|Diagram of a standard parking space by author.|
One aspect of providing off-street parking that often gets overlooked is its impact on the design of a site. Parking spaces take up a substantial amount of land. As the figure above shows, a standard parking space is about 180 square feet (16.7 square meters). However, to be fair, the land impact of parking goes beyond the space itself to the driveway that must serve it. Where parking spaces are set at a 90 degree angle to a two-way driveway, the driveway is typically about 24 feet (7.3 meters) wide. Therefore, in this arrangement, commonly found throughout the United States, we should add half of the driveway area behind the parking space (assuming there is another row of parking spaces on the other side of the driveway) to the parking space area to get a more accurate sense of one parking space's land footprint. In this example we would add half of 24 feet times the width of nine feet or 108 square feet (10.0 square meters). This yields a total of 288 square feet (26.7 square meters) per parking space. If a two-way driveway serves a single row of parking spaces, each space plus its share of the driveway consumes a whopping 396 square feet (36.8 square meters)!
Now consider that a common suburban parking requirement for retail space is one parking space for every 250 square feet of floor area. This means, if you are planning a retail building, you have to provide 288 square feet of parking space for every 250 square feet of retail space. That's right: you have to provide more than one square foot of parking for every square foot of actual space that you are trying to build.
What does that mean for your site? It means that, if we are talking about a one-story building and you aren't using expensive structured parking, the parking lot will consume more land than the building itself! Depending on how much area you dedicate to landscaping, over half of your site could easily be parking lot, as required by the local zoning code which is imposing the parking requirement.
As people like Donald Shoup have pointed out, this has huge implications. It means that you need to control more land, your project costs more to build, and if the parking spaces are offered free to their users, those extra costs have to be covered by more expensive goods and services. When someone goes to the store without driving, they pay that higher cost, thus subsidizing everyone who drives. This leads to increased traffic and increases in other problems associated with driving such as greenhouse gas emissions, air pollution, and the destruction of natural habitat. Another impact is that aesthetically, we get vast soul-crushing parking lots all over our visual landscape.
I agree with Shoup that cities should not require minimum amounts of off-street parking and should instead let developers decide how much parking they need, price on-street parking to match demand and keep a few spaces open on every block, and send parking meter money back to the neighborhoods that generate it. However, in the real world, we are a long way from this approach in many places. Thus, a good incremental step would be to at least not set parking requirements at a level where the amount of parking space (as land area) one needs to provide exceeds the actual space that is being built. This means that the strictest parking requirement cities should set is approximately one parking space for every 288 square feet of floor space, since that reflects the space consumed by a typical parking space. Let's just round that to don't require parking in excess of one space for every 300 square feet of floor area. That is, unless you're okay with parking lots that are bigger than the buildings they serve (and hopefully you're not).