key and underexplored issue, and this study may help open a needed discussion on topic.

(h/t Laurence Aurbach for the study).


  1. Re: Las Vegas Residential Street Width

    The answer is very straightforward; a narrower street allows the developers to squeeze in more lots.

  2. I fail to see any value in this study, and indeed think a "parking optional" recommendation for residential streets is absurd. It would seem the authors subscribe to the pack-em and stack-em philosophy of how we should live. No thanks.

    1. Off-street parking and high densities are not inherently linked.

  3. I've often wondered why the government is expected to provide storage for private vehicles. It's great to see this sort of study and your post.

  4. Actually, this is not really a "parking policy," it is a "small town america policy." By that I mean that the basic U.S. suburban street width was actually created around 1780, with the introduction of "19th Century Hypertrophism" in the U.S. in place of Traditional European urbanism. This was 140 years before automobiles became commonplace. It wasn't until automobiles appeared that people began using the excess street width as "onstreet parking." In other words, it was not as if people asked the question "where do we park the cars" and came up with the solution "on the street." If that was the case, streets wide enough to allow onstreet parking wouldn't have appeared until the 1950s. Rather, the question was: "what do we do with all this street?" and the answer was "park the cars there."

    The persistence of this notion is again irrational, merely a series of justifications to maintain the "small town America" format of overly wide 19th Century Hypertrophism streets, not any real utilitarian need. Most suburban homes have about four spaces of offstreet parking per house, two in a garage and two in the driveway in front of the garage. More than enough for anyone.

    1. What I am getting at is: a lot of the format of the U.S. suburbs today is wholly irrational. It is more like a cultural oddity, like eating turkey for Thanksgiving. Eating turkey is wholly arbitrary, but we cling to it as an expression of cultural identity. In a similar fashion, the overly wide street of "small town America" (i.e. a 19th Century Hypertrophic format for small towns in mostly rural areas) has become another expression of cultural identity for most people, which they will cling to in much the same fashion that they have a ritualistic attachment to turkey, mashed potatoes and cranberry sauce for Thanksgiving. They will defend this with all manner of logical-seeming justifications, when in fact it is not a matter of rational utility at all. This is simply the way people work. For now, the way forward will lie with that small portion of the population (under 5% really) that is capable of and interested in different and better arrangements, until enough of a precedent is established that the rote tradition-followers feel comfortable.

      I tried to get at this with the example of the Norse colony in Greenland. They came from a climate that was suitable for cattle raising. Alas, Greenland was too cold for cattle raising, but it was a paradise of fishing. Unfortunately, I interpret their history (of eventual starvation) as being one of cultural identity: they clung to cattle-raising with the same fervor that we cling to turkey for Thanksgiving, although, in this case, it was not simply irrelevant but actually led to their demise.

      I think that the better intellects and more adventurous souls among us will recognize this non-thought-process, and in that was be able to sidestep the endless swamps of argument that you encounter when you talk to people who will defend to the death (literally in the case of the Norse in Greenland) their attachment to cultural identifiers, using an endlessly shifting array of seemingly-rational arguments.

    2. Thanks Nathan -- I agree that these somewhat irrational dimensions long predate the street standards of the 20th century. I had (but ended up not posting) an image of a residential street in a single-family detached streetcar neighborhood of Nashville, laid out in the 1880s, with a 36-foot curb-to-curb width, *plus* sidewalks.

      What is more difficult to understand is why these same sorts of dimensions were adopted by the traffic engineers, men who prided themselves on their rationality and allegedly scientific thinking. It's possible they were culturally imprinted as well, or simply copied earlier examples, since there simply isn't much evidence of anyone giving conscious thought to street parking policy (except in American downtowns, where there was a lot of controversy on that issue in the 1920s). My best guess is that on-street parking was simply an unintended side effect of designing wide streets around other considerations, and that the attempt to account for this tendency to park along the curb resulted in a continual widening of the standard (as actually happened between the 1910s and the 1950s).

    3. Onstreet parking is actually a hideous solution for parking, as anyone who has tried to parallel park in heavy traffic should understand. I think most women will simply avoid it entirely. Not only do you need some space for the car, but eventually you conclude that you need even more space to open doors and get junior out of the carseat without being run over by a truck. No wonder people were so happy to get offstreet parking in the form of the suburban strip mall, and considered this a major step forward until their children began to point out that it was hideously ugly, and produced impossible car dependency.

  5. What would home buyers prefer given the choice of wider or narrower street, deeper or shallower lot depth, and cost? That 36-foot-wide street isn't cheap to build nor is the land for it isn't free.

    One study showed requiring a garage added $50,000 to the cost. Would some buyers opt out of the garage?

    1. Hi Peter -- very interesting question. Many of the planners in the survey believed that private builders, if given the opportunity, would not build on-street parking (the lesser required widths for private streets is indirect evidence of this). To really find out, I suppose one could look at private neighborhoods to see how often developers built streets in excess of the minimum, or simply interview homeowners themselves.

      The garages are another very interesting point. One of the planners mentioned that, in his city, people tend to park on the driveway, and use their garages as storage space. That seems easy to explain -- the garage can shelter a huge amount of stuff, serve as workshop space, a home gym, etc, whereas the car doesn't even really need the shelter at all, and may be more convenient to access sitting on the driveway in any event. Moving the car out onto the driveway results in a net gain of useful space for the household. Would some households rather not have it at all? For 50k, I'm sure the answer would be yes for many. Alternatively, the garage could be convertible into living space.

