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The Hidden Costs of Commuting


By Alex Wilson

Much of the focus of building green is on reducing the energy consumption of buildings. This is a good thing. By reducing unwanted heat gain, limiting wintertime heat loss, optimizing daylighting, and generally squeezing as much benefit as possible out of each kilowatt-hour of electricity, therm of natural gas, or gallon of heating oil, we protect the environment and reduce operating costs, propelling our designs to the shiniest levels of LEED performance.

The Hidden Costs of Commuting
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How do we  account for the Energy Used in Getting To and from Buildings?
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Given the emphasis we put on the energy performance of buildings, it’s a little surprising that for a typical office building, more energy is actually used to transport workers to and from the building each day than is consumed in the operation of the building itself—typically 30 percent more according to an analysis I did a year ago for Environmental Building News (EBN is published by BuildingGreen, McGraw-Hill’s editorial partner in GreenSource). New buildings that satisfy modern energy codes use less energy, and we found that in those buildings commuting uses, on average, 2.4 times as much energy as the building itself. This analysis factored in the average commute distance, mix of commuting options, vehicle fuel economy, and building occupancy (square feet per employee), so that transportation energy consumption per square foot could be calculated and compared with building energy consumption per square foot.

This means that if our goal is to reduce the overall environmental impact (or ecological footprint) of buildings, then we need to be paying much more attention to building location and alternative transportation. A good start would be to advance our understanding of how to measure the “transportation energy intensity,” or TEI, of buildings. Urban planners and transportation planners have a good understanding of the variables that predict how people get to work. Relevant factors are community density, access to services, distance to transit stops, cost of parking, and so forth. These variables can be quantified on a building-specific basis so that the predicted transportation energy intensity of a building can be measured. This new metric of building performance may be just as important as measures of building energy performance.

The next step would be to create incentives for reducing the transportation energy intensity of buildings. Perhaps buildings with predicted low transportation energy intensity should qualify for less expensive permitting, density bonuses, accelerated permit review, and other measures that would encourage developers to create high-density, mixed-use, transit-accessible buildings rather than conventional suburban office parks.

Once we figure out a quantitative approach for predicting this transportation-energy-intensity value, we can incorporate that into the LEED rating system. In the current version of LEED for New Construction, five points (out of 69) can be earned for prescriptive measures that may help to reduce commuting by car (development density, distance from public transit, bicycle storage and changing rooms, parking capacity limits, and alternative-fuel refueling stations). With the metric of transportation energy intensity, we can replace those prescriptive measures of transportation alternatives with a performance metric—as was done with energy credits in the change from the piloted LEED 1.0 to 2.0 five years ago. Already, the draft LEED 2009 changes include greater weighting for transportation and location, though the relevant credits are still prescriptive.

Encouraging buildings with low transportation energy intensity will help reverse the trend toward suburban sprawl with its inherent problems that include not only greater transportation energy use but also loss of open space and farmland, reduced productivity resulting from traffic congestion, air pollution, and pollution of surface waters from stormwater runoff.

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This article appeared in the September 2008 print issue of GreenSource Magazine.

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