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HCoFP: chapter 2: junk science

* As early as 1944, LA was requiring at least as much parking space as retail floor space.
* Now a Wiltshire Boulevard ordinance -- a stretch with the best bus service in LA -- requires at least 3 spaces per 1000 square feet of floor area, explicitly to be provided free to all patrons and employees. Which comes out to the same; previous chapter said 130 cars/acre, which is 335 square feet per car. 1000 square feet of floor, square feet of parking.
** And that's low. Nationally, cities have been converging on 4 spaces per 1000 square feet of floor. 1200 square feet for cars, 1000 square feet for humans. Even executives rarely have 300 square foot offices, let alone worker cubicles. Cars rule the city.
** Or for some big box/mall areas, 5 spaces per 1000 square feet.
** For fast food restaurants, median requirement is 10 spaces.
* The minimum parking space requirement tends to equal to the peak demand for free parking. Max occupancy = max demand at zero price = min required supply. As if restaurants had to provide enough free food to stuff a sudden party of overweight diners.
* Me: wow, the USA is king of socialized parking, requiring free parking assuming everyone has a car and drives everywhere. Hardly any market pricing of parking.
* Even Houston, famous for not zoning for use (residential, commercial) or bulk (setbacks, height), requires off-street parking for every use.
* There's little theory or data telling planners how much parking space is needed and why, they just copy each other, back to the dawn of parking zoning.
* Discussion of parking is absent from most professional books on urban planning and zoning.
* What data there is, ITE's _Parking Generation_, is mostly a handful of studies of peak demand at suburban locations. A graph is shown, with R^2 of 0.038 and basically no relation between floor space and parking demand, yet that turns into a recommendation of 9.995 spaces per 1000 square feet. And that's a repeated pattern: ITE claiming coefficients with three decimal places of precision, when the confidence interval includes *zero* and the data fails to support any relation between space and demand.
** Which isn't surprising when you remember the other factors behind demand: location, density, alternative transport modes, how successful the store is... plus the absurdly small number of studies being passed off as statistically valid data.
* A study of Home Depot stores found a peak occupancy of 2.5 spaces per 1000 square feet, 60% of that supplied, and less than 50% of that required of new stores.
* Occupancy (people not cars) of office building can range over a factor of 10, e.g. 0.5 to 6 people/1000 square feet.

* "When a parking lot overflows, we naturally conclude that it fails to meet the demand, not that parking is too cheap. And when parking lots routinely overflow, we conclude that parking requirements should be increased, not that we should pay more to park."
* "Demand is a function of price, not a fixed number."

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( 5 comments — Leave a comment )
Feb. 20th, 2013 04:47 am (UTC)
*is interested*
Feb. 20th, 2013 03:11 pm (UTC)
I'm following with interest and have a question/observation.

Nationally, cities have been converging on 4 spaces per 1000 square feet of floor. 1200 square feet for cars, 1000 square feet for humans. Even executives rarely have 300 square foot offices, let alone worker cubicles. Cars rule the city.

Where does the figure for space per parking spot come from? What's rattling around in my mind is the question of whether the square footage numbers for parking include the aisles between parking rows, walking space in lots, and so on? If so, then the square footage per employee should also include the human common space such as hallways, common spaces and maybe bathrooms.

But agree with the inference that parking is too cheap leading to too many cars. It makes me sad when I have to drive to a job rather than being able to take public transit.
Feb. 20th, 2013 03:21 pm (UTC)
Parking space includes aisles and such; area of parking lot divided by number of car spots. So yeah, just office is somewhat illegitimate, but hallways aren't that big. And the parking regulations are N spaces per 1000 square feet of commercial use (residential reqs are N per unit), and we quickly see there cars may take up half (N=3) or 2/3 (N=6) or 3/4 (N=9, common for restaurants) of the land occupied by a business.
Feb. 20th, 2013 03:43 pm (UTC)
As it happens I know the rule of thumb for common space as percentage of total space in an office building: on the order of 30-33%.
Feb. 20th, 2013 03:50 pm (UTC)
Thanks. Do you happen to know the rule for common space within a city? Like how much is taken up by streets and sidewalks?
( 5 comments — Leave a comment )


Damien Sullivan

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