The Pseudo-Science of Parking Ratios

Continuing in our series on the problems with parking ordinances, today I want to look at fundamental problem with parking ratio requirements. Tomorrow I’ll follow up with a local example of the consequences of these poor policies. Because he explains these things better than I ever could hope to, I’m going to quote heavily from Donald Shoup’s excellent resource on this subject matter, The High Cost of Free Parking.

Where did these requirements come from?

Shoup explains the origin of parking requirements in the US at the beginning of his book:

Why is most parking free to the driver? When only the rich owned cars at the beginning of the twentieth century, motorists simply parked their new cars at the curb where they had formerly tethered their horses and carriages. But when car ownership grew rapidly during the 1910s and 1920s, the parking problem developed. Curb parking remained free (the parking meter was not invented until 1935), but there were no longer enough spaces for everyone to park whenever and wherever they wanted. Drivers circled in vain looking for a vacant curb space, and their cars congested traffic.

This is essentially the same issue as raised by residents today. When there is more demand for parking than supply (such as a popular urban cafe) then people will park on the nearby streets instead. This upsets owners (especially residential owners) who would like the public, free parking in front of their property not to be used up by other people.

Thus in the 1930′s cities began incorporating parking requirements as part of their zoning ordinances, to make businesses provide ample off-street parking attached to any new building. This ensured that enough free parking was available to meet the demand for free parking.

Parking requirements are built on faulty economics

The underlying problem with parking requirements is that they are attempting to solve a MARKET problem (balancing supply and demand for parking) without using MARKET mechanisms (price) in their solution. This grossly distorts the behavior of the economic participants (drivers) creating an even bigger problem.

Chris Anderson’s book, Free, examines the market effects of a $0.00 price tag. Malcolm Gladwell later reviewed the book and summarized the key lesson as follows:

…when prices hit zero extraordinary things happen. Anderson describes an experiment conducted by the M.I.T. behavioral economist Dan Ariely, the author of “Predictably Irrational.” Ariely offered a group of subjects a choice between two kinds of chocolate—Hershey’s Kisses, for one cent, and Lindt truffles, for fifteen cents. Three-quarters of the subjects chose the truffles. Then he redid the experiment, reducing the price of both chocolates by one cent. The Kisses were now free. What happened? The order of preference was reversed. Sixty-nine per cent of the subjects chose the Kisses. The price difference between the two chocolates was exactly the same, but that magic word “free” has the power to create a consumer stampede. Amazon has had the same experience with its offer of free shipping for orders over twenty-five dollars. The idea is to induce you to buy a second book, if your first book comes in at less than the twenty-five-dollar threshold. And that’s exactly what it does. In France, however, the offer was mistakenly set at the equivalent of twenty cents—and consumers didn’t buy the second book. “From the consumer’s perspective, there is a huge difference between cheap and free,” Anderson writes. “Give a product away, and it can go viral. Charge a single cent for it and you’re in an entirely different business. . . . The truth is that zero is one market and any other price is another.”

So we see that trying to rationally balance supply and demand while refusing to price a scarce good (parking) is illogical if not impossible.

Donald Shoup explains the correlation to parking ordinances in American Cities:

Planners have identified the source of the [parking] problem not as the city’s failure to charge market prices for curb parking, but as the market’s failure to supply enough off-street parking. Cities therefore require ample on-site parking for all new buildings. The logic behind this policy is simple: development may increase the demand for parking, but cities can require developers to provide enough on-site spaces to satisfy this new demand. If a new building increases the demand for parking by 100 spaces, for example, cities can require it to provide 100 new spaces so that competition for the scarce curb parking doesn’t increase. Curb parking remains a commons, and cities require enough off-street parking to satisfy the increased demand.

A major flaw in this solution, however, is the way planners estimate demand: they do not estimate it as a function of price. Instead they make the unstated (perhaps even unconscious) assumption that all parking is free. They estimate the demand for free parking and then require enough spaces to meet this demand. In effect, urban planners treat free parking as an entitlement, and they consider the resulting demand for free parking a “need” that must be met. Off-street parking requirements create an abundance of parking spaces, driving the market price of parking to zero, which explains why drivers can park free for 99 percent of their trips. Off-street parking requirements are a fertility drug for cars.

