When my wife and I lived in New York City, we never owned a car.  Then the kids came, and, like other many other New Yorkers, we moved to the suburbs.

Despite our commitment to the environment, there was no choice but to drive.  Our town isn’t walkable.  I tried getting around by bike for a while, but I always felt moments away from death on our narrow, winding, potholed and bike-lane-less roads. In Westchester County, NY, conventional wisdom is that you need one car per adult.

Our household actually has three adults, but when the kids were little we managed well with two cars. Now that the kids are older, our transportation needs are getting more complicated.

The Smart ForTwo Electric Drive, produced by Daimler AG (Mercedes-Benz), was a natural choice for our third car.  It’s a two-seat Electric Vehicle (EV) with little storage space, but it’s surprisingly roomy for the driver, it’s maneuverable and it doesn’t take up much space in the driveway.  It also feels surprisingly stable on the highway for such a tiny car.

Best of all, it uses no gasoline. Its range is 70 miles per overnight charge from an ordinary household wall outlet.  It’s the perfect car to putter around town, but not for long trips or to cart the kids around.

The American Council for an Energy Efficient Economy (ACEEE) rates the Smart Electric the greenest car in the U.S.[1] Unfortunately, that doesn’t mean that there is no environmental footprint.  I set out to conduct a “life-cycle analysis” of our transportation choices, including the energy we used as well as all of the other greenhouse gas emissions that go into the process.  I knew that there was no way to get an exact figure, but I was less interested in scientific precision than in understanding the factors that affected our real-life emissions.

Operating Emissions

Smart Car

Although the Smart Car has no tailpipe emissions, the electricity that it uses isn’t carbon free. Emissions from power plants depend on the mix of fuels used. The U.S. EPA has a website that provides the average mix of fuel and carbon emissions of power plants for each region of each state.[2]

My region of New York relies a little less than 60% on natural gas and about 40% on nuclear energy, with a bit of renewables (wind and/or solar) and oil.  The EPA estimates my local electricity footprint to be the equivalent of about 0.65 pounds of carbon per kilowatt-hour (lbs. CO2e/KWH). There is some uncertainty about these estimates because the actual mix of fuels varies considerably throughout the day, because of inefficiencies in transmission, and because the carbon emissions of each fuel type is subject to some dispute.

According to my documentation, my car uses 32 kilowatt-hours per 100 miles (.32 KWH/mi).  This will vary depending on how much highway vs. city driving I do, the weather (the battery drains faster in the cold but air conditioning is usually on in hot weather) and how effectively I use the car’s regenerative braking capability, which converts friction from the brakes into electricity to run the car.

Accounting for a 30% loss of power because of all of these uncertainties,[3] then I can estimate that my car emits about 0.27 lbs. CO2e per mile.[4]


To understand the environmental impacts of my car, I also had to know more about the alternatives.  In my case, my alternative is my family’s 2011 Subaru Outback, which I shared with our au pair before purchasing the Smart Car.

My Subaru Outback is safe, reliable and durable, which are the top priorities given that my children are the usual passengers.  It’s better on gas than the typical SUV, but still not great: the dashboard tells me that in practice we get about 21 miles per gallon (mpg).

Burning a gallon of gas emits about 19.64 pounds of CO2. [5] However, this estimate does not include production, which includes extraction, refining, and distribution.  Historically, production of gasoline has been estimated at about ¼ of the total life cycle emissions, but this has increased over the last few years as more of our oil comes from Canadian oil sands, which emit as much as 80% more greenhouse gases than conventional oil wells.[6]

My estimate of the life cycle carbon emissions of a gallon of gas is about 27 lbs. CO2e.  For my Subaru, that works out to about 1.3 lbs CO2/mi[7], or about 4.8 times the operating emissions of my Smart Car.[8]

Embodied Emissions

The full carbon footprint of a car also includes the “embodied” emissions, which include everything from mining the raw materials to manufacturing and distribution of the car itself. A precise calculation of the many variables related to embodied emissions would be overwhelming and impractical.

ACEEE has developed a method of estimating embodied emissions[9] based on vehicle weight and engine type.  Manufacture of internal combustion engines, with thousands of moving parts, is more carbon intensive than electric motors, which aren’t much different, except in power, from the motor that runs a food processor.  On the other hand, manufacture of the lithium-ion batteries that power electric cars emit more than twice the carbon equivalents per pound of any other part of either kind of car.

The ACEEE method estimates that it took 3,162 lbs CO2e to produce and deliver my Smart Car and 4,485 CO2e for my Subaru Outback.[10]  The production of my Subaru emitted more than 40% more carbon equivalents than my Smart Car, mainly because it is nearly twice as heavy.

For comparison purposes, it is helpful to think about the embodied emissions per mile of driving.  To minimize the cost per mile, my wife and I always intend to keep our cars as long as possible.  With the Subaru, there is no way to know how many miles the car will end up being driven (I might crash it tomorrow), but today’s cars are engineered to last about 150,000 miles.

