ohio department of public safety · 70 mph that occurred in 2013. this speed limit increase...

Ohio Department of Public Safety

June 2017

Speed Limit Analysis – 70 MPH June 2017

1

Executive Summary

The Ohio State Highway Patrol Speed Limit Analysis – 70 MPH provides important information

concerning crashes on Ohio’s roadways before and after the recent speed limit increase from 65 mph to

70 mph that occurred in 2013. This speed limit increase impacted approximately 570 miles of rural

interstates (effective 7/1/2013) and 398 miles of rural freeways (effective 9/29/2013). Researchers

examined crash data from two years before (i.e., 2011-2012) and two years after (i.e., 2014-2015) the

speed limit change. The analyses and results presented in this report are offered to help better

understand the safety impacts of this recent speed limit increase. Notable findings include:

24% increase in crashes on 70 mph roads from before (7,884) to after (9,812) the speed limit

change. This includes 22% more fatal and injury crashes (1,915 to 2,341).

27% increase in commercial-involved crashes on 70 mph roads (2,184 to 2,775), including a 33%

increase in fatal and injury crashes (490 to 651).

16% increase in speed-related crashes on 70 mph roads (4,525 to 5,254). This includes an 18%

increase in fatal and injury crashes (1,270 to 1,498).

66% increase in lane change-related crashes on 70 mph roads (1,391 to 2,307). This includes

66% more fatal and injury crashes (368 to 610).

20% increase in rear-end crashes on 70 mph roads (1,182 to 1,416), including a 35% increase in

fatal and injury crashes (453 to 611).

23% increase in sideswipe (same direction) crashes on 70 mph roads (1,066 to 1,316). This

includes a 23% increase in fatal and injury crashes (185 to 228).

57% increase in weekend crashes (i.e., Saturday-Sunday) on 70 mph roads (1,975 to 3,102).

78% of five mile segments on 70 mph roads showed an increase in crashes from before to after

the speed limit change.

Results from a linear regression model revealed statistically significant increases in severe (i.e.,

fatal and injury) crashes on 70 mph roads after the speed limit change.


2

Crash Comparison by Five Mile Segments


3

Comparison of Major Findings

Before Period 1/1/2011 – 12/31/2012

After Period 1/1/2014 – 12/31/2015

Interstates Freeways All 70 mph Roads All Other Roads

Fatal Crashes -5% change

(2 fewer crashes) +58% change

(7 more crashes) +9% change

(5 more crashes) -3% change

(50 fewer crashes)

Injury Crashes +21% change




(984 fewer crashes)

PDO Crashes +23% change

(1,121 more crashes) +32% change



(1,881 more crashes)

Total Crashes +23% change



(1,928 more crashes) +0.2% change

(847 more crashes) Vehicles

Commercial Crashes

+23% change (450 more crashes)



+9% change (3,364 more crashes)

Commercial At-Fault Crashes




+7% change (1,498 more crashes)

Motorcycle Crashes




-12% change (905 fewer crashes)

Drivers Young Driver

Crashes +20% change




(7,463 fewer crashes) Older Driver

Crashes +23% change




(7,755 more crashes) OVI-Related

Crashes +24% change


(23 fewer crashes) +9% change


(372 more crashes)

Contributing Circumstances Speed-Related

Crashes +13% change




(12,164 more crashes) Lane Change-

Related Crashes +71% change





Manner of Collision

Rear-End Crashes +16% change




(2,186 fewer crashes) Sideswipe (Same

Direction) Crashes +21% change





Temporal Factors

Weekend +61% change




(1,061 more crashes) Best Environ.

Conditions +8% change




(5,847 fewer crashes) Interstates: ~570 miles of rural interstates that increased speed limits to 70 mph on 7/1/2013.

Freeways: ~398 miles of rural freeways (i.e., US and State routes) that increased speed limits to 70 mph on 9/29/2013. Does not include 19.5

miles of US-24 and 9 miles of US-33 that were newly constructed roadways not open during the entire before period.

All 70 MPH Roads: all roads (i.e., interstates and freeways) that increased speed limits to 70 mph in 2013.

All Other Roads: all other roads in Ohio that did not experience an increase from 65 to 70 mph in 2013.


4

Ohio Roads Increased to 70 mph in 2013


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Data Parameters

Before: January 1, 2011 – December 31, 2012

After: January 1, 2014 – December 31, 2015

Interstates: ~570 miles of rural interstates that increased speed limits to 70 mph on 7/1/2013.

Freeways: ~398 miles of rural freeways (i.e., US and State routes) that increased speed limits to

70 mph on 9/29/2013; does not include 19.5 miles of US-24 and 9 miles of US-33 (newly

constructed roadways not open during the entire before period).

All 70 MPH Roads: all roads (i.e., interstates and freeways) that increased speed limits to 70 mph in

2013.

All Other Roads: all other roads in Ohio that did not experience an increase from 65 to 70 mph in 2013.

Crash: all crashes referenced in this report exclude those that were animal-related or occurred on

private property, an entrance/exit ramp, or in a construction zone.

Definitions and Acronyms

Angle: crash with CollisionTypeID = 6.

At-Fault CMV: crash with any UnitTypeID = 13-22 and CircumstanceID = 2-21.

Best Environmental Conditions: crash with PrimaryRoadConditionID = 1; PrimaryLightConditionID = 1;

WeatherConditionID = 1; and SecondaryLightConditionID = 7.

CMV: commercial motor vehicle (medium/heavy trucks or combo units greater than 10,000 pounds, including

buses); UnitTypeID = 13-22.

Day of Week: weekday (Monday-Friday); weekend (Saturday-Sunday).

Defective Equipment: crash with CircumstanceID = 19.

Lane Change-related: crash with CircumstanceID = 8 or 10.

Load Shift: crash with CircumstanceID = 20.

Motorcycle: crash with any UnitTypeID = 9 or 10.

MPH: miles per hour.

MVMT: million vehicle miles traveled.

Not Collision: crash with CollisionTypeID = 1.

OH1: official Ohio Traffic Crash report.

Older Driver: crash with any Driver Age 55-119.

Other Circumstance: crash with CircumstanceID = 2-4, 7, 11-14, 16, 18, 21, 23-30, or 99.

Other/Unknown Manner of Collision: crash with CollisionTypeID = 3-5, 8, or 9.

OVI: operating a vehicle while impaired (alcohol and/or drug related); crash with IsAlcoholRelated = yes and/or

IsDrugRelated = yes.

PDO: property damage only.

Rear-End: crash with CollisionTypeID = 2.

Season: spring (March-May); summer (June-August); fall (September-November); winter (December-February).

Severe: crash with a fatality and/or injury; SeverityID = 1 or 2.

Sideswipe (same direction): crash with CollisionTypeID = 7.

Speed-related: crash with CircumstanceID = 5, 6, 9, or 17; or IsSpeedRelated = yes.

Swerving: crash with CircumstanceID = 15.

Time of Day: night (12:00am-5:59am); morning (6:00am-11:59am); afternoon (12:00pm-5:59pm); evening

(6:00pm-11:59pm).

Young Driver: crash with any Driver Age 12-24.


