Enhancing highway Loop Safety Level through proactive risk-based assessment of geometric configuration using lateral acceleration.

Abstract

Objective: Loop ramps are complex due to their combination of horizontal curves and vertical alignments. Analyzing driving behavior and measuring safety levels can provide insights for designers, helping to improve the performance and alignment of design assumptions with actual driving behavior on loops. Therefore, the primary objective of this research is to explore the safety, performance and geometric configuration of the main body and general shape of free-flow loop ramps in the free-following mode.

Methods: The study uses data from a UAV to investigate vehicle demand behavior. Maximum lateral acceleration (a_y,i) in loops is used as a Surrogate Safety Measure (SSM), along with a new parameter, the a/b ratio, to determine the general shape of loop bodies. The study presents the Loop Safety Level (LSL), an approach for proactive risk analysis and ranking that relies on threshold lateral acceleration (a_t), 85th percentile maximum lateral acceleration ($a$_y,max,85%), and crash analysis.

Results: A higher LSL value points to a more critical safety concern regarding the loop's shape in relation to lateral acceleration caused by driving behaviors. Comparing crash statistics with lateral acceleration results enables the LSL to provide appropriate safety ratings and diagnose loop segment safety. A prediction model for maximum lateral acceleration, based on loop geometry, demonstrates a good fit (R²=0.88) between observed and predicted data.

Conclusions: The study enhances understanding of safety considerations in geometric configuration and general shape enhancement of loops during the design process.