Emission Facts
 

Sample Calculation of Emission 

Reductions and Fuel Savings from a 

Carpool Program 

The amount of pollution that a vehicle emits and the rate at which 

it consumes fuel are dependent on many factors. The U.S. Environmental Protection Agency (EPA) has developed a series of computer 

models that estimate the average emissions for different types of highway vehicles. This fact sheet is one of a series on highway vehicle 

emission factors. It illustrates the use of national average annual 

emissions and fuel consumption for gasoline-fueled light-duty vehicles 

(passenger cars) and light-duty trucks (pickup trucks, sport-utility 

vehicles, and the like) in estimating the benefits of carpool and ridesharing programs. 

Introduction 

This fact sheet presents an example calculation illustrating how the emissions reductions and fuel savings resulting from implementation (or expansion) of a carpool or 

ride-share program can be estimated. The basic concept is to estimate the reduction 

in vehicle miles traveled (VMT) that will occur as a result of the program, and to 

combine that with estimates of average emissions and fuel consumption per vehicle 

per mile traveled, in order to obtain an estimate of the total fuel savings and emissions reductions. 

The most current version of the computer model that EPA uses to estimate average 

in-use emissions from highway vehicles is MOBILE6.2. EPA, the States, and others 

use this model to estimate total emissions of pollutants generated by highway vehicles 

in various geographic areas and over specific time periods. The emission rates (or 

“emission factors”) presented in this fact sheet are based on national average data 

representing the in-use fleet as of July 2008. 

Office of Transportation and Air Quality 

EPA420-F-08-028 

September 2008 
 

 

Emission Facts
 

The emission rates for hydrocarbons (HC), carbon 

monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), and particulate matter (PM10 and PM2.5) 

are presented in the following tables. The HC numbers include both tailpipe and evaporative emissions, 

whereas the rates for the other pollutants are for tailpipe emissions only. They assume an average, properly 

maintained vehicle operating on typical gasoline on 

a warm summer day. Emission rates can be higher in 

very hot weather (especially HC) or very cold weather 

(especially CO). 

The carbon dioxide (CO2) emission factor used in the 

following tables is based on the average fuel economy 

of the in-use fleet of gasoline-fueled light-duty vehicles, 

24.1 miles per gallon (mpg) for passenger cars, and 17.3 

mpg for light trucks (e.g., pickup trucks and SUVs). 

This corresponds to a fuel consumption rate of (1/24.1 

=) 0.042 gallons per mile driven (gal/mi) for cars and 

0.058 gallons per mile for light-duty trucks. An average of 19.4 lb (8.81 kg) of CO2

 is produced per gallon 

of gasoline consumed. 

More refined estimates of these benefits can be developed through use of the MOBILE6.2 highway vehicle 

emission factor model to estimate emission factors that 

are specific to the geographic area and time period 

of interest. However, for a first-order approximation 

of the benefits of such programs, use of the national 

average values as provided in this sample calculation 

should be sufficient. 

Sample Calculation 

Abbreviations and Acronyms 


Used
 

CO:	 Carbon monoxide; a regulated 

pollutant 

CO2

:	 Carbon dioxide; the primary 

byproduct of all fossil fuel 

combustion 

HC:	 Hydrocarbons; molecules 

formed of hydrogen and carbon that constitute gasoline, 

diesel, and other petroleumbased fuels; a precursor emission for ground-level ozone 

(“smog”) formation, which is 

a regulated pollutant 

NOx:	 Nitrogen oxides; a regulated 

criteria pollutant 

PM10:	 Particulate matter under 10 

microns diameter; a regulated 

pollutant 

PM2.5: Particulate matter under 2.5 

microns diameter, sometimes 

referred to as “fine particulate” 

SUV:	 Sport-utility vehicle 

VMT:	 Vehicle miles traveled 

VOC: Volatile organic compounds; 

equivalent to THC plus aldehydes minus both methane 

and ethane 

The first step in calculating the benefits of a new or expanded carpool or ride-share program is to 

estimate the reduction in total vehicle miles traveled (VMT) that will result from such a program. This value is the product of the number of people (vehicles) no longer commuting alone 

in their own vehicles and the average distance in miles that those people normally commute. In 

this sample calculation, the following assumptions are made: 

•	 The average commute is a 30 mile round trip 

•	 There are a total of 1000 employees that will participate in the program 

•	 Each of those employees currently commutes alone in their own vehicle 

•	 After implementation of the program, each vehicle will carry two occupants 

2 
Thus, without a carpool program, the total number of miles this group of employees travels each 

business day is 30,000: 

(1) 1000 employees x 1 vehicle/employee = 1000 vehicles 

(2) 1000 vehicles x 30 miles/vehicle = 30,000 miles 

With a carpool program that has two employees in each vehicle, the total number of miles is 

reduced to 15,000 each business day: 