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Table of Contents Executive Summary ............................................................................................................................................... 1

Map: Crash Comparison by Five Mile Segments .................................................................................................. 2

Comparison of Major Findings .............................................................................................................................. 3

Map: Ohio Roads Increased to 70 mph in 2013 ................................................................................................... 4

Data Parameters ................................................................................................................................................... 5

Definitions and Acronyms ..................................................................................................................................... 5

Traffic Safety on Ohio’s Roadways........................................................................................................................ 7

Historical Background on Speed Limits ................................................................................................................. 7

Identifying the Impact of Speed Limit Increases................................................................................................... 8

Methodology ........................................................................................................................................................ 9

Crash Analysis ....................................................................................................................................................... 9

Traffic Crashes ................................................................................................................................................ 10

Vehicles ........................................................................................................................................................... 10

Commercial Motor Vehicle Crashes ........................................................................................................... 10

At-Fault Commercial Motor Vehicle Crashes ............................................................................................. 11

Motorcycle Crashes .................................................................................................................................... 12

Drivers ............................................................................................................................................................. 12

Young Driver Crashes.................................................................................................................................. 12

Older Driver Crashes ................................................................................................................................... 13

OVI-Related Crashes ................................................................................................................................... 13

Contributing Circumstances ........................................................................................................................... 14

Speed-Related Crashes ............................................................................................................................... 14

Lane Change-Related Crashes .................................................................................................................... 15

Manner of Collision ........................................................................................................................................ 15

Rear-End Crashes ........................................................................................................................................ 16

Sideswipe (Same Direction) Crashes .......................................................................................................... 16

Temporal Factors ............................................................................................................................................ 17

Time of Day ................................................................................................................................................. 17

Day of Week ............................................................................................................................................... 17

Season ........................................................................................................................................................ 18

Best Environmental Conditions .................................................................................................................. 19

Location .......................................................................................................................................................... 19

Largest Change in Fatal and Injury Crashes ................................................................................................ 20

Regression Analysis ............................................................................................................................................. 21

Summary ............................................................................................................................................................. 23


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Traffic Safety on Ohio’s Roadways

Ohio ranks 35th among all states in terms of geographical size, but it maintains some of the largest

roadway infrastructures and volumes of traffic in the nation. More specifically, Ohio has over 121,000

miles of public roadways, including more than 1,500 miles of Interstate Highways; over 3,900 miles of US

Highways; and over 13,900 miles of State Highways.1 During the last 23 years, vehicle miles traveled in

Ohio (measured in millions; MVMT)

increased 21% (from 97,522 MVMT in

1993 to 117,829 MVMT in 2015; see

Figure 1). Conversely, traffic fatalities

decreased 25% during those same years

(from 1,479 to 1,110). Although Ohio

has experienced long-term trends of

decreased fatalities despite increased

exposure (i.e., MVMT), it is important to

examine the effects of the recent speed

limit increase on Ohio’s rural freeways

and interstates in 2013.

Historical Background on Speed Limits

During the past four decades, speed limits across the United States have experienced at least three

major changes.2 In 1974, the National Maximum Speed Law set a 55 miles per hour (mph) speed limit for

all states. Congress repealed this limit in 1987 by passing the Surface Transportation and Uniform

Relocation Assistance Act of 1987 which allowed states to raise the speed limit up to 65 mph on rural

interstates. Eight years later, the National Highway System Designation Act of 1995 removed federal

restrictions on speed limits by allowing states to set their own speed limits on the roadways within their

boundaries.

In Ohio, the first increase above 65 mph occurred in 2010 when the Ohio Turnpike Commission raised

the speed limit to 70 mph for all vehicles on the Ohio Turnpike (effective 4/1/2011).3 More recently,

during the 130th Ohio General Assembly, House Bill 51 proposed increasing the speed limit to 70 mph on

rural freeways.4 In 2013, Governor Kasich signed this into law (ORC 4511.21B14).5 This speed limit

increase went into effect for approximately 570 miles of rural interstate routes on 7/1/2013 and for 398

miles of rural freeways on 9/29/2013 (i.e., US and State Routes; see map on p. 3). To better understand

the impact of this recent speed limit increase, the next section provides a brief overview of previous

studies on the subject.

1 Ohio County Profiles. Retrieved December 23, 2016 from http://development.ohio.gov/files/research/C1001.pdf 2 For a brief review, see Friedman, L., Hedeker, D., & Richter, E. (2009). Long-term effects of repealing the national maximum speed limit in the United States. American Journal of Public Health, 99(9), 1626-1631. 3 Ohio Turnpike Commission Resolution No. 48-2010. Retrieved December 16, 2016 from http://www.ohioturnpike.org/docs/default-source/resolutions/resolutions-2010/48-2010_Speed_Limit_70_MPH.pdf 4 House Bill 51, 130th General Assembly. Retrieved December 16, 2016 from http://archives.legislature.state.oh.us/BillText130/130_HB_51_EN_N.pdf 5 Ohio Revised Code § 4511.21. Retrieved December 16, 2016 from http://codes.ohio.gov/orc/4511.21

60,000

70,000

80,000

90,000

100,000

110,000

120,000

130,000

400

600

800

1,000

1,200

1,400

1,600

19

93

19

95

19

97

19

99

20

01

20

03

20

05

20

07

20

09

20

11

20

13

20

15

MV

MT

Traf

fic

Fata

litie

s

Figure 1. Fatalities and MVMT in Ohio

Traffic Fatalities

MVMT


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Identifying the Impact of Speed Limit Increases

Over the years, an abundance of research has analyzed traffic crashes in order to improve traffic safety.

This research has largely focused on crash frequency and crash severity, and a variety of different

samples and analytic techniques have been used.6 For example, when considering the impact of

increased speed limits, some researchers examine only the subset of crashes on specific roadways

where the speed limit increase occurred,7 while others suggest looking at the system-wide effects by

analyzing statewide crashes.8 Additionally, to identify changes in traffic safety, one must have at least

two groups to compare. Previous research has used a variety of comparison groups including increased

roadways versus similar non-increased roadways;9 crashes on roads before versus after the increase;10

and states that raised speed limits versus states that did not.11

Moreover, analytic techniques have ranged from descriptive statistics12 and odds ratios13 to ordered

probit models14 and a variety of regression models including time series regression,15 Poisson mixed-

regression,16, 17 and multinomial logit models.18 Taken together, there is not a universal way to analyze

the impact of speed limit increases on traffic safety. Decisions about what data to analyze and how to

analyze it depend on data availability, areas of interest, and elapsed time since the speed limit change

occurred.

Finally, research on the effects of increased speed limits has yielded mixed results. Some studies show

increased speed limits are associated with more fatalities,19 both in states which increased from 55 to 65

mph20 and from 65 to 70 mph.21 However, at least one study showed a decrease in statewide fatality

rates for some states that increased from 55 to 65 mph.22 Still other research has shown no statistically

significant association between increased speed limits and crashes23 or crash severity24 for some states

that increased from 65 to 70 mph. Overall, findings on the effects of speed limit increases have been

6 For a comprehensive review, see Mannering, F., & Bhat, C. (2014). Analytic methods in accident research: Methodological frontier and future directions. Analytic Methods in Accident Research, 1, 1-22. 7 Baum, H., Lund, A., & Wells, J. (1989). The mortality consequences of raising the speed limit to 65 mph on rural interstates. American Journal of Public Health, 79(10), 1392-1395. 8 Lave, C., & Elias, P. (1994). Did the 65 mph speed limit save lives? Accident Analysis and Prevention, 26(1), 49-62. 9 Renski, H., Khattak, A., & Council, F. (1999). Impact of speed limit increases on crash injury severity: Analysis of single-vehicle crashes on North Carolina interstate highways. Transportation Research Board, 78th Annual Meeting (preprint). 10 Malyshkina, N., & Mannering, F. (2008). Effect of increases in speed limits on severities of injuries in accidents. Transportation Research Record, No. 2083, 122-127. 11 Lave, C., & Elias, P. (1994). 12 Souleyrette, R., Stout, T., & Carriquiry, A. (2009). Evaluation of Iowa’s 70 mph speed limit – 2.5 year update. Final Report (Center for Transportation Research and Education, Iowa State University). 13 Baum, H., Lund, A., & Wells, J. (1989). 14 Renski, H., Khattak, A., & Council, F. (1999). 15 Garber, S., & Graham, J. (1990). The effects of the new 65 mile-per-hour speed limit on rural highway fatalities: A state-by-state analysis. Accident Analysis and Prevention, 22(2), 137-149. 16 Friedman, L., Hedeker, D., & Richter, E. (2009). 17 Farmer, C. (2016). Relationship of traffic fatality rates to maximum state speed limits. Insurance Institute for Highway Safety, April 2016, 1-14. 18 Malyshkina, N., & Mannering, F. (2008). 19 Farmer, C. (2016). 20 Garber, S., & Graham, J. (1990). 21 Friedman, L., Hedeker, D., & Richter, E. (2009). 22 Lave, C., & Elias, P. (1994). 23 Souleyrette, R., Stout, T., & Carriquiry, A. (2009). 24 Malyshkina, N., & Mannering, F. (2008).


