The Paradox of Cheap Parking, in Real Time

Last spring, I heard about an interesting dataset about Ann Arbor, Michigan, where I lived for four years as an undergraduate student. Busy with the flurry of activity leading up to my completion of graduate school, I stored it away to look at later. After all, real-time information on cities is hard enough to come by, let alone on the simultaneously ubiquitous and fascinating topic of parking.

The Data
The parking lots and structures in downtown Ann Arbor are operated by a quasi-public organization, the Ann Arbor Downtown Development Authority (DDA). Together with their parking vendor, last April they implemented a system that provides real-time information about the number of parking spaces available in several lots and garages through digital signs at each garage and through their website. An old Ann Arbor friend Brian Kerr wrote a simple script to scrape that page every 20 minutes and record the number of spaces available at each facility. After letting it run for about two weeks, he posted the data file online. Subsequently a local blogger interviewed the DDA’s IT manager about how the system was implemented, and even posted some charts encouraging visitors to match the chart with the garage. The data sparked a bit of interest on local blogs but the conversation soon died out.

At the time of the completion of a recent parking study in 2007, the DDA operated lots and structures containing 5,770 parking spaces in downtown Ann Arbor. These facilities are concentrated in a relatively small physical area, as shown in this map from the study:
Parking4 (72 pages)

For my first pass at the data I thought I’d look at just one garage, indicated by the arrow above. As is shown, the Maynard Street structure is near two movie theaters, a busy commercial district, and one block from the University of Michigan Central Campus Diag, with many classroom buildings and a large auditorium. The first chart is the number of spaces available in just one day – Monday, April 7, 2008:

DDA Parking

The first thing to notice is that the garage is never full during any 20-minute measurement. Although the technical capacity of the garage is 797, the garage flat-lines at 618 (perhaps due to long-term permits or construction). The garage is only filled over 90% of this reduced capacity for one 40-minute period, from 1:40 p.m. to 2:20 p.m, or roughly 2.7% of the entire 24-hour period.

Expanding the time frame for the next 7 consecutive days reveals this pattern:

Maynard Garage

The spikes correspond with the midday rush, and the garage only fills once, around 1:00 p.m. on Friday, April 11th. This seemingly dry data can tell a rich sociological story; everyone rushes in just after nine, with various people lingering around into long into the evening. In a sense, the curve represents a unique DNA of the local land uses and the preferences and customs of their auto-using patrons, residents, and visitors.

Based on the data we can make a couple observations. First, the vast majority of the parking lots and structures are almost totally empty the majority of the time. This means they represent a huge amount of inactive urban space. A common rule of thumb is each structured space takes up 300 square feet of floor space for the bay and associated aisles and ramps. If we use this standard, the same floor area in this garage could be 239 apartments (assuming they average a generous 1,000 square feet). Certainly good design would demand a residential structure be taller or configured differently on the site. However, given the extremely fickle use of the garage now, a residential use would mean more people physically at the site on average than are now.

Second, from the chart above we can see that parking demand at the DDA’s prevailing price structure is very spiky, with extremely high demand only at limited times. (This garage costs $.80 an hour, or $175 for a monthly permit) It would seem logical for the DDA to use variable or tiered pricing to create a market incentive for a more efficient use of their space. For example, parking overnight could be inexpensive given the very low demand, with parking around the midday peak much more expensive. Even a modest form of performance parking may change this observed pattern.

Maynard Street Parking Structure2

Despite nearly 5,800 spaces the DDA continues to develop more parking, this October publishing on their website details about a proposed underground lot near the library boasting green design. How will the city know when they have enough parking? After all, parking policy guru Donald Shoup points out one can rarely provide enough of something that’s under priced. The proposal for the new garage advises readers to “review the findings of the 2007 Parking Study to learn why vehicle parking is needed even with extensive investment in alternative transportation.” Unfortunately the 2007 Parking Study doesn’t exactly settle the matter, including as one of its final recommendations “Maintain a formalized process for determining when new supply is needed.” The study, by the alternative transportation experts Nelson/Nygaard, is chock full of state-of-the-art policy suggestions (including variable pricing discussed above) but avoids the sticky question of determining how much is necessary. Perhaps it’s because like other seemingly scientific questions in urban planning the answer is not scientific but value-laden and political. (A similar question: How many freeways and/or lanes do we need?) And in Ann Arbor, the people want more parking.

