On the Road

I’ve always wanted to go on a road trip through Utah. Does renting an RV or a pop-up van for vacation provide greenhouse gas savings? How does it compare to driving and camping or flying and renting a car?

Asked by Jacob Englander, ’10, MS ’13 Stanford, Calif.

Essential Answer:

Although carbon emissions accounting can get rather complicated, with just a little research, anyone can do a back-of-the-envelope calculation and get a sense of the impact of his or her travels. For aspiring carbon accountants, the first step is to break your travel plans down into smaller parts. For our Utah trip, we’re accounting for:

·      transportation to and from Utah;

·      transportation within Utah, and

·      nights spent camping either outdoors or in the RV.

The table below summarizes the results of my calculations, which I explain in greater detail in the Nitty-Gritty Answer. The different travel scenarios are based on the same five-day itinerary through Utah for a San Francisco family of four. Scenario 1 involves driving an RV or camper van throughout the entire trip and spending a total of seven nights (two to and from Utah; five during the road trip) in the vehicle. Scenario 2 is similar to Scenario 1, but we rent an SUV instead and camp out at night. Scenario 3 flies us straight into Salt Lake City and we road trip with an SUV, again camping out under the desert sky for five nights.

A table listing the carbon footprints of each travel scenario described above. Scenarios 2 and 4 are the lowest, at 1093 and 1045 Kg of carbon dioxide, respectively. Scenario three is the third best at 1178 kg of carbon dioxide.

According to my calculations, driving an RV emits by far the most CO2, due to poor fuel economy. On the other hand, driving an SUV turned out to be the best option of the three scenarios. Getting to Utah by plane is an acceptable alternative given that the itinerary emits only 8 percent more greenhouse gasses than driving an SUV.

However, let’s not forget that there’s plenty of room for creativity to customize your own emission reduction strategy. One possibility, which I outlined as Scenario 4 in the table above, is to substitute a hybrid vehicle for the SUV in Scenario 3. Wondering what would happen if you were to drive a hybrid the whole way? Learn how to calculate for yourself, below in the Nitty-Gritty Answer.

Nitty-Gritty Answer:

As I explained in the Essential Answer, these calculations are only rough estimates, since a comprehensive CO2 accounting would require much more detailed information about the trip. Our analysis is also limited to transportation and camping emissions, and does not include other possible emission sources. Furthermore, professional emissions analyses focus on the difference in emissions when the action yields the same products or services. Given that flying and driving are inherently different services, our analysis may not pass the most stringent scrutiny. Nevertheless, our back-of-the-envelope calculation can help us gain a basic idea of our impact on the environment.

Before we dive into detailed calculations, there are some key assumptions I made to set up our analysis. Again, our analysis is based on a family of four departing for Utah from the Bay Area. If the family opts for Scenario 1 or 2, the roundtrip mileage between San Francisco and Salt Lake City is approximately 1,470 miles, and they will stop for one night each way. Vehicle fuel economy data is based on the average MPG for a typical Class-C motorhome (for RV), 2013 Ford Explorer (for SUV), and 2013 Ford C-Max Plug-in Hybrid (for hybrid vehicle).

If the family opts for Scenario 3 or 4, the roundtrip mileage between San Francisco International Airport and Salt Lake City International Airport is 1,198 nautical miles, according to the International Aviation Transportation Association. Most direct flights between these destinations are flown with either an Airbus A320-200 jet or a Boeing 737-300. For simplicity, our calculation is based on flying on an A320-200 aircraft. The road trip through Utah is about 650 miles long, and the family will make five overnight stops during the trip.

The next step is to break the trip into smaller, more manageable segments in order to calculate the associated CO2 emissions. As shown in the table from the Essential Answer, I calculated the round trip to and from Utah, the road trip through the state and the camping emissions separately. Now, we are ready to attack. Carbon accounting is most simply done in three steps: measure, convert and calculate.

Take our SUV emissions to get to and from Utah for example. Given that our roundtrip mileage is about 1,470 miles and the Ford Explorer gets 20 miles to the gallon on average, our fuel consumption for this portion of the vacation is approximately 73.55 gallons of gasoline.

However, carbon emissions statistics for fuels are usually described in terms of the quantity of CO2 produced in relation to the amount of energy provided. The energy a given amount of fuel can produce is called its “energy content.” Gasoline’s energy content is about 124,000 BTU (“British thermal unit,” a measure of energy content invented by the Brits) per gallon. With this conversion we know that we used 9.3 million BTUs of energy to get our SUV to and from Utah.

To express energy production in terms of its environmental impact, engineers came up with the concept of “carbon content” to quantify the greenhouse gas emissions released into the atmosphere by the consumption of a given amount of a particular fuel. The carbon content of gasoline is about 71.3 kilograms of CO2 for every million BTU. Since we already know how many BTUs we used, we know we are emitting roughly 653.34 kilograms of CO2 as we drive to and from Utah.

That’s it. Now you know the drill and can start doing your own calculations. Just keep in mind the three simple steps: Measure fuel use, convert to energy use and calculate total emissions. Give it a try next time when you’re contemplating whether to take your vintage Subaru or new BMW to work—or maybe park them both, and make new friends on your bus ride into town!

Vincent Chen, ’13, is a master’s student in civil and environmental engineering.