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inconsistent due, in part, to the variety of data sources, samples, and analytic techniques employed by

researchers. In this report, researchers analyzed data from Ohio crashes to gain a better understanding

of the impact on traffic safety related to the recent 70 mph speed limit increase in the state.

Methodology

Members of the Ohio State Highway Patrol’s (OSHP) Statistical Analysis Unit (SAU) identified crashes

from the State’s official electronic crash repository: Ohio Department of Public Safety’s (ODPS)

electronic crash database. While most previous research has been limited to examining overall crash

frequency or severity, the ODPS electronic crash database provides an abundance of information which

can be used in several important ways. First, the ODPS system contains location based information that

GIS Specialists can use to more accurately identify crash locations. Second, the ODPS system provides

data from all fields captured on the OH1 crash report. These include variables related to the crash as

well as persons and vehicles involved in the crash. Third, the retention period for electronic crash

records was recently extended from five to ten years, thereby allowing researchers more time to

thoroughly analyze crash issues. Overall, the ODPS electronic crash database allows for a detailed

analysis of crashes in the state.

Because the speed limit increase went into effect at different times for separate roadways during 2013,

this report compares crash data from two complete years before the increase (i.e., 2011-2012; ‘before’)

to two years after (i.e., 2014-2015; ‘after’). Crashes located on entrance or exit ramps, in construction

zones, on private property, or animal-related crashes were removed from the final sample. GIS

Specialists identified which crashes occurred on segments of interstate routes and freeways that

experienced the recent speed limit increase.25 Among the final sample of crashes, there were three

distinct subsamples of crashes that occurred on: 1) interstates that increased; 2) freeways that

increased; and 3) all other roads that did not experience an increase from 65 to 70 mph in 2013. The

primary focus of this report is on the 70 mph roadways. However, crashes on “all other roads” are

included here not as a similar comparison group but rather to provide perspective on the crash picture

on remaining roads in the state of Ohio.26

In addition to analyzing the frequency and severity of crashes before and after the speed limit increase,

the current report also explores the vehicles involved (e.g., CMV, motorcycle), drivers involved (e.g.,

young, older), contributing circumstances (e.g., speed-related), manner of collision (e.g., rear-end

collision), when crashes happened (e.g., weekend, season), and the location of crashes on specific

segments of roadway. Finally, a modeling analysis using linear regression was performed to explore the

effects of the speed limit increase while statistically controlling for other relevant variables.

Crash Analysis

Researchers first analyzed the frequency of crashes that occurred on roadways before and after the

speed limit increase followed by looking at smaller subsets of crashes. This includes an examination of

25 Because 19.5 miles of US-24 and 9 miles of US-33 were newly constructed roadways that were not open during the entire before period, crashes on those specific portions were excluded from the subset of freeways that increased. 26 Although a similar comparison group might be interstates and freeways that did not increase their speed limit to 70 mph, these are mostly urban roadways which differ characteristically from the rural roads on which the speed limit increased. Thus, this makes it difficult to find a similar comparison group.


10

the drivers, vehicles, circumstances, and locations which can all be influenced by changes in speed

limits. Additional analyses within these subsections are also presented, when sufficient sample size

allows for a reliable comparison.

Traffic Crashes

Crashes on 70 mph roads increased 24% from

before (7,884 crashes) to after (9,812 crashes)

the speed limit increase (see Table 1). This

includes a 23% increase on interstates (6,276 to

7,699) and a 31% increase on freeways (1,608

to 2,113). All other roads in Ohio experienced a

less than 1% increase in crashes (504,180 to

505,027) during the same time period.

In addition to looking at total crashes, it is

important to consider those with greater

severity such as fatal and injury crashes. Fatal

crashes on 70 mph interstates and freeways

went up 9% after the speed limit change (56 to

61), compared to a 3% decrease in fatal

crashes on all other roads (1,825 to 1,775)

during that time (see Figure 2). Moreover, the

number of injury crashes went up 23% on 70

mph roads (1,859 to 2,280) but decreased 1%

on all other roads (135,451 to 134,467). When

considering fatal and injury crashes together,

these increased 22% on 70 mph roads (1,915

to 2,341) and decreased 1% on all other roads

(137,276 to 136,242), a pattern of change that

was statistically significant [χ2(1) = 45.22, p <

.001].27

Vehicles

In addition to looking at all crashes on 70 mph roads, it is informative to explore how the speed limit

increase affected different types of vehicles. This section provides data on commercial motor vehicle

(CMV) involved crashes as well as motorcycle crashes.

Commercial Motor Vehicle Crashes

For the purposes of this report, commercial motor vehicles (CMVs) are medium/heavy trucks or combo

units greater than 10,000 pounds and include buses. Because larger vehicles require more time to

completely stop, allowing them to legally travel at faster speeds may subsequently result in more

27 A chi-square test of independence was used to compare the proportion of severe crashes by time period across road types. For more information see Siegel, S., & Castellan, N. J. (1988). Nonparametric statistics for the behavioral sciences (2nd ed.). New York, NY: McGraw-Hill.

9%

-3%

23%

-1%

25%

1%

-10%

0%

10%

20%

30%

Figure 2. Percent Change in Crashes by Severity

Fatal

Injury

PDO

All 70 mph Roads All Other Roads

Table 1. Crashes by Severity

Roadway Severity Before After Diff (%)

Interstates

Fatal 44 42 -5%

Injury 1,440 1,744 +21%

PDO 4,792 5,913 +23%

Total 6,276 7,699 +23%

Freeways

Fatal 12 19 +58%

Injury 419 536 +28%

PDO 1,177 1,558 +32%

Total 1,608 2,113 +31%

All 70 mph Roads

Fatal 56 61 +9%

Injury 1,859 2,280 +23%

PDO 5,969 7,471 +25%

Total 7,884 9,812 +24%

All Other Roads

Fatal 1,825 1,775 -3%

Injury 135,451 134,467 -1%

PDO 366,904 368,785 +1%

Total 504,180 505,027 +0.2%


11

crashes involving CMVs. Previous research on

Ohio Turnpike crashes showed a 32% increase

in CMV crashes when the speed limit increased

from 55 to 65 mph for commercial vehicles in

2004.28 Moreover, research has demonstrated

that crashes involving CMVs have more severe

injury levels than crashes not involving CMVs.29

Taken together, it is important to consider

whether the recent speed limit increase also

impacted CMV-involved crashes in the state.

When examining the subset of CMV-involved

crashes, those on 70 mph roads increased 27%

from before (2,184) to after (2,775) the speed

limit increase (see Table 2). More specifically,

CMV crashes increased 23% on interstates

(1,925 to 2,375) and 54% on freeways (259 to 400). On all other roads, commercial-related crashes

increased 9% (37,917 to 41,281) during this time frame.

