Examining Safety on Two-Lane and Multilane Highways in Consideration of Access Spacing

Abstract

Access management strategies, such as the introduction of minimum access point spacing criteria and turning movement restrictions, have been shown to be important elements in optimizing the operational and safety performance of roadway segments. The relationship between safety and these types of access policies is a complex issue, and the impacts of such features on traffic crashes is critical to the development of appropriate access management strategies. The purpose of this study was to provide a quantitative evaluation of how crash risk on multilane and two-lane highways varies with respect to access spacing in support of the development of a revised access management policy. Data were obtained for approximately 1,247 and 5,795 mi of segments across multilane and two-lane highways, respectively. Crash data were obtained for a five-year period from 2012 to 2016 and a series of random effect negative binomial regression models were estimated for each facility to examine the association between crash frequency, access point spacing, and traffic volume. For both facility types, crashes were found to increase consistently as the average spacing of access points along road segments decreased. Crash rates were highest when consecutive accesses were within 150 ft of one another and the frequency of crashes decreased substantively as spacing was increased to 300 ft and, particularly, 600 ft. With spacing beyond 600 ft, crash rates continued to decrease, although these improvements were less pronounced than at the lower range of values. These findings were generally consistent on multilane and two-lane highways.

Safety Evaluation of Freeway Exit Ramps with Advisory Speed Reductions

“…Crashes are known to be random, discrete, and non-negative integers. Two types of regression model are frequently used to develop SPFs based on prior studies: Poisson ( 26 ) and negative binomial (NB) models ( 26 – 28 ). Under the Poisson model, the probability of exit ramp i experiencing y i crashes during a specific time period can be calculated using Equation 1.…”