Report to Congress

The Effect of Increased Speed Limits in the Post-NMSL Era

National Highway Traffic Safety Administration

Federal Highway Administration

U. S. Department of Transportation

Washington, D. C. 20590

February 1998

i

TABLE OF CONTENTS

Executive Summary ......................................................... iii

SECTION I -- BACKGROUND

Legislative History of Speed Limit Requirements .................................... 1

Analytical Challenge ......................................................... 3

Status of States’ Speed Limit Laws .............................................. 4

SECTION II -- ASSESSING THE IMPACT OF INCREASED SPEED LIMITS ON TRAFFIC

 CRASHES

The National Picture ......................................................... 7

1995 vs. 1996 State Comparison ............................................... 13

Statistical Modeling ......................................................... 23

SECTION III -- SYNOPSIS OF STUDIES BY INDIVIDUAL STATES

Overview ................................................................. 33

California ................................................................. 33

Idaho .................................................................... 36

Iowa .................................................................... 40

Michigan ................................................................. 43

Missouri ................................................................. 44

Montana ................................................................. 44

Nebraska ................................................................. 47

New Mexico .............................................................. 47

Texas ................................................................... 49

Virginia .................................................................. 51

Summary of Individual State Findings ........................................... 52

SECTION IV -- DISCUSSION/RECOMMENDATIONS ............................ 55

APPENDIX A -- DETAILED INFORMATION ON INDIVIDUAL STATE SPEED LIMIT

 LEGISLATION ............................................ A-1

APPENDIX B -- FEDERAL REGISTER NOTICES ............................... B-1
ii

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iii

EXECUTIVE SUMMARY

The National Highway System (NHS) Designation Act (hereinafter referred to as “the

NHS Act”) of 1995 (Public Law [P. L.] 104-59) was signed into law on November 28, 1995. 

The NHS Act, among other things, established the National Highway System and eliminated the

Federal mandate for the National Maximum Speed Limit (NMSL). In so doing, the NHS Act

ended a period of more than 20 years of Federal involvement in the states’ establishment of speed

limits and ended the requirement for states’ submission of speed compliance data to the Federal

Highway Administration (FHWA). Section 347 of the NHS Act required the Secretary of

Transportation to study the impact of states’ actions to raise speed limits above 55/65 MPH and

report to the Congress by September 30, 1997.

Key Findings

! Due to the current unavailability of full vehicle miles traveled (VMT) and other data, it is not

known how increased travel on higher speed roads, shifts in travel, and other traffic safety

factors, (e.g., changes in alcohol involvement, belt use) or various economic factors (e.g.,

fuel consumption, roadway maintenance, travel time) may have contributed to an estimated

increase in Interstate fatalities and economic costs. Nevertheless, it is important to note that

data currently available from the National Highway Traffic Safety Administration’s (NHTSA)

Fatality Analysis Reporting System (FARS) shows that states that increased speed limits in

1996 experienced approximately 350 more Interstate fatalities than would have been

expected based on historical trends -- about 9 percent above expectations. Concurrently, the

Interstate fatalities experienced in states that did not increase speed limits in 1996 was

consistent with pre-1996 trends. The estimated increase in Interstate fatalities found in this

study, while smaller in magnitude compared to the estimated change in fatalities found in

1987 following the increase of speed limits on rural Interstates, does follow the historical

pattern of increases in fatalities being associated with increases in posted speed limits.

! An estimated increase in fatalities is typically associated with an increase in traffic crashes and

associated injuries. The total economic cost of the estimated 350 additional fatalities and the

associated injuries and crashes is more than $820 million in 1996 dollars. Although Section

347 of the NHS Act stated that the report should address the costs and benefits associated

with the repeal of the NMSL, no attempt was made at this time to estimate potential benefits,

as most States have not had increased limits in place for an extended period of time. 

! In addition to the analysis of the FARS data on Interstate fatalities, ten states also provided

information on the impact of increased speed limits in their respective states for inclusion in

this report. A consistent pattern of crash increases was cited in only one of the 10 states

(California). Each of the 10 states considered the findings preliminary or inconclusive due to

the limited amount of data available for analysis. This is not particularly surprising, since

each state had only its own data and experience to analyze, while it was possible for NHTSA

and FHWA to pool states together, yielding more data for analysis.
iv

In view of these findings, close monitoring of crash trends on roads with increased speed

limits should continue and, if warranted, countermanding actions taken. Also, it will be important

to continue to focus, at the national and state levels, on key program areas of traffic safety, e.g.,

increasing restraint use, enforcing traffic laws, informing and educating the public, implementing

roadway and traffic safety improvements, and ameliorating the effects of alcohol-involved driving

over the long term to compensate for possible increases in fatalities and injured persons that may

be related to increased speed limits and increases in VMT and shifts in travel to roads with higher

posted speed limits. 

Report Summary

NHTSA and FHWA were delegated responsibility for conducting the study of the impact

of increased speed limits. Section 347 of the NHS Act emphasized that the study should include

the costs and benefits associated with increasing the speed limit at the state level. Thus, NHTSA

and FHWA would need to incorporate information from individual states on their experience with

increased limits and possible impacts on safety. NHTSA and FHWA began a process to solicit

the states’ input and request their comments on a proposed strategy to address the inherent

complexities of determining the costs and benefits at the state and national levels, necessitating

that an analysis of state-specific data be conducted. As part of this process the agencies published

two Federal Register notices on the issue, the first of which invited comments and

recommendations from state highway and traffic safety officials on a proposed study outline and

methodology. The second notice presented a summary of comments from the states and others

on the proposed study and presented a modified approach for conducting the study.

From the beginning, NHTSA and FHWA recognized that the extent to which it would be

possible to address the impacts of increased speed limits, particularly at the state level, would

depend in large degree on the states’ submissions for inclusion in the study. Most of the 19 states

commenting on the first of the two notices expressed concerns that: while the initial study

methodology was reasonable, it was ambitious and would place an additional burden on the

states; data would either not be available or was not being collected at the level of detail needed;

and that meeting the deadline of September 30, 1997, would be difficult, “... impossible ...” or “...

unrealistic.”

To meet the NHS Act requirement and in light of the states’ comments on the first notice,

NHTSA and FHWA presented a modified approach for conducting the study in the second

Federal Register notice using the limited amount of data available. As 1996 was the first year of

experience with increased speed limits in the post-NMSL era, there were several analytical

challenges to conducting this study. Certain types of data, e.g., travel (vehicle miles traveled or

VMT) by roadway type, fuel consumption, medical costs, time, etc., were not available either at

the state or national level, making it impossible at this time to address the entire range of costs

and benefits typically associated with a study of this kind. In addition, some states have

selectively increased speed limits on certain road types, e.g., selected urban Interstate or certain

freeways or expressways, rather than systemwide, e.g., all Interstates. At the national level,

NHTSA and FHWA could only begin to determine the contribution that increased speed limits

would have on traffic fatalities using data from the Fatality Analysis Reporting System (FARS). 

Analyses were conducted on 3 groups of states: (1) those states that increased speed limits in late
1

 For more on linear regression analysis, see Draper, N. R. and Smith, H. Applied

Regression Analysis, J. Wiley & Sons, Inc., 1966. 

2

 Blincoe, L. J. The Economic Cost of Motor Vehicle Crashes, 1994. U. S. Department

of Transportation, NHTSA, Washington, DC. DOT HS 808 425, July 1996.

v

1995 through early in the first quarter of 1996, (2) those that increased speed limits later in 1996,

and (3) those that did not increase speed limits.

These analytical challenges aside, analysis of existing data has provided a preliminary

assessment of the possible effects of increased speed limits. While total fatalities and injured

persons changed very little at the national level in 1996 compared to 1995 (the increase in

fatalities from 1995 to 1996 was 90), fatalities, fatal crashes, injured persons and injury crashes all

increased at the national level on Interstate roads in 1996, while decreasing on all other roads. 

The pattern of change in Interstate fatalities was strongest for the group of eleven states that

raised their speed limits late in 1995 or early in 1996 (Arizona, California, Delaware, Illinois,

Massachusetts, Montana, Nevada, Oklahoma, Pennsylvania, Texas, and Wyoming) when

contrasted with the group of states that did not raise limits in 1996. The group of 21 states that

increased speed limits later in 1996 exhibited a pattern of increase that essentially paralleled the

group of 11 “early change” states.

In the absence of detailed information regarding where and when speed limits were raised,

it was possible to employ simple statistical models to analyze the fatality experience in these

groups of states during 1996 compared to expectations based on historical trends. With a linear

regression model1 for each of the three groups of states using data for 1991-1996 which

accounted for a time trend and an intervention for the post-NMSL time period, it was found that

Interstate fatalities experienced a statistically significant increase in those states that raised their

posted speed limits late in 1995 or early in 1996. The effect found in the group of states that

increased speeds later in 1996 was numerically consistent with the “early change” states, but failed

to reach statistical significance, while there was essentially no change in fatalities on Interstates for

states that did not raise their speed limits during 1995-1996. 

Based upon the analyses conducted in this study on the first year of experience with higher

speed limits, it is estimated that Interstate fatalities in the states that increased speed limits

experienced approximately 350 more fatalities than would have been expected based on historical

trends, about 9 percent above expectations. Based on economic cost models used by the National

Highway Traffic Safety Administration, the total economic cost of 350 additional fatalities and

associated injuries and crashes is more than $820 million in 1996 dollars. Nonfatal injuries and

non-injury crashes included in the total economic cost were estimated based on the relative

frequency of these events to fatalities in speed-related crashes.2 Due to the unavailability of

detailed VMT and other data at this time, it is not known how increased travel on higher speed

roads, shifts in travel, changes in average and top vehicle speeds and other traffic safety factors

may have contributed to the estimated increase in Interstate fatalities. While Section 347 of the

NHS Act stated that the report should address the costs and the benefits associated with the

repeal of the NMSL, no attempt was made at this time to estimate potential benefits, as most
vi

states have not had increased limits in place for an extended period of time. A large portion of the

potential benefits of increased speed limits would result from decreases in travel time, for

example, data which is not easily obtainable, particularly on an individual state basis. 

Studies of the impact of increased speed limits in individual states were obtained by

NHTSA and FHWA from 10 states (California, Idaho, Iowa, Michigan, Missouri, Montana,

Nebraska, New Mexico, Texas, and Virginia). These studies are summarized in this report. On a

state-by-state basis, the possible impact of increased speed limits does not follow a consistent

pattern. A consistent pattern of crash increases or decreases was cited in only one of the 10 states

(California). In addition, each of the states considered the findings preliminary or inconclusive,

again, due to the limited amount of data available for analysis.

NHTSA and FHWA plan to continue to study the impact of increased speed limits at the

national and state levels, particularly after states have additional years of experience with the

higher limits. Close monitoring of crash trends on roads with increased speed limits should

continue and, if warranted, countermanding actions taken. Also, it will also be important to

continue to focus on key program areas of traffic safety, e.g., increasing restraint use, enforcing

traffic laws, informing and educating the public, implementing roadway and traffic safety

improvements, and ameliorating the effects of alcohol-involved driving over the long term to

compensate for possible increases in fatalities and injured persons that may be related to increased

speed limits and increases in VMT and shifts in travel to roads with higher posted speed limits. 

The challenge will be to take these traffic safety initiatives into account in subsequent analyses of

the effects of increased speed limits. In addition, while some evidence of increases in fatalities and

fatal crashes was found at the national level, this study is based on only one year of data at higher

speed limits, and warrants further examination as the national and individual states’ experience

with higher speed limits matures. Lastly, this study does not account for possible changes in the

expected vehicle miles of travel patterns due to the unavailability of these exposure data at this

time. Subsequent analysis of this issue will need to address these effects, where possible. 

NHTSA, FHWA, and the Centers for Disease Control have also contracted with the

Transportation Research Board to examine the criteria used by states to establish speed limits and

to recommend improvements to the current methodology. The group of experts assembled for

this study come from a wide array of disciplines associated with highway traffic safety, e.g.,

engineering enforcement, and academia. 
3

 The Life-Saving Benefits of the 55 MPH NMSL: Report of the NHTSA/FHWA Task

Force, U. S. Department of Transportation, DOT HS 805-559, October 1980. 

4

 55: A Decade of Experience, TRB Special Report 204, National Research Council,

Washington DC, 1984.

1

SECTION I -- BACKGROUND

Legislative History of Speed Limit Requirements

The National Highway System Designation Act (hereinafter referred to as “the NHS Act”)

of 1995 (Public Law [P. L.] 104-59) was signed into law on November 28, 1995. The NHS Act,

among other things, established the National Highway System and eliminated the Federal mandate

for the National Maximum Speed Limit (NMSL). In so doing, P. L. 104-59 ended a period of

more than 20 years of Federal involvement in the states’ establishment of speed limits and ended

the requirement for states’ submission of speed compliance data to the Federal Highway

Administration (FHWA).

The NMSL, enacted during the Arab oil embargo of 1973 to conserve fuel, was initially

set at 55 miles per hour (MPH). By March 1974, all States were in compliance with the NMSL. 

In addition to conserving fuel, the annual traffic fatality toll declined from 54,052 in 1973 to

45,196 in 1974, a drop of over 16 percent. As a result of the apparent safety benefit in the form

of the reduction in traffic fatalities, the Congress passed P. L. 93-643, making the NMSL

permanent. P. L. 93-643 also required every state to certify that the NMSL was being enforced.

In 1978, the Congress enacted the Surface Transportation Assistance Act (STAA),

P. L. 95-599. The STAA required the states to submit data on the percentage of motor vehicles

exceeding 55 MPH on public highways with a 55 MPH posted speed limit.

Following the enactment of the NMSL, numerous studies of the benefits and costs of the

legislation were conducted. A joint National Highway Traffic Safety Administration (NHTSA)

and FHWA task force, charged with determining the safety benefits of the NMSL, conducted one

of these studies. The NHTSA/FHWA task force concluded that while the “... determination of a

precise, accurate estimate of lives saved by the NMSL ... is problematic, there were 20,000 to

30,000 lives saved by the NMSL during the period 1974-1978.”

3

 The STAA of 1982 required that a study of the ”benefits, both human and economic” of

the NMSL, with “particular attention to savings to the taxpayers ...” be conducted by the

National Academy of Sciences’ Transportation Research Board (TRB). In 1984, TRB published

its special report, 55: A Decade of Experience.

4

 The TRB study, conducted by a 19-member

committee composed of experts from a wide range of disciplines needed to evaluate the costs and

benefits of the NMSL, represents one of the most thorough and extensive examinations of this

important safety issue. Although the TRB committee recognized the inherent difficulties

associated with attempts to accurately estimate the safety, economic, and energy benefits of the 
5 Effects of the 65 MPH Speed Limit through 1990: A Report to Congress, U. S.

Department of Transportation, NHTSA, Washington, DC, May 1992.

2

NMSL, the study concluded that “... the slower speeds and more uniform pace of travel due to

the 55 mph speed limit accounted for 3,000 to 5,000 fewer traffic fatalities in 1974.” 

Furthermore, by the 1984 publication date, the report found that,

“The 55 mph speed limit saves 2,000 to 4,000 lives per year, reduces highway fuel use

slightly less than 2 percent (a savings of $2 billion in fuel costs at the then prevailing oil

prices), and saves taxpayers about $65 million per year. But it also requires motorists to

spend 1 billion additional hours driving each year, and the additional costs for

enforcement are about $118 million per year. (Fines collected from speeders yield

revenues that are roughly equal to these enforcement costs, so the net effect on

government budgets is small.)”

The TRB study also recognized several unresolved issues, including: the impact of

noncompliance; the containment of higher speeds, if permitted, on a limited subset of roads; and

whether the control of the speed limit is a state or Federal responsibility.

In 1987, the Surface Transportation and Uniform Relocation Assistance Act granted the

states the authority to raise the speed limit, not to exceed 65 MPH, on portions of the rural

Interstate system and some other “experimental” roads. Thirty-eight states raised speed limits to

65 MPH on rural Interstates in 1987, and two additional states adopted the 65 MPH speed limit

on rural Interstates in 1988, bringing approximately 90 percent of the 34,000 rural Interstate

mileage to 65 MPH. Congress asked for an evaluation of the effects of the 65 MPH speed limit

on rural Interstate traffic fatalities for the period 1987 through 1989. NHTSA published the

results of this evaluation in several reports to Congress, the last of which was published in 19925,

estimating the 1990 fatality toll on rural Interstates in the 38 states with 65 MPH limits to be “30

percent greater than might have been expected” or an increase of about 500 fatalities.

Section 347 of the NHS Act, in addition to eliminating the NMSL, also required the

Secretary of Transportation to study the impact of states’ actions to raise speed limits above

55/65 MPH by September 30, 1997. Section 347 also identified various aspects of increased

speed limits that the study should address, e.g., the costs to the states of deaths and injuries

resulting from motor vehicle crashes; and the benefits to the states associated with the NMSL

repeal, thus establishing the need to obtain specific information from the states’ on the impact of

increased speed limits on an individual state basis:

“Not later than September 30, 1997, the Secretary, in cooperation with any State which

raises any speed limit in such State to a level above the level permitted under section 154

of title 23, United States Code, as such section was in effect on September 15, 1995, shall

prepare and submit to Congress a study of-

(1) the costs to such State of deaths and injuries resulting from motor vehicle 

 crashes; and
3

(2) the benefits associated with the repeal of the national maximum speed limit.”

NHTSA and the FHWA were delegated the responsibility for conducting the NHS Act

study.

NHTSA and FHWA proposed a strategy for meeting the requirements of Section 347 of

the NHS Act, intended to address the complexities of determining the costs and benefits of

increased speed limits, while meeting the Congressional deadline of September 30, 1997. A major

aspect of the strategy was an emphasis on cooperation between NHTSA, FHWA, and the states

that increased their speed limits, as stated in the legislation, for preparation of the study. The

states’ participation in the NHS study process was considered to be a critical factor in determining

the impact of increased speed limits in a particular state, necessitating that an analysis of statespecific data be conducted. In addition, the strategy initially proposed by NHTSA and FHWA

was similar in approach to the extensive study conducted by TRB, in order to capitalize on the

thorough work done by the TRB committee to examine costs and benefits resulting from

decreasing the speed limit.

As the first step of the agencies’ strategy, NHTSA and FHWA published a Federal

Register (FR) notice on June 19, 1996, inviting comments, suggestions, and recommendations

from state highway and traffic safety officials, highway safety organizations, researchers, and

others on the agencies’ proposed plan for conducting the NHS Act study. The proposed strategy,

described in this notice, included a draft study outline, the minimum requirements for specific data

from states that have raised their speed limits, and a proposed schedule for completing the NHS

Act study in order to meet the September 30, 1997, deadline established by Section 347 of the

Act. A total of 39 official comments to the docket were received from state agencies, private

citizens, National Motorists Association (NMA) members, and others. Nineteen (19) states

commented on the notice. Eighteen (18) of the 19 states that commented have increased limits

since the NMSL was repealed or were planning to do so. Many of the comments from the states

included concerns regarding the complexity and/or comprehensiveness of the agencies’ proposed

study outline, often in terms of the burden that would be placed upon the states. Many of the

states also commented regarding the unavailability of data and the apparent difficulty in meeting

the proposed schedule.