    2. I think people with more modest incomes wouldn't go for the garage. A lot of new homes in suburban Montreal don't have garages. These aren't tiny homes, they are modest, but I think every North American city has quite a lot of similar sized homes.

      In the second example, you see a cheap little structure over the driveway, probably to prevent snow and ice from getting onto the car in the winter. It probably cost a tiny fraction of $50k.

      As for street width, many municipalities in Canada, including all the major suburbs of Toronto have minimum street width requirements of 24-28ft. This is wide enough for 2 lanes of traffic and 1 lane of parking, and it's quite rare for streets to exceed this minimum requirement. For private streets, I think the minimum is around 20ft, and again, it's rare that this gets exceeded, so I wouldn't be surprised if they'd be narrower if the street width requirements were reduced even more.

      Do all American cities/suburbs require curb to curb widths of 35-40ft?

    3. Hi Nicolas -- thanks as always for the interesting examples. Most American cities actually do not require widths of 36 feet or more. The average width is slightly over 30 feet according to the study, with some as low as 20 feet. The most common widths are 26, 28 and 36 feet.

  6. That wide street is also a lot harder to shade with trees, which makes the wide expanse of asphalt that much more overbearing and unpleasant.

    I'll say this though, a narrow street looks very strange when front yard setbacks are fairly large too, especially if the houses are pretty close together side-by-side. It's almost as if the wide streets with wide setbacks yield a bit better proportional relationship to one another.

    I do also wonder if in the past much of the width of the streets was rationalized because it was viewed as open space. They didn't really help a lot as firebreaks, but they do ensure access to light and air.

    1. An emphasis on light and air was definitely part of it. At the same time, some planners of the early modern era (late 1800s/early 1900s) had ecstatic visions of densification and urbanization, and saw the street dimensions as anticipating (inducing?) the high volumes of traffic that would eventually occur, even if decades out in the future. Setbacks, also, were partly a means of reserving a right of way for future widening.

      This was all at odds with the arrival of Euclidean zoning, yet somehow the street standards survived that event and even continued to increase, perhaps because the transportation technocrats and the zoning boards of the era were separate institutions. Even today, the Murfreesboro zoning code contains no requirements for street width -- these are listed in a separate document, and are under the control of the city engineer, rather than the planning commission. The engineer, in turn, relies on AASHTO, ITE and TDOT specifications. Thus we have low-density, residential-zoned neighborhoods with streets designed to what appear to be highway-like specifications. It's no surprise that the transportation planners in the study complain that the biggest problem of these streets is "speeding."

    2. "Thus we have low-density, residential-zoned neighborhoods with streets designed to what appear to be highway-like specifications. It's no surprise that the transportation planners in the study complain that the biggest problem of these streets is 'speeding.'"

      I am constantly amazed at how traffic/road engineers design residential streets to the specs of county highways, then they routinely express genuine befuddlement over the resulting pervasive problem of speeding!

      To me this is a perfect example of technocratic limitations and stunted overspecialization: the engineers are missing what is common sense to everyone else (i.e. wider, straighter roads = more speeding):

      Since most drivers will always travel at the max speed they feel comfortable based upon the cues and handling characteristics they pick up from the street, it would seem to be common sense among the engineering professions that narrower streets with bends, tighter geometries, terminating vistas, street trees, enclosing buildings, on-street parking, and rougher pavement would induce drivers to slow down. (Then maybe we'd need fewer costly traffic cops too.) Although things appear to be gradually changing, the technocratic street design manuals still seem to discourage many of the above street details (street trees are still officially "fixed hazardous objects," for example) under the guise of making the superwide streets safer for motorists.

      Another curious thing is that some municipalities mandate the wide streets AND ban on-street parking (either partially - with exceptions for yards sales and the like - or completely) too! So what's all the extra space for then?! Why should residents be taxed to maintain something useless that they could potentially opt-out of?

      Weird how we mandate public housing for all our cars (and then some!), but when it comes to housing for people...

    3. "Public housing for cars" -- I like that one. Prof. Eric Dumbaugh has done quite a bit of work in this area, showing how the prescribed streets tend to not even fulfill their promise of greater safety:

      Laurence Aurbach has also written about the "functional classification system" that produces these types of streets:

      As far as banning parking on wide streets, my guess is that it is in reaction to the tendency to park on-street as I mentioned. If the street is less than 36' across, to preserve two full 12' lanes as the traffic manuals have often shown, you'll need to ban parking along at least one side of the street -- and banning both may simply be easier to enforce.

    4. You see a bit of the narrow street, large front setbacks and houses close together in earlier suburbs of Vancouver:

      Newer suburban streets seem to be wider, more like elsewhere in Canada (around 25 ft). That's somewhat understandable though, since the newer streets aren't as "rural", they have a curb, lacking ditches and a place to pull over on a grass or gravel shoulder.

  7. The wide streets of pre-automobile America were utilitarian. They kept the horse pollution farther away from the house.

    1. Well, ample setbacks can fulfill that goal without the need for wide streets. Where lot depths are shallow, wider streets could actually bring those unpleasant sights and odors closer to the houses.

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