Paper presented at the 50th Annual Transportation Research Forum in
Portland, Oregon, March 16-18, 2009
A slightly updated version of this paper was presented at the ITE Annual Meeting and Exhibit,
San Antonio, Texas, August 9-12, 2009.
While research in the United States has consistently shown that freeway fatality rates increase with higher speed limits, freeway fatality rates in Germany with no general speed limit on the autobahns are about the same as they are in the United States. The paper explores different contributing factors which might explain this mystery and which lessons of interest to US freeway operations might be learned. It surmises that a very strict separation of traffic by speed (lane discipline) in Germany as opposed to the US might be the main explanatory factor for the low sensitivity of fatality rates to changes in speed limits in Germany versus a very high sensitivity in the United States.
All electronic sources were last accessed on 2008-12-29 unless otherwise noted.
In 1988 US Congress authorized an increase in the national speed limit from 55 mph to 65 mph on rural interstate highways. Since 1989 many studies were done to compare the number of accidents before and after the speed limit increase on rural freeways to 65 mph. Out of 21 studies between 1989 and 1995 evaluated by the author in 1996, 18 concluded that crash and fatality rates increased significantly after the speed limit was raised to 65 mph.
These studies were not selected randomly. They were all the studies available to the author at that time.
4. Baum, Herbert M.
The fatality consequences of the 65 mph speed limits, 1989 / Herbert M.
Baum, JoAnn K. Wells, and Adrian K. Lund.
IN: Journal of safety research. Vol. 22, no. 4 (Winter 1991)
UCB Trans See journal
“Among the 40 states that increased the speed limit to 65 mph on rural interstates, the number of fatalities was 29% higher than expected. Among the eight states retaining [the 55 mph speed limit] ... , the observed number of fatalities was 12% lower than expected, although this reduction was not statistically significant.”
5. Baum, Herbert M.
Motor vehicle crash fatalities in the second year of 65 MPH speed limits /
Herbert M. Baum, JoAnn K. Wells, and Adrian K. Lund.
IN: Journal of safety research. Vol. 21, no. 1 (spring 1990)
UCBTrans See journal
“It is estimated that the higher speed limit caused motor vehicle crash fatalities to be 26% to 29% higher in 1988 than they would have been if the speed limit had remained at 55 mph.”
7. Brown, David B.
The safety impact of the 65 mph speed limit : a case study using Alabama accident records / David B. Brown, Saeed Maghsoodloo, and Mary E. McArdle.
IN: Journal of safety research. Vol. 21, no. 4 (winter 1990)
UCBTrans See journal
“Although accident severity appeared to remain the same from before to after time periods, the frequency of accidents on rural interstates increased significantly, by 18.88 %”
10. Chang, Gang-Len.
Effects of 65-mph speed limit on traffic safety / by Gang-Len Chang and Jeffrey F. Paniati.
IN: Journal of transportation engineering. Vol. 116, no. 2 (Mar./Apr. 1990)
UCBTrans See journal
Because of the limited amount of “after” data, the effect of the increase in speed limit on fatalities “cannot be determined definitely at the current stage.” It was found that the predicted fatalities based on a continuation of the 55 mph limit were greater than the actual fatalities in 14 of the 15 months, but in only two of these months was the difference statistically significant.
11. Chang, Gang-Len.
Intervention analysis for the impacts of the 65 MPH speed limit on rural interstate highway fatalities / by Gang-Len Chang, Chao-Hua Chen and Everett C. Carter.
IN: Journal of safety research. Vol. 24, no. 1 (Spring 1993)
UCBTrans See journal
Some large states, such as Texas, California, and Illinois are insensitive to the speed limit increase, however for small states the interstate highway fatalities have increased significantly since the implementation of the 65 mph speed limit.
17. Garber, Steven.
The effects of the new 65 mile-per-hour speed limit on rural highway
fatalities : a state-by-state analysis / Steven Garber and John D. Graham.
IN: Accident analysis and prevention. Vol. 22, no. 2 (Apr. 1990)
UCBTrans See journal
“For rural interstate fatalities the estimates suggest a median (among the 40 states) effect of the increased speed limit of roughly 15% more fatalities; the median estimates for rural noninterstates suggest a 5% increase in fatalities due to the increased speed limits.”
20. Jernigan, Jack D.
Impact of 65-mph speed limit on Virginia's rural interstate highways
through 1989 / Jack D. Jernigan and Cheryl W. Lynn.
IN: Transportation research record. No. 1318 (1991)
UCBTrans TA1001.5 .T7 no. 1318
“Fatal crashes and fatalities increased on average more in Virginia than in other states that raised their maximum speed limit to 65 mph.”
21. Jernigan, Jack D.
Impact of the 65 mph speed limit on Virginia's rural interstate highways,
1989-1992 / Jack D. Jernigan, Sarah E. Strong, Cheryl W. Lynn.
Charlottesville, Va. : Virginia Transportation Research Council, [1994].
Series title: VTRC (Series) ; 95-R7.
UCBTrans HE5614.3.V8 J47 1994
“The data in this report clearly show that speeds, fatal crashes, and fatalities increased on Virginia’s rural interstates after the implementation of the 65 mph speed limit. However these increases appear to have plateaued in the last two years of the study.”
34. Lynn, Cheryl.
The impact of the 65 MPH speed limit on Virginia's rural interstate
highways through 1990 / Cheryl W. Lynn, Jack D. Jernigan. Charlottesville,
Va. : Virginia Transportation Research Council, [1992].
Series title: VTRC (Series) ; 90-R12.
