When speed limits on rural interstates are raised, travel speeds generally go up, and speeding violations continue. Behavior is similar on urban interstates. These are the results of an Institute survey conducted in six states.
In the majority of these states, more than two-thirds of vehicles on rural interstates were going 70 mph or faster. In Colorado nearly 1 of every 4 vehicles was traveling 80 mph or faster. The other five survey states were California, Georgia, Massachusetts, Maryland, and New Mexico. Travel speeds also were surveyed in five major cities.
"These are the fastest speeds we've ever observed," says Richard Retting, the Institute's senior transportation engineer. Institute researchers began surveying travel speeds on interstate highways in New Mexico in 1987 (see "More drivers exceed New Mexico's top speed of 65 mph," Dec. 26, 1987), when Congress began allowing states to set rural speed limits higher than 55 mph.
Speed limits typically are set higher on rural interstates than on urban ones. But speeds on the urban stretches often don't reflect the lower limits. Average travel speeds on urban interstates in Atlanta, Boston, and Washington, D.C., were the same or higher than the average on rural interstates near these cities. In Atlanta, where the highest urban speeds were observed, 78 percent of vehicles on one urban interstate were clocked at more than 70 mph and 18 percent were exceeding 80. Similar speeds were observed on a rural interstate in Georgia, where 68 percent of motorists were going faster than 70 and 20 percent were going more than 80 mph.
"Drivers tend to choose speeds they perceive as unlikely to result in a ticket," Retting says. "Presumably, differences in the perception of the amount of enforcement among these areas were major factors in the higher or lower travel speeds."
Institute data going back to 1987 in New Mexico show speeds on rural interstates increasing during 1987-96, when the speed limit was 65 mph. After it was raised to 75 in June 1996, speeds increased sharply. By last March they had increased even more, especially among cars. About 16 percent of cars were going 80 mph or more on New Mexico's rural interstates.
"When the Institute started measuring vehicle speeds in New Mexico, we didn't even report the percentage of cars going over 80 because they were so rare," Retting says. But even as speeds have escalated, not just in New Mexico but elsewhere, too, and researcher after researcher has quantified the price we're paying in lives for the faster travel, speeding still seems to be a forgotten public health issue."
Speeds (mph) on rural & urban interstates, 2003
| Rural Interstates |
Speed limit |
Mean speed |
Percent going faster than 70 |
Percent going faster than 80 |
| Georgia |
65 |
74 |
68 |
20 |
| Massachusetts |
65 |
69 |
44 |
2 |
| Maryland |
65 |
66 |
17 |
1 |
| New Mexico |
75 |
72 |
68 |
10 |
| Colorado |
75 |
76 |
84 |
24 |
| California |
70 |
74 |
69 |
19 |
| Urban Interstates |
Speed limit |
Mean speed |
Percent going faster than 70 |
Percent going faster than 80 |
| Atlanta, GA |
55 |
75 |
78 |
18 |
| Boston, MA |
55 |
69 |
38 |
3 |
| Washington, DC |
55 |
67 |
31 |
2 |
| Albuquerque, NM |
65 |
67 |
25 |
2 |
| Denver, CO |
55 |
64 |
11 |
<1 |
Car speeds (mph) on New Mexico rural interstates
| Speed Limit |
Date |
Mean speed |
Percent going faster than 75 |
Percent going faster than 80 |
| 65 mph |
4/1987 |
64 |
1 |
— |
| 65 mph |
4/1988 |
66 |
6 |
— |
| 65 mph |
4/1989 |
67 |
6 |
— |
| 65 mph |
4/1990 |
67 |
7 |
— |
| 65 mph |
4/1991 |
67 |
6 |
— |
| 65 mph |
4/1992 |
68 |
9 |
— |
| 65 mph |
4/1993 |
68 |
12 |
3 |
| 65 mph |
4/1994 |
68 |
8 |
3 |
| 65 mph |
4/1996 |
69 |
14 |
4 |
| 75 mph |
6/1996 |
72 |
26 |
5 |
| 75 mph |
6/1997 |
73 |
37 |
10 |
| 75 mph |
3/2003 |
75 |
55 |
16 |
Note: Percentages going faster than 80 mph weren't recorded until 4/1993.