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Montana: No Speed Limit-Safety Paradox
February 11, 2000

The no daytime speed limit results are in.

By Chad Dornsife

In 1996, the State of Montana reverted to the state speed limit policies that existed prior to 1974 and the National Maximum Speed Limit. The National Maximum Speed Limit was repealed in December of 1995. Montana returned to the use of Reasonable and Prudent speed limits on its federal and state highways.

Reasonable and Prudent speed limits are not based on numerical maximums, but rather they require motorists to drive at speeds considered safe for prevailing conditions.

Despite concerted efforts by the Montana State Patrol, Attorney General and Governor to replace the "reasonable and prudent" law with numerical speed limits, the state legislature refused to do so. The Montana State Patrol chose to enforce a de-facto threshold of an 80-90 mph limit for Reasonable and Prudent enforcement.

During a challenge of such a ticket, in 1998, the Montana Supreme Court declared the Reasonable and Prudent Speed Limit unconstitutional, on the basis of vagueness. For the following five months Montana had no form of daytime speed limit on its rural highways.

The following discussion is an analysis and comparison of Montana's experience with the Reasonable and Prudent speed limit, no speed limit in any form, and fixed numerical speed limits on two classifications of highway: 4 lane Interstate and rural federal-aid primary two lane highways.

In 1999, after 4 years of no numerical or posted daytime speed limit on these classifications of highways, outside of urban areas, Montana recorded its lowest fatality rate.

Research scientists and engineers have long known that there are sometimes unexpected results from changes in public policies. Ironically, the paradox of no posted speed limits and low fatalities is no surprise to the traffic safety engineering community.

For years, motorists' advocates have used engineering-based facts against artificially low speed limits. They have claimed that by raising speed limits to reasonable levels, accident and fatality rates will actually be reduced. This seemingly wild assertion has been documented by the traffic engineering profession for 50 plus years. This fact-based position has again been proven to be true by the repeal of the National Speed Limit. The nation has recorded the lowest highway fatality rate since such records have been kept.

What about the extreme of No Speed Limits on 4 lane Interstate and rural federal-aid primary two lane highways? These same fact-based engineers point to the German Autobahn, where, with no speed limits, authorities are consistently reporting lower fatality rates than comparable US highways.

For the last 5 months of no daytime limits in Montana, the period after its Supreme Court had ruled that the Reasonable and Prudent law was unconstitutional, reported fatal accident rate declined to a record low. Fixed speed limits were reinstated on Memorial Day weekend 1999. Since then, fatal accidents have begun to rise again.

This begs the question, do people change the way they drive when there is no speed limit? The evidence suggests the answer is yes. The measured vehicle speeds only changed a few miles per hour as predicted - comparable to data collected from other western states. What changed? The two most obvious changes were improved lane courtesy and increased seat belt use. Did other driving habits and patterns change as well?

The lower-than-US fatality rates on the German Autobahn (where flow management is the primary safety strategy), and now Montana's experience, would indicate that using speed limits and speed enforcement as the cornerstone of US highway safety policy is a major mistake. It is time to accept the fact that increases in traffic speeds are the natural byproduct of advancing technology. People do, in fact, act in a reasonable and responsible manner without constant government intervention.

The Montana experience solidifies the long held traffic engineering axioms, "people don't automatically drive faster when the speed limit is raised, speed limit signs will not automatically decrease accident rates nor increase safety, and highways with posted speed limits are not necessarily safer than highways without posted limits.

The study on the effects of no daytime speed limits in Montana is clear. Traffic safety, if anything, actually improved without posted limits or massive enforcement efforts. Highway safety wasn't compromised nor can the lowest fatality rates recorded in modern times be ignored. Something happened, it was positive, and it needs further research to analyze what worked and why.

The Findings

After 4 years of no daytime limits, the actual numbers provided by the Montana DOT tell the story. Here is how it breaks out, by month, first for the last 2 years.


