According to the Transportation Safety Board of Canada (TSB), sleep and fatigue often leave no clues for investigators to trace. Unlike alcohol-related crashes, no blood, breath, or other test is currently available to determine levels of sleepiness at the time of a crash. This leaves investigators with little hard data on which to base a conclusion of fatigue or sleep as a cause or contributing factor.
Despite the data limitations, the TSB estimates about 5% of fatal crashes are firmly established as being caused by drowsy driving. Experts suggest the actual number may be as high as 20% to 40%. And that makes drowsy driving as dangerous as drinking and driving, which accounts for approximately 24% of all victims in vehicle fatalities.