On November 27, 1996, NHTSA and FHWA published a second FR notice on the NHS

Act study. This notice summarized comments from the states and others on the earlier notice and

proposed an alternate strategy for meeting the legislative requirement, in view of the concerns

noted by the states. Copies of the two Federal Register notices appear in Appendix B.

Analytical Challenge

Due to the concerns expressed by the states in the areas of study methodology, data

availability, and scheduling, NHTSA and FHWA were faced with several major analytical

challenges to conducting the NHS Act study. Several of the states specifically indicated that

certain types of data, e.g., detailed travel by type of roadway, decreased travel time, increased fuel

consumption, and increased or decreased medical costs, would not be available in time for

inclusion in the report or was not presently being collected. Without this type of information from
4

the states, it will be difficult, if not impossible, for the agencies to address the entire range of costs

and benefits due to increased speed limits in this study. The issue of data availability is further

complicated in that many states selectively increased speed limits on certain road segments and/or

roadway types, e.g., 4-lane roads, rather than systemwide, e.g., all Interstates. While the selective

application of increased speed limits is indicative of the cautiousness on the part of many states in

adopting higher limits, it further complicates the issue of data availability by necessitating the

analysis of data by road segment.

At the national level, determining the impact of increased speed limits on traffic fatalities is

limited to the latest available data from the Fatality Analysis Reporting System (FARS) for

calendar 1996, focusing 3 groups of states: (1) the 11 states that increased speed limits in late

1995 or early in the first quarter of 1996, (2) the 21 states that increased speed limits later in

1996, and (3) the 18 states (and the District of Columbia) that did not increase speed limits in

1996. Finally, determining the impact of increased speed limits related to the amount of vehicle

miles traveled and the distribution of vehicle speeds on affected roadways was not possible due to

the unavailability of these data for calendar year 1996 at the time of the preparation of this report. 

With the repeal of the NMSL, states are no longer required to report data to FHWA on vehicle

speeds by roadway type.

Status of States’ Speed Limit Laws

By the end of calendar year 1996, a total of 32 states had passed laws to raise speed limits

on various types of roadways. Of the 32 states, 11 had increased speed limits at the end of 1995

after the passage of the NHS Act or early in the first quarter of 1996. Some states opted to

increase speed limits on a systemwide basis, e.g., on all Interstate highways; while other states

selectively increased limits on specific road segments and types, e.g., on all turnpike roadways. 

Exhibit 1 presents information on the states in 3 “groups”, those which raised limits before or

early in 1996, those which increased speed limits later in 1996, and those that did not raise limits

during 1996. As of August 15, 1997, 3 additional states (Louisiana, Minnesota, North Dakota)

had raised speed limits during 1997 and another state (Wisconsin) passed legislation authorizing

the Commissioner to increase limits on selected roads. This brings the total number of states with

increased speed limits to 35 as of August 15, 1997. Appendix A presents a detailed listing of the

status of state speed limit legislation by affected roadways, date of law passage, and previous

limit(s).
5

Exhibit 1

Timing of States’ Speed Limit Changes in 1996

Timing of Speed Limit

Change

No. Of

States

States Included

Raised Limit in Late 1995 or

Early in 1st Quarter of 1996

11 Arizona, California, Delaware, Illinois,

Massachusetts, Montana, Nevada, Oklahoma,

Pennsylvania, Texas, Wyoming

Raised Limit Later in 1996 21 Alabama, Arkansas, Colorado, Florida, Georgia,

Idaho, Iowa, Kansas, Maryland, Michigan,

Mississippi, Missouri, Nebraska, New Mexico,

North Carolina, Ohio, Rhode Island, South

Dakota, Tennessee, Utah, Washington

Maintained Previous Limit,

i.e., No Changes in 1996

19 Alaska, Connecticut, DC, Hawaii, Indiana,

Kentucky, Louisiana, Maine, Minnesota, New

Hampshire, New Jersey, New York, North

Dakota, Oregon, South Carolina, Vermont,

Virginia, West Virginia, Wisconsin

Exhibit 2 is a map of the U.S. showing states in the above 3 groups. The lightest shaded

states raised speed limits in late 1995 or early in first quarter of 1996. The darkest shaded states

maintained the previous limit through 1996.
6

Exhibit 2

State Status of Speed Limit Changes

Early Change

Later Change

No Change
6

 Fatality and fatal crash data are from NHTSA’s Fatality Analysis Reporting System

(FARS). FARS contains data on a census of fatal traffic crashes within the 50 states, the District

of Columbia, and Puerto Rico (although Puerto Rico is not included in national totals). A crash

must involve a motor vehicle traveling on a public roadway and must result in the death of an

occupant of a vehicle or a nonmotorist within 30 days of the crash to be included in FARS. Injury

data are from NHTSA’s General Estimates System (GES). GES data are obtained from a

nationally representative probability sample selected from all police-reported crashes.

7

SECTION II -- ASSESSING THE IMPACT OF INCREASED SPEED LIMITS

ON TRAFFIC CRASHES

The National Picture

In 1996, 37,351 fatal crashes occurred on the nation’s roadways, accounting for 41,907

fatalities. An additional 3,511,000 persons were injured.6 The following exhibit presents these

national crash statistics in comparison to similar crash statistics for 1995.

Exhibit 3

Changes in U. S. Traffic Fatalities and Persons Injured

1996 vs. 1995 

1995 1996 % Change

Fatalities 41,817 41,907 --

1

Fatal Crashes 37,241 37,351 --

1

Injuries 3,386,000 3,511,000 +4%

Injury Crashes 2,167,000 2,256,000 +4%

 

1/ The percentage change is less than 0.5 percent.

Total fatalities and fatal crashes experienced essentially no change in 1996 compared to

1995, while the number of injured persons and injury crashes are estimated to have increased by 4

percent. Contrasting the changes in the distribution of fatalities, injuries, and fatal and injury

crashes on Interstate and non-Interstate roadways shows a different picture, and may point to the

possible impact of increased speed limits on the nation’s highways. The following exhibits present

data from FARS on fatalities and fatal crashes and from GES on persons injured and injury

crashes on rural and urban Interstates and non-Interstates in 1996 compared to 1995.
7

 As GES data are obtained from a nationally representative probability sample of all

police-reported crashes, the GES statistics are estimates of persons injured and injury crashes and

are subject to sampling and nonsampling errors. For more information, see National Accident

Sampling System GES Technical Note, DOT HS 807-796.

8

Exhibit 4

Changes in Fatalities and Fatal Crashes 

on U. S. Interstates and Non-Interstates

1995 vs. 1996 

Roadway

Type

Fatalities %

Change

Fatal Crashes %

Change

1995 1996 1995 1996

Rural

Interstates

2,658 2,920 +10% 2,210 2,438 +10%

Urban

Interstates

2,177 2,311 + 6% 1,919 2,045 + 7%

All

Interstates

4,835 5,231 + 8% 4,129 4,483 + 9%

NonInterstates36,699 36,174 - 1% 32,850 32,402 - 1%

Total 41,817 41,907 --

1

37,241 37,351 --

1

1/ The percentage change is less than 0.5 percent.

Exhibit 5

Changes in Persons Injured and Injury Crashes

on U. S. Interstates and Non-Interstates

1995 vs. 1996 

Roadway

Type

Persons Injured %

Change

Injury Crashes %

Change

1995 1996 1995 1996

All

Interstates

200,000 230,000 +15% 126,000 143,000 +13%

NonInterstates3,186,000 3,281,000 + 3% 2,041,000 2,113,000 + 4%

Exhibit 6 summarizes the percentage changes nationally for Interstate vs. non-Interstate

roadways.7
8 Effects of the 65 MPH Speed Limit through 1990: A Report to Congress, U. S.

Department of Transportation, NHTSA, Washington, DC, May 1992.

9

-5%

0%

5%

10%

15%

20%

Fatalities Injured Persons

Interstates Non-Interstates

Total U.S. Percentage Change in

Fatalities & Injuries (1995 vs. 1996)

Exhibit 6

As can be seen from the previous exhibits, while there has been about a 1 percent decrease

in fatalities and fatal crashes on non-Interstate highways from 1995 to 1996, there has been an

increase of approximately 10 percent in fatalities and fatal crashes on the nation’s rural Interstates. 

Fatalities and fatal crashes on urban Interstates increased 6 percent and 7 percent, respectively. 

The number of injured persons increased 15 percent on Interstates in 1996, while increasing only

3 percent on all other roads. A similar pattern occurred for injury crashes. 

The size of the increase in fatalities and fatal crashes on rural Interstates in 1996 is of

particular interest, as these highways were set at 65 MPH in many states prior to the passage of

the NHS Act. Following action in 38 states to raise speed limits on rural Interstates to 65 MPH in

1987 and adoption of the 65 MPH limit on rural Interstates by two additional states in 1988,

NHTSA’s evaluation8 of the effects of the 65 MPH speed limit on rural Interstate traffic fatalities
9

 Ibid.

10

estimated the 1990 fatality toll on rural Interstates in the 38 states with 65 MPH limits to be 30

percent greater than might have been expected, i.e., an increase of about 500 fatalities. While the

loss of 500 lives is extremely significant, such an increase in fatalities on rural Interstates would

represent little more than a 1 percent increase in total fatalities. In 1996, the increase of almost

300 fatalities on rural Interstates represents a 10 percent increase in fatalities occurring on these

roads compared to 1995. This translates into an increase of about 1 percent in total fatalities,

compared to 1995. These increases are consistent with the estimated impact of the 65 MPH

reported in NHTSA’s 1992 report.9 

In 1996, with more roadway miles posted at 65 MPH and above, the proportion of

fatalities occurring on higher speed roads increased. The following exhibit presents data for

fatalities and fatal crashes by posted speed limit in 1995 and 1996.

Exhibit 7

Changes in Fatalities and Fatal Crashes 

by Posted Speed Limit

1995 vs. 1996 

Posted Speed

Limit

Fatalities Fatal Crashes

1995 1996 1995 1996

Less than 55

MPH

18,798 18,360 17,369 16,963

55-60 MPH 19,403 16,669 16,769 14,522

65 MPH and

Above*

2,839 5,768 2,371 4,838

No Speed Limit 75 175 70 153

Unknown 702 935 662 875

Total 41,817 41,907 37,241 37,351

* Note No roads were posted at speed limits above 65 MPH prior to December 1995.

In 1995, fatalities and fatal crashes occurring on roads with speed limits of 65 MPH and

greater represented approximately 7 percent of total fatalities, while in 1996, almost 14 percent of

total fatalities and total fatal crashes occurred on roads posted at 65 MPH and above. Most of

the shift in fatalities occurring on roads with higher speed limits appears to have come from roads

previously posted at 55 MPH and now posted at 65 MPH, i.e., fatalities on roads posted 55-60

MPH declined 14 percent in 1996 compared to 1995 (16,669 vs. 19,403).
10 Two statistical procedures, univariate and hot-deck imputation, are used in GES to

complete values for unknown data. For more information, see Imputation in the General

Estimates System, DOT HS 807-985. 

11

The following exhibit presents data on injured persons and injury crashes by posted speed

limits for 1995 and 1996.10 In 1996, similar to the shift in total traffic fatalities occurring on

roadways with higher posted speed limits, a greater number of injured persons and injury crashes

occurred on roads posted at 65 MPH and above.

Exhibit 8

Changes in Injured Persons and Injury Crashes 

by Posted Speed Limit

1995 vs. 1996 

Posted Speed

Limit

 Injured Persons %

Change

Injury Crashes %

Change

1995 1996 1995 1996

Less than 55

MPH

2,635,000 2,722,000 + 3% 1,697,000 1,768,000 + 4%

55-60 MPH 699,000 649,000 - 7% 436,000 401,000 - 8%

65 MPH and

Above*

51,000 138,000 +171% 32,000 85,000 +166%

No Limit 2,000 2,800 +40% 1,000 2,000 +50%

* Note No roads were posted at speed limits above 65 MPH prior to December 1995.

Fatalities and persons injured in traffic crashes occurring on roads with higher speed limits

have been commanding an increasing share of the total traffic crash toll for some time. A large

part of this increase in 1996 is a direct result of increasing speed limits, resulting in a greater

amount of exposure occurring at higher travel speeds. In 1990, 52.6 percent of all fatalities

occurred on roads posted 55 MPH and greater, while the percentage of fatalities occurring on

these roads increased to over 56 percent in 1996. At this time, the extent to which overall

increases in the amount of travel affected these counts is not known. For example, if drivers

prefer traveling at higher speed limits, alternate routes might be used, leading to greater than

expected increases in motor vehicle travel on higher speed limit roads and less than expected

changes on roads that maintained their previous limits.

Unfortunately, vehicle miles traveled (VMT) estimates are not tabulated according to

posted speed limit (which would be an incredibly difficult, if not impossible task). To complicate

matters, detailed information on exactly when and which roadway segments experienced increases

in their posted speed limits is not now available. This makes it impossible at this time to identify a

suitable “baseline” of roadways that experienced increased posted speed limits against which to
12

compare the 1996 fatality outcome. Due to these difficulties, and the absence of travel data for

such road segments, it is likely that analyses by posted speed limit (instead of roadway type) will

never be capable of separating changes in exposure from changes in risk, and will require a

relatively large analytical investment to correctly tabulate the baseline fatality experience so that a

meaningful analysis can be conducted.

Therefore, the detailed analyses presented at the end of this section focus on contrasting

the experience of Interstate highways with non-Interstate roadways, a well-defined categorization. 

VMT data for this categorization will be available later this year, to address the possible effects of

changes in travel in subsequent analyses.
13

1995 vs. 1996 State Comparison

While the national fatality toll for 1996 changed very little compared to 1995 (refer to

Exhibit 2), the change in the fatality toll for individual states ranged from as much as an increase

of 18 percent (Texas) to a decrease of 17 percent (Vermont). Exhibit 9 contains data for fatalities

by state for 1995 and 1996, with the percentage change.

Exhibit 9

Fatalities by State - 1995 vs. 1996

Fatalities 1996 vs. 1995

State 1995 1996 Chg % Chg

Alabama 1114 1143 29 3%

Alaska 87 80 -7 -8%

Arizona 1035 993 -42 -4%

Arkansas 631 615 -16 -3%

California 4192 3989 -203 -5%

Colorado 645 617 -28 -4%

Connecticut 317 310 -7 -2%

Delaware 121 116 -5 -4%

District of Columbia 58 62 4 7%

Florida 2805 2753 -52 -2%

Georgia 1488 1574 86 6%

Hawaii 130 148 18 14%

Idaho 262 258 -4 -2%

Illinois 1586 1477 -109 -7%

Indiana 960 984 24 3%

Iowa 527 465 -62 -12%

Kansas 442 491 49 11%

Kentucky 849 841 -8 -1%

Louisiana 894 781 -113 -13%

Maine 187 169 -18 -10%

Maryland 671 608 -63 -9%

Massachusetts 444 417 -27 -6%

Michigan 1530 1505 -25 -2%

Minnesota 597 576 -21 -4%

Mississippi 868 811 -57 -7%

Missouri 1109 1149 40 4%

Montana 215 200 -15 -7%

Nebraska 254 293 39 15%

Nevada 313 348 35 11%

New Hampshire 118 134 16 14%

New Jersey 774 818 44 6%

New Mexico 485 481 -4 -1%

New York 1679 1564 -115 -7%

North Carolina 1448 1493 45 3%

North Dakota 74 85 11 15%
11 Traffic Safety Facts 1995: State Traffic Data Fact Sheet, National Center for Statistics

and Analysis, NHTSA, U. S. Department of Transportation. 

14

Exhibit 9 - Continued

Fatalities by State - 1995 vs. 1996

Fatalities 1996 vs. 1995

State 1995 1996 Chg % Chg

Ohio 1360 1395 35 3%

Oklahoma 669 772 103 15%

Oregon 574 524 -50 -9%

Pennsylvania 1480 1469 -11 -1%

Rhode Island 69 69 0 0%

South Carolina 881 930 49 6%

South Dakota 158 175 17 11%

Tennessee 1259 1239 -20 -2%

Texas 3183 3741 558 18%

Utah 325 321 -4 -1%

Vermont 106 88 -18 -17%

Virginia 900 875 -25 -3%

Washington 653 712 59 9%

West Virginia 376 345 -31 -8%

Wisconsin 745 761 16 2%

Wyoming 170 143 -27 -16%

The first group of 11 states that increased speed limits and the characteristics of the

increased limits are presented in Exhibit 10. In 1995, these states accounted for approximately 32

percent of the total national fatality toll, while representing 35 percent of the population, 34

percent of all licensed drivers and 33 percent of all vehicle miles traveled in 1995.11

Exhibit 11 presents the characteristics of the increased speed limits for the 21 states that

raised limits later in 1996. 
12 See Footnote 4.

15

Exhibit 10

States Which Raised Speed Limits Prior to or in 1st Quarter 1996

State Speed Limit Change Effective Date

Arizona To 75 MPH on Rural Interstates December 8, 1995

California To 65 MPH on Freeways/Expressways; Later

to 70 MPH for Rural Freeways

Increased to 65 MPH on 

December 10, 1995;

Increased to 70 MPH on

January 7, 1996

Delaware To 65 MPH on Interstate 495 and one

portion of US 1

January 26, 1996

Illinois To 65 MPH for some Urban Interstates November 29, 1995

Massachusetts To 65 MPH on 13 Major Interstates &

Highways 

January 29, 1996

Montana Unlimited during Day; To 65 MPH at Night December 8, 1995

Nevada To 75 MPH on Interstates; To 70 MPH on

Other Primary

December 8, 1995

Oklahoma To 70 MPH on Interstates & 4 Lanes; To 65

MPH all Other State Roads

December 1995

Pennsylvania On Turnpike Roads to 75 MPH; Selected

Roads to 65 MPH

December 1995

Texas To 70 MPH on all Roads for Passenger Cars

(65 MPH at Night); To 60 MPH on all Roads

for Trucks (55 MPH at Night)

December 8, 1995

Wyoming To 75 MPH Rural Interstate/To 70 MPH

Urban Interstate/To 65 MPH on 4 & 2 Lane

Roadways

January 24, 1996

In NHTSA’s last report to Congress on the effects of the 65 MPH speed limit, the focus

of the analysis was on rural Interstates in the 38 states that increased limits to 65 MPH.12 For

most states opting to increase speed limits following passage of the NHS Act, limits were

typically set higher for rural Interstates than for other roads in the state, including urban

Interstates. Exhibit 12 shows the revised maximum posted speed limits for rural and urban

Interstates for the 11 states which raised speed limits immediately following passage of the NHS

Act or early in the first quarter of 1996.