Finally, the more severe crashes (i.e., fatal and injury) increased 33% (from 490 to 651) on all 70 mph

roadways. This includes a 30% increase on interstates (426 to 553) and a 53% increase on freeways (64

to 98). Commercial-involved fatal and injury crashes on all other roads increased 11% (from 7,759 to

8,626) during the same time. This pattern of change was statistically significant [χ2(1) = 8.33, p < .01].

At-Fault Commercial Motor Vehicle Crashes

A further way to analyze commercial-involved

crashes is by considering only those where the

CMV driver was at-fault in the crash. As shown

in Table 3, at-fault CMV crashes increased 27%

on 70 mph roads from before (1,414) to after

(1,798) the speed limit increase. This includes a

22% increase on interstates (1,250 to 1,524)

and a 67% increase on freeways (164 to 274).

At-fault CMV crashes on all other roads

experienced a 7% increase (21,784 to 23,282)

over this time. Additionally, examining only the

more severe crashes (i.e., fatal and injury)

revealed a 37% increase (286 to 391) on 70 mph

roads that included a 29% increase on

interstates (252 to 326) and a 91% increase on

freeways (34 to 65). On all other roads in the

28 Ohio State Highway Patrol, Office of Strategic Services (2007). Ohio Turnpike and parallel routes project – Safety and traffic report. Final Evaluation. 29 Castro, M., Paleti, R., & Bhat, C. (2013). A spatial generalized ordered response model to examine highway crash injury severity. Accident Analysis and Prevention, 52, 188-203.

Table 3. At-Fault CMV Crashes by Severity


Interstates

Fatal 6 11 +83%

Injury 246 315 +28%

PDO 998 1,198 +20%

Total 1,250 1,524 +22%

Freeways

Fatal 1 3 +200%

Injury 33 62 +88%

PDO 130 209 +61%

Total 164 274 +67%

All 70 mph Roads

Fatal 7 14 +100%

Injury 279 377 +35%

PDO 1,128 1,407 +25%

Total 1,414 1,798 +27%

All Other Roads

Fatal 73 73 0%

Injury 3,703 4,044 +9%

PDO 18,008 19,165 +6%

Total 21,784 23,282 +7%

Table 2. CMV Crashes by Severity


Interstates

Fatal 21 21 0%

Injury 405 532 +31%

PDO 1,499 1,822 +22%

Total 1,925 2,375 +23%

Freeways

Fatal 3 4 +33%

Injury 61 94 +54%

PDO 195 302 +55%

Total 259 400 +54%

All 70 mph Roads

Fatal 24 25 +4%

Injury 466 626 +34%

PDO 1,694 2,124 +25%

Total 2,184 2,775 +27%

All Other Roads

Fatal 248 251 +1%

Injury 7,511 8,375 +12%

PDO 30,158 32,655 +8%

Total 37,917 41,281 +9%


12

state, at-fault CMV fatal and injury crashes increased 9% during this time (3,776 to 4,117). This pattern

of change was significantly different across 70 mph roads versus all other roads [χ2(1) = 7.83, p < .01].

Motorcycle Crashes

In addition to CMV-involved crashes, it is also informative to examine crashes involving motorcycles as

these are associated with more severe injuries.30 Motorcycle-involved crashes on 70 mph roads

increased 16%, from 58 (before) to 67 (after; see Table 4).31 In particular, motorcycle crashes increased

9% on 70 mph interstates (46 to 50) and 42% on

70 mph freeways (12 to 17). On all other roads in

Ohio, motorcycle-involved crashes decreased

12% (7,657 to 6,752) during the same time

period. Although motorcycle crashes increased

on 70 mph roads and decreased on all other

roads, this pattern of change was not statistically

significant [χ2(1) = 2.26, p = .13].

Drivers

Researchers also looked at how the speed limit increase impacted the individuals involved in crashes.

This section provides results for crashes involving young, older, and impaired drivers.

Young Driver Crashes

For the purposes of this report, young driver

crashes include all crashes that involved at least

one driver under the age of 25. As shown in

Table 5, crashes involving young drivers

increased 22% on 70 mph roads (from 2,186 to

2,669 crashes). This includes a 20% increase on

interstates (1,704 to 2,043) and a 30% increase

on freeways (482 to 626). By comparison,

crashes involving young drivers decreased 4%

on all other roads in Ohio (188,748 to 181,285)

during the same time period. Similar trends

were seen in the subset of fatal and injury

crashes with these more severe crashes

increasing 15% on 70 mph roads (577 to 664)

but decreasing 5% on all other Ohio roads

(54,714 to 52,220) from before to after the speed limit increase. This pattern of change was statistically

significant [χ2(1) = 10.71, p < .01].

30 National Center for Statistics and Analysis. (2015, May). Motorcycles: 2013 data. (Traffic Safety Facts. Report No. DOT HS 812 148). Washington, DC: National Highway Traffic Safety Administration. 31 There are not enough motorcycle-involved crashes across the three severity levels to warrant a robust comparison; thus, only the total number of motorcycle-involved crashes are reported here.

Table 4. Motorcycle Crashes

Roadway Before After Diff (%)

Interstates 46 50 +9%

Freeways 12 17 +42%

All 70 mph Roads 58 67 +16%

All Other Roads 7,657 6,752 -12%

Table 5. Young Driver Crashes by Severity


Interstates

Fatal 14 13 -7%

Injury 440 492 +12%

PDO 1,250 1,538 +23%

Total 1,704 2,043 +20%

Freeways

Fatal 2 4 +100%

Injury 121 155 +28%

PDO 359 467 +30%

Total 482 626 +30%

All 70 mph Roads

Fatal 16 17 +6%

Injury 561 647 +15%

PDO 1,609 2,005 +25%

Total 2,186 2,669 +22%

All Other Roads

Fatal 541 501 -7%

Injury 54,173 51,719 -5%

PDO 134,034 129,065 -4%

Total 188,748 181,285 -4%


13

Older Driver Crashes

In addition to focusing on crashes involving young drivers, it is also important to consider how the speed

limit increase affected older drivers. For the purposes of this report, crashes involving older drivers are

those with at least one driver who was age 55 or older. As shown in Table 6, crashes involving older

drivers increased 27% on 70 mph roads from

before (2,082) to after (2,645) the 70 mph

speed limit increase. This includes a 23%

increase on interstates (1,707 to 2,104) and a

44% increase on freeways (375 to 541). On all

other roads in Ohio, crashes involving older

drivers increased 5% (159,943 to 167,698)

during the same time frame. Considering only

those crashes with greater severity, fatal and

injury crashes increased 38% on 70 mph roads

(513 to 710), including a 36% increase on


freeways (107 to 159). Severe crashes involving

older drivers on all other roads increased 5%

(45,532 to 47,682) during the same time. This

pattern of change was significantly different

between 70 mph roads versus all other roads [χ2(1) = 23.01, p < .001].

OVI-Related Crashes

One final group of drivers to consider are those

who were impaired by alcohol or drugs. In the

current dataset, an OVI-related crash is one that

involved at least one driver who was under the

influence of alcohol, drugs, or both. On 70 mph

roadways, OVI-related crashes increased 9%

from before (307) to after (335; see Table 7).

This includes a 24% increase on interstates (212

to 263) but a 24% decrease on freeways (95 to

72). OVI-related crashes on all other roads

increased 1% (26,603 to 26,975) during the

same time comparison.

A further way to examine OVI-related crashes is

by considering only those with greater severity.

OVI-related fatal and injury crashes increased 3% on all 70 mph roads (153 to 158). This includes a 16%

increase on interstates (103 to 119) but a 22% decrease on freeways (50 to 39). On all other roads, OVI-

related fatal and injury crashes decreased 1% (12,121 to 11,990) during the same time period. However,

this pattern of change was not statistically significantly different [χ2(1) = 0.14, p = .71].

