Dimensions of Parking Demand
Allan Kessler, Draft: February 13, 2017
A pervasive force that occupies parking spaces, drives people to circle blocks with their vehicles, and promotes congestion and pollution, parking demand is never seen nor felt in entirety. Just how can it be described?
Considering a vehicle driver looking for parking brings to mind the story of the blind men and an elephant.
In various versions of the tale, a group of blind men (or men in the dark) touch an elephant to learn what it is like. Each one feels a different part, but only one part, such as the side of the tusk. Then they compare notes and learn that they are in complete disagreement. Wikipedia
In our story here, a giant parking demand elephant straddles the locale. We see manifestations of demand as vehicles vie for parking spaces, scrambling for some and passing others by. Transportation planners grapple with it by regulating the supply of parking hoping the elephant will not trample their efforts.
Our elephant, taking after the leopard, has evolved by changing its colors to multi-colored patches on its grey skin. It has accommodated itself to the multiplicity of parking regulations, represented here by a table of colors.
The colors correspond to a spectrum that in part reflects the color curb markings for parking, e.g. green for
short term parking, yellow for commercial loading etc. The elephants patches cover the distribution of occupied parking spaces in a locale.
Vehicle drivers may circle looking for all day parking while seeing only open short term spaces. At full public garages, drivers may queue up waiting for vehicles to leave. The grey skin area of the elephant reflects this latent demand for spaces as drivers seek places suitable for their intentions. As drivers search for spaces, occupy them with their vehicles, and later depart from those spaces, parking demand fluctuates though time.
When few drivers are looking for parking, say in the late night, there could be little latent demand. Meter regulated space may become occupied early as 7 AM until early evening. Commercial loading zones are generally regulated only during the day and are less used in the late afternoon.
The occupied space component of parking demand cannot exceed the total inventory of parking space in the locale. The inventory changes over long periods of time, in contrast to daily, as new spaces are created and as spaces are removed. e.g. a new development with a parking garage constructed on a former parking lot. Should the inventory be completely occupied, there may be drivers seeking spaces that comprise a latent demand component.
Where parking spaces are delineated on-street or off-street, they can be reliably counted. However, curb length along some streets is not delineated into spaces. A variable number of vehicles can occupy a parallel curb length depending on their size. Similarly for unmarked perpendicular parking, the number depends how on how efficiently they are occupied.
The measure of parking inventory is best described as two dimensional area rather than a count of spaces. The area may be subdivided into spaces with a variety of rules. Individual spaces can be marked out or not.
The total inventory of parking is rarely 100% accessible to drivers. For example, during rush hours the on-street inventory for parking may be repurposed for traffic. Thus the actual supply of parking at any time will almost always be less than the inventory, due to that inventory not being accessible.
Parking supply is regulated. For this discussion, the term unregulated which is commonly applied to parking that has no specified time limit during a day is considered to be a NO LIMIT class. This class is commonly restricted to a day limit, e.g. 3 days or 72 hours. All of the parking supply falls in one class or another.
The number of supply classes is very large due to the many day and time limited combinations.
- 2 HOUR 9AM 6PM, (NO LIMIT during other hours) Except Sunday & Holidays
- METERED LOADING 8AM 1PM, GENERAL METERED 1PM 6PM, (NO LIMIT otherwise) M-Sat
- 1 HOUR 7AM 4PM, NO STOPPING TOW-AWAY 4PM 7PM, (NO LIMIT otherwise) M-F
NO PARKING is included as a class because vehicles do park in those areas. There are instances when vehicles occupy NO STOPPING during lane conversion to traffic and these violations are here considered in the NOT ACCESSIBLE class.
Street cleaning regulations require NO STOPPING until the street cleaner has passed by. The parking supply dramatically changes with day- time street cleaning in locales with high parking demand, as drivers time the cleaners and quickly refill spaces.
During street cleaning, latent demand associated with these drivers is very visible as vehicles closely follow behind the cleaners. It is during these short term sizeable fluctuations in supply that the process of local demand coming into balance with local supply is most revealed to the observers of our parking demand elephant.
For the driver seeking parking at a given moment, it is the parking supply in the vicinity of their intended destination that is foremost in their mind. That vicinity area will have a small number of the total possible parking classes. The driver has to determine which of those classes suits the desired estimated length of time associated with their intention. For example, if the vicinity is primarily 2 hour parking with a few 10 minute green spaces, drivers will pass by the green spaces if their interest is in parking for an hour. However, if they are looking for a short occupancy to pick up an item at the corner grocery, they can park both at an available green zone in front of the grocery or in any of the 2 hour available spaces.
Each driver has a personal conception of the vicinity area. This conception is based on the proximity of parking spaces to the destination and on the amount of walking associated with traveling between a space and that destination. The cost of parking within the vicinity may be acceptable or not. The probability of suitable available spaces is a consideration. Other factors such as the perception of safety may be considered. The conception of the vicinity area may change as the drivers search experience in the initial vicinity is not satisfied.
Vicinity Search Considerations
|Within Vicinity||Outside Vicinity|
|Proximity||Yes||Too far away|
|Walkability||OK||Too long a walk|
|Availability||Suitable/Non-Suitable Regulations||If Non-Suitable|
|Other Factor||OK||If Not OK|
A driver who is planning a vehicle trip may entertain these vicinity considerations prior to departing.
If we could know these considerations we could estimate the accumulation of latent demand in advance of arrivals at the vicinity.
At the same time, a driver with access to the estimated accumulation could employ that information in re-considering their planned trip or during the trip.
Each drivers understanding and experience with the parking demand elephant for the vicinities they travel to may benefit their satisfaction with their vehicle trips. Transportation planners grappling with the elephant, would welcome opportunities for drivers to incorporate in their understanding of parking demand the consideration of public transit in place of private vehicle trips.