Is Underground Parking Really That Expensive?

I spent some time in our Site Construction and Measurement (Construction Management CMP305) class talking about parking lots. (Shocking, I know). The class, which include two weekly lectures and a two-hour lab, is an intensive, deep dive into everything ranging from how to map and measure sites to how to manage stormwater, trenching, but also the business context. I emphasize the ways that the primacy of parking as a land use creates massive additional costs, additional traffic and therefore additional pollution, and how the construction industry theoretically has at least an obligation to think about how to get rid of things like parking minimums. Why? Because parking lots represent a lot of buildable land, and the success of the construction industry is predicated on, well, building things! So, this leads us to ask about the elephant in the room: Can’t we just put the parking underground?

The answer is generally “yes.” It’s very expensive. We know this. But it can be priced out relatively simply. And illustrating it– which we did in one of our lab classes- helped us show how some of the tradeoffs actually look in a practical context.

Recap: Parking Land Use Efficiency

For our final projects in the class, students have been tasked with developing a site plan and a site management plan for a hypothetical construction project on a real life site. For the sites, I picked all parking lots, in part because they’re easy to quantify and delineate– they often occupy whole parcels and have clear edges. This is contrasted with something like a cornfield that is platted and divided and subdivided based on thoroughly arbitrary decisions. My scapegoat of construction and development typologies is the “Wal-Mart in the Cornfield”– the boogeyman that illustrates how greenfield development continually devours valuable arable land (based on a thoroughly stale, heteropatriarchal idea of perpetually conquering new virgin territory) and creates massive externalities in the process.

The project requires planning based on a rubric with a few dozen line items. I made underground parking mandatory for most projects, and I also gave our lab classes an exercise where they had to model the spatial efficiency of parking, borrowing from my agéd Detroit Park City project many moons ago. This showed some interesting things, but mostly that there are a lot of different ways to design parking lots, and most of them are thoroughly inefficient uses of space.

Spatial Efficiency Isn’t The Only Objective In Parking Lots

For the Detroit Park City project, I calculated a spatial efficiency ratio for a parking lot by dividing the area of actual parking spaces into the total area. While designing a parking lot with an efficiency approaching 100% is theoretically possible, the average “efficient” parking lot could have as much as 70% of its area occupied by parking spaces. Parking structures are the least efficient (maybe 40%), and underground parking structures even less so (around 30%) because of how much area has to be dedicated not just to aisles, but also corners, HVAC equipment, stairwells, and more.

In a parking lot that is purely hardscaping, one really doesn’t have an excuse to be that inefficient. But many parking lots have things like sidewalks or islands– landscaping with trees, for example, that can mitigate urban heat island effects. These, of course, provide benefits to offset the “bad” parts of an asphalt surface parking lot.

But most parking lots are poorly landscaped, if at all. As my lab co-instructor reminded us, most municipalities have some sort of requirements about landscaping. Detroit does (you evidently don’t have to comply with them if your last name is Ilitch, though).

We found in lab– analyzing about fifteen sites- that the average area of parking lots that was occupied by parking spaces (as opposed to aisles or dead space) was only around 50%. Some sites– including one in downtown Lansing with virtually no landscaping whatsoever were as little as 30% efficient.

So, underground parking costs?

Yes! We’re getting there, don’t worry.

My rule of thumb is that probably two standard deviations of all problems can be solved with napkin math. The rest we leave up to the quantitative nerds and the engineers. In this case, we figured that an underground parking space might cost as much as $65,000 (many idealized estimates are lower, but most construction projects are vastly over budget and behind schedule, which is why I have a job).

Imagining that the financial lifespan of the capital to finance the construction of a parking garage is 7-11 years, we show that one parking space can pay for itself at a cost of $3-5 per hour for eight hours per workday.

That’s cheaper than the average parking in a structure in most major cities. And many of those structures are completely depreciated.

cost	$   65,000.00	per workday	for 8 hours
7 years	$      9,285.71	$            37.14	$          4.64
11 years	$      5,909.09	$            23.64	$          2.95

I also returned to the hallmark of the Detroit Park City project, which was to illustrate that a single parking space represents as much as half of a whole apartment that could be built in its place. At the time, I figured that the average parking space was 162 square feet and the average apartment was 872 square feet. At an efficiency of 40%, one single parking space represents half of an apartment.

I am sure that many of my students will go on to build Wal-Marts in cornfields, because as long as we have cheap carbon and poor land use regulation, that’s what’s for dinner. But I remind them every day that it’s possible to ask questions– especially as the construction industry increasingly integrates itself into the development process earlier than it used to- to drive better, more sustainable, more equitable outcomes. Parking is a great place to begin.

Starting by thinking about parking to achieve those outcomes has never been seen as a particularly sexy solution. Parking is, after all, just asphalt and concrete. But it’s also one of the largest land uses in this country, and that needs to be interrogated.

This is not to say that we should get rid of all parking forever. Options are always good. But putting the parking underground based on the above math is not actually as crazy as people make it out to be. It also allows us to think about building denser cities, which is a great step in challenging the automotive paradigm.

Learn more about the Construction Management program at Michigan State University in East Lansing, Michigan. The views of the author are his own and do not reflect the policy or positions of the School of Planning, Design, and Construction, nor those of the University.