Parking in the Real-Time City
In another vein, publishing this real-time data (especially on a still forthcoming mobile format) could itself have profound implications for the transportation system. Could real-time data allow people to avoid full structures and make use of the resource more efficient? The Washington, D.C. suburban rail station lots tend to fill up early, and I’ve heard stories of people driving downtown stopping at each station to look for a spot. What if the space was beamed to their home computer or car? (The more important question might be, “How much parking should they provide to begin with, and what should it be priced?” One suggestive study I saw of San Francisco’s BART concluded replacing parking with offices would boost the agency’s riders and revenue) If the DDA makes summary data available on the website, it would make costly data collection unnecessary for this data point. All citizens would know exactly how full or empty the garages were, and the DDA would be able to observe the impact of pricing or policy changes in real time.

> Previous parking posts: The Urbanists’ Panacea: Parking Reform, Are Expensive Parking Meters Fair?, more
> Homeless Dave’s Interview with the DDA’s Stephen Smith
> Ann Arbor Downtown Development Authority

Author: Rob Goodspeed


  1. You and your readers should check out Park It DC @ The site has to do with parking in Washington, DC and i am trying to make parking data and meter data available to people in real time. I am also working to bring in more real time data like space availability.

    In the coming weeks you will see an iPhone app with this data on it!

  2. It’s great to see some actual data proving what many of us knows to be true. That parking garages are more often then not empty and a better solution needs to be implemented.

  3. Rob,

    Great post! Your comparison of the value-laden, political nature of parking to freeway size & construction is particularly apt. Parking structures and lots are the end caps on the auto based transportation system.

    Having known a large number of auto-commuters in Ann Arbor who made heavy use of parking structures (and having been one myself for a brief time), the conversation of taking away (or stopping) construction of parking has to go together with a conversation about creating more viable & practical commuting options into the city core.

    Also, it’s easier to make the “this could be apartments or offices” argument for above-ground structures (that aren’t in flood plains or other problematic locations). Underground structures and structures in places inhabitable buildings would be problematic (i.e., a flood zone) are using space that would be less likely to find another use — leaving aside the ubiquitous price subsidy…

  4. First of all, many residential streets are vacant nearly the entire day with only sporadic use. Given your logic about the parking structure, does that mean that we should measure the value and usefulness of residential streets by how much of the day there is an actual car using the street?

    And second, the A2DDA, which is the organization sponsoring the new structure is the largest local funder of alternative transportation options for downtown workers. This includes programs like free bus passes for all downtown workers, sponsoring a zipcar program, a downtown circulator, a free ride home for evening workers, bike lockers/bike hoops throughout downtown, walk map, and providing a slew of grants for things like the City’s NonMotorized Study. The funding for these great programs comes from their parking revenues. Your comments suggest that the parking structure and commuting options are in opposition somehow. In addition to the programs noted above, there are active conversations (and initial DDA funding) underway for new initiatives like commuter rail, streets cars, additional express bus service, and new park & ride lots. Lots of exciting transportation initiatives – as well as a new underground downtown public parking structure.

  5. Urban Girl, thank you for your comment. I’ll address the points you raise:

    1. Blocks of downtown Ann Arbor are different from residential streets in fundamental ways. They have higher land values, different surrounding uses, and different zoning. So yes, unused parking lots and spaces inserts massive voids into the city, disrupting the fabric of the city. This makes it less pleasant, less walkable, and may reduce the tax base of the downtown area. Concerning under-used residential streets, certainly many are quiet and this is to be expected. However, many streets are too wide, and if they aren’t being used would be great candidates for bike lanes, treed medians, wider sidewalks, etc.

    2. Regarding the DDA, you are absolutely right, they have invested in many forms of alternative transportation. In fact, I point out your own studies are chock full of innovative ideas — such as the pricing scheme here that I propose. Ironically, adopting performance parking as I propose would likely increase the revenue from parking to the DDA, providing even more money for all the other activities you mention.

    2a. Finally, you assert I think parking and commuting are opposites. I don’t think this is true – they are both parts of the same transportation system. What I pointed out in my article and what you have not responded to is that the DDA has no formal way to determine how much parking there “should” be, other than through politics. Looking at the data here it would seem there is plenty of parking almost all of the time. The DDA seems to be building infrastructure to support peak demand, only experienced for a few minutes a day or during special events. I don’t think that’s an appropriate policy choice.

