Safety diagnosis: are we doing a good job?

Area of Science:

• Transportation Engineering
• Road Safety Analysis
• Statistical Methods in Traffic Safety

Background:

• Collision diagnosis is a key step in road safety management, aiming to identify prevalent collision types at specific locations.
• The Highway Safety Manual (HSM) suggests descriptive data analysis as the primary method, using tools like collision diagrams and histograms.
• The beta-binomial (BB) test is a secondary diagnostic tool, comparing local collision proportions to similar reference locations.

Purpose of the Study:

• To compare the outcomes of descriptive data analysis and the beta-binomial (BB) test in collision diagnosis.
• To determine if both methods identify the same collision configurations at the same locations.
• To ascertain which method's results should be prioritized in engineering practice when discrepancies arise.

Main Methods:

• Analysis of five years (2005-2009) of collision and roadway data for 143 signalized intersections in Saskatoon, Saskatchewan.
• Application of descriptive data analysis techniques (e.g., frequency counts, charts) to identify dominant collision configurations.
• Implementation of the beta-binomial (BB) test to compare collision proportions against reference sites with similar traffic and roadway characteristics.

Main Results:

• Descriptive data analysis and the beta-binomial (BB) test may yield different results in identifying critical collision configurations.
• The study indicates that the BB test's diagnostic capability is significant and comparable to descriptive methods.
• The findings suggest that the BB test plays a crucial role in road safety engineering projects.

Conclusions:

• The beta-binomial (BB) test is a valuable tool for collision diagnosis in road safety engineering.
• Both descriptive data analysis and the BB test should be considered for a comprehensive understanding of safety concerns.
• The BB test's importance in diagnosing safety issues in existing roadways is comparable to traditional descriptive methods.