Safety sensitivity to roadway characteristics: A comparison across highway classes

Area of Science:

• Transportation Engineering
• Road Safety Analysis
• Traffic Management

Background:

• Roadway design and traffic volume are critical factors influencing highway safety.
• Accident severity varies across different highway classes and design elements.
• Understanding these relationships is crucial for effective road safety policies.

Purpose of the Study:

• To investigate accident risk factors across three U.S. highway classes (Interstates, US Roads, State Roads).
• To analyze the differential sensitivity of accident severity (no-casualty vs. casualty) to various roadway design and traffic parameters.
• To provide insights for evaluating and updating highway design standards.

Main Methods:

• Utilized a bivariate modeling framework to analyze two levels of accident severity.
• Examined accident data in relation to traffic volume, roadway geometry (lane width, shoulder width, median width, vertical grade), and pavement condition.
• Compared sensitivity analyses across different highway classes.

Main Results:

• Casualty accidents on Interstates are more sensitive to traffic volume and vertical grade than no-casualty accidents.
• US Roads show casualty accidents more sensitive to traffic volume, outside shoulder width, pavement condition, and median width.
• State Roads indicate casualty accidents are more sensitive to traffic volume, lane width, outside shoulder width, and pavement condition.

Conclusions:

• Highway class significantly influences the relationship between design factors and accident severity.
• Road geometry standards appear to strongly affect accident occurrence and severity.
• The developed models can aid engineers in assessing safety impacts of design standard modifications.