CRASH MODIFICATION FACTORS CLEARINGHOUSE

Study Details

Study Title: Efficacies of roadway safety improvements across functional subclasses of rural two-lane highways

Authors: Labi

Publication Date:JAN, 2011

Abstract: Introduction: Highway crash occurrence is a leading cause of unnatural deaths, and highway agencies continually seek to identify engineering measures to reduce crashes and to assess the efficacy of such measures. Most past studies on the effectiveness of roadway improvements in terms of crash reduction considered all rural two-lane sections as a single category of roads. However, it may be hypothesized that the differences in the mobility and accessibility characteristics that are rejected in (and due to) the different design standards between different functional subclasses in the rural two-lane highway system can lead to differences in efficacies of safety improvements at these subclasses. This paper investigates the efficacy of roadway improvements, in terms of crash reduction, at the various subclasses of rural twolane highways. Methods: An empirical analysis of safety performance at each of the three subclasses of rural two-lane highways was carried out using the negative binomial modeling technique. For each subclass, crash prediction models were developed separately for the three levels of crash severity: property-damage only, injury, and fatal/injury. The crash factors that were considered include lane width, shoulder width, pavement surface friction, pavement condition, and horizontal and vertical alignments. After having developed the safety performance functions, the effectiveness (in terms of the extent of crash reduction, for different levels of crash severity) of highway safety enhancements at each highway subclass were determined using the theoretical concepts established in past literature. These enhancements include widening lanes, widening shoulders, enhancing pavement surface friction, and improving the vertical or horizontal alignment. Results and Conclusion: The study found that there is empirical evidence to justify the decomposition of the family of rural two-lane roads into its constituent subclasses for purposes of analyzing the effectiveness of safety enhancement projects and thus to avoid underestimation or overestimation of benefits of safety improvements at this class of highways.

Study Citation: Labi, S. "Efficacies of roadway safety improvements across functional subclasses of rural two-lane highways." Journal of Safety Research. Vol. 42, pp. 231-239. (2011)

CMFs Associated With This Study

Category: Alignment

Countermeasure: Change in average horizontal curve radius from X to Y (in miles)

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
			All	K,A,B,C	Principal Arterial Other	Rural

All

K,A,B,C

Major Collector

Rural

All

O

Major Collector

Rural

All

A,B,C

Major Collector

Rural

All

O

Principal Arterial Other

Rural

All

A,B,C

Principal Arterial Other

Rural

All

K,A,B,C

Minor Arterial

Rural

All

O

Minor Arterial

Rural

All

A,B,C

Minor Arterial

Rural

Countermeasure: Change in average vertical curve grade from X to Y (% grade)

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
			All	A,B,C	Major Collector	Rural

All

O

Major Collector

Rural

All

K,A,B,C

Major Collector

Rural

All

A,B,C

Minor Arterial

Rural

All

O

Minor Arterial

Rural

All

K,A,B,C

Minor Arterial

Rural

All

A,B,C

Principal Arterial Other

Rural

All

O

Principal Arterial Other

Rural

All

K,A,B,C

Principal Arterial Other

Rural

Category:Roadway

Countermeasure: Change in pavement condition from X to Y

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
			All	K,A,B,C	Principal Arterial Other	Rural

All

O

Principal Arterial Other

Rural

All

A,B,C

Principal Arterial Other

Rural

Countermeasure: Change in pavement friction from X to Y (in friction number)

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
			All	A,B,C	Major Collector	Rural

All

O

Major Collector

Rural

All

K,A,B,C

Major Collector

Rural

All

A,B,C

Minor Arterial

Rural

All

O

Minor Arterial

Rural

All

K,A,B,C

Minor Arterial

Rural

Countermeasure: Change lane width from X to Y (in feet)

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
			All	O	Major Collector	Rural

All

K,A,B,C

Major Collector

Rural

All

A,B,C

Minor Arterial

Rural

All

O

Minor Arterial

Rural

All

K,A,B,C

Minor Arterial

Rural

All

A,B,C

Principal Arterial Other

Rural

All

K,A,B,C

Principal Arterial Other

Rural

All

O

Principal Arterial Other

Rural

All

A,B,C

Major Collector

Rural

Category:Shoulder treatments

Countermeasure: Change shoulder width from X to Y (in feet)

CMF	CRF(%)	Quality	Crash Type	Crash Severity	Roadway Type	Area Type
			All	K,A,B,C	Principal Arterial Other	Rural

All

O

Principal Arterial Other

Rural

All

A,B,C

Principal Arterial Other

Rural

All

K,A,B,C

Minor Arterial

Rural

All

O

Minor Arterial

Rural

All

A,B,C

Minor Arterial

Rural

All

K,A,B,C

Major Collector

Rural

All

O

Major Collector

Rural

All

A,B,C

Major Collector

Rural

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