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On an average day, people using cars generate more polution than the people using public transport.

Say for example:

Person A uses a personal car.

Person B doesn't have a car and it uses public transport.

On a national average, how many times more the carbon emissions of Person A are bigger than of Person B in an year? (or in a day)

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TL;DR -- had to pull a lot of data together for this one. Per passenger mile traveled, private vehicles in the U.S. have an average emissions rate of 0.27 kg CO2, while public transit has a rate of 0.24 kg.

On a per trip basis, private vehicles result in 2.59 kg CO2 emissions, and public transit trips result in 1.27 kg emissions. Here's a table with compiled average results:

MODE             Trip distance (mi)    kg CO2 / mi      kg CO2 / trip
Trolleybus             1.6                 0.31             0.51
Heavy Rail             4.8                 0.18             0.85
Bus                    3.9                 0.27             1.05
Light Rail             4.7                 0.26             1.23
Other transit         13.4                 0.12             1.60
Private vehicle        9.7                 0.27             2.59
Commuter Rail         24.0                 0.21             4.93
Ferryboat              6.1                 0.91             5.57
Demand Response        8.8                 0.96             8.41

This doesn't fully answer the question, because I haven't found data on public transit ridership (i.e. how many people use public transit per year), to compare to the data on household vehicle use. Most ridership data counts passenger trips, so a person who takes the bus to work every day is counted every day.


Private vehicles

Data

Private vehicle data is from the Bureau of Transportation Statistics. All figures for 2009 (the most recent available covering all statistics) unless otherwise stated.

Calculations

  • Working through the data, we can figure out that the average person travels 13,187.54 miles a year, but the average vehicle only travels 10,651.28 miles per year.
  • This means that part of the time, private vehicles are carrying more than one person, so we can't attribute all of that vehicle's emissions to one person.
  • The average vehicle is carrying 1.24 people per mile -- or to put it another way, the average person uses 81% of a car when they travel, meaning that they're "responsible" for only 81% of the emissions of the vehicle each time it travels a mile.
  • (13,187.54 miles per year) / (21.7 miles per gallon) = 490.84 gallons per vehicle
  • 81% of this is 396.44 gallons (1500 L)
  • Resulting CO2 emissions per passenger from private vehicles is 3,524.37 kg CO2 per year, or 0.27 kg per passenger mile traveled.
  • With an average trip length of 9.7 miles, this equals 2.59 kg CO2 per trip per person in a private vehicle.

Public transit

Data

Public transit data is from the National Transit Database, for 2009. The tables are full of acronyms, so you'll need to use the glossary to decipher them.

  • Total transit passenger miles and trips

        MODE            TRIPS              MILES
    Bus             5,359,274,947     21,099,988,629 
    Commuter Rail     463,965,983     11,129,418,953 
    Demand Response   100,196,024        881,048,515 
    Ferryboat          59,496,556        364,671,729 
    Heavy Rail      3,489,503,588     16,805,109,970 
    Light Rail        464,354,520      2,196,117,518 
    Other              93,616,555      1,253,960,289 
    Trolleybus        103,853,889        168,066,937 
    TOTAL          10,134,262,062     53,898,382,540 
    
  • Total passenger miles for walking and cycling: 27,943,000,000 and 8,956,000,000 respectively.

  • Fuel consumption, in gallons, by transit type:

    MODE                 Diesel       Gasoline       Kerosene      BioDiesel      LPG            LNG             CNG       Electricity (kWh)
    Bus               447,876,760      6,291,716      467,827     39,541,271    2,913,821     25,195,388     139,562,108           804,539
    Commuter Rail      91,303,122                                                                                            1,779,699,164
    Demand Response    41,374,620     44,360,579       34,324      3,972,804    1,890,771                      2,590,337            51,204
    Ferryboat          32,612,447          9,972                     168,822 
    Heavy Rail                                                                                                               3,885,608,599
    Light Rail          1,028,660                                                                                              735,067,349
    Other                 237,795     14,689,106                                                                   3,719        22,511,081
    Trolleybus                                                                                                                  68,707,427
    TOTAL             614,433,404     65,351,373      502,151     43,682,897    4,804,592     25,195,388     142,156,164     6,492,449,363 
    
  • Emissions by fuel type

    Diesel       10.16 kg CO2 / gallon
    Gasoline      8.89
    Kerosene      9.75
    LPG           5.61
    LNG           3.98
    CNG           6.36
    Electricity   0.76 kg CO2 / kWh
    

Calculations

  • Multiplying all emissions factors by fuel consumption gives a total CO2 emissions from public transit of 12.82 million tonnes per year.

  • Dividing by passenger miles gives a value of 0.24 kg CO2 per passenger mile traveled on public transit. Below is the data by transit mode. Several of these are higher than the private vehicle average -- this is likely because transit tends to operate in urban areas, where the combination of lower speed and traffic result in lower efficiencies. By contrast, private vehicles spend more time on highways, where higher speeds increase efficiencies.

    Bus               0.27 kg CO2 per passenger mile
    Commuter Rail     0.21
    Demand Response   0.96
    Ferryboat         0.91
    Heavy Rail        0.18
    Light Rail        0.26
    Other             0.12
    Trolleybus        0.31
    
  • The average trip length on public transit is 5.32 miles, resulting in 1.27 kg CO2 emissions per trip.

  • If we include walking and biking, emissions per mile drops to 0.14 kg CO2 per passenger mile.

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  • And then the people using cars create two times more polution (with transportation) than the people who don't. – Joe Jobs Sep 17 '20 at 10:02

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