CO grams per mile
| Year | Automobile | Light Trucks |
|---|---|---|
| 1966 | 80 | 102 |
| 1967 | 34 | 102 |
| 1968 | 34 | 102 |
| 1969 | 34 | 102 |
| 1970 | 34 | 102 |
| 1971 | 34 | 102 |
| 1972 | 28 | 102 |
| 1973 | 28 | 102 |
| 1974 | 28 | 102 |
| 1975 | 15 | 20 |
| 1976 | 15 | 20 |
| 1977 | 15 | 20 |
| 1978 | 15 | 20 |
| 1979 | 15 | 18 |
| 1980 | 7 | 18 |
| 1981 | 3.4 | 18 |
| 1982 | 3.4 | 18 |
| 1983 | 3.4 | 18 |
| 1984 | 3.4 | 10 |
| 1985 | 3.4 | 10 |
| 1986 | 3.4 | 10 |
| 1987 | 3.4 | 10 |
| 1988 | 3.4 | 10 |
| 1989 | 3.4 | 10 |
| 1990 | 3.4 | 10 |
| 1991 | 3.4 | 10 |
| 1992 | 3.4 | 10 |
| 1993 | 3.4 | 10 |
| 1994 | 3.4 | 3.4 |
| 1995 | 3.4 | 3.4 |
| 1996 | 3.4 | 3.4 |
| 1997 | 3.4 | 3.4 |
| 1998 | 3.4 | 3.4 |
| 1999 | 3.4 | 3.4 |
| 2000 | 3.4 | 3.4 |
| 2001 | 3.4 | 3.4 |
| 2002 | 3.4 | 3.4 |
| 2003 | 3.4 | 3.4 |
| 2004 | 3.4 | 3.4 |
