The SHOUP Controversy – Are 30% of the cars in a given neighborhood looking for parking?
JVH Blogged yesterday about this issue, Shoup and Paul Barter Responded
Most of the support for Don Shoup’s theories is based on the concept that 30% of all cars driving in the city are actually looking for parking and if they took the first available spot, it would cut down traffic by a third thus saving whales, polar bears, and a lot of gasoline.
In fact, many of the parking programs like SF Park, and others, justify, either in whole or in part, on this 30% reduction.
I had dinner the other night with a parking guru who said, in essence “balderdash.” He told me that he had personally done a survey and he thinks the real number is like 2%. He said that you can’t just follow cars and somehow determine which are looking for space and which are driving directly to their parking destination.
You must first categorize the cars. In other words, have they passed their location and are beginning a search. In other words, you must actually interview them after their park and find out where they were going. If you don’t do that, how could you know whether they were wandering aimlessly or they were focused like a laser beam on their destination parking spot?
He told me that he actually did this, informally. He followed a set number of cars (I think over a few weeks about 200 and actually asked the driver what their destination was. The response in the vast majority of cases was that they were going to the building adjacent or very near their parking space. He noted that they didn’t circle back looking for space, but found a space and parked. He did this as a part of a traffic survey he had done for a major US city.
My friend admitted, after a few adult beverages, that his method wasn’t the most scientific but commented that students standing on rooftops in Westwood near UCLA had little more idea of where people were going or who was cruising and looking.
He added that this number is too critical to how parking programs are approved to be left to a number that was perhaps a SWAG (Scientific Wild Ass Guess) estimate. He felt a grant needed to be garnered and a true survey done with actual interviews of drivers after they parked.
I have sent this to Don and asked him to respond.
The Shoup Dog read my blog below and responded — Here it is:
I sympathize with your friend who doubted that 30 percent of city traffic is cruising for parking. Unfortunately, many people who have never read The High Cost of Free Parking often quote me as saying that 30 percent of city traffic is cruising for parking.
I did summarize the results of 16 studies of cruising in 11 cities on four continents. Researchers found that between 8 and 74 percent of traffic was searching for parking, and it took between 3.5 and 13.9 minutes to find a curb space. For the 16 studies the average share of traffic that was cruising was 30 percent and the average search time was 8.1 minutes.
These studies date back to 1927. The data were probably not very accurate when they were collected, and the results depended on the time of day, the specific place, and the season when the observations were made. The studies were selective because researchers measured cruising only when and where they expected to find it—where curb parking is underpriced and overcrowded. Nevertheless, cruising today is similar to what drivers have done since the 1920s, and the studies at least show that searching for underpriced curb parking has wasted time and fuel for many decades.
On most streets at most times, no one is cruising. But many people want a number, and I can’t stop anyone from saying that 30 percent of traffic is cruising. Nevertheless, on busy streets where all the curb spaces are occupied and traffic is congested, a substantial share of traffic may be cruising.
For example, when researchers interviewed drivers who were stopped at traffic signals in New York City, they found that 28 percent of the drivers on one street in Manhattan and 45 percent on a street in Brooklyn were cruising for curb parking. This doesn’t mean, however, that 28 percent of all traffic in Manhattan is cruising for parking or that 45 percent of all traffic in Brooklyn is cruising for parking.
On a congested street where all the curb spaces are occupied, one simple way to estimate how much of the traffic is cruising is to observe whether the first car that approaches a newly vacated space parks in it. If, for example, the first or second driver who approaches a newly vacated curb space always parks in it, this suggests that most of the traffic is cruising for parking.
An even simpler and quicker (though perhaps less humane) way to sample the traffic flow is to approach the driver-side door of a car parked at the curb with a key in your hand, as if to open the door. If the first driver to see you with a key apparently poised to unlock the door always stops to wait for the space, most of the traffic is probably cruising. The stopped car blocks a lane of traffic just like a double-parked car. Unfortunately, you must then use body language to suggest that you have changed your plans and have decided not to leave, regrettably disappointing the driver who expected to park in the space. If you do this several times, and the first or second driver to see you with a key in your hand always stops to wait for a space, what share of the cars in traffic would you think are cruising? When I did this on Pike Place in Seattle, the first driver who saw me with a key in my hand always stopped traffic to wait for the space.
Because most streets usually have some vacant curb spaces, the share of traffic that is cruising on most streets is probably zero. Because curb parking is underpriced and overcrowded in the busiest parts of most of the world’s biggest cities, however, the sun never sets on cruising.
Paul Barter says:
I agree to some extent. There has been a lot of sloppy quoting of the 30% thing!
But it is not as bad as you imply here. Cruising for parking CAN cause a huge mess, especially in busy areas, at busy times, and especially when parking is mismanaged.
How much traffic is cruising for parking? Well, it depends. Often there is no cruising for parking. But at the places where it really matters, there it is potentially a LOT of cruising (sometimes more than 30% of traffic).
I tackled this question too: http://www.reinventingparking.org/2013/10/is-30-of-traffic-actually-searching-for.html