Exhibit 11
16

States Which Raised Speed Limits After Early 1st Quarter 1996

State Speed Limit Change Effective Date

Alabama To 70 MPH on Interstates; To 65 MPH on other 4 Lanes; To 55

MPH on other Primary

May 9, 1996

Arkansas To 70 MPH on Rural 4 Lane divided highways July 17, 1996

Colorado To 75 MPH on Highway; To 65 MPH for 4 Lanes; May 28, 1996

Florida To 70 MPH for some Interstate segments; To 65 MPH for some

other 4 Lane segments

April 8, 1996 for Interstates;

November 1996 for other 4 Lanes

Georgia To 70 MPH on Interstates and look-alikes; To 65 MPH On Urban

Interstates and some other divided

July 1, 1996

Idaho To 75 MPH on Interstates; To 65 MPH on other primary May 1, 1996

Iowa To 65 MPH on selected 4 lane divided May 16, 1996

Kansas To 70 MPH on Interstates; To 65 MPH on other primary March 22, 1996

Maryland To 60 or 65 MPH on selected Urban Interstates July 18, 1996

Michigan To 70 MPH on Interstates August 1996 study began; became

permanent December 18, 1996

Mississippi To 70 MPH on Interstates March 12, 1996

Missouri To 70 MPH on Interstates, and on any road with safety study March 13, 1996

Nebraska To 75 MPH on Interstates; To 60 MPH on 2 Lanes; To 65 MPH

on 4 Lanes

April 15, 1996 signed,

June 1, 1996 effective for

Interstates; September 1, 1996 for

other roads

New Mexico To 75 MPH on Interstates; To 70 MPH on 4 Lanes with

shoulders; To 65 MPH on 2 Lanes with shoulders; To 60 MPH

on 2 Lanes without shoulders

May 13, 1996

North Carolina To 70 MPH on Interstates and some controlled-access nonInterstateAugust 1996 for Interstates;

October 1, 1996 for non-Interstates

Ohio To 65 MPH on Interstates; To 65 MPH on other roads after 360

days with review

February 29, 1996 effective;

May 29, 1996 Implemented

Rhode Island To 65 MPH on some Interstates May 12, 1996

South Dakota To 75 MPH on Interstates; To 65 MPH on major 2 Lanes April 1, 1996 effective

Tennessee To 65 MPH on some Urban Interstates; To 65 MPH on some 4

Lanes

April 22, 1996 for Urban

Interstates; July 1, 1996 for 4 Lanes

Utah To 75 MPH on Interstates March 13, 1996

Washington To 70 MPH on Interstates March 11, 1996
17

Exhibit 12

Revised Maximum Speed Limits on Rural and Urban Interstates for

States Which Raised Speed Limits in 1995 or Early in 1st Quarter 1996

State Rural Interstate Speed

Limit 

Urban Interstate Speed

Limit

Arizona 75 MPH Remained at 55 MPH

California 70 MPH 65 MPH

Delaware Remained at 65 MPH 65 MPH

Illinois Remained at 65 MPH 65 MPH

Massachusetts Remained at 65 MPH 65 MPH

Montana Unlimited for Passenger

Cars (Day)

65 MPH

Nevada 75 MPH 70 MPH

Oklahoma 70 MPH 60 MPH

Pennsylvania Remained at 65 MPH 65 MPH

Texas 70 MPH for Passenger Cars

(Day)

70 MPH for Passenger Cars

(Day)

Wyoming 75 MPH 60 MPH

Total Interstate fatalities in FARS for 1996 for the 11 states, the group of 21 states that

raised limits later in 1996 and the 19 states that made no change in limits during 1996 are

compared to fatalities on total Interstates in 1995 and presented in the following exhibit.
18

Exhibit 13

Changes in Total Interstate Fatalities by

Timing of States’ Speed Limit Changes

Timing of

States’ Speed

Limit Change

1995

Fatalities

1996

Fatalities

% Change

In 1995 or

Early in 1996

1,874 2,038 + 9%

Later in 1996 1,954 2,188 +12%

No Change in

1996

1,007 1,005 No Change

From Exhibit 13, total Interstate fatalities increased 9 percent for the 11 states as a group

that increased speed limits early in 1996 (an actual increase of 164 fatalities) and increased 12

percent (an actual increase of 234 fatalities) for the 21 states that increased speed limits later in

1996. Total Interstate fatalities essentially did not change (an actual decrease of 2 fatalities) for

the group of states that did not increase speed limits in 1996. As shown in Exhibit 14, fatalities

on rural Interstates increased 5 percent for the 11 states that increased speed limits early in 1996

(an actual increase of 45 fatalities) and increased 20 percent (+218 fatalities) for the remaining 21

states that increased limits later in 1996. Fatalities on rural Interstates for states that did not

increase speed limits in 1996 essentially did not change (-1 fatality) in 1996 compared to 1995. 

Exhibit 14 also presents similar data from 1996 FARS for changes in urban Interstate fatalities. 

For the 11 states whose limits changed early in 1996, fatalities on urban Interstates increased the

greatest of the 3 groups of states, i.e., by 13 percent (+119 fatalities) in 1996 compared to 1995. 

The 21 states that raised limits later in 1996 experienced a 2 percent increase in fatalities (+16

fatalities) on urban Interstates, while those states that did not raise limits in 1996 had no change in

fatalities (-1 fatality) on urban Interstates. Fatalities on non-Interstate roads decreased for all 3

groups of states in 1996. These data are shown in Exhibit 15.
19

Exhibit 14

Changes in Rural and Urban Interstate Fatalities by

Timing of States’ Speed Limit Changes

Timing of

States’ Speed

Limit Change

1995

Fatalities

1996

Fatalities

% Change

Rural Interstates

In 1995 or

Early in 1996 

956 1,001 + 5%

Later in 1996 1,114 1,332 +20%

No Change in

1996

588 587 No Change

Urban Interstates

In 1995 or

Early in 1996

918 1,037 +13%

Later in 1996 840 856 + 2%

No Change in

1996

419 418 No Change

Exhibit 15

Changes in Non-Interstate Fatalities by

Timing of States’ Speed Limit Changes

Timing of

States’ Speed

Limit Change

1995

Fatalities

1996

Fatalities

% Change

In 1995 or

Early in 1996 

11,506 11,605 - 1%

Later in 1996 16,091 15,663 - 3%

No Change in

1996

9,102 8, 906 - 2%

While there were no apparent patterns of association between the states with increased

limits in 1996 and changes in total fatalities (from Exhibit 9), there does appear to be an impact on

fatalities occurring on Interstates associated with the higher speed limits. For both groups of

states (32 states) that increased limits during 1996, fatalities on Interstates increased in 1996

compared to 1995, while Interstate fatalities essentially did not change for states that did not
20

increase speed limits in 1996. A pattern of association between the states with increased speed

limits in 1996 and increases in total Interstate fatalities can also be seen in the following exhibit. 

Exhibit 16 presents changes in total Interstate fatalities for 1996 compared to 1995 for each of the

states in the three groups, i.e., early change, later change, and no change in 1996. Exhibit 16 also

presents changes in the proportion of Interstate fatalities, relative to total fatalities, for 1996

compared to 1995, for each state in the three groups. Increases from 1995 to 1996 are shown in

bold in Exhibit 16. 
21

Exhibit 16

Interstate/Non-Interstate Fatalities by State

by Timing of States’ Speed Limit Changes-1995 vs. 1996

Interstate Non-Interstate % of Fatalities on Interstate

Early Change 1995 1996

%

Change 1995 1996

%

Change 1995 1996

%

Change

Arizona 168 168 0.0% 846 808 -4.5% 16.6% 17.2% 3.9%

California 548 572 4.4% 3,644 3,417 -6.2% 13.1% 14.3% 9.7%

Delaware 10 13 30.0% 111 103 -7.2% 8.3% 11.2% 35.6%

Illinois 181 198 9.4% 1,405 1,279 -9.0% 11.4% 13.4% 17.5%

Massachusetts 51 68 33.3% 393 349 -11.2% 11.5% 16.3% 42.0%

Montana 39 46 17.9% 176 154 -12.5% 18.1% 23.0% 26.8%

Nevada 67 79 17.9% 246 269 9.4% 21.4% 22.7% 6.1%

Oklahoma 88 118 34.1% 581 654 12.6% 13.2% 15.3% 16.2%

Pennsylvania 129 120 -7.0% 1,351 1,349 -0.1% 8.7% 8.2% -6.3%

Texas 539 619 14.8% 2,639 3,122 18.3% 17.0% 16.5% -2.4%

Wyoming 54 37 -31.5% 114 101 -11.4% 32.1% 26.8% -16.6%

Total 1,874 2,038 8.8% 11,506 11,605 0.9% 14.0% 14.9% 6.7%

Late Change

Interstate Non-Interstate % of Fatalities on Interstate

1995 1996

%

Change 1995 1996

%

Change 1995 1996

%

Change

Alabama 98 122 24.5% 1,006 1,020 1.4% 8.9% 10.7% 20.3%

Arkansas 46 65 41.3% 585 550 -6.0% 7.3% 10.6% 45.0%

Colorado 136 110 -19.1% 509 507 -0.4% 21.1% 17.8% -15.4%

Florida 257 278 8.2% 2,546 2,231 -12.4% 9.2% 11.1% 20.8%

Georgia 165 218 32.1% 1,319 1,341 1.7% 11.1% 14.0% 25.8%

Idaho 39 32 -17.9% 219 226 3.2% 15.1% 12.4% -17.9%

Iowa 29 41 41.4% 495 424 -14.3% 5.5% 8.8% 59.3%

Kansas 45 39 -13.3% 397 452 13.9% 10.2% 7.9% -22.0%

Maryland 55 54 -1.8% 596 513 -13.9% 8.4% 9.5% 12.7%

Michigan 140 129 -7.9% 1,383 1,370 -0.9% 9.2% 8.6% -6.4%

Mississippi 85 100 17.6% 782 710 -9.2% 9.8% 12.3% 25.9%

Missouri 138 208 50.7% 969 939 -3.1% 12.5% 18.1% 45.5%

Nebraska 24 39 62.5% 230 254 10.4% 9.4% 13.3% 40.9%

New Mexico 117 121 3.4% 368 360 -2.2% 24.1% 25.2% 4.3%

North Carolina 112 118 5.4% 1,336 1,375 2.9% 7.7% 7.9% 2.2%

Ohio 127 129 1.6% 1,232 1,261 2.4% 9.3% 9.3% -0.7%

Rhode Island 11 13 18.2% 58 56 -3.4% 15.9% 18.8% 18.2%

South Dakota 18 22 22.2% 140 153 9.3% 11.4% 12.6% 10.3%

Tennessee 149 155 4.0% 1,110 1,084 -2.3% 11.8% 12.5% 5.7%

Utah 96 105 9.4% 225 216 -4.0% 29.9% 32.7% 9.4%

Washington 67 90 34.3% 586 621 6.0% 10.3% 12.7% 23.4%

Total 1954 2188 12.0% 16091 15663 -2.7% 10.8% 12.3% 13.2%
13 See Fleiss, Joseph L. Statistical Methods for Rates and Proportions, Second Edition,

John Wiley & Sons, Inc., 1981, for a discussion of tests for statistical significance for differences

in proportions.

22

Exhibit 16- Continued

Interstate/Non-Interstate Fatalities by State

by Timing of States’ Speed Limit Changes-1995 vs. 1996

No Change

Interstate Non-Interstate % of Fatalities on Interstate

1995 1996

%

Change 1995 1996

%

Change 1995 1996

%

Change

Alaska 31 22 -29.0% 54 55 1.9% 36.5% 28.6% -21.7%

Connecticut 45 43 -4.4% 272 267 -1.8% 14.2% 13.9% -2.3%

Dist of Columbia 5 1 -80.0% 53 61 15.1% 8.6% 1.6% -81.3%

Hawaii 8 6 -25.0% 122 142 16.4% 6.2% 4.1% -34.1%

Indiana 106 92 -13.2% 696 781 12.2% 13.2% 10.5% -20.3%

Kentucky 88 91 3.4% 761 750 -1.4% 10.4% 10.8% 4.4%

Louisiana 93 88 -5.4% 801 687 -14.2% 10.4% 11.4% 9.2%

Maine 14 12 -14.3% 162 154 -4.9% 8.0% 7.2% -9.1%

Minnesota 37 41 10.8% 560 535 -4.5% 6.2% 7.1% 14.9%

New Hampshire 20 16 -20.0% 91 114 25.3% 18.0% 12.3% -31.7%

New Jersey 59 85 44.1% 712 730 2.5% 7.7% 10.4% 36.3%

New York 124 112 -9.7% 1,549 1,435 -7.4% 7.4% 7.2% -2.3%

North Dakota 4 2 -50.0% 70 83 18.6% 5.4% 2.4% -56.5%

Oregon 61 51 -16.4% 512 472 -7.8% 10.6% 9.8% -8.4%

South Carolina 78 103 32.1% 803 825 2.7% 8.9% 11.1% 25.4%

Vermont 17 10 -41.2% 89 78 -12.4% 16.0% 11.4% -29.1%

Virginia 132 120 -9.1% 767 749 -2.3% 14.7% 13.8% -6.0%

West Virginia 56 69 23.2% 320 275 -14.1% 14.9% 20.1% 34.7%

Wisconsin 29 41 41.4% 708 713 0.7% 3.9% 5.4% 38.2%

Total 1,007 1,005 -0.2% 9,102 8,906 -2.2% 10.0% 10.1% 1.8%

As seen in Exhibit 16, Interstate fatalities increased for eight of the 11 states (about 73

percent of the states) in the early change group and increased for seventeen of the 21 states (about

80 percent of the states) in the later change group, while increased for only six of the 19 states

whose limits did not change in 1996 (about 31 percent of the states). The difference between the

proportion of states in the early change group with increases in Interstate fatalities, 73%, is

statistically significant when compared to the proportion of states in the no change group, 31%,

with increases in Interstate fatalities (P

2 = 4.739, 1 d.f., p = 0.029). Similarly, the difference

between the proportion of states in the later change group, 80 percent, compared to the no

change group, was also statistically significant (P

2

 = 9.950, 1 d.f., p = 0.002).13 In other words,

both Interstate and non-Interstate fatalities for the no change states either remained steady or

slightly declined in 1996 compared to 1995, while fatalities on Interstates increased for the

majority of the early and later change states.
23

Statistical Modeling

The previous discussion demonstrated increases in fatalities during 1996 compared to

1995 on Interstate highways in those states that increased posted speed limits beyond those

permitted under the now defunct NMSL. However, as stated earlier in this report, there has been

an increasing trend in the portion of the fatalities that occur on roads posted 55 MPH or greater. 

Thus, at least some increase in fatalities on the Interstates might be expected from one year to the

next. A longer-term picture permits investigation of this trend, as well as additional insight into

what happened in 1996. Exhibit 17 presents fatalities on Interstate highways for the 3 groups of

states for 1991-1996, while Exhibit 18 is a similar graph for non-Interstate roadways.
24

800 

1000 

1200 

1400 

1600 

1800 

2000 

2200 

Fatalities

1991 1992 1993 1994 1995 1996

Early Chg No Chg Later Chg

Fatalities on Interstate Highways

For 3 Groups of States

Exhibit 17

A quick review of this graph shows that fatalities on Interstate highways have been

generally increasing over time for the two groups of states that changed speed limits, Both the

“early change” and “later change” groups of states have experienced steady growth in Interstate

fatalities since 1992, while the “no change” group of states experienced an almost steady 1,000

fatalities per year from 1991-1996.
25

8000 

10000 

12000 

14000 

16000 

18000 

Fatalities

1991 1992 1993 1994 1995 1996

Early Chg No Chg Later Chg

Fatalities on Non-Interstate Roadways

For 3 Groups of States

Exhibit 18

An interesting aspect of this exhibit is the fairly parallel experience of the “early change”

and “no change” groups of states during the 1991-1995 time frame, with declining fatalities

during 1991-1993, and slight increases during 1993-1995. The two groups diverge in 1996, with

the “early change” group continuing its upward trend while the “no change” states exhibited a

decline in fatalities. In contrast to this, non-Interstate fatalities in the “later change” group of

states grew steadily, and at a faster rate, between 1992-1995, and declined in 1996. A convenient

and revealing way of combining the Interstate and non-Interstate patterns is to look at the

percentage of total fatalities that occurred on Interstate highways, which appears in Exhibit 19.
14 See Footnote 1.

26

9 

10 

11 

12 

13 

14 

15 

Percentage

1991 1992 1993 1994 1995 1996

Early Chg No Chg Later Chg

Percentage of Fatalities on Interstate

For 3 Groups of States

Exhibit 19

The percentage of Interstate fatalities in the “early change” states has been increasing

steadily since 1992, and experienced a relatively large increase between 1995 and 1996. This

same relatively large increase in 1996 occurred in the “later change” states after several years of

decline (1993-1995), paralleling the “early change” states. In contrast to this, the percentage of

fatalities on Interstate highways in the “no change” states was relatively steady during 1993-1996,

and showed a slight increase between 1995-1996.

Also noteworthy is the fact that the “early change” states as a group exhibit the greatest

percentage of fatalities on Interstate highways, followed by the “later change” states, with the “no

change” states exhibiting the lowest percentage of Interstate fatalities. However, the differences

among the 3 groups are not particularly large, ranging from 3-5 percentage points over time.

To analytically investigate the changes in Interstate fatalities for the 3 groups of states, a

linear regression14 model was estimated for each of the 3 groups of states using 6 years of data

(that is, 6 data points for each model). These models included 2 “dummy” variables representing

the linear trend over time (with values of x1 = 1, 2, ... , 6) and the 1996 intervention of increased
27

posted speed limits (with values of x2 = 0, 0, 0, 0, 0, 1); i.e., the post-NMSL era. If these simple

models of the percentage of fatalities on Interstate highways prove to be reasonably strong

predictors of the percentage of Interstate fatalities in 1996, based upon the percentage from the

five previous years, then the changes observed in 1996 may be given added perspective, especially

if they can be compared to what one would have expected in the absence of speed limit changes

(that is, predictions based on the statistical models). The following exhibit summarizes the results

of the 3 regression models, one for each of the three groups of states, estimated in this analysis.

Exhibit 20

Linear Regression Modeling Results

Early Change Later Change No Change

Trend 0.195 0.114 0.206

 Standard Error 0.055 0.105 0.072

 t-Test 3.541 1.081 2.875

Speed Limit Change 0.862 1.072 -0.227

 Standard Error 0.252 0.483 0.329

 t-Test 3.418 2.217 -0.690

R

2 0.96 0.84 0.78

Note: Statistically significant results appear as bold italics for t-Test results. The critical value for a 2-tailed

test at the " = 0.05 level, 3 degrees of freedom is 3.182.

The analysis indicates that the “early change” group of states exhibited a statistically

significant upward trend (0.195 percentage points per year) in the percentage of fatalities that

occurred on Interstate highways. Even in light of this, the increase in 1996, estimated to be

almost 1 percentage point (0.862) greater than expected, was also statistically significant. The

statistical model for the “early change” states accounted for 96 percent (R2 = 0.96) of the

variation in the percentage of Interstate fatalities. The “later change” states as a group exhibited a

lesser upward trend (not statistically significant) and the increase (1.072) in the percentage of

Interstate fatalities, while larger in magnitude than that for the “early change” states, was not

found to be statistically significant. The “no change” group of states also exhibited an upward

trend that just failed to reach statistical significance, but more importantly, there was essentially

no difference in the percentage of Interstate fatalities in 1996 compared with expectations. The

results of these analyses were used to estimate the change in the number of Interstate fatalities in

1996 in states that increased their speed limits.

