01474148

Component

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. Three years of crash data were used for model estimation. 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.

This paper was sponsored by TRB committee AHB65 Operational Effects of Geometrics.

01470560

13-5120

English

17p

2013

Transportation Research Board 92nd Annual Meeting

Digital/other

Figures; References; Tables

Cross sections; Highway design; Regression analysis; Road shoulders; Traffic lanes; Traffic safety; Width

Design; Highways; Safety and Human Factors; I22: Design of Pavements, Railways and Guideways; I82: Accidents and Transport Infrastructure

Transportation Research Board Annual Meeting 2013 Paper #13-5120

TRIS, TRB, ATRI

Feb 5 2013 12:58PM