Montana Fatal Accident Data

Interstates: 4 Lane Divided

1998: No Daytime Speed Limits
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
4 0 2 4 5 1 5 4 0 1 3 2
Jan - May Average Month: 3.0 Jun - Dec Average Month: 2.0

1999: No Daytime Speed Limits 75 Maximum Limit
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
2 2 4 2 1 0 2 7 4 1 1 4
Jan - May Average Month: 2.2 June - Dec Average Month: 3.4
Last Year of No Limits: 27.0 Annual Rate: 40.8

Rural Federal Aid Primary Highways: 2 Lane*

1998: No Daytime Speed Limits
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
9 1 7 6 5 6 8 11 9 9 3 8
Jan - May Average Month: 5.6 June - Dec Average Month: 8.0


1999: No Daytime Speed Limits 65/75 Maximum Limit
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
3 5 5 2 5 8 5 5 12 6 10 6
Jan - May Average Month: 4.0 June - Dec Average Month: 7.8
Last Year of No Limits: 74.0 Annual Rate: 93.6

Here is the actual fatal accident data charted for the entire six years of the study. No daytime limits were in place from the end of '95 through mid '99. 1994 is representative of a low point for the previous decade.



Fatal Accidents: source Montana DOT

  Interstate Primary Sub Total % of T Total

'94

41 70 111 61% 182

'95

33 72 105 56% 186

'96

39 75 114 64% 179

'97

51 91 140 63% 223

'98

31 82 113 54% 208

'99

30 72 102 50% 206
6 Year Average 37 77 114 58% 197
Last 12 Months
With No Daytime Limit		 27 74 101    


Note that the last 12 month period of no daytime speed limits ended in May of 1999 with the lowest number of fatal accidents despite the estimated 12-18% increase in traffic volumes during this 6 year period.

Taking a different approach to examining the effects of no posted limits, the author decided to take a look at multiple vehicle accidents to see if there were any changes or trends.


Montana: percentage of daytime accidents involving multiple vehicles

  Interstate Primary

'94

24% 53%

'95

26% 53%

'96

29% 52%

'97

25% 50%

'98

22% 49%

'99

26% 48%
6 Year Average 25% 51%
(Fall 95 - mid 99 no daytime speed limits)



On these classifications of highway, the no daytime speed limit appears to have reduced the multiple vehicle accident rate on Montana's 2 lane Primary Highways.

This information was requested because the author's personal observations indicated that a culture had developed of slower traffic yielding the left lane by keeping right and/or moving closer to the shoulder to allow safe overtaking. Instead of increasing accidents, with the expectation of higher speeds, there should be fewer multiple vehicle accident because of better lane courtesy. It appears to be the case, as indicated by the reduction in the percentage of multiple vehicle accidents on the rural primary 2 lane highways.

Summary of the effects of no daytime speed limits:

  1. Fatal accident rates on these highways reached an all time low in modern times.

  2. On 2 lane highways with no posted limits the frequency of multiple vehicle accidents dropped 5 percent.

  3. Seat belt usage rose to 88% percent, with only a secondary enforcement law.

  4. Posted limits and their enforcement, had either no or a negative effect on traffic safety.

  5. As predicted by the engineering models, traffic speeds did not significantly change and remained consistent with other western states with like conditions.

  6. The people of Montana and its visitors continued to drive at speeds they were comfortable with, which were often speeds lower than their counter parts on high density urban freeways* with low posted limits.

  7. The theory behind posting speed limits on this classification of road is to reduce conflicts in traffic flow, thereby reducing accidents. The paradox is that the desired effect from posting speed limits was achieved by removing them.

*Interesting side bar: During this 6 year period, Montana's rural interstates daytime speeds (no speed limit) were consistently lower (on average 5-10 mph and more) than the speeds being reported on many sections of Southern California's 65 mph posted urban interstates.

Credits: Special thanks to Jack Williams, Research & Evaluation Bureau Chief, Traffic Safety Bureau, Montana Department of Transportation, for his assistance in collecting the highway accident data.

Contact Information

Chad Dornsife
chad@hwysafety.com
775.721.2423 cell
800.708.5723 voice mail/fax

Nevada Chapter, National Motorists Association
c/o The Highway Safety Group: "Making Driving Safer"
Box 141, Zephyr Cove, Nevada 89448

OR

National Motorists Association
402 West 2nd Street
Waunakee, WI 53597-1342
http://www.motorists.org

Contact: Eric Skrum, Communications Director
nma@motorists.org
608.849.6000