The first step in estimating the difference in fatalities experienced in 1996 involves

comparing the actual vs. predicted number of fatalities on Interstate highways. This is in contrast

to comparing the 1996 fatality experience to 1995, especially in light of the upward trend in

several of the series. The actual percentages for the “early change”, “later change”, and “no

change” groups of states are 15.0 percent, 12.3 percent, and 10.1 percent, respectively. The
28

9 

10 

11 

12 

13 

14 

15 

Percentage

1991 1992 1993 1994 1995 1996

Early Chg No Chg Later Chg

Actual vs. Pred Percentage Interstate

Fatalities (w/o SL Change)

predicted percentages are calculated by using the linear regression modeling results, without the

variable representing the post-NMSL “effect”, presented graphically in Exhibit 21.

Exhibit 21

Exhibit 21 presents the actual percentage of fatalities that occurred on the Interstates,

compared with the predicted percentages had there been no change in posted speed limits during

1996 (of course, there was no change in the “no change” states). As can be seen, the predicted

percentages for 1996 for the two groups of states that raised speed limits is greater than the actual

1995 percentage, so any calculations comparing actual vs. predicted will not only be more

conservative than those based on comparing actual fatalities in 1996 vs. 1995, but also more

meaningful.

The basic method of estimation involves answering the question: “If the predicted

percentage of fatalities on Interstates had actually occurred, how many fatalities would have

occurred?” and comparing this number to the actual fatality count. For example, the “early

change” states experienced 14.9 percent of total fatalities on Interstates. Thus, if the 11,605 nonInterstate fatalities represented 85.1 percent of total fatalities (100-14.9 percent), then total

fatalities were 13,643 (11,605 / 0.851; remembering that while the actual calculations were

performed to many decimal places, the estimates presented herein have been rounded). In fact,

total fatalities were 13,665, with the difference representing fatalities with unknown roadway

types. The ratio of these two numbers provides an inflation factor to account for unknowns (here,
29

the ratio is 1.002). The appropriate ratios were used to account for unknown fatalities for each of

the three groups of states. 

Repeating this computation for the predicted percentage of fatalities (14.1 percent) and

adjusting for fatalities with unknown roadway type yields a predicted 13,528 fatalities. The

difference between the actual (13,665) and predicted (13,528) number of fatalities in this group of

states yields 137, the number of additional fatalities that occurred compared to what would have

been expected had the previously existing trend continued in 1996. Exhibit 22 presents the results

of these calculations for the three groups of states.

Exhibit 22

Actual vs. Predicted Fatalities in 1996 and Percentage Change vs. Expectations

Early

Change

Later

Change

No

Change Total

Actual Total Fatalities 13,665 18,167 10,075 41,907

Predicted Total Fatalities 13,528 17,948 10,101 41,576

Difference 137 219 - 26 331

“Actual” Interstate Fatalities 2,041 2,226 1,023 5,290

Predicted Interstate Fatalities 1,904 2,007 1,047 4,945

Percentage Difference 7.2% 10.9% - 2.4% 7.0%

Difference for “Change” States 137 219 356

Predicted Interstate Fatalities 1,904 2,007 3,912

Percentage Difference 7.2% 10.9% 9.1%

Note: Totals may not add due to rounding. “Actual” Interstate Fatalities have been adjusted to account for

unknowns.

The group of “early change” states that increased speed limits during 1996 experienced

7.2 percent more fatalities on Interstates than what would have been expected. The 10.9 percent

increase for the “later change” states was not a statistically significant change in 1996, based on

the statistical model. The 2.4 percent decrease for the “no change” states was not based on a

statistically significant change in 1996, nor did any increase in posted speed limits actually occur. 

Thus, the “no change” group was not included in the estimate of effect associated with increased

speed limits. These calculations appear in the bottom half of Exhibit 22. It is also worth

comparing the percentage differences from the statistical modeling (7.2 percent for the early

change group and 10.9 percent for the later change group) to the actual differences from Exhibit

13 (9 percent and 12 percent, respectively). As hypothesized earlier, the statistical models’

accounting for the historical upward trend in the percentage of Interstate fatalities has resulted in 

more conservative and more meaningful estimates of change.
15

 Effects of the 65 MPH Speed Limit through 1990: A Report to Congress, U. S.

Department of Transportation, NHTSA, Washington, DC, May 1992.

30

In conclusion, the group of states that increased speed limits in late 1995 and 1996

experienced approximately 350 more fatalities on Interstate highways in 1996, or about 9 percent

greater than would have been expected had previous trends continued.

Several issues regarding the above analysis require discussion. The first of these involves

the estimated 9 percent increase above expected Interstate fatalities. How should this estimate be

interpreted? The current calculations use total Interstate fatalities for the analysis and estimating

the change, both in absolute and percentage terms. However, if much less than 100 percent of the

Interstate mileage was affected by increased speed limits, then the baseline number of fatalities,

used in the denominator for computing the percentage change, would be too large, and the

percentage change would be too small. There is ample reason to believe that this is the case,

inasmuch as Exhibit 10 indicates, for example, that Arizona increased posted speed limits to 75

MPH on rural Interstates, while Illinois increased posted speed limits to 65 MPH for some urban

Interstates. In this case, the cited estimates of the percentage change would be the lower bound,

or the smallest percentage change, in the absence of an accurate accounting of how many fatalities

occurred on roads where speed limits were raised. If, for example, only one-half of the Interstate

fatalities occurred on roads where posted speed limits increased, then the 9 percent increase in

fatalities would actually be 18 percent, when restricted to only those roads that experienced

higher speed limits. At this time, the actual prevalence of increased speed limits in each state is

not known. Thus, the interpretation should be that fatalities were at least 9 percent greater than

expected.

The second issue that requires attention relates to where speed limits increased. A review

of the states’ speed limit changes shows that speed limits were increased on some non-Interstate

roadways. For example, Massachusetts increased speed limits to 65 MPH on 13 major Interstates

and highways, and Oklahoma went to 70 MPH on Interstates and 4-lane roads, and to 65 MPH

on all other state roads. While it is uncertain to what degree this may affect the preceding analysis

and conclusions, it is possible to speculate this.

The current analysis includes these affected non-Interstate roads in the comparison group,

rather than the treatment (i.e., higher speed limit) group. If the impact observed on the Interstates

translated to the same percentage increase on the non-Interstates, then the estimated absolute

increase in fatalities would become greater, as the percentage increase would be applied to a

greater base of affected fatalities. There is every reason to believe that the effect on nonInterstate roads would be at least as great as the percentage change observed on Interstates. The

fatality rate per mile traveled on non-Interstate roads is greater than that for Interstates, indicating

greater risk of fatality, which may be due, in part, to the more rigorous roadway design standards

associated with the Interstate designation. NHTSA’s report to Congress on the effect of raising

speed limits to 65 MPH on the rural Interstates found a 30 percent greater fatality experience than

what would have been expected, resulting from a 10 MPH increase on these roads.15 With this

recent repeal of the NMSL, several states increased speed limits to 65 MPH on some nonInterstate roads. In light of the current and previous analysis of raising speed limits, one would

have to conclude that the current effect of raising speed limits is associated with at least 350
31

additional fatalities.

Lastly, the current analysis does not account for changes in vehicle miles traveled on any

of these roads, due to the current unavailability of these data (the data will, however, be available

later this year). If the trend in miles traveled was affected by changing the posted speed limit,

then this should be taken into account. As these data become available later this year and in the

future, subsequent analyses of this issue may be able to address exposure changes.

A specific example of the exposure issue may explain why the change in fatalities in the

early change states (an increase of 7.2 percent) is less than the change estimated in the later

change states (10.9 percent increase). Everything else being equal, one would expect that states

that increased speed limits earlier in the year would have experienced a greater percentage

increase in fatalities than did those states that increased speed limits later in the year, since the

higher speed limits were in force for a longer period of time. However, everything else is not

equal, and the actual number of roadway miles covered by higher speed limits may be greater in

the later change group of states. In other words, the “mile-months” of exposure, i.e., the product

of the number of miles and the number of months where and when higher speed limits were in

place in a given state, may be greater for the later change states than for the early change states. 

Thus, if a greater number of miles of roadway experienced higher speed limits in the later change

group of states compared to the early change group, this could compensate for the shorter

duration of time during which higher speed limits were in effect in the later change group and

possibly yield the larger percent increase in fatalities for these states.
32

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16 Informal study on California Traffic Fatalities (Provisional Data as of December 31,

1996.

33

SECTION III -- SYNOPSIS OF STUDIES BY INDIVIDUAL STATES

Overview

The 19 states commenting to the docket for the first FR notice on the NHS Act study

consistently voiced concerns that the schedule necessitated by the date specified in Section 347 of

the NHS Act was “ambitious” or “impossible.” At least one of the 19 states suggested requesting

a one year extension past the September 30, 1997, deadline to avoid creating a “second-rate

report.” Three of the 19 states commenting to the docket indicated that while plans existed to

study the impact of increased speed limits in their respective states, results from these studies

would not be available in time to submit to the agencies to be included as a part of this report.

Although increased speed limits have not been in place in most states for a time period

that is adequate to permit a meaningful analysis of the impact in safety and other areas, several

states have examined the impact on a limited basis. Ten of these states, California, Idaho,

Iowa, Michigan, Missouri, Montana, Nebraska, New Mexico, Texas, and Virginia, have

examined the impact (or the potential impact) of increased speed limits in their respective

states and forwarded copies of the findings to NHTSA and FHWA. Of these 10 states, two,

i.e., California and Montana, are among the group of states which raised speed limits late in 1995

or early in the first quarter of 1996. One state, Virginia, has not increased speed limits on a wide

scale and studied the potential impact to provide a basis for future decision making. The

remainder of this section presents information abstracted from reports supplied by the

states based upon data from the states’ crash data files for each of the individual state

studies followed by a summary of the findings from the 10 states.

California

California passed legislation to increase the speed limit to 65 MPH on freeways on

December 10, 1995. The speed limit for California’s rural freeways was later increased to 70

MPH on January 7, 1996. California was among the first of several states which passed

legislation to increase speed limits shortly after passage of the NHS Act.

In an informal study16 of the effects of increased speed limits on California’s freeways,

data for fatal and injury crashes were examined for comparable time periods before vs. after the

speed limit was changed. Following passage of legislation to increase the speed limit, crashes of

all severities on California’s freeways with the higher limits increased during the period January 1,

1996 through October 31, 1996, compared to the same 10-month period in 1995. Roughly 10

percent of California’s freeway mileage (433 miles) remained posted at 55 MPH. The posted

speed limit was increased from 55 MPH to 65 MPH on over two-thirds of the remaining freeway

mileage in California. Almost 1,300 freeway miles were increased from 65 MPH to 70 MPH. 

The largest increase, more than 17 percent, was found for fatal freeway crashes during the period

after speed limits were increased. The reported changes are summarized in Exhibit 23.
34

Exhibit 23

Changes in California Freeway Crashes Before vs. After Speed Limit Increases

Crash Type Before 1 After 2 % Change

Fatal 548 644 +17.5%

Injury 22,187 22,449 +1.2%

Property

Damage

45,787 48,210 +5.3%

Total 68,522 71,303 +4.1%

 

Note 1: January 1, 1995 through October 31, 1995

Note 2: January 1, 1996 through October 31, 1996

Crashes of all severities increased by more than 4 percent on California freeways in the 10

months following the speed limit increase. The possible contribution of the increased speed limit

to the increases may be seen when crashes occurring on freeways remaining at 55 MPH are

compared to those occurring on freeways with an increased speed limit. The following exhibits

present data for California freeways for fatal crashes, injury crashes, and for all crashes for the

period before the speed limit increases compared to the period after the speed limit increases.

Fatal crashes on California freeways with a posted speed limit remaining at 55 MPH

experienced a decrease of more than 8 percent while freeways with increases in the posted speed

limit to 65 MPH and 70 MPH experienced increases of more than 22 percent and 12 percent,

respectively. For California’s injury crashes, crashes on freeways with the limit remaining at 55

MPH experienced almost no change (an increase of 0.7 percent), while changes on freeways

where speed limits increased to 65 MPH and 70 MPH were more than 1 percent and more than 3

percent, respectively. While crashes of all severities increased for all groups of freeways, the

percentage increase (more than 3 percent) was lowest for those freeways remaining at 55 MPH.
35

Exhibit 24

Changes in California Fatal Freeway Crashes

Before vs. After Speed Limit Increases

Freeway Speed

Limit

Before 1 After 2 % Change

Remained at 55 MPH 62 57 -8.1%

Increased from

55 MPH to 65 MPH

330 403 +22.1%

Increased from

65 MPH to 70 MPH

165 185 +12.1%

All Freeways 557 645 +15.7%

 

Note 1: January 1, 1995 through October 31, 1995

Note 2: January 1, 1996 through October 31, 1996

Exhibit 25

Changes in California Injury Freeway Crashes

Before vs. After Speed Limit Increases

Freeway Speed

Limit

Before 1 After 2 % Change

Remained at 55 MPH 4043 4072 +0.7%

Increased from

55 MPH to 65 MPH

16,861 17,094 +1.4%

Increased from

65 MPH to 70 MPH

1,929 1,993 +3.3%

All Freeways 22,187 22,449 +1.2%

 

Note 1: January 1, 1995 through October 31, 1995

Note 2: January 1, 1996 through October 31, 1996
17 Laragan, Greg M., P. E. Six Month Report Comparing May-October for 1991 - 1996,

Idaho DOT. 

36

California also measured the average 85th percentile speed on freeways where the speed

limit was raised from 65 MPH to 70 MPH during the period November 1995 through January

1997. The increased speed limit of 70 MPH was in place for almost all of this period, with the

exception of the month of November 1995. The average 85th percentile speed on these freeways

increased slightly, from 71.6 MPH to 72.1 MPH.

Idaho

Speed limits on Idaho highways were increased to 75 MPH on Interstates and to 65 MPH

on other primary roads effective May 1, 1996. Prior to May 1996, the maximum speed limit was

65 MPH on Interstates and state highways and 55 MPH for all other roads. While most

legislation in Idaho typically has July 1 as an effective date, the effective date for the increased

speed limit legislation was set at May 1. The earlier effective date limited the amount of time

available to the Idaho Department of Transportation (Idaho DOT) for conducting engineering

studies and implementing speed limit changes. Idaho DOT conducted a 6-month study17 of the

effect of the NMSL repeal in Idaho, focusing on changes in the number of speeding relating

crashes. Idaho’s study also examined average and 85th percentile speeds on affected roadways. 

The Idaho study compared the crash and travel speed experience for study roadways, i.e., those

highways increased to 75 MPH (Interstates) or 65 MPH (all other roads) to control roadways,

i.e., those roadways for which the posted speed limit was maintained at 65 MPH or less. The

following exhibits present a comparison of the mileage, travel speed and crash experience for

study vs. control roadways in 3 groups: urban Interstates, rural Interstates, and non-Interstate

highways.
37

Exhibit 26

Changes on Idaho Urban Interstates

Before 1 vs. After 2 Speed Limit Increases

Measure Study 3 Control 4

Average Speed + 3 MPH - 3 MPH

85th Percentile Speed + 3 MPH - 4 MPH

% Exceeding Posted Speed

Limit

-31% +1%

Total Crash Rate +24% +15%

Speeding-Related Crash Rate +223% +28%

Fatal Crash Rate --

5 No Change

Speeding-Related Fatal Crash

Rate

--

5

-50%

Note 1: May 1995 through October 1995

Note 2: May 1996 through October 1996

Note 3: 14.3 Miles

Note 4: 23.2 Miles

Note 5: Percentage Change Not Valid As Before Rate = 0.0
38

Exhibit 27

Changes on Idaho Rural Interstates

Before 1 vs. After 2 Speed Limit Increases

Measure Study 3 Control 4

Average Speed + 3 MPH + 1 MPH

85th Percentile Speed + 3 MPH + 1 MPH

% Exceeding Posted Speed

Limit

-36% -2%

Total Crash Rate +29% -5%

Speeding-Related Crash Rate -28% No Change

Fatal Crash Rate -42% --

5

Speeding-Related Fatal Crash

Rate

-60% --

5

Note 1: May 1995 through October 1995

Note 2: May 1996 through October 1996

Note 3: 523.6 Miles

Note 4: 21.5 Miles

Note 5: Percentage Change Not Valid As After Rate = 0.0
39

Exhibit 28

Changes on Idaho Non-Interstates

Before 1 vs. After 2 Speed Limit Increases

Measure Study 3 Control 4

Average Speed + 2 MPH No Change

85th Percentile Speed + 2 MPH No Change

% Exceeding Posted Speed

Limit

-39% No Change

Total Crash Rate +13% No Change

Speeding-Related Crash Rate -30% -5%

Fatal Crash Rate +14% +52%

Speeding-Related Fatal Crash

Rate

-43% +20%

 

Note 1: May 1995 through October 1995

Note 2: May 1996 through October 1996

Note 3: 14.3 Miles

Note 4: 23.2 Mile

Note 5: Percentage Change Not Valid As Before Rate = 0.0
18

 Report on Results of Speed Limit Changes After Repeal of National Maximum Speed

Limit, Iowa Safety Management System Task Force on Speed Limits, January 1997.

40

Based upon the data in the above exhibits, Idaho’s first 6 months of experience with

increased speed limits indicates that:

C while average travel speeds and 85th percentile speeds increased 2 - 3 MPH on study

roadways, they decreased or showed no change on control roadways;

C the number of vehicles exceeding the higher posted speed limits declined on study

roadways while showing no change on control roadways; and

C while the total crash rate increased on all roads in the study group compared to decreases

or no change in the rate for the control roadways, there was no consistent pattern of

increases or decreases for the remaining 3 measures, the speeding-related crash rate, the

fatal crash rate and the speeding-related fatal crash rate.

Idaho’s study concluded that the data available in this 6-month comparison was not “...

adequate to make any conclusions regarding the impact of the increased speed limits.” The

study found that while crash rates are up on roadways where the speed limits were increased and

vehicle speeds have increased slightly, fatal crash rates on the affected roadway have decreased. 

In this 6-month comparison, fatal crash rates on Idaho’s rural Interstate highways decreased,

where speeds have increased the greatest.

Iowa

Legislation was signed on May 16, 1996 giving Iowa’s Department of Transportation 

(Iowa DOT) the authority to raise speed limits on selected 4-lane divided highways. Speed limits

on rural and urban Interstate highways in Iowa were maintained in the legislation at 65 MPH and

55 MPH, respectively. Iowa DOT reviewed 322 miles for consideration of possible increases in

the posted speed limit. By December 1996, the posted speed limit was increased to 65 MPH on

252 miles of the 322 miles, 78 percent of the highway mileage considered eligible for the speed

limit increase in Iowa.

Iowa completed a review18 of the impact of increased speed limits on its highways in

February 1997. Iowa’s review was conducted by the Safety Management System Task Force on

Speed Limits, composed of representatives from Iowa’s DOT, Departments of Public Health and

Public Safety, local enforcement, and FHWA. The task force examined the crash and travel speed

experience on 322 highway miles. The review also studied data on speeds and fatalities in 16

states adjacent to and surrounding Iowa. Upon completion of the review, speed limits were raised

on 252 miles in Iowa. Most importantly, the Iowa study indicated that at least 3 more years of

experience with increased speed limits was needed “... to determine the real impact of this change

... on actual speeds, accidents, injuries, and fatalities.”

