Previous commercial motor vehicle driver hours-of-service studies identified consistent increases in crash odds as driving time increased. These studies identified time-on-task as a significant indicator of the potential for a safety critical event (crash, near crash, or crash-relevant event). However, while these studies may have provided indication of a relationship between hours of service and the probability of a safety critical event, they largely failed to account for many potential confounding factors.
The hours-of-service relationship is frequently attributable to the fatigue of the driver. Confounding factors however, are factors that may also contribute to the likelihood of an incident and may potentially create a systematic bias or contribute to measured error. This study sought to uncover existing relationships between hours-of-service observations and a set of potential confounding factors related to time of day.
Because of data heterogeneity, advanced econometric methods were applied, to produce the most accurate estimates and to make inferences appropriately. Three issues were investigated to better understand the effects of hours of service on large truck drivers’ safety: finding safe and adequate parking, using a cell phone while driving, and lane changing behavior.
Conclusions drawn from hours-of-service related studies affect millions of people and have economic impacts in the billions. Faulty scientific inferences from these studies can have high human and economic costs. Therefore, the work described in this study was needed to validate the findings of these studies, as well as other studies using similar designs and variables. In addition, the work described could lead to deeper insights into commercial motor vehicle crash risk and causation, with safety implications and applications beyond hours-of-service regulations.
From a policy standpoint, agencies can enact policies at the strategic operating level for private carriers to address factors that influence large truck drivers’ performance. For instance, this study showed that factors related to fatigue and driving hours management, such as restrictions on the number of hours worked or schedules that enable drivers to easily take breaks when fatigued, are effective at reducing the likelihood that a truck driver will be involved in safety critical events. Moreover,
commercial motor vehicle carriers can develop and enforce similar policies within their companies to reduce the occurrence of distracted driving among their truck drivers.
Authors:
Salvador Hernandez
Nabeel Saleem Saad Al-Bdairi
Oregon State University
Eric L. Jessup, WSU School of Economic Sciences
Sponsor: PacTrans