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Union of Concerned Scientists

Appendix C: Automobile Data Per-trip emissions from automobiles are treated differently from those of airplanes, trains, and motor coaches. That’s because—unlike in other modes—the traveler determines the number of passengers in a car, truck, or SUV. What’s more, per-passenger carbon emissions from personal vehicles decline precipitously as the number of occupants rises. If a driver decides to travel alone, the vehicle’s carbon emissions are fully attributed to that individual. If, on the other hand, the driver brings a spouse, a friend, or an entire family along, he or she incurs a small carbon penalty for the extra weight but per-person emissions fall by a factor of two, three, four,

or more. In the case of airplanes, buses, and trains, we assume that those emission factors remain constant regardless of the number of passengers traveling.54 Per-trip emissions from automobiles vary dramatically with the type of vehicle. We estimated emissions for five different types of passenger vehicles: hybrid car, efficient conventional car, typical car, typical SUV, and large SUV. We evaluated each type of vehicle with one to five passengers, accounting for the modest drop in fuel economy that results from the additional people and their luggage.55

Table 11. Per-Vehicle CO2 Emissions by Vehicle Type and Number of Occupants Occupants 1

2

3

4

5

CO2 emissions in lbs./vehicle-mile (direct and indirect emissions) Hybrid car (46 mpg)

0.54

0.56

0.58

0.60

0.63

Efficient car (32 mpg)

0.78

0.81

0.85

0.89

0.93

Typical car (23 mpg)

1.08

1.12

1.16

1.21

1.26

Typical SUV (18 mpg)

1.39

1.42

1.46

1.51

1.55

Large SUV (12 mpg)

2.08

2.12

2.17

2.21

2.26

Assumptions regarding average weight, in pounds: Passenger

150

Luggage (per-passenger)

50

Hybrid car

3,500

Efficient car

3,000

Average car

3,500

Average SUV

4,500

Worst SUV

6,000

Constants: 19.564 pounds of CO2 per gallon of gasoline (direct emission factor) 27.5% (multiplier for indirect emissions)56 Sources: Fuel economies for different types of vehicles are based on assessments at www.fueleconomy.gov and in EPA, Office of Transportation and Air Quality, 2008, Light-duty automotive technology and fuel economy trends: 1975–2008.

Getting There Greener - Travel Report  

While the idea of "green" vacations has attracted recent attention, most information focuses on what to do when you get to your destination,...

Getting There Greener - Travel Report  

While the idea of "green" vacations has attracted recent attention, most information focuses on what to do when you get to your destination,...

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