(3) 1000 employees x (1 vehicle / 2 employees) = 500 vehicles 

(4) 500 vehicles x 30 miles/vehicle = 15,000 miles 

Note that if the average vehicle occupancy under the carpool or ride-share program is greater 

than two, that average occupancy can be substituted for (persons/vehicle) in equation (3). For 

example, if it is estimated that the average occupancy of each vehicle under the program will 

increase to 2.5 persons (equivalent to two vehicles in use per five employees), then equations 

(3) and (4) become: 

(3a) 1000 employees x (1 vehicle / 2.5 employees) = 400 vehicles 

(4a) 400 vehicles x 30 miles/vehicle = 12,000 miles 

To calculate the reduction in VMT resulting from the carpool program, subtract the new VMT 

(in equation 4) from the original VMT (in equation 2): 

(5) 30,000 miles (daily VMT before program) - 15,000 miles (daily VMT after program) = 


15,000 miles (daily VMT reduction)
 

(5a) 30,000 miles (daily VMT before program) - 12,000 miles (daily VMT after program) = 


18,000 miles (daily VMT reduction)
 

The second step in calculating the benefits of a carpool program is to combine the estimated 

reduction in VMT with the emission factors (in grams per mile [g/mi]) and fuel consumption (in 

gallons per mile [gal/mi]) rates for the average vehicle.

Emission Facts
 


 
Average Emission Reductions and Fuel Savings
 

Per Day Per Vehicle for Gasoline Passenger Cars
 

Pollutant/ 

Fuel 

Emission 

Factor 

Reduction 

in VMT 

Calculations 

Bene.t

(Emission 

Reduction & 

Fuel Savings) 

VOC 1.034 g/mi 15,000 miles 

1.034 g/mi x 

15,000 mi x 

1 lb/454 g 

34.2 lb VOC 

CO 9.400 g/mi 15,000 miles 

9.400 g/mi x 

15,000 mi x 

1 lb/454 g 

311 lb CO 

NOx 0.693 g/mi 15,000 miles 

0.693 g/mi x 

15,000 mi x 

1 lb/454 g 

22.9 lb NOx 

PM10 0.0044 g/mi 15,000 miles 

0.0044 g/mi x 

15,000 mi x 

1 lb/454 g 

0.14 lb PM10 

PM2.5 0.0041 g/mi 15,000 miles 

0.0041 g/mi x 

15,000 mi x 

1 lb/454 g 

0.14 lb PM2.5 

CO2 368.4 g/mi 15,000 miles 

368.4 g/mi x 

15,000 mi x 

1 lb/454 g 

12,172 lb CO2 

Gasoline 

Consumption 0.042 gal/mi 15,000 miles 

0.042 g/mi x 

15,000 mi x 

1 lb/454 g 

630 gallons 

gasoline

Emission Facts
 

4 
Average Emission Reductions and Fuel Savings
 

Per Day Per Vehicle for Gasoline Light Trucks
 

Pollutant/ 

Fuel 

Emission 

Factor 

Reduction 

in VMT 

Calculations 

Benefit

(Emission 

Reduction & Fuel 

Savings) 

VOC 1.224 grams (g) 15,000 miles 

1.224 g/mi x 

15,000 mi x 

1 lb/454 g 

40.4 lb VOC 

CO 11.84 g 15,000 miles 

11.84 g/mi x 

15,000 mi x 

1 lb/454 g 

391 lb CO 

NOx 0.95 g 15,000 miles 

0.95 g/mi x 

15,000 mi x 

1 lb/454 g 

31.4 lb NOx 

PM10 0.0049 g 15,000 miles 

0.0049 g/mi x 

15,000 mi x 

1 lb/454 g 

0.16 lb PM10 

PM2.5 0.0045 g 15,000 miles 

0.0045 g/mi x 

15,000 mi x 

1 lb/454 g 

0.15 lb PM2.5 

CO2 513.5 g 15,000 miles 

513.5 g/mi x 

15,000 mi x 

1 lb/454 g 

16,966 lb CO2 

Gasoline 

Consumption 0.058 gallons (gal) 15,000 miles 0.058 g/mi x 15,000 mi 

870 gallons 

gasoline

Emission Facts
 


 
 

 

 

 

 

 

 

 

For More Information 

The other fact sheets in this series and additional information are available on the Office of 

Transportation and Air Quality’s Web site at: 

Emission factor fact sheets: www.epa.gov/otaq/consumer.htm 

Modeling and estimating vehicle emissions: www.epa.gov/otaq/models.htm 

Fuel economy: www.epa.gov/fueleconomy 

www.fueleconomy.gov 

Improving fuel economy and reducing emissions: www.epa.gov/epahome/trans.htm 

www.fueleconomy.gov/feg/drive.shtml 

Finding the “greenest” vehicle: www.epa.gov/greenvehicles 

Voluntary emission reduction programs: www.bestworkplacesforcommuters.org 

www.italladdsup.gov 

Emission Facts