Table 6. Older Driver Crashes by Severity


Interstates

Fatal 16 16 0%

Injury 390 535 +37%

PDO 1,301 1,553 +19%

Total 1,707 2,104 +23%

Freeways

Fatal 4 11 +175%

Injury 103 148 +44%

PDO 268 382 +43%

Total 375 541 +44%

All 70 mph Roads

Fatal 20 27 +35%

Injury 493 683 +39%

PDO 1,569 1,935 +23%

Total 2,082 2,645 +27%

All Other Roads

Fatal 644 687 +7%

Injury 44,888 46,995 +5%

PDO 114,411 120,016 +5%

Total 159,943 167,698 +5%

Table 7. OVI-Related Crashes by Severity


Interstates

Fatal 13 11 -15%

Injury 90 108 +20%

PDO 109 144 +32%

Total 212 263 +24%

Freeways

Fatal 7 2 -71%

Injury 43 37 -14%

PDO 45 33 -27%

Total 95 72 -24%

All 70 mph Roads

Fatal 20 13 -35%

Injury 133 145 +9%

PDO 154 177 +15%

Total 307 335 +9%

All Other Roads

Fatal 774 654 -16%

Injury 11,347 11,336 -0.1%

PDO 14,482 14,985 +3%

Total 26,603 26,975 +1%


14

Contributing Circumstances

In addition to examining the vehicles and

drivers involved in crashes, researchers

also analyzed why crashes occurred (i.e.,

contributing circumstances). There are a

variety of circumstances that can

contribute to a crash, and OH1 crash

reports allow for a primary contributing

circumstance to be assigned to each driver

involved in the crash. Some of the more

common contributing circumstances are

shown in Table 8.32 In the following

sections, researchers further explored two

of the more common contributing

circumstances in crashes: speed and lane

change.

Speed-Related Crashes

For purposes of this report, speed-related

includes any crash that: 1) involved a

primary contributing circumstance of

exceeded speed limit, unsafe speed,

followed too closely/ACDA, or failure to

control; or 2) involved at least one vehicle whose speed exceeded the posted speed limit on that road.

Overall, speed-related crashes on 70 mph roads increased 16% from before (4,525) to after (5,254) the

speed limit increase (see Table 9). By

comparison, speed-related crashes on all other

roads increased 5% during that time (248,193 to

260,357).

Additionally, there were 18% more fatal and

injury speed-related crashes on 70 mph roads

after the speed limit increase (1,498) than

before (1,270). In particular, there was a 14%

increase in fatal and injury speed-related

crashes on interstates (998 to 1,139) and a 32%

increase on freeways (272 to 359). On all other

roads, severe speed-related crashes increased

3% (71,145 to 73,569) during the same time

period. This pattern of change in severe crashes

32 To provide a more reliable comparison of changes, only those specific contributing circumstances with at least 200 crashes total on 70 mph roadways are presented separately in Table 8. For comparison purposes, similar types of contributing circumstances are grouped together (see Definitions and Acronyms section).

Table 8. Crashes by Contributing Circumstances

Roadway Circumstance Before After Diff (%)

Interstates

Speed 3,607 4,085 +13%

Lane Change 1,110 1,896 +71%

Swerving 193 180 -7%

Defect. Equip. 608 440 -28%

Load Shift 142 217 +53%

Other 800 520 -35%

Freeways

Speed 918 1,169 +27%

Lane Change 281 411 +46%

Swerving 47 60 +28%

Defect. Equip. 106 144 +36%

Load Shift 53 67 +26%

Other 216 137 -37%

All 70 mph Roads

Speed 4,525 5,254 +16%

Lane Change 1,391 2,307 +66%

Swerving 240 240 0%

Defect. Equip. 714 584 -18%

Load Shift 195 284 +46%

Other 1,016 657 -35%

All Other Roads

Speed 248,193 260,357 +5%

Lane Change 45,485 55,220 +21%

Swerving 7,845 5,418 -31%

Defect. Equip. 5,639 3,831 -32%

Load Shift 2,182 2,352 +8%

Other 206,061 183,985 -11% Note. Each driver involved in a crash may be given a primary contributing circumstance; thus, the total contributing circumstances sums to more than the total number of crashes.

Table 9. Speed-Related Crashes by Severity


Interstates

Fatal 21 21 0%

Injury 977 1,118 +14%

PDO 2,609 2,946 +13%

Total 3,607 4,085 +13%

Freeways

Fatal 4 7 +75%

Injury 268 352 +31%

PDO 646 810 +25%

Total 918 1,169 +27%

All 70 mph Roads

Fatal 25 28 +12%

Injury 1,245 1,470 +18%

PDO 3,255 3,756 +15%

Total 4,525 5,254 +16%

All Other Roads

Fatal 780 856 +10%

Injury 70,365 72,713 +3%

PDO 177,048 186,788 +6%

Total 248,193 260,357 +5%


15

was significantly different across 70 mph roads versus all other roads [χ2(1) = 11.70, p < .001].

Finally, within these speed-related crashes, those involving CMVs increased 25% (928 to 1,163), crashes

involving young drivers increased 15% (1,501 to 1,723), and those involving older drivers increased 21%

(1,056 to 1,275) on 70 mph roads. These increases outpaced crash changes for these subsets on all other

roads in the state (see Appendix).

Lane Change-Related Crashes

In addition to examining speed-related crashes

in more detail, researchers also further analyzed

lane change-related crashes. These contributing

circumstances include driving left of center as

well as improper lane change/passing/off road

actions. Overall, lane change-related crashes

increased 66% on 70 mph roads (1,391 to 2,307;

see Table 10), a pattern that was constant even

when focusing only on more severe fatal and

injury crashes (368 to 610; 66% increase).

Specifically, lane change-related fatal and injury

crashes increased 75% on interstates (279 to

487) and 38% on freeways (89 to 123). On all

other roads, these more severe lane change-

related crashes increased 23% (11,449 to 14,059) during the same time frame. This pattern of change

was significantly different [χ2(1) = 20.07, p < .001].

Finally, within these lane change-related crashes, those involving CMVs increased 49% (551 to 819),

crashes involving young drivers increased

56% (403 to 630), and those involving

older drivers increased 56% (455 to 710)

on 70 mph roads. These increases were

larger than crash increases for each of

these subsets on all other roads in Ohio

(see Appendix).

Manner of Collision

Another important consideration is how

crashes occurred before and after the

speed limit increase. Each OH1 crash

report lists one manner of collision,

including impacts such as rear-end, head-

on, angle, and not a collision between two

motor vehicles in transport, among others.

