What Really Causes Parking Spillover?

Most North American cities continue to apply zoning by-laws with parking minimums whose logic and purpose is rooted in the fundamentally different planning, economic, demographic and environmental context of the mid-twentieth century. And yet they persist, even as they routinely and systematically produce urban landscapes ranging from the kind of disappointing to the utterly dystopian.
  If you lived in an asphalt wasteland optimized for easy automobile access at the expense of almost literally all other considerations, you'd be home now!

This approach is rooted in a fear of parking spillover: the excessive use, abuse or outright poaching of on-street parking or neighbour's off-street spaces by drivers who can't find a place to park at their actual destination. It's a reasonable concern and one that has to be managed.
Conventional parking minimums don't manage parking spillover--they carpet-bomb it from 30,000 feet.

From the early days of mass car ownership, North American cities have typically required almost every new development to include on-site parking. The default requirement is enough to provide free parking for everyone who might conceivably show up on nearly the busiest day of the year.
That approach usually does prevent parking spillover, albeit with Soviet efficiency and with disastrous unintended consequences that are so widespread that you can probably look out your window and see some of them right now.

Parking spillover is not simply a matter of "not enough parking," and it's obtuse to keep treating it as such. Parking spillover results from a combination and interaction of factors that influence people's decisions around where to go and how and when to go there. It becomes more likely at destinations where:

Development attracts a large number of drivers relative to the amount of parking provided on-site. This is the obvious problem that parking minima are designed to solve.

Users expect parking to be available and cheap or free. People decide to make a certain trip by car if they think they can park when they get there; otherwise, what's the point? If they expect to be able to park next to the door and there isn't a space available, or if they expect it to be free and it costs money to park, they may look around for a parking space that more closely meets their expectations. Conversely, if they know when they leave home that it will cost them $5.00 to park for two hours, then when they arrive, they're willing to pay that amount. The key here is the alignment (or lack thereof) between expectations and reality.

Users have no choice but to go to that destination, and have to go during its busier times. Someone who knows the parking lot will be full at a certain time, or that parking will correspondingly be difficult or expensive, may be able to go to an alternate destination. Or they can time their trip differently, so that they arrive when it's less busy or when the meter rate is cheaper. But if the user has no such discretion, they may have to park somewhere inappropriate.

Alternatives to driving are impractical for that user. If parking is difficult, but good transit is available or the user can walk, it becomes easier to avoid driving altogether and many people will choose to do so. Conversely, origin-destination pairs that are far apart, unwalkable, unbikeable, and poorly served by transit rule out this option. In those situations, the user will drive. This is also true where users have a physical infirmity or a particular trip purpose that prevents them from walking, biking or using transit.

Users do not go there regularly, so they are unfamiliar with either the parking situation or the alternatives for getting there. When someone goes somewhere on a regular basis (for instance, to their place of work) they become very familiar with what the parking situation is like and what the transit is like. They know that parking is difficult at such-and-such a place because they’ve been there before; and they know which bus they can take because, since they make the trip often, it’s been worth it to learn the route and schedule. But someone making a single, isolated trip doesn’t benefit from this knowledge; it may appear easier to drive, even if they don’t realize that parking will be difficult when they get there. Once they get there, it’s too late to turn back.

Free parking, or parking that is cheaper or more convenient than the parking provided on-site, can be found (lawfully or not) on neighbouring properties or on the street. In urban areas in particular, where land is scarce and expensive, off-site parking lots and garages typically charge money. But if the garage charges $4.00 an hour and there is a nearby street space that only costs $2.00, then those cheaper street spaces will be taken up first. If there is unmetered parking nearby, this becomes even more likely; and still more, if...

Use of neighbouring or on-street parking is unregulated or poorly patrolled or enforced. If there is parking on the street or in a neighbouring lot, and there appear to be no consequences for misusing it (parking somewhere it is not permitted, or overstaying the time limit), many people will do so if it seems easier than parking in the appropriate location. This can be innocent enough; if parking does not obviously harm or inconvenience other users, many parkers will consider it a minor, victimless crime.

The user does not care about the social, legal and/or moral consequences of inappropriate parking. Some people are willing to risk the occasional parking ticket in order to avoid paying or searching for parking. Some people see free parking as a right and refuse on principle to pay for it. And some people are just jerks who don't care if they block someone else’s driveway.

Several points can be made here.

Firstly, one or more of the situations described above can be seen at pretty much any point in any city, for some people, at any given time. One or two of these conditions is probably not enough to create unmanageable spillover.

Secondly, parking spillover becomes more likely the more of these circumstances are at play, because each blocks off an opportunity for a traveler to adapt effectively. But it only becomes truly inevitable and unmanageable when all or nearly all of these circumstances combine to close off any viable adaptation strategy.

Thirdly, in the inner parts of major cities at least--the parts that pre-date mass car ownership and parking minimums--this perfect storm is extremely rare. Downtown offers relatively few goods and services that truly cannot be found elsewhere, if someone really wants to drive. Transit service to and within the inner urban area is usually good, if someone is willing to use it. Opportunities to live and work downtown are also available, so people can and do walk on a regular basis. Most people do not expect to find free parking downtown whenever they want it, so most people accept that they will have to feed a parking meter.

Parking will continue to be an issue for as long as there are cars. But people aren't robots, and they can often adapt their behaviour more easily than we can predict it. It's essential that our planning practices recognize and take advantage of this fact, and put in place parking and land use regimes that leave space for people and places to grow and evolve, make mistakes and learn from them.