| Highway class | Percentage | Average | |||||
|---|---|---|---|---|---|---|---|
| 1991 | 1992 | 1993 | 1994 | 1995 | |||
| Interstates | Rural | 12.53 | 11.7 | 11.65 | 12.04 | 11.9 | 11.97 |
| Urban | 6.06 | 5.75 | 6.40 | 6.21 | 6.25 | 6.13 | |
| U.S. roads | Rural | 19.46 | 19.55 | 18.51 | 18.99 | 17.55 | 18.81 |
| Urban | 13.57 | 14.10 | 14.30 | 14.98 | 15.67 | 14.52 | |
| State roads | Rural | 34.41 | 34.61 | 33.73 | 32.72 | 32.56 | 33.61 |
| Urban | 13.97 | 14.29 | 15.41 | 15.06 | 16.07 | 14.96 | |
| Total | 100 | 100 | 100 | 100 | 100 | 100 | |