The most common manners of collision

Table 10. Lane Change-Related Crashes by Severity


Interstates

Fatal 10 14 +40%

Injury 269 473 +76%

PDO 831 1,409 +70%

Total 1,110 1,896 +71%

Freeways

Fatal 5 10 +100%

Injury 84 113 +35%

PDO 192 288 +50%

Total 281 411 +46%

All 70 mph Roads

Fatal 15 24 +60%

Injury 353 586 +66%

PDO 1,023 1,697 +66%

Total 1,391 2,307 +66%

All Other Roads

Fatal 439 447 +2%

Injury 11,010 13,612 +24%

PDO 34,036 41,161 +21%

Total 45,485 55,220 +21%

Table 11. Crashes by Manner of Collision

Roadway Circumstance Before After Diff (%)

Interstates

Angle 399 433 +9%

Not Collision 3,907 4,920 +26%

Rear-End 964 1,122 +16%

Sideswipe/same 921 1,116 +21%

Other/Unknown 85 108 +27%

Freeways

Angle 108 131 +21%


Rear-End 218 294 +35%

Sideswipe/same 145 200 +38%

Other/Unknown 37 33 -11%

All 70 mph Roads

Angle 507 564 +11%


Rear-End 1,182 1,416 +20%

Sideswipe/same 1,066 1,316 +23%

Other/Unknown 122 141 +16%

All Other Roads

Angle 128,535 125,938 -2%

Not Collision 130,097 131,306 +1%

Rear-End 155,375 153,189 -1%

Sideswipe/same 40,103 44,063 +10%

Other/Unknown 50,070 50,531 +1%


16

are listed in Table 11.33 In particular, rear-end crashes on 70 mph roads increased 20% from before

(1,182) to after (1,416) the speed limit increase. On all other roads in Ohio, rear-end crashes decreased

1% during that time (155,375 to 153,189). Additionally, sideswipe (same direction) crashes increased

23% on 70 mph roads (1,066 to 1,316) while these type of crashes were up only 10% on all other roads

(40,103 to 44,063). The next two sections explore these specific types of crashes in greater detail.

Rear-End Crashes

Researchers further analyzed the subset of rear-

end crashes. As discussed previously, rear-end

crashes increased 20% on all 70 mph roads

(1,182 to 1,416) which includes a 16% increase

on interstates (964 to 1,122) and a 35% increase

on freeways (218 to 294; see Table 12). When

considering only the rear-end crashes that

resulted in greater severity, there was a 35%

increase in fatal and injury crashes on 70 mph

roads (453 to 611). This includes a 33% increase

in fatal and injury rear-end crashes on


freeways (81 to 116). These more severe rear-

end crashes decreased 2% on all other roads

(41,811 to 40,955) over the same time period. This pattern of change was statistically significantly

different between 70 mph roads and all other roads [χ2(1) = 26.51, p < .001].

Among rear-end crashes, those involving CMVs increased 51% (323 to 489), crashes involving young

drivers increased less than 1% (452 to 454), and those involving older drivers increased 27% (440 to 558)

on 70 mph roads. These increases were each

higher than changes seen on all other roads in

the state (see Appendix).

Sideswipe (Same Direction) Crashes

Researchers also examined sideswipe (same

direction) crashes in greater detail. Considering

only the more severe (i.e., fatal and injury)

sideswipe crashes, these increased 23% on 70

mph roads (185 to 228; see Table 13). In

particular, there were 35% more fatal and injury

sideswipe crashes on interstates (146 to 197)

and 21% fewer on freeways (39 to 31) from

before to after the speed limit increase.

Moreover, fatal and injury sideswipe crashes

increased 8% on all other roads (3,984 to 4,309)

33 To provide a more reliable comparison of changes, only those specific manners of collision with at least 200 crashes total on 70 mph roadways are presented separately in Table 11.

Table 12. Rear-End Crashes by Severity


Interstates

Fatal 11 13 +18%

Injury 361 482 +34%

PDO 592 627 +6%

Total 964 1,122 +16%

Freeways

Fatal 3 2 -33%

Injury 78 114 +46%

PDO 137 178 +30%

Total 218 294 +35%

All 70 mph Roads

Fatal 14 15 +7%

Injury 439 596 +36%

PDO 729 805 +10%

Total 1,182 1,416 +20%

All Other Roads

Fatal 87 96 +10%

Injury 41,724 40,859 -2%

PDO 113,564 112,234 -1%

Total 155,375 153,189 -1%

Table 13. Sideswipe (Same Direction) Crashes by Severity


Interstates

Fatal 1 1 0%

Injury 145 196 +35%

PDO 775 919 +19%

Total 921 1,116 +21%

Freeways

Fatal 1 0 -100%

Injury 38 31 -18%

PDO 106 169 +59%

Total 145 200 +38%

All 70 mph Roads

Fatal 2 1 -50%

Injury 183 227 +24%

PDO 881 1,088 +23%

Total 1,066 1,316 +23%

All Other Roads

Fatal 15 22 +47%

Injury 3,969 4,287 +8%

PDO 36,119 39,754 +10%

Total 40,103 44,063 +10%


17

over the same time frame. This pattern of increases was not significantly different across the road types

[χ2(1) = 1.66, p = .20].

As previously mentioned, sideswipe (same direction) crashes increased 23% on all 70 mph roads. Among

these sideswipe crashes, those involving CMVs increased 19% (622 to 742), those involving young

drivers increased 13% (288 to 325), and those involving older drivers increased 30% (420 to 546) on 70

mph roads. These increases mostly outpaced crash increases in similar subsets on all other roads in the

state (see Appendix).

Temporal Factors

In addition to the aforementioned analyses, it is also important to consider aspects related to when

crashes occurred before and after the speed limit increase. This section presents results on time of day,

day of week, season, and environmental conditions.

Time of Day

Researchers examined the specific time of day

to see if certain times were affected differently

by the recent speed limit increase. For the

purposes of this report, crashes were grouped

into four separate times of day when they

occurred: night (12:00am-5:59am); morning

(6:00am-11:59am); afternoon (12:00pm-

5:59pm); and evening (6:00pm-11:59pm). As

shown in Table 14, crashes on 70 mph roads

increased during all four time groups, ranging

from a 12% increase (3,018 to 3,388) during the

afternoon to a 44% increase (2,130 to 3,062)

during the morning. Moreover, morning hours

showed the largest increases for both

interstates (+41%; 1,649 to 2,331) and freeways (+52%; 481 to 731). On all other roads in Ohio, crashes

during the morning increased 5% (125,460 to 132,189) over the same time comparison. Crashes on all

other roads decreased during night (-3%; 41,158 to 39,815), afternoon (-1%; 229,497 to 226,075), and

evening (-1%; 108,065 to 106,948) hours.

Day of Week

In addition to time of day, researchers also

analyzed whether crashes happened on a

weekday (i.e., Monday-Friday) or a weekend

(i.e., Saturday-Sunday). Weekday crashes on 70

mph roads increased 14% from before (5,909)

to after (6,710) the speed limit increase (see

Table 15). This includes a 10% increase on

interstates (4,690 to 5,148) and a 28% increase

on freeways (1,219 to 1,562). Weekday crashes

Table 14. Crashes by Time of Day

Roadway Time Before After Diff (%)

Interstates

Night 752 1,003 +33%

Morning 1,649 2,331 +41%

Afternoon 2,461 2,659 +8%

Evening 1,414 1,706 +21%

Freeways

Night 210 225 +7%

Morning 481 731 +52%

Afternoon 557 729 +31%

Evening 360 428 +19%

All 70 mph Roads

Night 962 1,228 +28%

Morning 2,130 3,062 +44%

Afternoon 3,018 3,388 +12%

Evening 1,774 2,134 +20%

All Other Roads

Night 41,158 39,815 -3%

Morning 125,460 132,189 +5%

Afternoon 229,497 226,075 -1%

Evening 108,065 106,948 -1%

Table 15. Crashes by Day of Week


Interstates Weekday 4,690 5,148 +10%

Weekend 1,586 2,551 +61%

Freeways Weekday 1,219 1,562 +28%

Weekend 389 551 +42%

All 70 mph Roads

Weekday 5,909 6,710 +14%

Weekend 1,975 3,102 +57%

All Other Roads

Weekday 386,509 386,295 -0.1%

Weekend 117,671 118,732 +1%


18

on all other roads decreased less than 1% (386,509 to 386,295) during this same time frame. This

pattern of change was significant [χ2(1) = 50.47, p < .001].