Parking ratios are unscientific

From The High Cost of Free Parking:

Planning education provides no instruction on how practicing planners should set parking requirements, and textbooks offer no help. Consider the four editions of Urban Land Use Planning by F. Stuart Chapin and his coauthors. This distinguished text is the bible of urban land-use planning, yet no edition mentions parking. Most texts in regional science, transportation planning, and urban economics also ignore parking. I have asked many professors of urban planning if their departments offer any instruction on how planners set parking requirements, and the answer is always no. Perhaps planning students learn almost nothing about parking requirements because their professors know almost nothing to teach them. Somehow, the urban land use with the biggest footprint and a profound effect on the transportation system has been invisible to scholars in every discipline.

Despite their lack of professional training, practicing planners in every city must set the parking requirements for every land use. Zoning codes throughout the country contain thousands of different parking requirements – the Ten Thousand Commandments for off-street parking. Planners set parking requirements almost as if they were physicians prescribing drugs, but they have no theory, no training, and often no data to help them. No textbook explains the theory of parking requirements because there is none. Professors cannot teach their students how to set parking requirements because no one has carried out research on how to do it.

Without clairvoyance, how do practicing planners predict how much parking every land use needs? To find out, Richard Willson surveyed planning directors and senior planners, and asked, What sources of information do you normally use to set minimum parking requirements for workplaces? Forty-five percent of the respondents ranked “Survey nearby cities” as most important, and “Institute of Transportation Engineers handbooks” came in second place at 15 percent. More planners responded “Don’t know” (5 percent) than responded that they commissioned parking studies (3 percent).

With regards to the validity of existing parking requirements (which are almost always the basis of new parking requirements as cities copy each others standards), the Planning Advisory Service (PAS) has reported that:

“The Underlying assumptions used in drafting parking requirements are unknown.” (PAS 1964, 1)


“Many communities have created parking standards that require developments to build parking spaces far in excess of demand.” (PAS 2002, 6)

Shoup cites Connecticut zoning administrator Carol Gould’s writing in Transportation Planning:

Parking requirements in most zoning regulations are not founded on an empirical analysis of what any land use will require to meet patrons’ needs, but appear to have been “handed down” from one community to another.

…and finally, Shoup concludes:

As a result, most parking requirements amount to little more than a collective hunch.

Houston’s Bad Hunch

Houston is a unique example of the absurdity of a pseudo-science where the most frequent course of action is to copy other cities. The one and only large city in the United States that doesn’t directly employ a zoning map, Houston employs a parking ordinance that looks virtually identical to that of every zoned city in the US.

Houston’s parking ordinance (PDF) breaks land-uses down into 69 different categories, distinguishing things like “Clinic (Medical Complex)” and “Clinic (Medical or Dental)”, as well as “Retirement Community (without Kitchen Facilities)” and “Retirement Community (With Kitchen Facilities).”

Yet, at the April 7 Parking Ordinance meeting Marlene Gaffrick (the Director of the Planning Department) stated:

“Maybe the issue is we’re not distinguishing enough between different land-uses. For instance, the parking demand for a really popular restaurant is obviously different from the parking demand for a smaller neighborhood-oriented place.”

In the City of Houston’s “Draft Issues” packet, issue #4 is listed as follows:

Parking Ratio Requirement
Issue(s): The parking requirements for specific uses have not been examined since the ordinance was first written. Development trends have changed and the parking requirements may not be reflective of current trends. Also some of the requirements are based upon the number of employees or students. This is an ineffective measure because the number of employees or students can increase within a building and not trigger another parking review.

Recommendation: Review the parking requirements for specific uses and determine if the uses need to be expanded and the ratios revised.

Notice that no consideration is given to reducing the number of use-categories that the City uses to control parking. The city’s language implies that this isn’t even an available consideration!

Planners are predisposed to believe that if the ordinance isn’t working for residents and businesses that it must not control enough of the variables. The problem with this mentality is that there are nearly an infinite number of variables in play in the complex economy of our City, and they cannot possibly account for, predict, and control them all. Not only that, but the more the City tries to do this the more they are going to create an untenable situation for business, where every case becomes an exception that must be laboriously forced through a bureaucratic review in order for development activity to resume.

