Does Every Car Need 8 Parking Spaces? Ride-Sharing Can Save Emissions by Reducing Parking, Too

What does attending the recent LiveRideShare conference in Los Angeles have in common with developing a paper on supply chain energy for an industrial energy efficiency conference? More than you think - and it all comes down to how shared mobility can cut our need for parking spaces and reduce climate-altering emissions in the process.

Shared mobility means using one vehicle--a car, a bike, etc.--to serve a number of different people. Well-known forms of shared mobility include taxicabs and rental cars (and mass transit). Newer forms include public bike-share systems and private, often technology-enabled solutions such as car sharing, ride sharing, or real-time transit tracking and trip planning.

Supply chain energy is the energy used to manufacture the materials needed to support consumer purchases. For example, if you are "buying" automotive transportation, you are not only consuming gasoline, but also the energy to produce the steel and plastic and glass needed to make the car, along with the energy to produce the concrete and asphalt for the roads, parking spaces, etc., necessary for driving that car.

Let's focus on the provision of parking. I wouldn't have thought that parking was a big deal, but that's because I was failing to ask a key question:

But how many parking spaces do we need?

Parking turns out to be surprisingly important in terms of supply chain energy, and even more so in terms of supply chain greenhouse gas pollution, as I discovered in researching the conference paper two weeks ago. The University of California at Berkeley's Department of Civil and Environmental Engineering found that one can document that there are about 3.4 parking spaces in America for each car, and that many well-cited and informed guesstimates say there may be as many as EIGHT parking spaces per car.

Why so many? Think about it: most people drive to work and need one parking space for each car at work and at home; they also need a space at their shopping center(s), friends' or families' homes, their church or other such facility, the sports stadium or school football field, at their restaurants or coffee shops and cleaners, and at their recreation facilities such as parks, movie theaters, etc.

Well, it turns out that all of those parking spaces cost a LOT of energy--and even more emissions--to build and maintain. If you believe that the lower estimate is correct, then the emissions consequences are 67 million metric tons of carbon equivalent annually, some 6 percent of the total emissions from all of the gasoline sold every year.

And if you think the higher estimate of eight spaces per vehicle is on target, the emissions are 150 million metric per year, or almost 15 percent of those from gasoline.

Why shared mobility is important?

At the Feb. 23 LiveRideShare conference organized by my colleague Amanda Eaken we learned that participants in a car-sharing program can cut their travel demand by 27-43 percent.

But we also saw that demand for parking drops much more: even for trips where a shared ride does not reduce travel (the case where a driver takes a person from point A to point B without wanting to go there otherwise), it still cuts the demand for parking on that trip by one full space. Or by two spaces if the car share participant had decides there is no longer a need to own a car (which is what is observed: ride share participants reduce their ownership of cars by about half).

You can see this by looking at my own experience. When I first worked at NRDC, my family owned one car, and we drove it about 5000 miles a year. This is pretty typical behavior for people of my income living in my neighborhood, which is very walkable and has great transit options.

I kept the car parked on the street most of the time, consuming 1 parking space. Counting the spaces I used when I drove somewhere, that probably meant using 1.1 parking space.

Since giving up the car when my younger child was born, I reduced my driving by about half--the remaining half coming from rental cars and taxis--older, lower-tech but still effective forms of shared mobility. But my use of parking was less than .05 parking space.

So the calculus was, for my case, 50 percent reduction in driving but 95 percent reduction in parking needs.

Car sharing could become very widely used, since it is an information-based service that relies on people who are already driving from a given point A to point B -- or would be willing to do so for pay. So it could be deployed rapidly even in suburbs or rural areas that cannot be served well by public transportation or even by taxicabs. And with all the new technologies, there are a myriad of affordable, shared and sustainable transportation options that reduce greenhouse gas emissions - while increasing choice for consumers and cutting cost.

So, just looking at the problem from the 100,000- foot level, if half of the households eventually participate in some sort of shared mobility program, and it reduces car ownership by half, that should reduce parking demands by much more than half. The result: the emissions from parking construction and operation would be slashed by very roughly 50 million metric tons per year, equivalent to cutting driving by 5 percent. And that's on top of any savings from less driving. In other words, we have an additional savings potential of 50 million metric tons that no one has yet counted on, or even counted.

This is why I am so optimistic about America's ability to cut climate pollution by at least 80 percent before the year 2050, as we need to in order to stabilize climate.

In addition to all the savings that I could quantify from hidden energy efficiency based on current knowledge--and that was enough to get us to even more than 80 percent reductions in climate pollution, I keep finding large new opportunities in unexpected places - like our parking lots.


About the Authors

David B. Goldstein

Codirector, Energy program

Join Us