Operational Analysis of Transit Bus Collisions

Many factors can influence bus crashes and other incidents. In this study, James Strathman of Portland State University sought to quantify the relationship between bus crashes and crash determinants in the Portland-area TriMet system using a spatially disaggregate, risk-based approach. Strathman examined 4,631 collision and non-collision incidents between 2006 and 2009 to determine how operator demographics, employment status, assignment characteristics, service delivery, performance indicators, temporal factors and customer information influence the frequency of incidents. Of the incidents, 57 percent involved collisions, half of those with another vehicle. Non-collision incidents included passenger slips, trips and falls. Among Strathman’s findings: the frequency…

Many factors can influence bus crashes and other incidents. In this study, James Strathman of Portland State University sought to quantify the relationship between bus crashes and crash determinants in the Portland-area TriMet system using a spatially disaggregate, risk-based approach.

Strathman examined 4,631 collision and non-collision incidents between 2006 and 2009 to determine how operator demographics, employment status, assignment characteristics, service delivery, performance indicators, temporal factors and customer information influence the frequency of incidents. Of the incidents, 57 percent involved collisions, half of those with another vehicle. Non-collision incidents included passenger slips, trips and falls.

Among Strathman’s findings: the frequency of incidents decreases for a driver’s first 33 years of service and then starts increasing. Drivers’ frequency of incidents decreases until they reach 33.3 years of age and then similarly increases. The average driver has 10.2 years of experience and is 49.4 years old.

Strathman recommends refresher training courses for drivers and steps designed to reduce absenteeism, which causes the agency to rely more heavily on substitute drivers. He cautions that steps taken to save operating costs, such as scheduling split shifts and other variable work assignments, have a tradeoff in the form of higher safety costs. He also asserts that drivers’ adherence to tight schedules can be a safety concern, as drivers who start to fall behind schedule may take more risks to make up for lost time.

The research was made possible by the emergence of data from Intelligent Transportation Systems (ITS), data warehousing, and geographic information systems (GIS), which has created an opportunity to explore a dimension of safety that had not been systematically analyzed — the transit operating environment.  The study empirically analyzed accident frequency and severity using data from multiple TriMet databases, including the Accident/Incident Tracking System (ACID), the Bus Dispatch System (BDS), and Trans HR.  These databases provide information on vehicle characteristics, operating conditions, the nature of collisions and injuries sustained, and operator characteristics. Information on socio-demographics, land use, and transportation facilities was drawn from geographic databases maintained by Metro and the city of Portland.