1) I have driven automobiles around the world 30 times.
2) Total distance is 750,000 miles.
3a) Speed was 2/3 of a circuit per year ,
3b) or 16,667 miles/year (45 years),
3c) or 45.6… miles/day (45 years).
4a) Fuel used was 30,000 gallons of gasoline
4b) at 25 mpg (assumed).
5a) CO2 produced was 589,200 pounds ,
5b) or 13,093.3… pounds/year, 45 years.
6) Number of travellers 1 to 5 (average ~2).
7) CO2/average traveller is 6,546.6… pound/year.
8) CO2/mile is 0.7856 pounds/mile.
9) Equivalent # US drivers/year, if use my rate of CO2 production = 143 million. 
10) Average # cars/trucks owned per Equivalent driver = 1.78. 
 Circumference of the Earth is 24,901 miles (rounded up to 25 kmile).
 “About 19.64 pounds of carbon dioxide (CO2) are produced from burning a gallon of gasoline that does not contain ethanol.” (US-EIA)
 US CO2 from autos and gasoline powered trucks is >50%, probably <66%, of the CO2 emissions from the entire transportation sector, which produces 26% of the total US emission of CO2 (2014, but similar since 1990). The total greenhouse gas emissions for the US (2014) is 6870 x 10^6 metric tons, and CO2 is 82% of that greenhouse gas total. (US-EPA). [1 metric ton (1000 kg) = 2204 pounds.] So:
a1) Total greenhouse gas/year = 6,870 million metric tonnes.
a2) Total greenhouse gas/year = 15,141,480 million pounds
(15.141 trillion pounds).
b1) Total CO2/year = 5633 million metric tonnes.
b2) Total CO2/year = 12,416,013 million pounds
(12.416 trillion pounds).
c1) Transportation CO2/year = 1465 million metric tonnes.
c2) Transportation CO2/year = 3,228,163 million pounds
(3.228 trillion pounds).
d1) Auto/truck CO2/year (@ 58%) = 849.5 million metric tonnes.
d2) Auto/truck CO2/year (@ 58%) = 1,872,334 million pounds
(1.872 trillion pounds).
 “According to the Bureau of Transportation Statistics for 2012, there were 254,639,386 registered vehicles” in the U.S. (rounded up to 255 million) (wikipedia)
If you drive a 30 mpg vehicle, and you usually fill the seats so on average you transport 3 people:
– then the CO2 production per person is only 55.5%
(of the 25 mpg vehicle with 2 people);
– or your transport is 1.8x improved,
– or 80% MORE efficient, on a per person basis,
– [achieving 180% of the efficiency of the baseline case].
A single driver in a 22 mpg vehicle (typical of light trucks, and big motor/less efficient SUVs):
– then the CO2 production per person is 227.3% of the baseline case
(baseline = 25 mpg @ 2 people)
– or your transport is 0.44x “improved” (= 2.273x degraded),
– or is 56% LESS efficient per person than the baseline case,
– [achieving only 44% of the efficiency of the baseline case].
Photo taken by handheld 35 mm camera with slide film in May 1976 at dusk (“low light”), aperture wide open (F1.4, 58 mm lens), speed 1/30 second (or slower) to get acceptable exposure, at the bottom of a slow exhalation to minimize camera shake, last frame on the last film roll of the day so no second try possible. Image here is a scan of the original slide.