SAFETY EVALUATION OF CLEAR ZONE/SIDESLOPE IN RURAL TWO-LANE ROADS BASED ON RELIABILITY ANALYSIS Mohammad Jalayer Ph.D. Candidate Dept. of Civil Engineering Auburn University Auburn AL 36849-5337 jalayer@auburn.edu Huaguo Zhou Associate Professor Dept. of Civil Engineering Auburn University Auburn AL 36849-5337 zhouhugo@auburn.edu ABSTRACT The severity of roadway departure crashes mainly depends on the roadside features, including sideslope, fixed-object density, offset to fixed objects, shoulder width, etc. Collision with fixed object is identified as the first harmful event in run-off-road (ROR) crashes. Common engineering countermeasures regarding roadside safety include: cross section improvements, hazard removal or modification, and delineation. It should be noted that it is not always feasible to maintain object-free roadside clear zone as design guidance recommends. Currently, clear zone width and sideslope are used to determine roadside hazard rating (RHR) to quantify roadside safety for rural two-lane roadways using 1 to 7 discrete levels. Since these two variables are continuous and can be treated as random variables, using probabilistic analysis to account for uncertainty can be an alternative applicable method. To be more specific, by emphasizing on the reliability analysis, it is possible to quantify the roadside safety level by treating clear zone width and sideslope as two continuous variables, rather than discrete variables. The objective of this manuscript is to present an approach to define the reliability index for measuring roadside safety on rural two-lane roads. The segments were randomly selected from three counties in Illinois and utilized in the analysis for a more pragmatic approach. Based on the obtained results, the reliability indices can serve as the indicators to measure the level of safety, showing the greater the reliability indices, the less the ROR crash rate. KEYWORDS Clear zone, Sideslope, Reliability Index, Probability of Failure, Reliability Analysis. INTRODUCTION A roadway departure (RwD) crash is defined by the Federal Highway Administration (FHWA) as “A crash in which a vehicle crosses an edge line, a centerline, or otherwise leaves the traveled way.” (FHWA 2014). These crashes, comprised of run-off-road (ROR) and head-on collisions, tend to be more severe than any other crash types (Neuman et. al 2003). Based on the FHWA, in 2012, 56 percent of fatal motor vehicle traffic crashes involved RwD crashes. According to a query of six years of crash data (2007-2012) from the Fatality Analysis Reporting System (FARS) database, an average of 57 percent of motor vehicle traffic fatalities occurred each year due to RwD, and a total of 7,416 people perished in crashes involving roadside fixed objects in 2012, accounting for 22 percent of the total fatalities in the United States (NHTSA 2015). It should be noted that the majority of RwD crashes happened during the nighttime and inclement weather conditions (e.g., fog, snow). Moreover, the rural highways accounted for 70 percent of total ROR fatalities, considering 90 percent occurred in rural two-lane two-way roads (OKLADOT 2014). Roadside features (e.g., sideslope, fixed-object density, offset to fixed objects) can significantly impact the frequency and severity of ROR crashes (Jalayer et al. 2015; Jalayer et al. 2014; Gong et al. 2012). In the 2010 Highway Safety Manual (HSM), the roadside features are important inputs for crash prediction models for rural two- lane roadways. The HSM predicts the average crash frequency for three different facilities including, [1] rural two- lane two-way roads, [2] rural multilane highways, and [3] urban and suburban arterials on the basis of cross-sectional