There’s a widely-known term for this kind of governmental control of the market. It’s called communism.

Tomorrow we’ll take a look at how this government interference in the market plays out at a local level.

UPDATE: Due to the high traffic on this post, I’m going to leave it featured move the next installment back a day. Thanks for the links, and please continue to leave your comments!

Posted: Tuesday, April 20th, 2010 at 4:27 pm
Categories: featured, move
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  1. And no where, anywhere, does the City require any type of bicycle parking, even though bike parking is probably 10 times more dense than car parking, cheap to deploy, and it gets resource-grabbing (fuel, space, roadway capital expense) cars off of the roads.

  2. Last time I was in Houston it was nearly impossible to find free pizza! The city needs to require businesses to provide free pizza for their customers. Based on a study I conducted at a 8-year-old’s birthday party, the demand for free pizza increases along with the gross floor area of a building. Therefore, the new Houston Pizza Ordinance should require a new office building to provide 2 free pizzas per 1000 sq ft GFA. Next the city must spend at least $500,000 on a study to determine the best way to bring buildings that were built in the pre-pizza era up to code with the new Pizza Ordinances.

  3. Great breakdown of the failed economics of parking ratios. It’s remarkable how few people understand this concept–Donald Shoup is in fact the only person to have even written extensively on the subject. Meanwhile, I’m sure there are cases where zoning administrators are so unreasonable that they won’t allow parking requirement variances (reductions) even when parking lots have been shown to be completely underutilized. And we’re talking easily about billions of dollars in construction and maintenance costs being thrown away on unnecessary parking every year in this country alone, just because no one has the guts to implement the free market economics that those who benefit most from auto-dependency (that is, those who can afford multiple, luxury cars) claim to support.

  4. Andrew, can you help me visualize how these free-market ideas could be phased in? Would we get rid of parking ratios cold turkey? If so, what would be the responsible party for doing so? The planning department? City council?

    After the parking ratios are removed, then what? I suppose at that time new buildings would be built with however much parking the business owners and investors felt was needed. In some places (new suburban development where land is cheap, for example) that amount of free parking may be unchanged, but in other places (Montrose) the amount of free parking would possibly be reduced. Instead of parking in spacious lots, drivers are then forced to find street parking in the neighborhoods. This ticks off the residents, who then complain to the City. The City offers to install parking meters along any street that has a certain percentage of residents petitioning for it (would “no parking” signs still be allowed, or would meters be the only option?) Some drivers will not want to pay for parking every time they go to grocery store, and they may consider walking/biking/transiting instead. However, others will be put off by the lack of parking and may choose to shop elsewhere — presumably, this will be a cost that the business owner accounted for when deciding on the correct amount of free parking. On the other hand, parking at the Rice Village isn’t always easy, yet that doesn’t seem to drive too many people away.

    Is this how you are imagining it? We wouldn’t have to install parking meters on every road, right? Some neighborhood streets are so quiet that the meters wouldn’t pay for themselves. . .Are parking meters the only way to do it anyway?

    • Ian,

      I think the process you’re imagining is mostly on-target. I imagine the process would go something like this.

      1. The parking ordinance goes away. Simultaneously the city establishes a process by which residents can petition for parking control on their streets. This would include a combination of parking meters and selective use of no-parking zones.

      2. Quickly, the streets where overflow parking is already a problem are metered. Other streets remain as-is. Overflow parking begins to diffuse throughout a broader area, and some people choose to carpool or walk/bike more often.

      3. A moderate spike of new development occurs in places like Midtown where small lot owners have not been able to build due to parking constraints. As these new developments begin to fill in, new meters continue to pop up in areas where the increased on-street parking demand justifies them.

      4. New and old businesses begin coming up with a variety of means to deal with providing increased parking as parking scarcity limits their future growth. New shared garages (such as the one in the center of Rice Village) with vouchers for customers and a charge for others become widespread.

      Thanks for the question, I hope this answer makes sense. I expect to write more about what free-market solutions exist for parking in the near future!

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