Parking spaces occupy limited land resources. In many urban areas, parking has high opportunity cost, meaning that by dedicating a piece of land for parking cars, we are giving up other uses of the land that could generate greater economic growth and public benefits. Like any other vacant real estate, unused parking means we are wasting valuable land resources. Parking is also a perishable resource, meaning an unused parking space at 6 AM cannot be saved and used later at 1 PM. Therefore, parking is not about 3-dimensional physical space, but has a 4th dimension — “time”.
Are time and space an illusion? No. They are both very important metrics to consider when making parking management decisions.
Many innovative parking initiatives consider the 4-dimensional capacity of parking inventory, and seek to balance parking supply and demand across the entire time span to increase the overall utilization of a parking resource. For example, shared parking encourages different parkers whose parking needs are temporally complementary — for instance, day-time employees and night-time restaurant customers — to share the same parking space so that the spaces can stay in active use for more hours.
Another example is the flexible parking zone which temporarily converts parking spaces to loading spaces or pop-up event venue during periods of low parking demand. The former adjusts the demand while the latter adjusts the supply.
On Friday nights in San Francisco, the parking lot at Fort Mason is transformed into a dynamic event venue called “Off The Grid” — learn more about it here
To this end, we introduce the concept of the “space-hour”, meaning the amount of parking hours a given amount of parking inventory can provide within a set period of time. At Smarking, we think the “space-hour’ measurement of parking utilization can compliment existing metrics and enable better parking policy decision making.
Allow us to illustrate the “space-hour” via an example: Parking Lot A has 10 spaces and is open 20 hours a day. Stated in “space-hours” Parking Lot A has a supply of 200 space-hours, meaning that it can support 200 units of 1-hour parking demand. Now let’s consider two extreme scenarios:
In scenario 1, Parking Lot A is full for 1 hour of the day and empty for the other 19 operating hours. In this scenario 10 units of space-hours out of 200 are used, resulting in an utilization rate of 5%.
In scenario 2, Lot A constantly has 2 spaces occupied during the 20 hours, resulting in an utilization rate of (2*20)/200 = 20%, much higher than in scenario 1.
In other words, although the lot in scenario 2 never reached the widely used threshold of “high occupancy” (80% — 90% occupied), it had a higher utilization level in terms of space -hours. Which is more desirable? The lot in scenario 1 allows for repurposing of the lot during off peak times — think food trucks or pop up shops like Off The Grid in San Francisco, while the lot in scenario 2 allows for a permanent reallocation of space — housing, retail, office space, etc.
To be clear, peak occupancy remains an important metric in evaluating the utilization of a parking facility, but using peak occupancy as the sole metric of parking utilization can be misleading, which is why we recommend using a confluence of metrics.
Using “Space-hour” to Measure Parking Resource Utilization
For illustrative purposes, we applied this concept to two cases of parking policy changes in two California cities: Walnut Creek and Santa Monica, and measured the changes in space-hour utilization levels following the changes of parking rates and parking time limits.
The City of Walnut Creek used to have a 2-hour parking limit for all the downtown on-street parking spaces. The City studied demand patterns in different areas of downtown and found that while the parking in downtown core was often congested, the periphery constantly had low occupancy. This was largely due to employees parking in the core. The City initiated the“Purple Pole” program in September 2017 to eliminate time restrictions in the peripheral zones.
We looked into the parking data over the October 2017 — March 2018 period across the 818 paid parking spaces in the periphery zones that operate 7 days a week from 10 AM to 8 PM. Compared with the previous year (October 2016 — March 2017), the average occupancy increased (Figure 1 Left), indicating overall higher parking usage. However, the total number of transactions decreased (Figure 1 Right) — as more parkers parked for longer durations than before (Figure 2).
Did this policy change result in a more efficient use of space? Using the space-hour measurement, we saw the space-hour utilization rates on weekdays increased from 36% to 40%, and on weekends increased from 24% to 29%. The utilization level increased most on Friday (from 38% to 45%), and least on Monday (from 29% to 30%). In short, by allowing for long parking hours in the periphery, the Purple Pole program not only provided convenience to long-term parkers, but also successfully increased the utilization efficiency of the previously underutilized inventory outside of the downtown core.
The City of Santa Monica, CA also experiences high parking demand in the downtown area. In July of 2016, the City raised parking rates at several garages that were most congested while keeping the rates unchanged at the Main Library garage, which is further away from the commercial core and had lower peak occupancy. We analyzed the parking usage data at the Library garage and found out that in the year following the rate change, both the average transient occupancy and number of transient transactions increased (Figure 3).
Has the utilization also improved? The answer is yes — the space-hour utilization rates increased from 33% to 35% on weekdays; the change on weekends was moderate but still positive. This suggests that by differentiating the rates at high-occupancy and low-occupancy garages, Santa Monica successfully incentivized some parkers to switch garages and increased the space-hour utilization across the City’s parking structures.
When crafting parking policies to influence parking behavior and increase the efficiency of a parking operation, we should consider “time” as a dimension, and look for ways not only to balance the supply and demand between different parking locations through location-based strategies, but also to optimize the utilization across different time periods with time-based strategies. This means thinking bigger than parking cars — how else can this space be used during off peak hours? Food trucks are a great start, but given the affordable housing issues we have here in California, we might think about repurposing unused parking into housing or some other higher use.
Update — 5.16.18
At Smarking we are all about giving credit where credit is due — to that end we heard from Professor Shoup that a similar concept to “space-hours” was introduced in his seminal text “The High Cost of Free Parking” on page 274. Professor Shoup also mentioned that the idea is similar to the concept of Erlang in telecom — a unit used to measure the load of a telephone circuit. As always, we are deeply indebted to Professor Shoup — much of the opportunity Smarking has within our municipal client base stems from implementing the ideas he first published many years ago.
Thank you Professor Shoup!