Iowa’s study focused on the impact of speed limit changes in Iowa and presented findings
41

from a 3-part survey of other states. Regarding the impact of speed limit changes in Iowa, the

task force found that:

C Operating speeds (the 85th percentile travel speed) increased an average of 6 MPH on 4-

lane roads for which the speed limit was increased from 55 MPH to 65 MPH.

C Four fatalities occurred in 1996 on these 4-lane roads, compared to an average of 1.7

fatalities for the period 1993-1995.

C Travel speeds increased 1 - 5 MPH on roadways where the speed limits increased in the

seven states surveyed by Iowa.

C Preliminary fatality data for the midwestern states indicate that for states with speed limit

increases, fatalities increased 10 percent or more, while for states without speed limit

increases, fatalities decreased approximately 4 percent or more.

Iowa’s study examined the experience of eight midwestern states (Kansas, Illinois, Iowa,

Missouri, Minnesota, Nebraska, South Dakota, and Wisconsin) in two groups, those that raised

the speed limit beyond 65 MPH and those that did not raise the speed limit above 65 MPH. 

Fatalities for the 8-month period January to August 1995 were compared to the same period in

1996 for 8 midwestern states. For the midwestern states, those that did not raise the speed limit

above 65 MPH all experienced decreases in traffic fatalities, while those that raised the speed limit

above 65 MPH all experienced increases in traffic fatalities. Exhibit 29 presents the percentage

change in fatalities for the two groups of midwestern states compared in the Iowa study.
42

Exhibit 29

Changes in Traffic Fatalities for Selected Midwestern States

Jan-Aug 1995 vs. Jan-Aug 1996 

States that Did Not Raise the

Speed Limit Above 65 MPH

States that Increased the Speed

Limit Above 65 MPH

State % Change State % Change

Illinois - 4.2% Kansas +10.2%

Iowa -17.9% Missouri +13.3%

Minnesota - 4.3% Nebraska +11.2%

Wisconsin - 3.5% South Dakota +20.8%

Iowa also examined the change in traffic fatalities using the same comparison periods for

selected states in other areas of the nation. The percentage change in fatalities for the comparison

time periods are shown in the following exhibit for 11 states outside the Midwest.

Exhibit 30

Changes in Traffic Fatalities for Selected States Outside the Midwest

Jan-Aug 1995 vs. Jan-Aug 1996 

States that Did Not Raise the

Speed Limit Above 65 MPH

States that Increased the Speed

Limit Above 65 MPH

State % Change State % Change

Indiana + 5.2% Arizona + 3.1%

Massachusetts - 8.2% California + 5.9%

New York - 18.0% Florida - 3.7%

Ohio - 6.8% Montana - 4.4%

Pennsylvania - 8.3% Nevada + 5.1%

Texas + 15.5%

For states outside the Midwest compared in the Iowa study, all but one of the 5 states

(Indiana) that did not raise the speed limit above 65 MPH experienced decreases in traffic

fatalities. Of the 6 states that did raise the limit above 65 MPH, all but 2 states (Florida and

Montana) experienced increases in traffic fatalities. In addition, the Iowa study noted that 
19 Taylor, William C., and Maleck, Thomas L. An Evaluation of the Michigan 70 MPH

Speed Limit, College of Engineering, Michigan Sate University, December 9, 1996.

43

Montana significantly increased fines for speeding and Florida announced a tightening of speed

enforcement.

Iowa concluded in its study that as limited data were available to the task force for the

review, more time and information, i.e., at least 3 years, were needed to determine the “ ... full

impact of these changes in actual speeds, crashes, injuries, and fatalities ...”

Michigan

Michigan increased the speed limit to 70 MPH on approximately 500 highway miles,

effective December 12, 1996. An additional 660 miles of non-Interstate freeway mileage were

increased from 55 MPH to 65 MPH. All 2-lane state roads and approximately 120 miles of nonInterstate freeways remained at 55 MPH.

Michigan increased speed limits upon the completion of a study in December 1996 to

determine the effects of the increase on safety and capacity. The study was conducted by

Michigan State University on behalf of the Michigan Department of Transportation.19 

The Michigan study focused on comparisons of the average travel speeds and the 85th

percentile speeds on “test” sites vs. “control” sites. The test sites were segments of Michigan

freeways where the speed limit was raised to 70 MPH for the study period. The control sites

were similar segments on Michigan freeways. The study also examined changes in speeds on 5

non-freeway highway segments to determine if there was any spill-over effect in travel speeds as a

result of proximity to the test segments. The Michigan study also examined the crash experience

of the test and control segments. Some of the study conclusions are:

C While average and 85th percentile speeds increased slightly on test roadways, there was

no indication that speeds increased on control roadways.

C No spill-over effect of increased speeds was found on the non-freeway segments in

proximity to the test roadway segments.

C Congestion had little impact on recorded speeds during the before or after periods.

C During the 1-month period after speed limits were raised, traffic crashes increased by more

than 16 percent on test road segments, i.e., those roadways where the speed limit was

raised.

The Michigan study also concluded that the results of the safety impact analyses, i.e.,

comparisons of traffic crashes on test roadway segments, were “... preliminary and inconclusive

because of insufficient data.”
44

Missouri

Effective March 13, 1996, speed limits could be raised to 70 MPH on any roadway in

Missouri upon the completion of a safety study. Missouri conducted a review of the average

speed and the 85th percentile speed on several roadway types. A comparison of traffic crashes

for before vs. after the speed limit was increased was also made. The period March 14-September

30, 1995 was compared to the same period in 1996 to determine the change in traffic crashes.

Average speeds on Missouri’s roads increased from more than 2 percent to approximately

8 percent, while the percentage change in the 85th percentile speeds varied from a decrease of

more than 3 percent to an increase of almost 8 percent. The following exhibit presents the

percentage change in average and 85th percentile speeds for 5 types of Missouri roads.

Exhibit 31

Changes in Average and 85th Percentile Speeds on Missouri Roads

1995 vs. 1996 

Highway Type % Change In

Average Speed 85th Percentile

Speed

Rural Interstate + 4.6% + 1.5%

Urban Interstate + 7.9% + 5.5%

Urban Freeway + 2.9% - 3.5%

Rural Divided + 7.9% + 7.7%

Rural Non-Divided + 2.3% + 1.6%

Missouri also compared traffic crashes and traffic fatalities on selected roadways. Crashes

(including fatal crashes) increased on Interstates, but decreased on state lettered routes after the

speed limit was raised.

Montana

Montana increased the speed limit on Interstate highways to a maximum of “reasonable

and prudent” for passenger cars during the daylight hours, effective December 8, 1995. The

maximum speed limit was limited to 65 MPH on Interstates and 55 MPH on all other roads for

passenger cars during the nighttime hours. The maximum speed limit of 65 MPH at all times was

established for trucks on Interstate highways.
20 Montana DOT and Montana Highway Patrol, State of Montana Data Reference

Related Montana Speed Laws, December 1996.

45

Two Montana agencies, the Department of Transportation and the Highway Patrol, issued

findings from a review of speed survey data, crash data and related information.20 Based upon the

review of speed survey data, Montana found that:

C The daytime 85th percentile speed on Interstate and primary roads increased

approximately 5 MPH in 1996 compared to 1995, to about 78 MPH on the Interstates and

to about 72 MPH on primary roads. The nighttime 85th percentile speeds remained

unchanged, at about 70 MPH on Interstate roads and 67 MPH on primary roads.

C Since the return to “reasonable and prudent,” there are greater variances in vehicle speeds,

and speeds are less uniform, with more drivers traveling at higher speeds.

C Sixty percent of vehicles observed at speeds greater than 85 MPH were out-of-state

vehicles. Seventy-five percent of vehicles traveling above 95 MPH were identified as out

of state.

Montana also studied changes in its crash statistics for the first 3 quarters (9 months) of

1996, recognizing that crashes in this part of the nation can be greatly influenced by weather

conditions. [Montana experienced severe weather conditions during the winter of 1996, i.e.,

January, February, and March 1996.] The Montana study also found that misunderstanding

existed among the driving public regarding the difference between no set speed limit and

Montana’s “basic rule”, i.e., reasonable and prudent. With these caveats, Montana examined

changes in traffic crashes, fatalities, and injuries for the period 1992 - 1996. Daytime and

nighttime crashes in Montana significantly increased during the January - March 1996 quarter. 

While Montana attributed the “... significant increases ...” in total crashes and in injury crashes to

“... icy, snowy, roadway conditions ...” these increases appeared to continue beyond the first

quarter of 1996.

The following exhibits present data for all crashes, fatal + injury crashes, injuries, and

incapacitating injuries occurring on Montana’s rural and urban roads for a 9-month comparison

period before (January - September 1995) vs. after (January - September 1996) the increased

speed limits were in place. 
46

Exhibit 32

Changes in Safety Measures on Montana Rural Roadways

Before 1 vs. After 2 Speed Limit Increases

Safety Measure Before 1 After 2 % Change

Total Crashes 6735 7925 +18%

Fatal + Injury Crashes 2846 2152 -24%

All Injuries 4322 4635 + 7%

Incapacitating

Injuries

1326 1261 - 5%

Note 1: January through September 1995

Note 2: January through September 1996

Exhibit 33

Changes in Safety Measures on Montana Urban Roadways

Before 1 vs. After 2 Speed Limit Increases

Safety Measure Before 1 After 2 % Change

Total Crashes 7845 9008 +15%

Fatal + Injury Crashes 2273 2115 - 7%

All Injuries 3187 2997 - 6%

Incapacitating

Injuries

472 289 -39%

Note 1: January through September 1995

Note 2: January through September 1996
21 Nebraska Office of Highway Safety, Nebraska--Comparative Crash Data, Pre and

Post Speed Limit Increases, May 7, 1997.

22 Davis, James W., The Effects of Higher Speed Limits in New Mexico, Division of

Government Research, University of New Mexico, March 1997.

47

Total crashes increased on Montana’s rural and urban roadways after the speed limit was

raised. While injuries increased on rural roadways, decreases occurred for fatal + injury crashes

and incapacitating injuries, following the speed limit increase. On urban roadways, an increase

occurred in total crashes, while decreases occurred for all other measures. One of the conclusions

in the Montana report was that “... no long term conclusions ...” could be made as the impact of

increased speed limits due to the limited amount of data available with a short time period. 

Nebraska 

Legislation to increase the posted speed limit to 75 MPH on Nebraska’s Interstates

became effective on June 1, 1996. The speed limit was raised to 60 MPH on 2-lane roads and to

65 MPH on 4-lane expressways, effective September 1, 1996. Fines for speeding were also

substantially increased.

Nebraska conducted a study of the impact of the increased speed limits on traffic crashes,

using the period June through December, 1990 - 1996.21 The Nebraska study focused on changes

in the number of crashes on rural Interstates. Rural Interstate highways “... experienced the

largest single increase, 19.6% ...”, in total crashes comparing June through December for the

period 1990-1996. The Nebraska study also indicated that its State Patrol officers reported a “ ...

marked increase in the extent of vehicle damage of the vehicles involved in crashes since the

speed limit increases have occurred.” The study concluded, however, that the brief review

should not be considered conclusive and recommended that a more thorough evaluation be

conducted.

New Mexico

New Mexico increased speed limits on its highways effective May 13, 1996. Speed limits

were raised on almost all road categories: limits were raised to 75 MPH on Interstate highways;

to 70 MPH on 4-lane roads with shoulders; to 65 MPH on 2-lane roads with shoulders; and to 60

MPH on 2-lane roads without shoulders.

The University of New Mexico conducted a study of the effect of higher speed limits on

behalf of the New Mexico Highway and Transportation Department.22 The study was conducted

after the increased speed limits had been in place in New Mexico for 6 months. The purpose of

the New Mexico study was threefold: “... to provide a clear picture of the effects of higher speed

limits, to provide information ... for enforcement and public information ..., and to contribute

data ...” to this study. The New Mexico study posed the following questions:

1. Did travel speeds increase after the speed limits changed, and, if so, by how much?
48

2. Did the frequency of crashes increase on roadways where speeds increased?

3. Did the severity of crashes increase on roadways where speeds increased?

4. If crash frequency and/or severity increased, what other factors (e.g., type of vehicle,

driver characteristics, weather, alcohol, occupant restraints) were involved?

The focus of New Mexico’s study was Interstate roads posted at 75 MPH. Average and

85th percentile speeds on separate segments of rural Interstate roads increased during the 6-

month period the higher limits were in place, as did the percentage of vehicles traveling over 80

MPH. The following exhibit from New Mexico’s study presents changes in the average and 85th

percentile speeds following the increase in speed limit.

Exhibit 34

Changes in Travel Speeds on New Mexico Rural Interstate Segments

Before1 vs. After2 Speed Limit Increase

Highway Segment % Change In

Average

Speed

85th

Percentile

Speed

% Over 80

MPH

Interstates I-25 and I-40 + 3.5% + 2.9% + 93%

Interstate I-10 + 7.9% + 5.5% + 11%

Note 1: April 1996

Note 2: June through August 1996

Crash data for the same segments of New Mexico’s Interstate highways were also

analyzed, using 14 weeks of data for approximately the same time periods in 1994, 1995, and

1996. The study compared the average weekly differences for the 1994 - 1996 time period and

tested the differences for statistical significance. The New Mexico study concluded that the

severity of crashes increased on Interstates 25 and 40, where speeds increased, as evidenced by

increases in the number of fatalities and incapacitating injuries. The opposite occurred on

Interstate 10, where speeds did not increase as much. However, the New Mexico study also

found that when the January - April time period is used for comparison, crashes and injuries

decreased in 1996, relative to the same periods in 1994 and 1995. The study concluded that the

results should be considered preliminary and that there were not enough data available for a time

period adequate for conducting a thorough evaluation. 
23 Pezoldt, V. J., Brackett, R. Quinn, & Morris, Daniel E. The Impact of the Change in

Speed Limits on Texas Highways: A Nine-Month Evaluation, February 19, 1997.

49

Texas

Texas was one of the 11 states which raised its speed limits shortly following passage of

the NHS Act. Effective December 8, 1995, the posted speed limits in Texas were eligible to be

increased to 70 MPH for passenger cars and 60 MPH for trucks during daylight hours and to 65

MPH for passenger cars and 55 MPH for trucks during nighttime hours, on all roads.

The Texas Transportation Institute conducted a preliminary evaluation of the impact of

the change in speed limits for the Texas Department of Transportation (TxDOT), using data for

the first 9 months of experience with the higher limits.23 The TTI study indicated that the

evaluation was in its early stages as “... changes in speed limits were phased-in ...” through June

1996 and due to the lag between the occurrence of a motor vehicle crash and the recording of that

crash in the state’s data files. At the time of the TTI study, 47,400 of Texas’ highway miles were

set at 70 MPH, approximately 62 percent of the total state road mileage. More than 81 percent

(2,700) of the state’s 3,000 Interstate mileage was set at a maximum of 70 MPH.

The TTI study compared vehicle speed and crash data for January through September

1991-1996, focusing on changes on Interstate highways. On rural Interstates where the speed

limit was increased to 70 MPH, the study found that the average speed, the 85th percentile speed,

and the percentage of vehicles exceeding 70 MPH all increased. The average speed on Texas’

rural Interstates increased from 64 MPH to 66 MPH, while the 85th percentile speed increased

from 72.3 MPH to 74 MPH. The percentage of vehicles exceeding 70 MPH, the maximum limit,

rose to 27.2 percent from 16.3 percent on rural Interstates. While speeds were much less than

those found on the rural Interstates, substantial increases were found for these speed measures on

urban Interstates where the speed limit was raised to 70 MPH. These comparisons are shown in

the following exhibit.
50

Exhibit 35

Changes in Travel Speeds on Texas Interstates

Before1 vs. After2 Speed Limit Increase

Highway Type % Change In

Average

Speed

85th

Percentile

Speed

% Over 70

MPH

Rural Interstate + 3.1% + 2.4% + 67%

Urban Interstate + 4.7% + 5.6% + 200%

Note 1: January - September 1995

Note 2: January - September 1996

The TTI study also compared changes in the average monthly number of serious crashes

and the serious crash rate per 100 million vehicle miles traveled for the same time periods on rural

and urban Interstates. These comparisons are shown in the following exhibit. The percentage

increase in these safety measures for rural Interstates was considered not significant and possibly

related to increases in travel or other factors. Significant increases in serious crashes and the

serious crash rate were found for urban Interstates; however, the number of fatal crashes and the

fatal crash rate did not change significantly following the speed limit increase. The TTI study

concluded that while there was evidence suggesting that the increases in serious crashes and

injuries on urban Interstates were associated with the higher speed limit, further monitoring and

evaluation of crash and speed data was recommended. 

Exhibit 36

Changes in Safety Measures on Texas Interstates

Before1 vs. After2 Speed Limit Increase

Highway Type % Change In

Serious

Crashes

Serious

Crash Rate 3

Rural Interstate + 8.2% + 5.2%

Urban Interstate + 44.7% + 38.5%

Note 1: January - September 1995

Note 2: January - September 1996

Note 3: Serious Crashes per 100 million vehicles miles traveled

Following the release of the TTI study, TxDOT was asked by the Governor’s office to

review the data to support the conclusion that the increased frequency and rate of serious crashes
24 Texas Department of Transportation. A Review of Urban Interstates Where the Speed

Limit was Raised to 70 MPH.

25 The speed limit was increased to 65 MPH on the Dulles Greenway, a private, urban

controlled access toll road.

26 Commonwealth of Virginia. A Report of the Special Task Force Studying Safe

Minimum Highway Speed Limits in Response to Senate Joint Resolution 7, December 1996.

27 Virginia Transportation Research Council. Virginia’s Speed Limit Fact Sheet, January

17, 1997.

51

on Texas’ urban Interstates appeared to be associated with the higher speed limit.24 Based upon

its review, TxDOT concluded that there were inaccuracies in the speed data provided to TTI and

also, that TTI may not have identified other factors affecting the data. The TxDOT review

concluded that the actual difference between 1995 and 1996 in the crash data may not be

statistically significant. TXDOT also recommended that a state speed database system be

developed and implemented and that TTI consider weather and surface conditions in future

analyses.

Virginia

While Virginia raised the posted speed limit to 65 MPH on only one roadway, the Dulles

Greenway25, the potential impact of speed limit increases has been studied by 2 state

organizations. One study was conducted by a task force appointed to study Virginia Senate Joint

Resolution 7 (VA SJR 7).26 The VA SJR 7 study was conducted for “... the purpose of

recommending appropriate maximum highway speed limits for ...” Virginia’s highways. 

