Impact of Combined Alignments and Different Weather Conditions on Vehicle Rollovers

Abstract

Combined horizontal and vertical alignments are frequently utilized in mountainous interstates in Wyoming. These challenging terrain conditions, coupled with adverse weather conditions, affect vehicle stability and may lead to hazards. There is a dearth of research on systematically examining the effects of different combined alignments on safety in terms of rollover propensity including their interactions. Researchers resorted to observational methods that inhibited the control of key variables. Instead, vehicle dynamics simulation modeling was employed to investigate the rollover propensity of vehicles navigating curves of varying geometric design and environmental characteristics. Instead of simulating the full range of curve geometries throughout this study, we considered the most critical curves that were identified as areas of concern. A multinomial regression model was then developed to further quantify the impact of several key factors in terms of roll stability. Results show that: 1) tight degrees of curvature and steep downgrades raised the lateral acceleration and, with higher operating speeds, the impact was more critical. 2) Compared to passenger cars and sports utility vehicles (SUVs), the highest lateral acceleration was acting on semi-trailer trucks. Moreover, SUVs and semi-trailer trucks decrease the rollover margins compared to passenger cars by 0.144 and 0.158 respectively. The study provides new insights regarding the impact of various interactions between the factors, particularly when applying brakes. The study provides a safety assessment for curves' speed limits that could assist Wyoming Department of Transportation (WYDOT) in assigning appropriate speed limits. To the best of the authors' knowledge, no previous studies were conducted to investigate these impacts for combined curves. This study is beneficial to transportation agencies in Wyoming and all other locations that are characterized by mountainous terrain since hazardous sections, having combined horizontal and vertical curves, were identified. Also, situations that require additional attention from law enforcement agencies are pinpointed.