New Paper Says Emissions Cuts Should Start with Buildings, Not Transportation



A new study co-authored by an MIT professor says the best way for cities to reduce emissions is to focus on residential buildings, not transportation.

The research paper, “Intersecting Residential and Transportation CO2 Emissions,” analyzes how extensively local planning policies could either complement the Obama administration’s Clean Power Plan (CPP) of 2015 or compensate for its absence. The Trump administration has announced it intends to unwind the CPP.

According to, the researchers also found that policies with the biggest local impact vary from city to city, with faster-growing Sun Belt cities such as Houston and Phoenix having the potential to enact a bigger reduction in residential emissions than older cities such as Boston or Philadelphia, which see less change in their housing stock.

The research found that simply requiring newly built homes to be more energy efficient would reduce residential emissions by an average of 6 percent by 2030. But requiring existing homes to be retrofitted would yield a further 19 percent reduction of residential emission, on average, across the 11 cities.

David Hsu, an assistant professor in MIT’s Department of Urban Studies and Planning, and one of three co-authors of the report writes that, “Shifting people to multifamily buildings is what planners have always wanted to do, but that’s actually not as effective as most advocates would have thought.”

The main reason for this, the researchers find, is that as new homes become more energy-efficient, the energy-use differences between larger single-family homes and homes in multifamily dwellings will shrink, thus “reducing the energy and emissions benefits of any substituting attached homes for detached ones,” as the paper states. (The study did find that in Phoenix, one of the 11 cities examined, greater density would have a notable effect on emissions.)

Still, Hsu believes the impact of policies related to construction standards and retrofitting are important, noting these standards are often equivalent or more aggressive than those found in the CPP.

Housing vs. transportation

The researchers also modeled urban emissions growth through the year 2030. They again evaluated a baseline scenario in which current conditions essentially continue intact, as well as a handful of alternate scenarios in which total vehicle-miles traveled varies due to increased use of mass transit and changes in housing density.

They also compared the effects of these local planning efforts to the reduction in emissions that would occur under the Obama administration’s plan to increase the fuel efficiency of the automobile fleet to 54.5 miles per gallon by the year 2027.

The study’s bottom-line finding is that, by 2030, a federal mandate increasing vehicle fuel efficiency to 54.5 miles per gallon would reduce auto-based emissions in the 11 cities by 38%, in the absence of any additional mass transit or density programs. That number would increase to 46%, on average, if the cities adopted robust transit and density policies. (The Trump administration has stated it will review and may possibly drop the existing fuel-efficiency plan.)


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