Truck drivers in California and around the country are subject to a federal regulation which attempts to prevent drivers who are ill or extremely tired from operating their vehicles. Unfortunately, it provides no standard by which fatigue can be fairly judged, and scientific efforts to develop a reliable test have yet to come to fruition.
The U.S. Department of Transportation has sponsored a report that collects and organizes research into fatigue measurement. One of the major conclusions of the study is that there is still a long way to go. Although there is a link between driver fatigue and the risk of a vehicle crash, attempts to quantify it precisely and render it subject to rigorous scientific testing have so far been unsuccessful.
In fact, there is currently no reliable method to detect fatigue. It is not even known precisely what relationship sleep impairment disorders such as apnea might have on rest, recuperation, exhaustion and driver fatigue. The current system limits the hours of operation, but the regulations cannot cover what people do during the off hours. There is no way to ensure that they rest, only that they do not drive for some time.
Proving fatigue may be complex. If an 18-wheeler accident causes others who are on the road at the time to be seriously injured, then a personal injury attorney may have to review accident investigation reports, eyewitness testimony and other evidence in order to pinpoint responsibility. In many cases, the trucking company itself could be named as a defendant under the theory of vicarious liability.
Source: Overdrive Online, "Amid 'fatigued driver' out-of-service discussions, panel releases report on research into fatigue measurement", Todd Dills, March 10, 2016