Table 5-11: Estimated National Average Vehicle Emissions Rates of Heavy-duty and Light-duty Vehicles (grams per mile)

Air quality is affected by emissions from freight vehicles. Compared with gasoline fueled cars and trucks, diesel fueled heavy trucks emit small amounts of carbon monoxide (CO) but large amounts of nitrogen oxides (NO_x).

Freight transportation is a major source of NO_x emissions accounting for 27 percent of all U.S. NO_x emissions and half of emissions from mobile sources. Freight transportation also accounts for about one-third of emissions of particulate matter 10 microns in diameter (PM-10) from mobile sources. Most PM-10, however, comes from agricultural fields, wildfires, and fugitive dust. Consequently, freight transportation is a minor factor when considering total PM-10 emissions.

Table in Excel format | Historical data

	1990	2000	2002	2004	2005
Gasoline (assuming zero RFG)
Cars
Exhaust HC	2.79	0.97	0.81	0.61	0.52
Nonexhaust HC	1.21	0.92	0.84	0.77	0.72
Total HC	3.99	1.89	1.65	1.37	1.25
Exhaust CO	42.89	18.53	17.58	13.79	12.57
Exhaust NOx	2.70	1.29	1.20	1.00	0.92
Light trucks
Exhaust HC	3.68	1.45	1.24	0.96	0.78
Nonexhaust HC	1.36	0.97	0.89	0.80	0.76
Total HC	5.04	2.42	2.13	1.76	1.54
Exhaust CO	56.23	26.81	24.32	18.76	16.23
Exhaust NOx	2.62	1.54	1.50	1.32	1.21
Heavy trucks
Exhaust HC	3.66	1.22	0.98	0.73	0.64
Nonexhaust HC	2.74	1.62	1.48	1.35	1.24
Total HC	6.40	2.84	2.46	2.08	1.88
Exhaust CO	85.61	31.08	24.73	18.46	16.73
Exhaust NOx	7.19	5.26	5.01	4.62	4.28
Diesel
Cars
Exhaust HC	0.68	0.80	0.73	0.60	0.58
Exhaust CO	1.49	1.78	1.73	1.59	1.57
Exhaust NOx	1.83	1.81	1.62	1.43	1.32
Light trucks
Exhaust HC	1.59	1.02	0.96	0.98	0.80
Exhaust CO	2.67	1.77	1.66	1.68	1.37
Exhaust NOx	2.71	1.76	1.67	1.59	1.37
Heavy trucks
Exhaust HC	2.21	0.79	0.69	0.58	0.54
Exhaust CO	10.06	4.10	3.58	3.19	3.05
Exhaust NOx	23.34	18.05	15.52	12.50	11.45

Key: CO = carbon monoxide; hc = hydrocarbon; NO_x = nitrogen oxides; RFG = reformulated gasoline.

Source: U.S. Environmental Protection Agency, National Vehicle and Fuel Emissions Laboratory.