Virginia’s Transportation Research Council (VTRC) also studied the changes in travel speed and

crashes over the period 1985-1995 to provide reference material for decisions on whether to raise

state speed limits.27

The VA SJR 7 study, indicating that “... data regarding the impact of increased speed

limits is ... limited”, reviewed literature on speed limits and the impact on safety. The SJR 7

study concluded that increasing speed limits in Virginia could “... result in a reduction in speed

variance ... in the short run” and hypothesized that this reduction could be “... expected to result

in a decrease in ... crashes.” Meanwhile, based upon past history and Virginia’s experiences

with changes in the speed limit, the study predicted that travel speeds would increase and that

traffic fatalities and injuries would increase, as “... crashes at higher speeds are more severe.”
52

The VTRC study reviewed crash data and average and 85th percentile speeds on

Virginia’s highways for the period 1985 - 1995. VTRC studied changes in speeds and crashes on

rural Interstates, urban Interstates, limited access highways, and divided and undivided highways

with at least 4 lanes. On rural Interstates, VTRC concluded that:

C The average speed and 85th percentile speed increased by more than 5 MPH. These

speeds were slightly higher in the last four years, i.e., 1992 - 1995, than in the 3 years

immediately following the speed limit increase, i.e., 1989 - 1991.

C Fatalities and fatal crashes experienced a sustained increase of about 50 percent during the

time periods studied, i.e., 1985 - 1987, 1989 - 1991, 1992 - 1995. While fatalities and

fatal crashes increased, the fatal crash and fatality rates, however, remained stable.

Earlier crash data (1969 - 1977) for Virginia’s rural Interstates were also studied by

VTRC, as the speed limit was increased and then decreased during this time period. VTRC found

that fatalities increased more than 27 percent on rural Interstates in 1973, following the increase

of the speed limit to 70 MPH. Fatalities, injuries, and fatal and injury crashes on rural Interstates

all decreased during the period 1975 - 1997, following the establishment of the 55 MPH NMSL,

which lowered the speed limit from 70 MPH.

For Virginia’s urban Interstates, VTRC found that:

C The average and 85th percentile speed increased by 3 MPH, comparing the periods 1985 -

1987 to 1989 - 1991, about half the increase experienced on rural Interstates.

C Comparing the period 1969 - 1971 when the speed limit was 65 MPH to 1973, when the

speed limit was raised to 70 MPH, fatal crashes and fatalities decreased, while injury

crashes and injuries increased. After the speed limit was lowered to 55 MPH, fatalities,

injuries and fatal and injury crashes all increased.

The VTRC study also examined data for Virginia’s limited access highways and divided

highways and again found inconsistent patterns of changes associated with increases and

decreases in the posted speed limits.

Summary of Individual State Findings

The previous section illustrates the inherent difficulties in assessing the impact of increased

speed limits on a state-by-state basis. Among the 10 states (California, Idaho, Iowa, Michigan,

Missouri, Montana, Nebraska, New Mexico, Texas, and Virginia) whose study findings are

presented in this report, while there appears to be some evidence of an association between the

higher speed limits and increases in crashes, the impact of increased speed limits did not follow a

consistent pattern across all states. Possible explanations for the inconsistency in findings are

limited data, limited time periods with the increased limits in effect, increased law enforcement

and fines, focus on public information and education, increase in the public’s use of occupant

restraints, decrease in alcohol involved driving, etc.

Of the 10 states whose studies are presented above, two, California and Montana, have
53

had higher speed limits in place for most of calendar year 1996. Following passage of legislation

to increase the speed limit, crashes of all severities on California’s freeways with the higher limits

increased during the period January 1, 1996 through October 31, 1996, compared to the same 10-

month period in 1995. In Montana, however, while total crashes increased on both rural and

urban roads, decreases occurred in the most severe crashes, i.e., fatal + injury. The Montana

report indicated that the lack of consistency in findings could be due to the limited data available

as a result of the speed limit being in place for a short time period and due to adverse weather

conditions in the state during the winter of 1995 - 1996.

Seven of the 10 states whose studies are presented above (Idaho, Iowa, Michigan,

Missouri, Nebraska, New Mexico, and Texas) passed legislation to raise speed limits later in

calendar year 1996, i.e., second quarter or later. In each of these studies, while increases in either

crash rates and/or vehicle travel speeds were found, these increases were not consistent for all

highways with the higher limits nor were they consistent for all safety measures, i.e., for fatal

crashes, injury crashes, total crashes, etc. Each of these studies concluded that the findings should

be considered preliminary, inconclusive, etc. due to the limited amount of time that the increased

limits have been in place and, as a result, the unavailability of data to conduct a thorough

assessment.

The last state summarized in the previous section, Virginia, conducted studies of the

possible impact of increased speed limits to have as a basis for decision making on raising speed

limits. The VTRC study examined data from various time periods, from pre-NMSL (1969-1973)

to NMSL (1975 -1995). While the VTRC study found significant increases in fatalities, injuries

and the associated crashes on some state highways, decreases were also found. Although the

VTRC study did not draw conclusions, the study by a task force of Virginia’s General Assembly

concluded that while “... increasing the speed limit would ... result in a reduction in speed

variance ... in the short run” travel speeds would increase and fatalities and injuries would

increase in the long run.
54

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55

SECTION IV -- DISCUSSION/RECOMMENDATIONS

While there were several analytical challenges to conducting this study following the first

year of the states’ experience with the increased speed limits, there appears to be some indication

of the nature of the impact of the higher limits on traffic safety. Certain types of data at the

national and state levels were not available for use in this study, e.g., increases and/or shifts in

VMT, decreased travel time, increased fuel consumption, increased or decreased medical costs,

and VMT by roadway type. Without these data, it was not possible to address the benefits

associated with repeal of the NMSL, as called for in Section 347 of the NHS Act, at this time.

However, gross estimates of the potential impact, in terms of increases in fatalities and the

associated economic cost at the national level in states that increased speed limits, were addressed

in this study.

The prudent approach being taken by many of the states in adopting higher speed limits is

noteworthy. Although several states moved fairly quickly to raise speed limits, i.e., raising limits

in 1995 or in the first month of 1996 following passage of the NHS Act, most that did so also

simultaneously conducted safety and/or engineering reviews. Many states have opted to

selectively increase speed limits on certain road segments and/or roadway types, e.g., on certain

urban Interstates, or on selected freeways and expressways, rather than systemwide or statewide.

While the selective application of increased speed limits is indicative of the cautiousness on the

part of many states in adopting higher limits, it further complicated the issue of data availability by

necessitating the analysis of data by road segment over a limited time period. As a result, the

analyses conducted in this study was limited to focusing on gross estimates of the potential effects

of increased speed limits.

These analytical challenges aside, however, at the national level, the short-term impact of

the states’ adoption of increased speed limits can be characterized in two ways. First, while total

fatalities and injured persons changed very little at the national level in 1996 compared to 1995

(i.e., an increase of 90 fatalities), fatalities and persons injured in traffic crashes occurring on

roads with higher speed limits continue to account for an increasing share of the total traffic crash

toll. Secondly, fatalities, fatal crashes, injured persons and injury crashes all increased at the

national level on Interstate roads in 1996, while decreasing on all other roads. As Interstate

highways are the nation’s safest roads, the increasing fatality trend on these roads is of concern.

Studies of the impact of speed limit changes in the past provide insight into the resulting

effect on traffic fatalities. Since the early 1970's, the nation has experienced both decreases and

increases in posted speed limits, along with associated decreases and increases in traffic fatalities. 

The National Maximum Speed Limit (NMSL), enacted during the Arab oil embargo of 1973 to

conserve fuel, was set at 55 miles per hour (MPH). In addition to conserving fuel, the annual

traffic fatality toll declined from 54,052 in 1973 to 45,196 in 1974, a drop of over 16%.In 1987,

the Surface Transportation and Uniform Relocation Assistance Act granted the states the

authority to raise the speed limit, not to exceed 65 MPH, on portions of the rural Interstate

system. Thirty-eight states raised speed limits on rural Interstates to 65 MPH in 1987, and two

additional states adopted the 65 MPH speed limit on rural Interstates in 1988, bringing

approximately 90 percent of the 34,000 rural Interstate mileage to 65 MPH. Congress asked for

an evaluation of the effects of the 65 MPH speed limit on rural Interstate traffic fatalities for the

period 1987 through 1989. NHTSA published the results of this evaluation in several reports to
28 Effects of the 65 MPH Speed Limit through 1990: A Report to Congress, U. S.

Department of Transportation, NHTSA, Washington, DC, May 1992.

29 Blincoe, L. J. The Economic Cost of Motor Vehicle Crashes, 1994. U. S. Department

of Transportation, NHTSA, Washington, DC. DOT HS 808 425, July 1996.

56

Congress, the last of which was published in 199228, estimating the 1990 fatality toll on rural

Interstates in the 38 states with 65 MPH limits to be “30 percent greater than might have been

expected” or an increase of about 500 fatalities. The estimated increase in Interstate fatalities

found in this study, while smaller in magnitude compared to the estimated changes found in 1974

and 1987, does follow the pattern of increases in fatalities being associated with increases in

posted speed limits.

Based upon the analysis conducted in this study, it is estimated that Interstate fatalities in

the 32 states that increased speed limits experienced approximately 350 more fatalities than would

have been expected based on historical trends, about 9 percent above expectations. Based on

economic cost models used by the National Highway Traffic Safety Administration, the total

economic cost of 350 additional fatalities and associated injuries and crashes is more than $820

million in 1996 dollars. Nonfatal injuries and non-injury crashes included in the total economic

cost were estimated based on the relative frequency of these events to fatalities in speed-related

crashes.29 Due to the unavailability of detailed VMT and other data at this time, it is not known

how increased travel on higher speed roads, shifts in travel, changes in average and top vehicle

speeds, and other traffic safety factors may have contributed to this estimated increase in

Interstate fatalities.

At the state level, while there were no consistent patterns of association for those states

that raised speed limits and total fatalities, the impact of increased speed limits in the short term

was indicated by increases in fatalities on the Interstates. For the states that raised speed limits at

any time during 1996, fatalities increased considerably on Interstate highways. Fatalities on

Interstates did not change, however, for states that did not raise speed limits in 1996. On a stateby-state basis, the picture was not as clear. Of the 10 states whose studies were summarized in

Section III, while there appears to be a clear association between the increased speed limits and

increases in crashes of all severities in California, for example, a consistent pattern of crash

increases or decreases was not found for the remaining states. Each of the state studies

considered these findings preliminary or inconclusive due to the limited amount of data available

for analysis.

NHTSA and FHWA plan to continue to study the impact of increased speed limits at the

national and state levels, particularly after states have had several years of experience with the

higher limits. In view of the findings, close monitoring of crash trends on roads with increased

speed limits should continue and, if warranted, countermanding actions taken. Also, it will also be

important to continue to focus on other key program areas of traffic safety, e.g., increasing

restraint use, enforcing traffic laws, informing and educating the public, implementing roadway

and traffic safety improvements, and ameliorating the effects of alcohol-involved driving over the

long term to offset possible increases in fatalities and injured persons that may be related to

increased speed limits and increases in VMT and shifts in travel to roads with higher posted speed
57

limits. The challenge will be to take these traffic safety initiatives into account in subsequent

analyses of the effects of increased speed limits. In addition, while some evidence of increases in

fatalities and fatal crashes was found at the national level, this study is based on only 1 year of

data at higher speed limits, and warrants further examination as the national and individual states’

experience with higher speed limits matures. Lastly, this study does not account for possible

changes in the expected vehicle miles of travel patterns due to the unavailability of these exposure

data at this time. Subsequent analysis of this issue will need to address these effects, where

possible. NHTSA, FHWA, and the Centers for Disease Control have also contracted with the

Transportation Research Board to examine the criteria used by states to establish speed limits and

to recommend improvements to the current methodology. The group of experts assembled for

this study come from a wide array of disciplines, e.g., engineering enforcement, and academia,

associated with highway safety. 
A - 1

APPENDIX A -- DETAILED INFORMATION ON

INDIVIDUAL STATE SPEED LIMIT LEGISLATION

The following exhibit presents the latest information available to NHTSA and FHWA as

of August 15, 1997 regarding specific details on speed limit legislation in specific states. As such,

the information presented in the exhibit may contain some inaccuracies in that legislative action

taken in the states after this date is not reflected.
A - 2

Pre Exceeds Cars Trucks August 15, 1997

State NMSL

Max

Old

 NMSL

Interstate Other Interstate Other NOTES: The following is provided for information purposes only. Every

effort has been made to ensure that the information is accurate as of

the above date. Some States may have made administrative or other

changes that are not reflected here. Please contact the individual

State for the latest information.

(mph) Provisions Primary Primary

Alabama 70 Y 70 55 70 55 Eff 5/9/96 - 70 mph on Interstates, 65 mph on other 4 lane highways

Alaska 70 N 65 55 65 55

Arizona 75 Y 75/55* 55 75/55 55 Eff 12/8/95 - 75 rural Interstates; urban Interstates remain 55

Arkansas 75 Y 70 55 65 55 Eff 7/17/96 - AR Hwy.. Commission raised speed limit from 65 to 70

mph on rural four-lane divided highways (passenger vehicles only -

trucks stay 65 mph). Restriction includes any truck that weighs more

than 26,000 and requires a commercial driver's license to operate. 

Will not take effect for approximately one month to give the state time

to post the new speed limit signs statewide.

California 70 Y 70 65 55 55 Freeways and expressways to 65 mph (12/10/95). Freeways and

expressways to 65 mph and 70 mph (rural) (1/7/96). Other city, county

and State roadways remain at 55 mph until 3/30/96, after which, based

on engineering and traffic surveys they may go to 65 mph.

Colorado 70 Y 75 55 75 55 Eff 5/28/96 - Prima facie is 55 mph for 2 lane; 65 mph for 4 lane

divided. Maximum can now be 75 mph for any highway. CO DOT

engineering study will determine maximum limits for all road segments

within one year.

Connecticut 60 N 55 55 55 55

Delaware 60 Y 65 50 65 50 Raised I-495 and part of US 1 to 65 (1/26/96)

Dist. of Col. 60 N 55* 50 50 50 Only part of Woodrow Wilson bridge eligible. No changes considered

at this time.

Florida 70 Y 70 55 65 55 Eff 4/8/96 - Only on part of Interstate 10 (Jacksonville to Pensacola);

additional segments of I-75 and I-95 pending. Eff 11/96 Some nonInterstate 4 lane divided segments posted at 65 mph.

Georgia 70 Y 70 55 70 55 Eff 7/1/96 - 70 mph on Interstate and look-alike; 65 mph urban

Interstates; 65 mph physically divided w/out controlled access. Based

on engineering and traffic investigation studies.

Hawaii 70 N 55 55 55 55

Idaho 70 Y 75 65 75 65 Eff 5/1/96 - 75 mph Interstates (cars and trucks); 65 mph other primary

(cars and trucks)

Illinois 70 Y 65/55* 55 55 55 Gov action - some urban Interstates 65 mph (11/29/95) ; restricted

unmarked county and township roads to 55 (1/25/96)

Indiana 70 N 65 55 60 55 Legislation to raise defeated in House (1/96)
Pre Exceeds Cars Trucks August 15, 1997

State NMSL

Max

Old

 NMSL

Interstate Other Interstate Other NOTES: The following is provided for information purposes only. Every

effort has been made to ensure that the information is accurate as of

the above date. Some States may have made administrative or other

changes that are not reflected here. Please contact the individual

State for the latest information.

(mph) Provisions Primary Primary

A - 3

Iowa 75 Y 65 55 65 55 Gov signed legislation on 5/16/96 giving IOWA DOT authority to raise

limits up to 65 mph on selected 4-lane divided. Rural and urban

Interstates remain at 65 and 55 respectively. Only portions of US 20

have been increased.

Kansas 75 Y 70 65 70 65 Eff 3/22/96

Kentucky 70 N 65 55 65 55 No bills passed. Gov stated he would veto any bills to raise S/L. 

Louisiana 70 N 70 65 70 65 Eff 8/15/97 - Interstate or controlled access highway 70 MPH; multilane divided highway with partial or no controlled access 65 MPH. LA

DOT to develop criteria to determine which portions of a highway

warrant a speed limit lower than the speed limits established by new

law.

Maine 70 N 65 55 65 55

Maryland 70 Y 65 55 65 55 Eff 7/18/96 - Gov approved speed limit increases on 85 additional

miles of highway currently posted at 55 mph. Limits will be increased

to 60 mph on 65 miles of highway and to 65 mph on 20 miles of

highway. (total mileage posted above 55 mph will be 333 miles). 

Includes: Interstate 81 near the West Virginia and Pennsylvania state

lines (to 65 mph), and Interstate 81 in the vicinity of Hagerstown (to 60

mph). 

Massachusetts 65 Y 65 55 65 55 (1/29/96) Raised to 65 mph on 13 major Interstates and highways, 2

sections of Turnpike(1/29/96). (7/1/96) Massachusetts Turnpike,

Interstate 90, between I-95/Route 128 and the New York State line had

several sections raised from 55 mph to 65 mph (the entire turnpike is

now 65 mph from I-95 to the New York State line on the turnpike).

Michigan 70 Y 65 55 65 55 Eff 12/18/96 70 mph permanent on about 500 miles of roads after

safety study which began 8/96. Includes parts of I-94, I-69, I-96, I-75,

US-131. Currently, most highways posted at 65 mph; 170 miles of

urban highways at 55 mph; 500 mostly rural at 70 mph.

Minnesota 65 Y 70 70 65 95 Eff 7/1/97 - Increase 70 mph on approximately 650 miles of interstate

freeway in Greater Minnesota (I-35, I-94 and I-90). Increase from 55

mph to 65 mph on approx. 660 miles of non-interstate freeway and

expressways (4-lane divided highways). Approximately 120 miles of

non-interstate freeway and expressways will remain at 55 mph. All

two-lane state highways (approx.10,000 miles) will remain 55 mph. 

Mississippi 70 Y 70 65 70 65 Eff 3/12/96

Missouri 70 Y 70/60 65 70/60 65 Eff 3/13/96 - State can raise any road to 70 mph with safety study.
Pre Exceeds Cars Trucks August 15, 1997

State NMSL

Max

Old

 NMSL

Interstate Other Interstate Other NOTES: The following is provided for information purposes only. Every

effort has been made to ensure that the information is accurate as of

the above date. Some States may have made administrative or other

changes that are not reflected here. Please contact the individual

State for the latest information.

(mph) Provisions Primary Primary

A - 4

Montana unlimited Y * * 65* 60* Eff 12/8/95 - No max posted limit “reasonable and prudent” (cars/day);

65 mph Interstate, 55 mph all other (cars/night); Trucks max 65 day/

night on Interstate; Triple truck comb. 55 mph (day/night) all roads.

Nebraska 75 Y 75 60 75 60 4/15/96 Gov signed - Eff 6/1/96 increase Interstates to 75 mph (urban

60 mph); Eff 9/1/96 - 2 lane roads 60 mph; 4 lane expressways 65

mph with some exceptions (unless Dept. Of Roads determines

otherwise) Substantial increase in fines.

Nevada unlimited Y 75 70 75 55 75 and 70 (12/8/95)

New

Hampshire

70 N 65 55 65 55

New Jersey 70 N 55 50 55 50

New Mexico 70 Y 75 60 75 60 Eff 5/13/96 - 75 mph on interstates; 70 mph on 4 lane with shoulders;

65 on 2 lanes with shoulders; 60 mph on 2 lane highways without

shoulders.

New York 55 N 65 55 65 55

North Carolina 70 Y 70 55 70 55 August, 1996 approximately 400 miles of Interstate to 70 MPH.