UCBTrans HE5620.S6 L96 1992
UCDShieldsDOC-STA VA1000 Govt Docs Stacks
“The data in this report clearly show that speeds, fatal crashes, and fatalities increased on Virginia’s rural interstates after implementation of the 65 mph speed limit. However these data do not reflect causation.”
38. McKnight, A. James.
Relationship of 65-mph limit to speeds and fatal accidents / A. James
McKnight and Terry M. Klein.
IN: Transportation research record. No. 1281 (1990)
UCBTrans TA1001.5 .T7 no. 1281
In the states that raised the limit to 65 mph, fatal accidents increased by 27% over projections based on previous trends. In the states that kept the 55 mph limit, fatal accidents increased by slightly more than 10%. “The total increase in fatal accidents attributed to the raised speed limit, ... , was estimated at approximately 300/year.”
40. Miller, Ted R.
65 mph : winners and losers / [Ted R. Miller]. [Washington, D.C.] : U.S.
Dept. of Transportation, National Highway Traffic Safety Administration ;
Springfield, Va. : Available from the National Technical Information
Service, [1989].
UCBTrans HE5620.S6 M55 1989
“The 65 mph speed limit costs at least as much time as it saves, when the years lost to deaths, injuries, and travel delays are compared to the years of travel time saved. The out-of-pocket costs and benefits of raising the speed limit to 65 mph are roughly equal.”
44. Pant, Prahlad D.
Effects of the 65 mph speed limit on traffic accidents in Ohio / Prahlad
D. Pant, Jamal A. Adhami, and John C. Niehaus.
IN: Transportation research record. No. 1375 (1992)
UCBTrans TA1001.5 .T7 no. 1375
“It was found that fatal accident rates on rural Interstate highways posted at 65 mph or rural non-Interstate highways posted at 55 mph had not significantly changed after the implementation of the 65 mph speed limit.”
45. Pfefer, Ronald C.
The safety impact of the 65 mph speed limit : a time series analysis /
[Ronald C. Pfefer, William W. Stenzel]. Washington, D.C. : U.S. Dept. of
Transportation, National Highway Traffic Safety Administration ;
[Springfield, Va. : Available through the National Technical Information
Service, 1989].
UCBTrans HE5620.S6 P52 1989
This report examines the effects of the speed limit change in Illinois. “The frequency of all accidents increased on the order of 14 percent, in correlation with the law change. However, the same evidence could not be found for increases in either the frequency of serious accidents, or the accident rate.”
46. Pfefer, Ronald C.
Safety impact of the 65-mph speed limit : a time series analysis / Ronald
C. Pferer, William W. Stenzel, and Byoung Doo Lee.
IN: Transportation research record. No. 1318 (1991)
UCBTrans TA1001.5 .T7 no. 1318
This report examines the effects of the speed limit change in Illinois. “ ... an increase of 18.5% was detected in the rate for fatal and injury accidents only.”
48. Report to Congress on the effects of the 65 mph speed limit during 1987 /
National Highway Traffic Safety Administration. Washington, D.C. :
National Highway Traffic Safety Administration, [1989].
UCBTrans HE5614.2 .E5 1989
“Collectively, the 38 states that raised their speed limit had a 19 percent average increase in rural Interstate fatalities. A large portion (64 percent) of this increase is from only 6 states. The 10 states that retained 55 mph also had an increase in fatalities on their rural Interstates of 7 percent.”“... , but NHTSA emphasizes that with only one year of data, it is too early to draw any conclusions as to the long term effect of the increased speed limit on fatalities.”
53. Serious accident count still rising four years after rural interstate speed
limit raised to 65.
IN: Texas transportation researcher. Vol. 27, no. 3 (Fall 1991)
UCBTrans See journal
“The number of serious accidents (those involving injuries or fatalities) on rural interstate highways has risen more than 25 percent, from an average of 207 to 259 per month while the number of vehicle miles driven has risen only slightly during the same period.”
59. Upchurch, Jonathan.
Arizona's experience with the 65-mph speed limit / Jonathan Upchurch.
IN: Transportation research record. No.1244 (1989)
UCBTrans TA1001.5 .T7 no. 1244
and
60. Upchurch, Jonathan.
Safety and operational impacts of raising the speed limit to 65 mph /
prepared by Jonathan Upchurch, Mushtaqur Rahman. [Phoenix] : Arizona Dept.
of Transportation, [1990].
UCBTrans HE5614.3.A8 U63 1990
“Accident rate on the rural Interstate did increase for total accidents and for injury accidents when the one year after period is compared with 1986. However, the [overall] accident rate is approximately the same as in 1984. ... The fatal accident rate on the rural Interstate was higher in the one year after period than in any of the years 1983 through 1986.”
62. Wagenaar, Alexander C.
Effects of the 65 MPH speed limit on injury morbidity and mortality /
Alexander C. Wagenaar and Frederic M. Streff and Robert H. Schultz.
IN: Accident analysis and prevention. Vol. 22, no. 6 (Dec. 1990)
UCBTrans See journal
Research was limited to Michigan and revealed a 19.2% increase in fatalities, a 39.8% increase in serious injuries, and a 25.4% increase in moderate injuries.
##. Lave, Charles
Higher Speed Limits May Save Lives
IN: Access, Fall 1995, No. 7, page 23
Most studies look at only local effects: fatalities on a particular highway before and after the speed limit change. This approach ignores resource allocation. By measuring systemwide effects, he found that statewide fatality rates fell by 3.4 to 5.1 % in the group of states that adopted the 65 mph limit.