For very good reasons, we focus a great deal of effort in green building on reducing the energy consumption of our structures—after all, these directly account for more than 35% of our energy use and carbon dioxide emissions. But if you factor in the energy used in getting to and from our buildings—usually in single-occupancy cars and pickup trucks—those percentages grow significantly. And while it’s relatively easy to reduce the use of carbon-dioxide-spewing fossil fuels to operate buildings (through efficiency improvements and solar energy, for example), that’s much harder with vehicles, where we rely almost entirely on gasoline and diesel.
If we are to make a significant dent in our fossil fuel consumption, we need to focus attention on where we build, and on ensuring access to public transit and human-powered transit (bicycle paths, bicycle lanes, and walkways).
A few years ago (2007), I dug into the “transportation energy intensity” of buildings for an article in Environmental Building News. I did this for office buildings, but many of the ideas transfer reasonably well to homes. We know how to measure building energy use (often using the metric of Btus per square foot per year); I sought to come up with a parallel metric for the transportation energy associated with buildings.
To do this, I used statistics from the U.S. Census Bureau and U.S. Department of Transportation on commuting distances (12.2 miles each way), how Americans commute to work (76% in single-occupancy vehicles, 11% in two-person carpools, most of the rest via public transit or walking), and average fuel economy of vehicles (21 mpg). To estimate the square footage of office space per employee, I used a U.S. General Services Administration figure of 230 square feet (which I’m told may be significantly lower than in private office buildings). I assumed 235 work days per year.
The bottom line
I found that, based on national averages, the annual commuting energy consumption for a typical office building is about 121,000 Btu/sq. ft. This compares with average office building energy use of 93,000 Btu/sq. ft. In other words, more energy is expended getting people to work than the office buildings themselves use. If, instead of an average office building, we consider one built to the most common energy code (ASHRAE 90.1-2004), this transportation energy use is 2.3 times that of the building energy use.
What this means is that if we want to significantly reduce energy use and carbon emissions, we need to re-examine where we’re putting our houses. Urban infill housing and renovation of older houses in more densely developed neighborhoods is greener than building new houses in suburban and rural areas. If homeowners can walk to the store or a coffee shop, they will be less likely to use their cars all the time.
Building within a quarter- to a half-mile of a transit stop (bus, light rail, or heavy rail) allows easy walking to the stop and use of public transit. It’s no coincidence that in the Washington, DC area property values near METRO stops have continued going up, even while most property values in the region have been dropping the past few years. The same argument applies with bicycle paths—properties close to many bike trails are more in demand and the values are going up.
As they say in the real estate industry: location, location, location!
There are also things we can do in designing or reorganizing homes to facilitate alternatives to driving. Convenient storage of bicycles is one strategy—making it easy to get a bicycle out and use it. If it’s easy, more of us will bike.
At the workplace, providing safe, covered bike storage and shower facilities can help to encourage this alternative to driving. More convenient, premium parking for carpool vehicles may inspire more workers to share rides.
Companies and institutions can also implement a wide range of measures to reduce commuting by single-occupancy vehicle: elimination of free parking, vouchers for public transit (as an employee benefit, or at least using pre-tax income so you’re not paying tax on public transit expense), flexible hours for bicycle commuters to avoid rush hour biking, and other rewards or recognition for avoiding vehicle use.
My top-10 list of green building priorities so far:
#4. Reduce the need for driving
In addition to this Energy Solutions blog, Alex writes the weekly blog on BuildingGreen.com Alex’s Cool Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail—enter your e-mail address in the upper right corner of any blog page.
Get building science and energy efficiency advice, plus special offers, in your inbox.