Effective Oct. 1, 1996, 340 miles of non-Interstate controlled access to

70 MPH based on DOT studies. 

North Dakota 75 Y 70 65 70 65 Eff 7/1/97 - Speed limits (subject to review by NDDOT) of 70 mph on

Interstates (day and night); 65 mph on 2-lane (day) and multi-lane

highways (day and night); and 55 mph on gravel roads (day and night)

and two-lane highways (night) 

Ohio 70 Y 65 55 55 55 Eff 2/29/96 Implement 5/29/96 - Buses to 65; maintains S/L for cars

and trucks for 120 days; can automatically raise Interstate and

freeways to 65 after 120 days if OH DOT, OH DPS and local

municipality agree to geometry and traffic patterns. After 360 days

raise or lower S/L to 65 for rural, divided, multi-lane hwys with same

conditions as 120 day option

Oklahoma 70 Y 75/70* 65/55* 75/70* 55 *Gov raised to 70 on Interstates (60 for urban) and other 4 lane

divided; 65 other state roads and hwys; 55 on state roads and other

hwys night. Turnpike auth raised to 75 rural (min 50); 65 urban (min

40) (6/13/96)

Oregon 75 N 65 55 55 55

Pennsylvania 65 Y 65 65 65 65 Parts of US 15, 22/232, 119, 220, 222, 422, PA 43 to 65 mph (7/13/95)

Rhode Island 60 Y 65 55 65 55 Eff 5/12/96 - Increase to 65 mph on approx 45 miles of Interstate

highways.
Pre Exceeds Cars Trucks August 15, 1997

State NMSL

Max

Old

 NMSL

Interstate Other Interstate Other NOTES: The following is provided for information purposes only. Every

effort has been made to ensure that the information is accurate as of

the above date. Some States may have made administrative or other

changes that are not reflected here. Please contact the individual

State for the latest information.

(mph) Provisions Primary Primary

A - 5

Puerto Rico 65 N 55 55 55 55 No change expected

South Carolina 70 N 65 55 65 55 Bill to raise Interstate to 70 passed House and in Senate.

South Dakota 75 Y 75 65 75 65 Eff 4/1/96 - 75 mph Interstates, 65 mph major 2 lane highways (40

counties will keep 55 mph, 11 to 65 mph, rest undecided (3/25/96)

Tennessee 75 Y 65 55 65 55 Eff 4/22/96 - Legislature approved raising some urban Interstates to 65

mph. (Memphis, Jackson, Knoxville, Chattanooga, Tri-Cities areas)

Eff 07/01/96 - divided 4-lane limited access to 65 mph.

Texas 70 Y 70 70 65 60 Eff 12/8/95 - Cars - 70 day/65 night; 60 day/55 night for trucks - on all

roads. (3/25/96) TX DOT studies indicate about 23,000 miles will be

70 mph (7/15/96) Texas Transportation Commission approved speed

limits lower than the state maximum of 70 mph on about half of the

State’s 40,748 farm-to-market system. 

Utah 70 Y 75 55 75 55 Gov signed bill 3/13/96 - Pending UT DOT posting signs

Vermont 65 N 65 50 65 50

Virginia 70 Y 65 55 65 55 Dulles Greenway (private, urban, controlled access toll road) raised to

65. Other increases defeated (2/96)

Washington 70 Y 70 55 60 55 Eff 3/11/96

West Virginia 70 N 65 55 65 55 Legislation introduced to allow Commissioner to raise to 70 mph (2/96)

Wisconsin 70 N 65 55 65 55 Bill sent to Gov - increase to 65 on multilane roads after safety study.

Wyoming 75 Y 75 65 75 65 75 rural Interstates; 60 urban Interstates; 65 on 4 and 2 lane roads;

some secondary and mountainous roads remain at 55. (being studied)

1/24/96
B - 1

APPENDIX B -- FEDERAL REGISTER NOTICES
30

 Traffic Safety Facts 1994: Speed, U. S. Department of Transportation, NHTSA,

National Center for Statistics and Analysis, 400 Seventh Street, S. W., Washington, DC 20590.

B - 2

National Highway Traffic Safety Administration

Federal Highway Administration

[Docket No. 96-047-NO1]

Study of State Costs and Benefits Associated with Repeal of the National Maximum Speed Limit (NMSL)

AGENCY: National Highway Traffic Safety Administration (NHTSA) and Federal Highway Administration

(FHWA), Department of Transportation (DOT).

ACTION: Notice and request for comments.

SUMMARY: This notice invites comments, suggestions and recommendations from State highway and traffic

safety officials, highway safety organizations, researchers, and others with an interest in the potential relationship

between increases in the speed limit and increases in motor vehicle fatalities and injuries. Specifically, in those

States that have raised their speed limits beyond that permitted by the former NMSL, this notice solicits the

participation and cooperation of the respective State highway safety officials in the preparation of the study of

costs and benefits associated with the repeal of the NMSL, pursuant to Section 347 of the National Highway

System Designation Act of 1995.

DATES: Comments are due no later than August 5, 1996.

ADDRESS: Written comments should refer to the docket number of this notice and should be submitted to: 

Docket Section, NHTSA, Room 5109, Nassif Building, 400 Seventh Street, SW, Washington, DC 20590. 

Docket hours are 9:30 am to 4:00 pm EST.

FOR FURTHER INFORMATION CONTACT: In NHTSA, Delmas Johnson, National Center for Statistics

and Analysis, Telephone 202/366-5382, Fax 202/366-7078, Internet address is djohnson@nhtsa.dot.gov. In

FHWA, Suzanne Stack, Office of Highway Safety, Telephone 202/366-2620, Fax 202/366-2249, Internet

address is sjstack@intergate.dot.gov.

SUPPLEMENTARY INFORMATION: Speeding (exceeding the posted speed limit or driving too fast for

conditions) is one of the most prevalent factors contributing to motor vehicle crashes, particularly fatal crashes. 

In calendar year 1994, speeding was a factor in 30 percent of all fatal crashes, and NHTSA estimates that 12,480

lives were lost in speed-related crashes. NHTSA estimates that an additional 23,000 persons sustained critical

injuries, 60,000 sustained moderate injuries, and 500,000 sustained minor injuries, for a total of an estimated

583,000 persons injured in speed-related crashes in 1994. NHTSA estimates the 1994 costs of speed-related

crashes to be more than $23 billion.30

The National Maximum Speed Limit (NMSL), enacted during the Arab oil embargo of 1973 to conserve

fuel, was set at 55 miles per hour (MPH). By March 1974, all States were in compliance with the NMSL. In

addition to conserving fuel, the annual traffic fatality toll declined from 54,052 in 1973 to 45,196 in 1974, a drop

of over 16%. As a result of the enormous safety benefits in the form of the reduction in traffic fatalities, the

Congress passed Public Law (P. L.) 93-643, making the NMSL permanent. P. L. 93-643 also required every

State to certify that the NMSL was being enforced.
31

 The Life-Saving Benefits of the 55 MPH NMSL: Report of the NHTSA/FHWA Task

Force, U. S. Department of Transportation, DOT HS 805-559, October 1980. 

32 55: A Decade of Experience, TRB Special Report 204, National Research Council,

Washington DC, 1984.

33 Effects of the 65 MPH Speed Limit through 1990: A Report to Congress, U. S.

Department of Transportation, NHTSA, Washington, DC, May 1992.

B - 3

In 1978, the Congress enacted the Surface Transportation Assistance Act (STAA), P. L. 95-599. The

STAA required the States to submit data on the percentage of motor vehicles exceeding 55 MPH on public

highways with a 55 MPH posted speed limit.

Following the enactment of the NMSL, numerous studies of the benefits and costs of the legislation were

conducted. A joint NHTSA/FHWA task force, charged with determining the safety benefits of the NMSL,

conducted one of these studies. The NHTSA/FHWA task force concluded that while the “... determination of a

precise, accurate estimate of lives saved by the NMSL ... is problematic, there were 20,000 to 30,000 lives saved

by the NMSL during the period 1974 - 1978.”31

 The STAA of 1982 required that a study of the ”benefits, both human and economic” of the NMSL,

with “particular attention to savings to the taxpayers ...” be conducted by the National Academy of Sciences’

Transportation Research Board (TRB). In 1984, TRB published its special report, 55: A Decade of 

Experience.

32 The TRB study, conducted by a 19 member committee composed of experts from a wide range of

disciplines needed to evaluate the costs and benefits of the NMSL, represents one of the most thorough and

extensive examinations of this important safety issue. Although the TRB committee recognized the inherent

difficulties associated with attempts to accurately estimate the safety, economic, and energy benefits of the

NMSL, the study concluded that annually 3,000 to 5,000 fewer traffic fatalities, a savings of $2 billion in fuel

costs, a savings of $65 million in taxpayer costs were the result of the NMSL, along with an increase of 1 billion

hours in travel time. The TRB study also recognized several unresolved issues, including: the impact of

noncompliance; the containment of higher speeds, if permitted, on a limited subset of roads; and whether the

control of the speed limit is a state or federal responsibility.

In 1987, the Surface Transportation and Uniform Relocation Assistance Act granted the states the

authority to raise the speed limit, not to exceed 65 MPH, on portions of the rural Interstate system. Thirty-eight

states raised speed limits on rural Interstates to 65 MPH in 1987, and two additional states adopted the 65 MPH

speed limit on rural Interstates in 1988, bringing approximately 90 percent of the 34,000 rural Interstate mileage

to 65 MPH. Congress asked for an evaluation of the effects of the 65 MPH speed limit on rural Interstate traffic

fatalities for the period 1987 through 1989. NHTSA published the results of this evaluation in several reports to

Congress, the last of which was published in 199233, estimating the 1990 fatality toll on rural Interstates in the 38

states with 65 MPH limits to be “30 percent greater than might have been expected” or an increase of about 500

fatalities.

National Highway System (NHS)

Designation Act

The National Highway System Designation Act (hereinafter referred to as “the NHS Act”) of 1995 (P. L.

104-59) was signed into law on November 28, 1995. The NHS Act, among other things, established the

National Highway System and eliminated the Federal mandate for the NMSL. In addition, Section 347 of the

NHS Act required the Secretary of Transportation to study the impact of states’ actions to raise speed limits

above 55/65 MPH:

Not later than September 30, 1997, the Secretary, in cooperation with any State which raises any speed limit in such State

to a level above the level permitted under section 154 of title 23, United States Code, as such section was in effect on

September 15, 1995, shall prepare and submit to Congress a study of-
B - 4

(1) the costs to such State of deaths and injuries resulting from motor vehicle crashes; and

(2) the benefits associated with the repeal of the national maximum speed limit.

Rep. James L. Oberstar, in remarks on his amendment which led to the requirement contained in P. L.

104-59, elaborated on the issues that the study (hereinafter referred to as the “NHS Act study”) should addressTo provide meaningful, useful information, the report should include information on the costs before the State changes its

safety laws, and after. It would thus be my intent that the Secretary’s report, due September 30, 1997, include information

on the costs of motor vehicle crashes in the year before changes go into effect; and again a year later.

The report should include, at a minimum, the costs of acute, rehabilitative and long-term medical care, sources of

reimbursement and the extent to which these sources of reimbursement and the extent to which these sources cover actual

costs, and the costs to all levels of government, to employers, and others.

All States are not alike. Each State will want to know its own data, so that it can determine whether its problems are

coming from alcohol-related or speed-related causes, from not wearing seatbelts and helmets, or other causes, and perhaps

adjust its laws accordingly.

The report should therefore also include additional factors such as whether excess speed or alcohol were involved in the

accident, whether seat belts and motorcycle helmets were used by those involved in the crash, and any other factors the

Secretary may wish to add or State to know.

NHTSA and FHWA (hereinafter referred to as “the agencies”) propose a strategy for meeting the

legislative requirements, as stated in Section 347 of the Act, in this notice. The proposed strategy is intended to

address the complexities of determining the costs and benefits of increased speed limits, while meeting the

Congressional deadline of September 30, 1997. A major aspect of the proposed strategy is an emphasis on

cooperation between the agencies and the States that have increased their speed limits, as stated in the

legislation, for preparation of the study. It is important that the States participate in the NHS study process, as

determining the impact of increased speed limits in a particular State will necessitate that an analysis of statespecific data be conducted. In addition, the proposed strategy uses an approach similar to that used in the

extensive study conducted by TRB, in order to capitalize on the thorough work done by the TRB committee to

examine costs and benefits resulting from decreasing the speed limit.

Data Needs

The agencies have identified several major categories of data needed, as a minimum, to conduct the NHS

Act study. These data are critical to studying, to a reasonable degree, the issues related to determining the costs

and benefits of increasing speed limits. The following table presents the minimum data requirements for

addressing key components of estimating the safety impact of increasing speed limits. It will be important to

collect the data described in the following table for a minimum time period of one year before the speed limit

change vs. one year after the speed limit change, if at all possible. 
B - 5

Minimum Data Requirements for Conducting NHS Act Study 

Purpose Data Description Performing Organization

Background Effective Dates of Change in

Limits, Roadway Types, New

Limit(s), Types of Vehicles

Covered,.

States

Determining the Impact of

Increased Speed Limits on

Traffic Fatalities

Fatalities - Fatality Analysis

Reporting System (FARS)

States -- state impacts

NHTSA -- national impacts

Determining the Impact of

Increased Speed Limits on

Injuries

Injury Crashes and Injured

Persons - by road, vehicle

types, by speed limit, alcohol

involvement, helmet use.

States

Determining the Impact of

Increased Speed Limits on

Crashes

Crashes of All Severities - by

road, vehicle types, by speed

limit, alcohol involvement,

helmet use.

States

Estimating Benefits Reduced Travel Time -

Commercial & Public

Transportation

States

Estimating Costs Economic Cost of Crashes -

Before vs. After Speed Limit

Changes, Medical Costs of

Crash-Involved Persons

States -- state impacts

NHTSA -- national impacts

Determining Exposure Vehicle Miles Traveled and

Speed Distribution

States/FHWA

 

The agencies request comments from the States and other interested highway safety officials on the

proposed data shown above. Specifically, the agencies request comments regarding data availability specific to

relevant time periods, data accuracy, suggestions for additional data not mentioned above, and any problems

inherent in collecting and/or reporting these data.
B - 6

Proposed NHS Study Outline

The agencies propose the following outline for the NHS study content. The proposed outline presents a

structure for addressing the entire range of issues identified in Section 347 of the Act. The outline is an

adaptation of the structure of the TRB special report, 55: A Decade of Experience. While the data described in

the table shown in the previous section, Data Needs, represents the minimum data requirement for conducting

the study, the following outline presents an approach for a thorough treatment of the entire range of issues

associated with estimating costs and benefits of increased speed limits. The agencies recognize that data may not

be available for all of these areas, but in the interest of completeness and to closely follow the TRB report’s

content, these areas are included. In some instances, collection of specific data may not be possible. However,

estimates may be available from past relationships and/or research, or applying some type of multiplicative

factors derived from other data sources.

Draft Outline for NHS Study

I. Introduction

A. Scope of the study / legislative language

B. Legislative history of NMSL and requirements

C. Summary of previous experiences

1. Safety

2. Economic

II. Effects on Travel and Vehicle Speeds

A. The highway system: mileage, travel and safety

B. Amount of travel affected

C. Speed and travel changes across highway systems

D. Adequacy of speed data for addressing issues

III. Impacts of Increased Speed Limits

A. Travel Time (Personal, work, etc.)

B. Required Monitoring & Compliance

C. Fuel Consumption

D. Highway Safety (Fatalities, Injuries, Property Damage, etc.)

IV. Economic Impacts of Increased Speed Limits

A. Value of the Effects on Travel Time

B. Required Monitoring & Compliance Certification Costs

C. Costs Associated with Fuel Consumption

D. Motor Vehicle Crash Costs (Medical Care, Lost Productivity,

Property Damage, etc.

V. Summary and Conclusions

The material outlined above poses a number of challenges to assessing the impacts of raised speed limits. 

First and foremost is the collection of appropriate data to address the safety and economic impacts. The crash

data collection should be straightforward, although the timing and availability of a sufficient amount of data to

meet the report’s current deadline may prove to be one of the biggest challenges. Another challenge will be in

the area of analyzing the data to provide estimates of effect.

The TRB’s report, 55: A Decade of Experience, is essentially a review of the existing literature on these

subjects, supplemented by what appears to be some new analysis at the national level, based on existing studies. 

The report contains hundreds of references of papers reviewed for consideration in their report. A copy of the
34 Interested parties may request a copy by contacting the TRB, National Research

Council, 2101 Constitution Avenue, NW, Washington, DC 20418. 

B - 7

TRB report has been placed in the docket.34 The report describes methods used to estimate various components

such as taxpayer costs and benefits, energy savings, and travel time. In many cases, external information was

used (such as the Nationwide Personal Transportation Study) to estimate, on a national level, the amount of

travel accounted for by work-related trips, and their average trip length. In some instances, changes proportional

to the changes in crashes, injuries and fatalities were assumed.

As stated earlier, one of the objectives of the current report is to study the effect of raised speed limits on,

“... the costs of acute, rehabilitative and long-term medical care, sources of reimbursement and the extent to

which these sources of reimbursement cover actual costs, and the costs to all levels of government, to employers,

and others.” This level of detail generally has been unavailable to the traffic safety community, with the possible

exception of special, small-scale studies. However, NHTSA recently completed a project, Crash Outcome Data

Evaluation Study (CODES), that consisted of grants to seven states. The CODES study employed methods

whereby statewide data from police crash reports, emergency medical services, hospital emergency departments,

hospital discharge files, claims and other sources were linked so that those people injured in motor vehicle

crashes could be followed through the health care system. A copy of the Report to Congress (DOT-HS-808-

347, February 1996) and the CODES Technical Report (DOT-HS-808-338, January 1996) have been placed in

the docket. Based upon the CODES experience, NHTSA continues to encourage states to link these data as a

resource for identifying and quantifying traffic safety problems within states, and for evaluating the health-care

consequences of various traffic safety policy decisions. In the absence of such linked databases within the states,

other approaches to estimating the economic effects on the health-care system will need to be employed.

Lastly, NHTSA’s last Report to Congress on the Effects of the 65 mph Speed Limit Through 1990

(DOT-HS-807-840, June 1992) has been placed in the docket. This report illustrates the type of analysis of

crash data that can be performed for estimating the effect of speed limit changes. In this report, a time series

regression model was used to estimate the data, using annual data from 1975 through 1986 as the baseline

period, and 1987 through 1990 as the 65 mph period. Fatalities on rural interstate highways in the 38 states that

increased their speed limits in 1987 were modeled as a function of fatalities on all other roads in these 38 states,

and a dummy (0,1) variable representing the absence/presence of the 65 mph speed limit. This approach resulted

in a model that fit the data well (i.e., 88 percent of the variation explained). In general, a longer time frame

permits more stable estimates than simply comparing the year before vs. the year after, and thus, would be

preferable for the current report.

