Modeling Lateral Acceleration on Ramp Curves for Consistency-Based Geometric Design

Previous interchange safety research has primarily focused on crash and operating speed prediction models, with no extensive evaluation related to the impact of different ramp types on lateral acceleration. The objective of this paper is to study lateral acceleration on ramp interchanges and develop safety charts for different ramps in India. For this, two sets of lateral acceleration models were investigated using geometric design elements and vehicle kinematic measurements, such as speed, obtained using an instrumented vehicle fitted with a high-end data logger. The results of the analysis reveal there is a barely detectable relationship between speed and lateral acceleration for various ramp types (diagonal, loop, and semidirect), but when separated by curve radius, the relationship is significant. In addition, various ramp-specific models were developed to measure the effects of geometric elements on lateral acceleration. Based on these models, safety charts were developed. To maintain safe lateral acceleration on diagonal and semidirect ramps, the safety charts indicate that the ramp curve radius should be greater than 90 and 100 m, respectively. For loop ramps with a length greater than 200 m, a radius of at least 95 m is required to maintain a speed of 40 km/h and maintain safe lateral acceleration. The insights presented in this research can be used to prioritize safety when designing freeway interchanges.