By comparison, crashes that happened on the weekend (i.e., Saturday-Sunday) were impacted to a

greater degree after the speed limit change. Specifically, weekend crashes on 70 mph roads increased

57% (1,975 to 3,102) including a 61% increase on interstates (1,586 to 2,551) and a 42% increase on

freeways (389 to 551). All other roads in Ohio experienced a 1% increase in weekend crashes (117,671

to 118,732) over the same time period. Finally,

this pattern of change for weekend crashes

was significantly different [χ2(1) = 235.13, p <

.001].

It is also of interest to examine the more

severe crashes (i.e., fatal and injury) that

happened on weekdays versus weekends. As

shown in Figure 3, fatal and injury crashes on

70 mph roads increased 12% on weekdays

(1,387 to 1,560) and 48% on weekends (528 to

781). Severe crashes on all other roads

decreased 1% on both weekdays (103,448 to

102,633) and weekends (33,828 to 33,609).

Season

Because seasonal differences may occur in

traffic patterns, and subsequently traffic

crashes, researchers also looked at the change

in crashes by season: spring (March-May),

summer (June-August), fall (September-

November), and winter (December, January-

February). As shown in Table 16, crashes on 70

mph roads increased during all four seasons,

ranging from an increase of 18% in winter (2,918

to 3,437) to an increase of 43% during spring

(1,520 to 2,172). On all other roads, crashes

increased 3% during winter (138,144 to

142,034) and decreased 5% during spring

(119,092 to 113,087).

Researchers also examined the more severe

crashes on these roads (i.e., fatal and injury).

During the spring months, fatal and injury

crashes increased 51% on 70 mph roads (350

to 530), while all other roads experienced a

6% decrease in fatal and injury crashes

(33,157 to 31,184; see Figure 4). Additionally,

severe crashes on 70 mph roads increased

12%

-1%

48%

-1%-20%

0%

20%

40%

60%

Figure 3. Percent Change in Fatal and Injury Crashes

Weekday

Weekend

70 mph Roads All Other Roads

51%

-6%

9%

-1%

26%

4%14%

0.1%

-20%

0%

20%

40%

60%

Figure 4. Percent Change in Fatal and Injury Crashes

SpringSummerFallWinter

70 mph Roads All Other Roads

Table 16. Crashes by Season


Interstates

Spring 1,197 1,709 +43%

Summer 1,426 1,688 +18%

Fall 1,407 1,605 +14%

Winter 2,246 2,697 +20%

Freeways

Spring 323 463 +43%

Summer 295 440 +49%

Fall 318 470 +48%

Winter 672 740 +10%

All 70 mph Roads

Spring 1,520 2,172 +43%

Summer 1,721 2,128 +24%

Fall 1,725 2,075 +20%

Winter 2,918 3,437 +18%

All Other Roads

Spring 119,092 113,087 -5%

Summer 119,691 118,872 -1%

Fall 127,253 131,034 +3%

Winter 138,144 142,034 +3%


19

26% during fall months (417 to 525) while all other roads showed a 4% increase during the same season

(34,817 to 36,224). Finally, fatal and injury crashes increased 14% during winter (670 to 764) and 9%

during summer (478 to 522) on 70 mph roads. Severe crashes on all other roads remained relatively

stable during those seasons [i.e., less than 1% increase during winter (33,936 to 33,984); 1% decrease

during summer (35,366 to 34,850)].

Best Environmental Conditions

In an effort to partially control for non-ideal driving conditions, researchers examined the subset of

crashes that occurred during the best environmental conditions: on dry roads, in clear weather, and

during daylight (no glare) lighting conditions. Crashes in these best conditions increased 15% on 70 mph

roads from before (2,101) to after (2,422) the speed limit increase (see Table 17). This includes an 8%

increase on interstates (1,734 to 1,877) and a 49% increase on freeways (367 to 545). Crashes in best

environmental conditions decreased 3% on all

other roads (186,708 to 180,861) during the

same time.

Researchers further analyzed the more severe

crashes (i.e., fatal and injury) that happened in

the best environmental conditions. On all 70

mph roads, fatal and injury crashes increased

13% (493 to 557), including an 11% increase on


freeways (103 to 125). On all other roads, fatal

and injury crashes in best environmental

conditions decreased 4% (52,166 to 50,089)

during the same time comparison. This pattern

of change was significantly different for 70 mph

roads versus all other roads [χ2(1) = 6.87, p <

.01].

Location

An additional way that researchers analyzed crashes was by crash location. GIS Specialists separated

each 70 mph roadway into five mile segments which resulted in 198 road segments. As shown in Map 1,

road segments that experienced an increase in crashes after the speed limit change are denoted in red,

those that decreased are shown in green, and those segments that experienced no change are shown in

gray. Of the 198 segments, 78% (154) experienced an increase in the number of crashes from before to

after the speed limit change. Conversely, 17% (34) showed a decrease in the number of crashes on that

segment while 5% (10) did not experience any change. Overall, segments that experienced more (or

less) crashes are located all over the state rather than on one particular roadway or area.34

34 The majority of Interstate 75 in Wood County shows a decrease in crashes, but this is due to construction projects on that roadway during the ‘after’ comparison period. Because the current dataset removed all crashes in construction zones, the ‘before’ and ‘after’ segments of this roadway are not comparable.

Table 17. Best Environmental Condition Crashes by Severity


Interstates

Fatal 13 11 -15%

Injury 377 421 +12%

PDO 1,344 1,445 +8%

Total 1,734 1,877 +8%

Freeways

Fatal 1 8 +700%

Injury 102 117 +15%

PDO 264 420 +59%

Total 367 545 +49%

All 70 mph Roads

Fatal 14 19 +36%

Injury 479 538 +12%

PDO 1,608 1,865 +16%

Total 2,101 2,422 +15%

All Other Roads

Fatal 578 543 -6%

Injury 51,588 49,546 -4%

PDO 134,542 130,772 -3%

Total 186,708 180,861 -3%


20

Largest Change in Fatal and Injury Crashes

In order to determine which roads may have been most affected by the speed limit increase,

researchers looked specifically at fatal and injury (i.e., severe) crashes per five mile segments of each 70

mph roadway. To identify those roads with the greatest change, researchers first created a trimmed

average and standard deviation of the change in severe crashes on segments with at least 20 severe

crashes total. This resulted in an average change of +35% (SD = 58%) across 100 segments (see Map 2).

To identify those segments that experienced the greatest change, researchers used two standard

deviations (SD) from the average as outlier thresholds.35 This resulted in five segments above two SD

and no segments less than two SD from the average. As shown in Map 2, the largest of these increases

occurred on State Route 2, Erie County (mile posts 5-9) which experienced a 900% increase in fatal and

injury crashes (2 to 20). Interstate 71, Ashland County (mile posts 180-184) experienced the next highest

change. Fatal and injury crashes on that segment increased 271% (7 to 26). Interstate 90, Lake County

(mile posts 205-209) experienced a 175% increase in fatal and injury crashes (8 to 22), and Interstate 70,

35 In a normal distribution, this corresponds to approximately the 2nd and 98th percentiles.

Map 1. Crash Change by Five Mile Segments


21

Licking County (mile posts 120-124) had a 167% increase in severe crashes (12 to 32). Finally, US Route

33, Union County (mile posts 20-24) experienced a 157% increase in fatal and injury crashes (7 to 18).

Overall, fatal and injury crashes on these top five segments increased 228% (36 to 118) after the speed

limit change, corresponding to an additional 82 severe crashes on these road segments.

Regression Analysis

This section provides the results of a modeling analysis in which linear regression models were fit to the

monthly frequency of severe (i.e., fatal and injury) crashes using the same data set described in the

methodology section. Although a full model similar to previous studies was not possible (e.g., data is

unavailable for traffic volume, miles traveled, and vehicle speeds), more simplified models were

estimated. These regression models explored the effects of the increased speed limit on crashes while

statistically controlling for relevant control variables, and separate models were estimated for two main

roadways: all 70 mph roads and all other roads.