Based on the above outline, the proposed NHS study would attempt to address a wide range of issues on

the benefits and costs of the increased speed limits, using a compilation of State-specific data and national

estimates. Chapter I - Introduction, would present an overview of the historical background on establishing

speed limits, specifically the NMSL, and a brief summary of findings from study of the costs and benefits of the

NMSL, similar to the material presented earlier in this notice in Supplementary Information. Chapter II - Effects

on Travel and Vehicle Speeds, would rely heavily on information received from the States with increased speed

limits, augmented by anecdotal information on the national impact. Chapter III - Impacts of Increased Speed

Limits, would present a detailed assessment, using data collected and analyzed by individual States, on the

estimated savings in reduced travel time and monitoring/compliance efforts and the estimated impact in terms of

increases in motor vehicle crashes, fatalities, injuries, traffic congestion, and fuel consumption. As such, Chapter

III encompasses a critical portion of the proposed study and will necessitate that the agencies rely upon the

individual States for detailed assessments of the impact of increased speed limits on crashes, particularly injury

and property damage crashes, traffic congestion, reduced air quality, and increased fuel consumption. It will be

extremely important to receive State information on these key areas for compiling the NHS study, as the agencies

will not have direct access to State specific data on these issues. Chapter IV - Economic Impacts of Increased

Speed Limits - would present an examination of the actual costs saved in reduction in travel time and the costs

incurred as a result of increases in the crash spectrum, fatalities, injuries, and property damage, in detail. As a
B - 8

result, Chapter IV extends the analysis of the data presented in Chapter III by supplementing estimates of

increases in motor vehicle crashes, with the economic cost of various components of crash costs. The agencies

plan to rely heavily on the State analyses for compiling Chapter IV and intends to augment, as necessary, the

State findings with economic cost estimates and a presentation of national estimates of economic costs, as well. 

Most importantly, the agencies will have to rely exclusively on State specific information for compiling one

particular component of Chapter IV, Section D - Impact on public revenues. Chapter V - Summary and

Conclusions - would present a summary of the State and National findings from previous chapters, along with

observations regarding difficulties encountered by the States and the agencies in the analytical process and

general conclusions.
B - 9

Proposed Schedule

The agencies propose the following schedule for completing the NHS study in order to meet the deadline

established by Section 347 of the Act. 

Proposed Schedule for Conducting NHS Study

Date Milestone

August 5, 1996 End 45-day comment period w/comments due to

NHTSA/FHWA.

September 27, 1996 Publish final notice on NHS Act study methodology and

summary of comments received.

October 1996 thru April 1997 Provide technical support to the States on an “as

requested” basis for preparing State-specific studies of the

costs/benefits of increased speed limits.

May 30, 1997 States’ individual studies on costs/benefits of increased

speed limits are due to NHTSA/FHWA.

June 30, 1997 NHTSA/FHWA complete draft NHS Act study report

including consolidation of individual State studies.

July 1997 Draft NHS study circulated for review within DOT and to

participating States.

August 1997 Final NHS study completed and reviewed/approved by

DOT.

September 30, 1997 NHS study sent to Congress.
B - 10

Issues Regarding Data Availability,

Proposed NHS Act Study Outline, and Schedule

The agencies recognize that the proposed NHS study outline, while comprehensive in addressing the

various aspects of determining the benefits and costs of increased speed limits, may present difficulties, based on

the timing of the schedule, particularly in terms of data availability. Data availability is a key concern for

completing the proposed study at the Federal and State levels. For example, while NHTSA maintains data on

traffic fatalities and fatal crashes for the nation in the Fatality Analysis Reporting System (FARS), FARS data for

1996 will be available for analysis in June 1997, three months from the legislative due date for the NHS Act

study. Additionally, 1996 data on vehicle miles traveled, a critical measure of exposure needed for fatality and

injury rate calculations, will be not available to FHWA until September 1997, at the same time the NHS Act

study is due to Congress. As a result, the agencies solicit comments on these proposed requirements, and are

particularly interested in answers to the following questions:

1. In the States with increased speed limits, are there data available in the State to address the specific

areas outlined in the proposed NHS Act study, especially Chapter III - Impacts of Increased Speed Limits and

Chapter IV - Economic Impacts of Increased Speed Limits? If so, to what extent?

2. Do plans currently exist within the State(s) to study the impact - safety and economic - of increased

speed limits? If yes, does the State anticipate meeting the proposed schedule for forwarding results of the study

to DOT? If there are no current plans to study the impact of increased speed limits, does the State intend to

participate in the proposed study effort by contributing information regarding the changes in the State related to

increased speed limits?

3. Is the proposed approach reasonable? Are there issues that should be studied that are not included in

the proposed outline? Are there issues included in the proposed outline that should be omitted or revised?

4. Is the proposed schedule reasonable? If not, what can reasonably be accomplished within the

proposed time frame? What is an alternative schedule that would be more reasonable?

5. Does the proposed schedule provide for a sufficient period of time to evaluate the effects of increased

speed limits? For example, the study is tasked with comparing one year before vs. one year after the change in

speed limits. States are asked to comment on the timing of their implemented or planned changes in the State

speed limit as it relates to the NHS Act study objectives.

The agencies invite public comment on the above questions and other areas of this notice. Interested

individuals, highway safety organizations, State highway officials, and others are encouraged to submit

comments on these and any related issues. It is requested (but not required) that ten (10) copies of each

comment be submitted. Written comments to the docket must be received on or before August 5, 1996. In

order to expedite review of this notice and the submission of comments, copies of this notice are being sent

simultaneously with issuance to members of the National Association of Governor’s Highway Safety

Representatives (NAGHSR) and the American Association of State Highway Safety and Traffic Officials

(AASHTO). Comments should not exceed fifteen (15) pages in length. Necessary attachments may be

appended to the submissions without regard to the fifteen page limit. This limitation is intended to encourage

commenters to detail their primary concerns in a concise manner. All comments received before the close of

business on the comment closing date listed above will be considered and will be available for examination in the

docket room at the above address both before and after that date. To the extent possible, comments filed after

the closing date will be considered. Those commenters wishing to be notified upon receipt of their comments by

the Docket should include a self-addressed, stamped envelope with their comments. Upon receipt of the

comments, the Docket supervisor will return the postcard by U.S. Mail.

Published June 19, 1996

Signed
B - 11

Donald C. Bischoff, 

Acting Executive Director, National Highway Traffic

Safety Administration

Anthony R. Kane,

Executive Director, Federal Highway

Administration

BILLING CODE 4910-59-P
 

35 55: A Decade of Experience, TRB Special Report 204, National Research Council,

Washington DC, 1984.

B - 12

National Highway Traffic Safety Administration

Federal Highway Administration

[Docket No. 96-047-NO2]

Study of State Costs and Benefits Associated with Repeal of the National Maximum Speed Limit (NMSL)

AGENCY: National Highway Traffic Safety Administration (NHTSA) and Federal Highway Administration

(FHWA), Department of Transportation (DOT).

ACTION: Final notice announcing NHTSA/FHWA plan to conduct a study of State costs and benefits

associated with the NMSL repeal, as required by Section 347 of the National Highway System (NHS)

Designation Act (Pub. L. 104-59).

SUMMARY: This notice is being issued to announce NHTSA’s and FHWA’s plan to conduct the study

(hereinafter referred to as the “NHS Act study”) of the State costs and benefits associated with repeal of the

National Maximum Speed Limit (NMSL), as required by the National Highway System (NHS) Designation Act

(Pub. L. 104-59). NHTSA and FHWA (hereinafter referred to as “the agencies”) published a notice in the

Federal Register (61 FR 31212) on June 19, 1996, inviting comments, suggestions, and recommendations from

State highway and traffic safety officials, highway safety organizations, researchers, and others on the agencies’

proposed strategy for conducting the NHS Act study. The proposed strategy, as described in the initial notice,

included a draft study outline, the minimum requirements for specific data from the States that have raised their

speed limits, and a proposed schedule for completing the NHS Act study in order to meet the September 30,

1997, deadline established by Section 347 of the Act. This notice summarizes comments from the States and

others on the proposed NHS Act Study and outlines the agencies’ plan to meet the legislative requirement, in

view of the concerns noted by the States.

FOR FURTHER INFORMATION CONTACT: In NHTSA, Delmas Johnson, National Center for Statistics

and Analysis, Telephone 202/366-5382, Fax 202/366-7078, Internet address is djohnson@nhtsa.dot.gov. In

FHWA, Suzanne Stack, Office of Highway Safety, Telephone 202/366-2620, Fax 202/366-2249, Internet

address is sjstack@intergate.dot.gov.

SUPPLEMENTARY INFORMATION: The National Maximum Speed Limit (NMSL), enacted by the

Congress during the Arab oil embargo of 1973 to conserve fuel, was initially set at 55 miles per hour (MPH). By

March 1974, all States were in compliance with the NMSL. The Congress later passed legislation to make the

NMSL permanent and to require the States to certify that the NMSL was being enforced. Congress also passed

legislation requiring that a study of the benefits of the NMSL be undertaken. The National Academy of

Sciences’ Transportation Research Board (TRB) conducted this study and in 1984, published its special report,

55: A Decade of Experience.

35 The TRB study, while one of the most thorough and extensive examinations of

this important safety issue, recognized the inherent difficulties associated with attempts to accurately estimate the

safety, economic, and energy benefits of the NMSL. Even with these difficulties, the TRB study concluded that

many lives and taxpayer dollars were saved each year with the NMSL. The TRB study also recognized several

unresolved issues, including whether the control of the speed limit is a state or Federal responsibility.
B - 13

In 1987, Congress passed legislation granting the states the authority to raise the speed limit to no more

than 65 MPH on the rural Interstate system and certain rural freeways. By 1988, forty states had raised limits on

rural Interstates to 65 MPH, bringing approximately 90 percent of the 34,000 rural Interstate mileage to 65

MPH. In 1995, the National Highway System Designation Act (hereinafter referred to as “the NHS Act”, Pub.

L. 104-59) was passed, establishing the National Highway System and eliminating the Federal mandate for the

NMSL. Section 347 of the NHS Act required the Secretary of Transportation to study the impact of actions to

raise speed limits above 55/65 MPH, “in cooperation with any State which raises any speed limit in such State to

a level above the level permitted under section 154 of title 23, United States Code...”, due September 30, 1997.

The agencies proposed a strategy for meeting the study requirements, as stated in Section 347 of the Act,

in the initial Federal Register (61 FR 31212) notice, published on June 19, 1996. The proposed strategy

emphasized cooperation between the agencies and the States that have increased their speed limits, as stated in

the legislation, for preparation of the study, along with a proposed schedule for completing the NHS Act study. 

The agencies recognized in the initial notice that the proposed NHS Act study outline, while comprehensive in

addressing the costs and benefits of increased speed limits, posed difficulties based on the proposed schedule,

particularly in terms of data availability. The initial notice requested comments on the reasonableness of the

proposed draft study outline, the feasibility of the proposed schedule, and the availability of state specific data.

This notice summarizes the comments received addressing the issues raised in the initial notice and

describes the agencies’ plan to meet the legislative requirement in view of the concerns identified in the

comments.

Summary of Comments

A total of 39 official comments to the docket were received from State agencies, private citizens,

National Motorists Association (NMA) members, and others. Nineteen (19) States were represented in the

official docket comments. Eighteen (18) of the 19 States commenting to the docket have increased limits since

the NMSL was repealed or are planning to do so. Many of the comments from the States included concerns

regarding the complexity and/or comprehensiveness of the agencies’ proposed study outline, often in terms of the

burden that would be placed upon the States. Many of the States commented regarding the unavailability of data

and the apparent difficulty in meeting the proposed schedule. Comments from private citizens generally

supported the repeal of the NMSL, with one exception. Several NMA members and officials commented,

expressing views supporting the NMSL repeal and criticizing the proposed study outline. Comments were also

received from the National Association of Governor’s Highway Safety Representatives (NAGHSR), the

Advocates for Highway and Auto Safety (AHAS), the American Trucking Association (ATA), and a consulting

firm, JCW Consulting.

Cooperation and participation from the States with increased speed limits is critical to conducting the

NHS Act study, as described in Section 347 of the Act. The States commenting to the docket recognized this

critical issue and generally commented in three specific areas: Study Methodology, Data Availability, and

Scheduling.

 

1. Study Methodology

While some of the States submitting comments to the docket indicated that the proposed approach was

“...solid” or “...reasonable”, most commented that the approach was too ambitious. The States also expressed

concerns, however, that the approach was too broad, posed an additional burden, and would be difficult to

accomplish due to the unavailability of data. NAGHSR commented that the proposed approach is reasonable

“...only if all states’ data were available..” AHAS commented that while the proposed approach was appropriate,

“...reliance on state analyses and failure to consider other...issues” were important concerns.

2. Data Availability

The issue of data availability was addressed to some extent in all of the comments received from the

States, along with some of the comments from private citizens and JCW Consulting. All of the States submitting
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comments to the docket expressed concerns related to the unavailability of data to meet the proposed NHS Act

study outline. Among the reasons cited for lack of available data were: specific data not presently collected by

the states, e.g., speed monitoring, medical costs related to crash injuries; not possible to provide data in time to

meet the proposed schedule; lack of resources; data currently collected inadequate for determining benefits and

costs specifically related to increased speeds. Some States suggested that the agencies develop standards for

estimating benefits and costs, particularly in the absence of specific state data collection efforts.

3. Scheduling

The States commenting to the docket consistently voiced the concern that the proposed schedule was

ambitious, unreasonable, impossible, or unrealistic. One State suggested extending the proposed schedule one

year past the September 30, 1997, deadline to avoid creating a “second-rate report.” Three of the 18 States

commenting to the docket indicated that plans existed to study the impact of increased speed limits in their

respective State. However, all three States indicated that results from such studies would not be available in time

to submit to the agencies for inclusion in the NHS Act Study. A concern regarding the before and after time

frame of one year, as specified in Section 347 of the Act, was also expressed by several States and the ATA. 

ATA suggested that the agencies use a ten year baseline for conducting the study. Many of the States

commented that one year of data after the increased limits became effective may not be adequate for analysis to

determine impact. This issue is further complicated in that only nine States (Arizona, California, Illinois,

Massachusetts, Montana, Nevada, Oklahoma, Pennsylvania, and Wyoming) may have had increased speed limits

in place for at least nine months of calendar year 1996. This would mean, at best, that only one calendar year of

data for the time frame after the increased speed limit was in place would be available for these nine States. 

States with increased speed limits becoming effective later in 1996, therefore, would not have one full year of

final data to forward to the agencies prior to the report due date of September 30, 1997. 

Analytical Challenges

Due to the concerns expressed by the States and others in the areas of study methodology, data

availability, and scheduling, the agencies are faced with several major analytical challenges to conducting the

NHS Act study. Several of the States specifically indicated that certain types of data, e.g., decreased travel time,

increased fuel consumption, and increased or decreased medical costs, would not be available in time for

inclusion in the report or was not presently being collected. Without this type of information from the States, it

will be difficult for the agencies to address the entire range of benefits due to increased speed limits in the NHS

Act study. The issue of data availability is further complicated in that many States are selectively increasing

speed limits on certain road segments and/or roadway types, e.g., 4-lane roads, rather than systemwide, e.g., all

Interstates. While the selective application of increased speed limits is indicative of the cautiousness on the part

of many States in adopting higher limits, it further complicates the issue of data availability by necessitating the

analysis of data by road segment. At the national level, determining the impact of increased speed limits on

traffic fatalities will be limited to the latest available data from the Fatality Analysis Reporting System (FARS) for

calendar 1996, focusing on the nine States that have had increased speed limits in place for most or all of 1996. 

Finally, determining the impact of increased speed limits related to the amount of vehicle miles traveled and the

distribution of vehicle speeds on affected roadways will be limited at best to the preliminary information available

to the agencies in the summer of 1997.

The agencies’ final plan for conducting the NHS Act study, in view of the States’ concerns and the

analytical challenges discussed above, is described in the following section.

NHS Act Study Data

The initial Federal Register notice described several major categories of data the agencies needed, as a

minimum, for addressing critical components of estimating the impacts of increasing speed limits. Based on the

comments from the States and others in the area of data availability, the agencies plan to conduct the NHS Act
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study using the data described in the following table. This table represents a subset of the minimum data

requirements included in the initial Federal Register notice. 
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NHS Act Study Data & Outline

Purpose Data Description Performing Organization

Background Effective Dates of Change in

Limits, Roadway Types, New

Limit(s), Types of Vehicles

Covered

NHTSA/FHWA & States

Determining the Impact of

Increased Speed Limits on

Traffic Fatalities

Fatalities - 1996 Fatality

Analysis Reporting System

(FARS) 

NHTSA -- national estimates

& impact on limited number of

States

Estimating Costs Economic Cost of Crashes -

Before vs. After Speed Limit

Changes, Costs of Fatalities

NHTSA -- national estimates

Determining Exposure Vehicle Miles Traveled and

Speed Distribution

FHWA -- VMT: preliminary

estimates, if available; Speed

monitoring: from those States

making voluntary submissions

 

As discussed in Analytical Challenges, the agencies’ ability to address the impacts of increased speed

limits on injury and other crashes and estimating benefits in the NHS Act study will depend on what the States

are able to provide within the study schedule. The agencies plan to use a methodology similar to that used in

NHTSA’s last Report to Congress on the Effects of the 65 mph Speed Limit Through 1990 (DOT-HS-807-840,

June 1992). This report illustrates the type of analysis of crash data that can be performed for estimating the

effect of speed limit changes. In this report, a time series regression model was used to estimate the data, using

annual data from 1975 through 1986 as the baseline period, and 1987 through 1990 as the 65 mph period. 

Fatalities on rural interstate highways in the 38 states that increased their speed limits in 1987 were modeled as a

function of fatalities on all other roads in these 38 states, and a dummy (0,1) variable representing the

absence/presence of the 65 mph speed limit. This approach resulted in a model that fit the data well (i.e., 88

percent of the variation explained).

In general, a longer time frame permits more stable estimates than simply comparing the year before vs. the year

after, and thus, would be preferable for the current report. 

Schedule for Conducting the NHS Act Study

The agencies plan to conduct the NHS Act study within the following schedule in order to meet the

deadline established by Section 347 of the Act.
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Schedule for Conducting NHS Study

Date Milestone

[insert date of publication in the

Federal Register]

Publish final notice on NHS Act study plan and summary

of comments received in response to initial notice.

April 1 - May 30, 1997 Informally canvas States on the availability of any Statespecific studies on the impact of increased speed limits.

June 30, 1997 NHTSA/FHWA complete draft NHS Act study report

including consolidation of individual State studies, as

available.

July 1997 Draft NHS study circulated for review within DOT (and

specific States, as appropriate).

August 1997 Final NHS study completed and reviewed/approved by

DOT.

September 30, 1997 Final NHS study sent to Congress.

The NHS Act Study as outlined above will provide the agencies and Congress with a preliminary

assessment of the impact of increased speed limits for a limited number of States. The agencies plan to continue

informally to communicate with the States regarding the impact of increased speed limits, as more States have

had the increased limits in effect for longer time periods.

Published November 27, 1996

Signed 

Donald C. Bischoff, 

Executive Director, National Highway Traffic

Safety Administration

Anthony R. Kane,

Executive Director, Federal Highway

Administration

BILLING CODE 4910-59-P
[ This page intentionally left blank. ]
U.S. Department

of Transportation

National Highway

Traffic Safety

Administration

400 Seventh St., S.W.

Washington, D.C. 20590

Official Business

Penalty for Private Use $300

DOT HS 808 637

NRD-31

February 1998