I am less optimistic about the life of my Smart Car.  I leased my car because it was much cheaper than purchasing it and because EV battery technology is advancing so quickly that three years from now my Smart Car will be completely obsolete.  This car may never be driven beyond my 30,000 mile limit, even though it will remain perfectly drivable for much longer.

There is a young but growing market for used EVs.  Might someone else drive this car with a new battery?  Might the battery itself be reused or recycled?  I hope so, but I believe that it is best to be conservative and assume that the car will be junked after 30,000 miles.

Embodied emissions represent 0.1 lbs./mile for my Smart Car and .03 lbs./mile for my Subaru. With my operating emissions for each car, the total life cycle emissions for my Subaru is 1.33 lbs. CO2e/ mile and 0.37 lbs./mile for my Smart Car.  Even with my very conservative estimate of the life of the Smart Car, it is still 3.5 times more efficient than my Subaru.

The Effect of More Driving

Some additional energy use was inevitable because we bought the car to serve our growing transportation needs. I carefully tracked the miles we traveled in each car for the first month and estimated the historical average traveled in the Subaru since we purchased the car in 2011. (I did not count occasional long trips, such as vacations, for which the Smart Car won’t be of use.)

I drove 541 miles in the Smart Car. I estimate that the Subaru was driven about 200 fewer miles than its previous monthly average, while the 2007 Prius, my wife’s commuting car, was unaffected. For some trips, the Smart Car replaced miles that would have been driven in the Subaru, but having the new car also allowed me to take some trips that would not have been possible because other family members needed the car.

The carbon emissions of operating the Smart Car were 146 lbs. CO2e,[11] and the savings from not driving the Subaru were 266 lbs. CO2 [12].  Overall, my family’s carbon footprint was 120 pounds lighter once we were driving our EV.

A Final Thought

It also may be worth considering the broader impact of my decision to buy a Smart Car.  On the one hand, by selling such a car Daimler gains experience with the technology that one day may lead to the development of a much more mass-market Electric vehicle. I play a small “early adopter” role in bringing more sustainable products to market.

On the other hand, I may also paradoxically be helping others obtain less fuel-efficient vehicles in the short term.  This is because of U.S. Corporate Average Fuel Economy (CAFE) standards, a federal law aimed at improving automobile emissions.  Under CAFE, each automaker is required to meet or exceed certain mpg standards for its cars on average across all of the cars it sells in the US, with some classes of vehicles excluded.

Selling a small number of very fuel-efficient cars allows the company to sell high-margin but gas-guzzling SUVs while still maintaining acceptable average fuel economy across the entire fleet.  In other words, my personal carbon footprint may be lighter, but I am enabling others to own far more polluting cars.

I managed to reduce my family’s carbon footprint (while driving more miles) by buying the right new car. But my own family’s carbon footprint, while important, is less important than the overall emissions of Daimler’s fleet, and these are determined by current legal and regulatory requirements, the state of the technology and the available public economic incentives.

Where consumers and companies who care about the environment can make a difference is in supporting policies to encourage more production and purchase of fuel-efficient cars, such as higher fuel efficiency standards, taxes on fossil fuels, and incentives for the technological development.  While reducing our own carbon footprint is important, what really matters is what we do collectively.

John Wilson is the Head of Corporate Governance, Engagement & Research at Cornerstone Capital Inc.  Prior to Cornerstone, he was the Director of Corporate Governance at TIAA-CREF and the Director of Socially Responsible Investing at the Christian Brothers Investment Services. He is also an Adjunct Assistant Professor at the Columbia University Graduate School of Business.

[3] This is somewhat back-of–the-envelope, but informed by two sources: “Does The Tesla Model S Electric Car Pollute More Than An SUV?” by David Nolan, Green Car Reports, May 31, 2013; also, “Rating The Environmental Impacts Of Motor Vehicles: Aceee’s Green Book”,Shruti Vaidyanathan and Therese Langer September 2011.
[4] .65 CO2 per KWH X .32 KWH/mi.  X 1.30 = CO2e/mi for the Smart Car
[6] How Bad are Banannas: The Carbon Footprint of Everything, by Mike Berners Lee, Profile Books, 2010, page 88.
[7] 27 CO2e per gallon / 21 mpg = CO2e/mi for the Subaru
[8] Confirming that this calculation is at least somewhat reasonable, my Smart Car’s documentation rates the car’s fuel economy as equivalent to 107 miles per gallon, which is a approximately 5 times the fuel efficiency of the Subaru’s 21 mpg.
[9] Vaidyananthan and Langer, see especially Appendix B, pages 27 & 29
[10]Ibid. The ACEEE formulas are as follows:  For ICE cars, Embodied Emissions = 1,367,377 + (2432 g/lb X weight of car (lbs)); for EV cars, Embodied Emissions = 1,034,184 + (1,943 g/lb X vehicle weight (lbs.)) + (5446 g/lb X battery weight)
[11] .27 X 541
[12] 1.33 X -200