Introduction

Did you know that there are enough parking spaces in the United States to fill up the state of Connecticut? There are approximately 2 billion parking spots in America (servicing the needs of about 200 million cars). On average, a quarter of every major city’s land is parking area — with some cities, like San Bernardino, dedicating fully half of their urban space to parking.

These numbers are shocking — and if you think they represent underutilized space and inefficient development, you’d be right. Parking lots have often been an urban planning afterthought: an unfortunate precondition of a car-dominated society whose design was given very little consideration. But there’s another problem: Pavement-centric development is not ideal from an environmental perspective, contributing to the heat island effect and producing an abundance of polluted stormwater (among other issues).

De-incentivizing driving is an important first step. Providing access to public transit and creating safe corridors for pedestrians and bikers lowers a community’s reliance on cars. Indeed, according to the Institute for Transportation & Development Policy, 18.6 billion pounds of carbon emissions are released into the atmosphere each year just from vehicles looking for parking.

But this will only get us so far — parking in some form is a necessity. So, how do we make these parking facilities more efficient and sustainable? With green design.

The Problem with Traditional Parking

For decades, many American developments were saddled with parking “minimums”: a required number of parking spaces that must be included in design plans. This makes some sense, in a society in which personal vehicles are the primary source of transportation.

The problem is that these parking facilities often serve as nothing more than vacant pavement islands with no ancillary purpose, instead becoming blights on a community’s landscape and sprawling examples of the inefficient utilization of urban and suburban space. They can also be precarious for walkers, who often have no place to safely traverse the area. And, particularly when viewed through the lens of climate change and the action we must take to mitigate its effects, large traditional parking lots are environmental burdens.

Let’s examine some of the reasons why traditional parking lots present problems for our cities.

Heat Islands

The onslaught of climate change equals a warmer planet — it seems like every summer we set a new global heat record. We’re particularly vulnerable to the negative effects of heat (everything from rising energy costs to heat-related deaths) in urban environments, where hardscapes are more abundant. Large, paved parking areas (typically with no shade) are especially problematic, as the temperature can be 20 degrees warmer than surrounding areas.

Stormwater Pollution

More hardscapes equal more stormwater runoff. And, given that cars drip everything from oil and gas to grease and coolants (to say nothing of the material erosion of the road surface itself), parking lot stormwater is often exceptionally polluted. If not properly treated, this runoff ends up contaminating our local watersheds.

Flooding

Impervious surfaces prevent stormwater from infiltrating into the ground — and during major storm events, this can mean an overabundance of stormwater entering the area’s gray infrastructure. Traditional stormwater management in parking lots is designed to whisk water away as quickly as possible, and this can create velocity and volume concerns downstream, as well as the possibility of flooding during peak flow times.

Pedestrian Safety

According to the Montgomery County Planning Commission, up to 20% of a community’s pedestrian injuries occur in parking lots. Why? Because walking zones to and from one’s vehicle are unclear or nonexistent. Likewise, large empty parking lots encourage drivers to cross lanes at high speed, creating unpredictable and dangerous conditions for pedestrians.

Going Green

So, how do we address these environmental and safety concerns in parking lots? By giving this urban space more consideration, both from a space-utilization and a sustainability perspective —and green design is a great place to start.

Vegetation is one of the most important factors in a green parking lot. This strategy allows for numerous simultaneous benefits. Firstly, open planting space reduces the amount of hardscape, which of course also reduces the stormwater runoff generated in the area. The dual benefit is that, in addition to lowering the total impervious area, vegetation can assist in treating the stormwater that is generated on site. Treat water as a resource instead of an obstacle to be removed — in this way, the burden on gray infrastructure is reduced and the vegetation receives natural irrigation.

A large component of this planting strategy is trees. Trees not only help manage stormwater, but their canopies reduce the ambient temperature and minimize the heat island effect. Likewise, lower temperatures mean lower energy consumption. It’s also a fact that people spend more time in shady green space than hot paved areas; this translates to additional sales in retail zones and increased demand for green residential communities.

Impervious surfaces are also beneficial. When stormwater infiltrates into the ground at its source, the runoff is cleaner and improves groundwater recharge. This water, once infiltrating the impervious pavement, can be redirected toward planting areas for cleaning and supplemental irrigation.

Though not always feasible, some developments allow for design creativity and the inclusion of flex space: paved areas that can transition from driving to parking to walking based on need, making the space that much more practical and efficient. One example of this is found in Bothell, Washington: a “side” street area along a five-block stretch of Main Street can be used as a walking path, bike lane, vehicle parking, or restaurant seating space.

Ultimately, by prioritizing creative and sustainable designs in our parking areas (rather than treating them as a burdensome design afterthought), we can more efficiently use this space while simultaneously tackling environmental issues and slowing the effects of climate change.

Examples of Successful Green Parking Zones

Turkey Lake / Orlando, FL

Trees: 57 / Silva Cells: 1,818 / Installed: 2022

SMUD Headquarters / Sacramento, CA

Trees: 9 / Silva Cells: 474 / Installed: 2018

Palo Alto Junior Museum and Zoo / Palo Alto, CA

Trees: 8 / Silva Cells: 84 / Installed: 2019

Mountlake Terrace Transit Station / Mountlake Terrace, WA

Trees: 8 / Silva Cells: 55 / Installed: 2010 (redesigned 2022)

Eugene O’Neill Drive / New Richmond, CT

Trees: 44 / Silva Cells: 354 / Installed: 2016

Hilton Fishing Village / Pompano Beach, FL

Trees: 8 / Silva Cells: 96 / Installed: 2020