  6. The more parking structures the DDA builds, the more money they have in their budget. Anything that’s not a parking structure is an expense; anything that is parking is a revenue source.

  7. Ed V. –

    At some point you should take a look at the DDA’s balance sheet. New construction parking structures are hardly a cash cow; I think the DDA only makes money off of a few of them. (Tally Hall was the biggest net positive structure last I kept track, because its age means most of the construction costs have been amortized, and the lack of human attendant means lower operating costs.) The on-street and surface parking lots are traditionally the more profitable parts of the parking system.

    If the DDA were only looking to parking revenues and nothing else, they’d probably prefer an all-surface-lot-meters strategy. Structures are closer to “necessary evil” status – they’re not there because the DDA makes mad bank from them, but because an all-surface-parking strategy would consume too much land.

    I’d certainly support Rob’s assertion that “how much is enough” is not something the DDA has (or can) determine in a completely neutral and “scientific” manner. But if we’re assuming that x off-street parking spaces is the right number, I personally would far rather see them in parking structures than in surface lots – if we have to take up land for parking, we may as well use as little of it as possible by going vertical.

  8. Hi – I suspect that the real cost of building and maintaining parking structures is much higher than is generally thought and they should charge more for parking. Especially at peak times.

    Unscientific – I am confident that when I drive downtown (I live three miles from State and Liberty) I can park relatively quickly in one of the structures. On street, not so sure. I generally feel that I will have to stress at least some to find a space – I hardly ever just cruise into an empty lot. If it were a lot more difficult to find a space, I might decide against the trip. I probably would not consider taking the bus as it does not run often enough. My kids will take the bus downtown when pressed.

    I like the idea of underground parking and would pay a higher price for it. Surface lots and structures are terrible land uses in downtown areas, and if we can’t get rid of them, build them underground.

  9. The comment at the DDA’s transportation committee meeting that I attended was that the worst thing possible was for there to be no parking available at peak times. The perception is that even one minute of FULL sign on the parking lot across from your downtown brewery means that you lost some business.

    That there is ample parking available on surface lots or structures or county lots after hours or anything else a few blocks away isn’t really relevant, if the FULL sign stares at you out the window.

  10. DDA is now (as I type) talking about raising rates for parking, though they are also not talking about any peak-hour pricing just a flat rate increase. The counter-argument is to delay the parking increase and to make up the revenue deficit from the TIF fund.

  11. Two things about Maynard that your data don’t fully take into account:

    1. Most of the lower levels are prohibited for parking until 10 a.m. – this is to keep workers and students from all-day parking there.
    2. They do indeed have a number of long-term permits, so the figures should be calculated from the 618 figure for the purpose here.

  12. Good analysis and good questions, Rob. I hope you’ll continue. I’ve looked at the data a bit myself, and so far it’s just triggered even more questions about what hasn’t been examined in terms of impacts and possible alternatives.

    I’ve also seen this as a “peaking” problem, one that could be addressed by various alternatives. Unfortunately, the city council directed the DDA board to develop a plan for an underground structure at that particular site. It’s analogous, in energy, greenhouse gas emissions, and sustainability terms, to commissioning a large coal plant with scrubbers, or maybe a big natural gas plant to generate peak-time electricity, as opposed to a combination of improved efficiency, wind turbines, and other solar sources.

    The Maynard structure is a good one to look at since it seems to be the one referenced as being “full” during the day, all week long. No study has been done to project the expected impact of the new structure on that structure or any other component of the parking system, that I’m aware of. My guess is that it will continue to have the same usage pattern even after the new structure is in place, except for the impact of other factors, such as increased bus ridership and higher gas prices.

  13. Fred Posner and I put together a telephone app that lets you get parking information in real time from your phone. We just did an interview today on the Lucy Ann Lance show which was fun. The local number is




    Operators are standing by, call now. (Calls may be recorded for quality purposes. Not intended for use while driving. No warranty of merchantability or fitness of purpose.)

  14. I received via FOIA another set of parking data, this one the bank deposit detail on a day by day basis for all of the lots in March 2009. It’s in a horrible format – scanned in PDFs – and it’s also not what I asked for. But it may be useful and I’ll fling it at you on request.

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