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Appendix A. Crash Modification Factors for Geometric Design Features

Publication Number: FHWA-HRT-14-020 Date: January 2015

Publication Number: FHWA-HRT-14-020
Date: January 2015

Factors Influencing Operating Speeds and Safety on Rural and Suburban Roads

APPENDIX A. CRASH MODIFICATION FACTORS FOR GEOMETRIC DESIGN FEATURES

Information for table 106 was gathered from the AASHTO Highway Safety Manual (2010).⁽³⁷⁾

Table 106. CMFs for Geometric Design Features

CMF	Area Type	Facility Type	Notes	Expected CMF (standard error)
Modify Lane Width	Rural	Two lane	None	See figure 13-1 in HSM
Modify Lane Width	Rural	Undivided multilane	None	See figure 13-2 in HSM
Modify Lane Width	Rural	Divided multilane	None	See figure 13-3 from HSM
Modify Lane Width	Rural	Frontage road	None	See figure 13-4 in HSM
Add or Widen Paved Shoulder	Rural	Two lane	None	See figure 13-5 from HSM
Add or Widen Paved Shoulder	Rural	Multilane	8- to 6-ft shoulder	1.04 (N/A)
			8- to 4-ft shoulder	1.09 (N/A)
			8- to 2-ft shoulder	1.13 (N/A)
			8- to 0-ft shoulder	1.18 (N/A)
Add or Widen Paved Shoulder	Rural	Frontage Road	None	See figure 13-6 in HSM
Provide a Raised Median	Rural	Multilane	Injury crashes	0.88 (0.03)
Provide a Raised Median	Rural	Multilane	Non-injury crashes	0.82 (0.03)
Change the Width of an Existing Median	Rural	Four Lane	Full access control	See table 13-12 in HSM
Change the Width of an Existing Median	Rural	Four Lane	Partial or no access control	See table 13-13 in HSM
Increase the Distance to Roadside Features	Rural	Two Lane and Freeways	3.3- to 16.7-ft offset	0.78 (0.02)
Increase the Distance to Roadside Features	Rural	Two Lane and Freeways	16.7- to 30.0-ft offset	0.56 (0.01)
Reduce Roadside Hazard Rating	Rural	Two Lane		See figure 13-8 in HSM
Modify Horizontal Curve Radius	Rural	Two Lane		See figure 13-9 in HSM
Improve Superelevation	Rural	Two lane	Improve superelevation variance < 0.01	1.00 (N/A)
			Improve SV 0.01≤ SV < 0.02	1.00 + 6 (SV – 0.01)
			Improve SV > 0.02	1.06 + 3 (SV – 0.02)
Change Vertical Grade	Rural	Two lane	Increase vertical grade by 1 % (SVROR)	1.04 (0.02)

CMF = Crash modification factor
HSM = Highway Safety Manual
N/A = Not applicable

Page Owner: Office of Research, Development, and Technology, Office of Safety, RDT

Topics: research, safety
Keywords: research, safety, crash mitigation, curve speed safety, horizontal curves, lane position, low-cost safety improvements, rural road safety, speed-activated displays, speed warning signs
TRT Terms: research, Safety and security, Safety, Transportation safety
Scheduled Update: Archive - No Update needed

This page last modified on 01/31/2017