To identify the relevant control variables (i.e., covariates) for inclusion in the final models, researchers

tested covariates already identified in the literature on speed limit increases, including: a linear time

trend (i.e., continuous variable to account for natural trends over time); separate month variables (to

account for seasonality effects or exposure during high travel months); and the number of weekend

Map 2. Fatal and Injury Crash Change by Five Mile Segments


22

days in a given month.36 The primary predictor variable of interest was a dichotomous variable

corresponding to when the speed limit increase occurred (0 for data prior to the increase to 70 mph; 1

for data after the 70 mph speed limit was in effect). The dependent variable (DV) was the monthly

number of fatal and injury crashes. Using SAS 9.3 software, researchers created trimmed models (in

which non-significant covariates were removed from the model until only significant covariates remain)

as they have been shown to yield more stable parameter estimates.37 The resulting trimmed models are

discussed here.

When predicting the number of severe

crashes on 70 mph roads, the overall

trimmed model fit the data well (F =

12.80, p < .0001) with an adjusted R2 = .60

(i.e., this model accounts for 60% of the

variance in the DV, adjusting for the

number of predictors in the model). As

shown in Table 18, the speed limit change

variable was positive and significant (b =

18.27, p < .01) suggesting severe crashes

on 70 mph roads increased significantly

after the speed limit change. More

specifically, after the speed limit increase,

the predicted value of monthly severe

crashes on these roads increased by 18.27

crashes (on average, holding all other

predictors in the model constant).

When predicting the number of fatal and

injury crashes on all other roads, the

overall trimmed model fit the data well (F

= 10.17, p < .0001) with an adjusted R2 =

.54 (i.e., this model accounts for 54% of

the variance in the DV, adjusting for the

number of predictors in the model). As

shown in Table 19, the speed limit change

variable was not significant (p = .65)

suggesting the speed limit increase did not

significantly affect the number of fatal and

injury crashes on all other roads in Ohio.

36 Garber, S., & Graham, J. (1990). 37 Bryk, A. S., & Raudenbush, S. W. (1992). Hierarchical linear models: Applications and data analysis methods. Newbury Park, CA: Sage.

Table 18. Linear regression of monthly fatal and injury crashes on 70

mph roads

Parameter Estimate Standard

Error t value p value

Intercept -7.60 43.79 -0.17 0.863

70 mph limit variable 18.27 5.86 3.12 0.003

# Fri/Sat/Sun 6.24 3.31 1.88 0.067

January 59.43 10.83 5.49 <.001

February 52.55 11.34 4.63 <.001

April -25.14 10.81 -2.33 0.025

May -18.32 10.83 -1.69 0.098 Note. Adjusted R2 = .60. Estimates are unstandardized regression coefficients (b) from trimmed models in which non-significant (i.e., p > .10) covariates were dropped from the model. Linear regressions set up as in Garber & Graham (1990), including dichotomous variables for months.

Table 19. Linear regression of monthly fatal and injury crashes on all

other roads

Parameter Estimate Standard

Error t value p value

Intercept 5896.08 77.11 76.46 <.001

70 mph limit variable -43.08 93.61 -0.46 0.648

February -553.29 173.33 -3.19 0.003

March -846.04 173.33 -4.88 <.001

April -813.04 173.33 -4.69 <.001

October 425.21 173.33 2.45 0.019

November -327.79 173.33 -1.89 0.066 Note. Adjusted R2 = .54. Estimates are unstandardized regression coefficients (b) from trimmed models in which non-significant (i.e., p > .10) covariates were dropped from the model. Linear regressions set up as in Garber & Graham (1990), including dichotomous variables for months.


23

Summary

During 2013, the speed limit increased to 70 mph on rural interstates and freeways in Ohio. To better

understand the traffic safety impacts, researchers analyzed crash data from two years before (i.e., 2011-

2012) and two years after (i.e., 2014-2015) the speed limit change. Crashes on 70 mph roads increased

24% from before (7,884) to after (9,812) the speed limit increase, including a 22% increase in fatal and

injury crashes (1,915 to 2,341). The increase in crashes on 70 mph roads was pervasive across a variety

of subsets, including: CMV-related crashes (+27%); crashes involving young (+22%) and older (+27%)

drivers; speed-related (+16%) and lane change-related (+66%) crashes; rear-end (+20%) and sideswipe

(same direction; +23%) crashes; and weekend crashes (+57%). Moreover, crash increases often occurred

on both interstates and freeways that raised their speed limits. Finally, for the more severe (i.e., fatal

and injury) crashes, the speed limit significantly increased these crashes on 70 mph roads (p < .01) but

did not significantly affect severe crashes on all other roads. The results in this report are offered to

better understand the impact of Ohio’s recent speed limit increase.


24

APPENDIX: CRASH SUMMARY TABLES BY SUBSETS


25

Table A1. Speed-Related Crashes by Subsets


Interstates

All Speed 3,607 4,085 +13%

CMV 812 996 +23%

Young 1,187 1,325 +12%

Older 861 1,020 +18%

Freeways

All Speed 918 1,169 +27%

CMV 116 167 +44%

Young 314 398 +27%

Older 195 255 +31%

All 70 mph Roads

All Speed 4,525 5,254 +16%

CMV 928 1,163 +25%

Young 1,501 1,723 +15%

Older 1,056 1,275 +21%

All Other Roads

All Speed 248,193 260,357 +5%

CMV 12,845 15,045 +17%

Young 103,129 102,246 -1%

Older 70,349 77,044 +10%

Table A2. Lane Change-Related Crashes by Subsets


Interstates

All Lane Change 1,110 1,896 +71%

CMV 491 731 +49%

Young 314 494 +57%

Older 384 592 +54%

Freeways

All Lane Change 281 411 +46%

CMV 60 88 +47%

Young 89 136 +53%

Older 71 118 +66%

All 70 mph Roads

All Lane Change 1,391 2,307 +66%

CMV 551 819 +49%

Young 403 630 +56%

Older 455 710 +56%

All Other Roads

All Lane Change 45,485 55,220 +21%

CMV 6,109 7,774 +27%

Young 15,892 18,421 +16%

Older 15,160 18,440 +22%

Table A3. Rear-End Crashes by Subsets


Interstates

All Rear-End 964 1,122 +16%

CMV 291 422 +45%

Young 371 363 -2%

Older 353 448 +27%

Freeways

All Rear-End 218 294 +35%

CMV 32 67 +109%

Young 81 91 +12%

Older 87 110 +26%

All 70 mph Roads

All Rear-End 1,182 1,416 +20%

CMV 323 489 +51%

Young 452 454 +0.4%

Older 440 558 +27%

All Other Roads

All Rear-End 155,375 153,189 -1%

CMV 7,189 8,064 +12%

Young 67,539 64,282 -5%

Older 56,702 58,820 +4%

Table A4. Sideswipe (Same Direction) Crashes by Subsets


Interstates

All Sideswipe 921 1,116 +21%

CMV 564 671 +19%

Young 239 255 +7%

Older 358 463 +29%

Freeways

All Sideswipe 145 200 +38%

CMV 58 71 +22%

Young 49 70 +43%

Older 62 83 +34%

All 70 mph Roads

All Sideswipe 1,066 1,316 +23%

CMV 622 742 +19%

Young 288 325 +13%

Older 420 546 +30%

All Other Roads

All Sideswipe 40,103 44,063 +10%

CMV 7,080 8,445 +19%

Young 11,928 12,420 +4%

Older 14,088 16,176 +15%

ohio department of public safety · 70 mph that occurred in 2013. this speed limit increase...

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