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

Area of Science:

• Traffic Engineering
• Road Safety Analysis
• Geometric Design

Background:

• Loop ramps present complex geometric challenges due to combined horizontal curves and vertical alignments.
• Understanding driving behavior on loop ramps is crucial for aligning design assumptions with real-world performance.

Purpose of the Study:

• To investigate the safety, performance, and geometric configuration of free-flow loop ramps.
• To analyze driving behavior and safety levels for design improvements.

Main Methods:

• Utilized Unmanned Aerial Vehicle (UAV) data to analyze vehicle behavior.
• Employed maximum lateral acceleration (a_y,i) as a Surrogate Safety Measure (SSM).
• Introduced the a/b ratio and Loop Safety Level (LSL) for shape determination and risk analysis, incorporating threshold lateral acceleration (a_t) and 85th percentile maximum lateral acceleration (a_y,max,85%).

Main Results:

• A prediction model for maximum lateral acceleration based on loop geometry showed a strong fit (R²=0.88).
• Higher LSL values indicate greater safety concerns related to loop shape and lateral acceleration.
• Crash statistics correlated with lateral acceleration data to provide safety ratings and diagnose segment safety.

Conclusions:

• The study enhances the understanding of safety considerations in loop ramp geometric configuration.
• It provides insights for improving the general shape of loops during the design process.
• The developed LSL aids in proactive risk analysis and ranking of loop ramps.