CRASH MODIFICATION FACTORS CLEARINGHOUSE

Study Details

Study Title: Speed Limit Change (55 mph to 60 mph) Safety Re-Evaluation

Authors: Saleem et al.

Publication Date: NOV, 2023

Abstract: The objective of this study was to evaluate the safety impacts of increasing the speed limit from 55 mph to 60 mph on two-lane, two-way state highway road segments in Minnesota. An empirical Bayes (EB) before-after analysis was used to estimate crash modification factors (CMFs) for both segments and intersections. The segment analysis showed an 8 percent reduction in total crashes that was statistically significant, alongside a significant 15 percent increase in combined fatal, serious injury, and minor injury (KAB) injury crashes. The range of most of the segment CMFs hovered close to 1. The intersection analysis was split into two groups (all traffic control types and thru-stop control only). The aggregate CMFs for all intersections within these two groups showed, on average, between a 10% and 20% statistically significant reduction in total and injury crashes. Analysis was also performed on four subgroups (3- and 4-leg, lighting/no lighting) within the two main intersection groups. Disaggregating the intersections into further groups led to smaller sample sizes that led to higher standard errors showing a widespread range of CMFs around 1 for the individual crash types and severities. The aggregate estimated crash safety effects (for total and injury crashes) for combined segments and intersection sites showed a reduction in total crashes but an increase in the KAB injury crashes.

Study Citation: Saleem, T., R. Srinivasan, B. Lan, R. Storm, R. Herring, B. Wemple. "Speed Limit Change (55 mph to 60 mph) Safety Re-Evaluation." Report No. MN 2023-41. Minnesota Department of Transportation. Roseville, Minnesota. (November 2023)

Study Report: Download the Study Report Document

CMFs Associated With This Study

Category: Speed management

Countermeasure: Increase speed limit from 55 mph to 60 mph

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
0.604	39.6		Rear end	All	Principal Arterial Other	Rural

0.785

21.5

All

All

Principal Arterial Other

Rural

0.865

13.5

All

K,A,B,C

Principal Arterial Other

Rural

0.876

12.4

All

K,A,B

Principal Arterial Other

Rural

0.879

12.1

Angle

All

Principal Arterial Other

Rural

0.683

31.7

Rear end

All

Principal Arterial Other

Rural

0.873

12.7

All

All

Principal Arterial Other

Rural

0.926

7.4

All

K,A,B,C

Principal Arterial Other

Rural

1.045

-4.5

All

K,A,B

Principal Arterial Other

Rural

0.922

7.8

All

All

Principal Arterial Other

Rural

0.951

4.9

All

K,A,B,C

Principal Arterial Other

Rural

1.152

-15.2

All

K,A,B

Principal Arterial Other

Rural

0.979

2.1

Head on

All

Principal Arterial Other

Rural

0.844

15.6

Run off road

All

Principal Arterial Other

Rural

0.981

1.9

All

All

Principal Arterial Other

Rural

0.922

7.8

All

K,A,B,C

Principal Arterial Other

Rural

0.809

19.1

All

K,A,B

Principal Arterial Other

Rural

1.268

-26.8

Angle

All

Principal Arterial Other

Rural

1.141

-14.1

Rear end

All

Principal Arterial Other

Rural

0.83

17

All

All

Principal Arterial Other

Rural

0.966

3.4

All

K,A,B,C

Principal Arterial Other

Rural

1.085

-8.5

All

K,A,B

Principal Arterial Other

Rural

1.033

-3.3

Angle

All

Principal Arterial Other

Rural

0.839

16.1

Rear end

All

Principal Arterial Other

Rural

0.903

9.7

All

All

Principal Arterial Other

Rural

0.891

10.9

All

K,A,B,C

Principal Arterial Other

Rural

0.926

7.4

All

K,A,B

Principal Arterial Other

Rural

0.942

5.8

Angle

All

Principal Arterial Other

Rural

1.053

-5.3

Rear end

All

Principal Arterial Other

Rural

0.548

45.2

All

All

Principal Arterial Other

Rural

0.776

22.4

All

K,A,B,C

Principal Arterial Other

Rural

0.796

20.4

All

K,A,B

Principal Arterial Other

Rural

0.607

39.3

Angle

All

Principal Arterial Other

Rural

0.28

72

Rear end

All

Principal Arterial Other

Rural

0.981

1.9

All

All

Principal Arterial Other

Rural

0.919

8.1

All

K,A,B,C

Principal Arterial Other

Rural

0.802

19.8

All

K,A,B

Principal Arterial Other

Rural

1.179

-17.9

Angle

All

Principal Arterial Other

Rural

1.144

-14.4

Rear end

All

Principal Arterial Other

Rural

0.809

19.1

All

All

Principal Arterial Other

Rural

0.871

12.9

All

K,A,B,C

Principal Arterial Other

Rural

0.995

0.5

All

K,A,B

Principal Arterial Other

Rural

1.036

-3.6

Angle

All

Principal Arterial Other

Rural

0.772

22.8

Rear end

All

Principal Arterial Other

Rural

0.906

9.4

All

All

Principal Arterial Other

Rural

0.892

10.8

All

K,A,B,C

Principal Arterial Other

Rural

0.936

6.4

All

K,A,B

Principal Arterial Other

Rural

1.255

-25.5

Angle

All

Principal Arterial Other

Rural

1.074

-7.4

Rear end

All

Principal Arterial Other

Rural

0.533

46.7

All

All

Principal Arterial Other

Rural

0.757

24.3

All

K,A,B,C

Principal Arterial Other

Rural

0.802

19.8

All

K,A,B

Principal Arterial Other

Rural

0.583

41.7

Angle

All

Principal Arterial Other

Rural

0.344

65.6

Rear end

All

Principal Arterial Other

Rural

0.791

20.9

All

All

Principal Arterial Other

Rural

0.88

12

All

K,A,B,C

Principal Arterial Other

Rural

0.88

12

All

K,A,B

Principal Arterial Other

Rural

0.821

17.9

Angle

All

Principal Arterial Other

Rural

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