Study Details

Study Title: Safety Effects of Cross Section Design on Urban and Suburban Roads

Authors: Le and Porter

Publication Date: NOV, 2012

Abstract: Understanding the safety effects of cross section allocation on urban and suburban roads is important for agencies implementing complete streets philosophies. Research on urban and suburban arterials, conducted as part of Highway Safety Manual development, found no consistent relationships between lane width and safety. Other studies indicated that urban streets with lanes narrower than 12 feet are not less safe, and may even be safer, than those with 12 foot and wider lanes. These studies addressed geometric elements in isolation, potentially leading to the inconsistent and counterintuitive findings. This paper takes a new look at the safety effects of cross section allocation on urban and suburban road segments. The effects of cross section element combinations and interactions, with a specific focus on lane width, shoulder width, and shoulder type, are considered as an inherent part of model estimation. The dataset for this study includes 1,577 urban street segments in Illinois, totaling nearly 380 miles in length and 3 years of crash data. Results show interactions between lane width and shoulder width that would not have been uncovered if these elements were considered in isolation. Shoulder width has a larger effect on safety when lanes are narrow and this safety effect decreases as lane width increases. Wider lanes do not always result in an increase in safety, particularly when shoulders are wider. Crash modification factors for cross section design element combinations were developed using modeling results. Safety performance functions for urban and suburban road segments are also presented.

Study Citation: Le, T. and Porter, R., Safety Effects of Cross Section Design on Urban and Suburban Roads. Presented at the 92nd Annual Meeting of the Transportation Research Board, Washington, D.C., (2012).


CMFs Associated With This Study

Category: Roadway

Countermeasure: convert lane width from 12 ft to 10 ft, with a total shoulder of X ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All K,A,B,C Not specified Urban and suburban

Countermeasure: Convert lane width from 12 ft to 11 ft, with a total shoulder of X ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All K,A,B,C Not specified Urban and suburban

Countermeasure: Convert lane width from 12 ft to 13 ft, with a total shoulder of X ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All K,A,B,C Not specified Urban and suburban

Countermeasure: Crash modification factor for 12 ft travel lane, with a total shoulder of X ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All K,A,B,C Not specified Urban and suburban

Countermeasure: Crash modification factor for median width of X ft

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All K,A,B,C Not specified Urban and suburban