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Driver impairment
Driver impairment describes factors that prevent the driver from driving at their normal level of skill. Common impairments include:Alcohol
According to the Government of Canada, coroner reports from 2008 suggested almost 40% of fatally injured drivers consumed some quantity of alcohol before the collision.
Physical impairment
Poor eyesight and/or physical impairment, with many jurisdictions setting simple sight tests and/or requiring appropriate vehicle modifications before being allowed to drive.
Youth
Insurance statistics demonstrate a notably higher incidence of collisions and fatalities among drivers aged in their teens or early twenties, with insurance rates reflecting this data. These drivers have the highest incidence of both collisions and fatalities among all driver age groups, a fact that was observed well before the advent of mobile phones.Females in this age group exhibit somewhat lower collision and fatality rates than males but still register well above the median for drivers of all ages. Also within this group, the highest collision incidence rate occurs within the first year of licensed driving. For this reason, many US states have enacted a zero-tolerance policy wherein receiving a moving violation within the first six months to one year of obtaining a license results in automatic license suspension. South Dakota is the only state that allows fourteen-year-olds to obtain drivers' licenses.
Old age
Old age, with some jurisdictions requiring driver retesting for reaction speed and eyesight after a certain age.
Sleep deprivationVarious factors such as fatigue or sleep deprivation might increase the risk, or numbers of hours driving might increase the risk of an incident. 41% of drivers self report having fallen asleep at the wheel.: 41  It is estimated that 15% of fatal crashes involve drowsiness (10% of day time crashes, and 24% of night time crashes). Work factors can increase the risk of drowsy driving such as long or irregular hours or driving at night.
Drug use
Including some prescription drugs, over the counter drugs (notably antihistamines, opioids and muscarinic antagonists), and illegal drugs.
Distraction
Research suggests that the driver's attention is affected by distracting sounds such as conversations and operating a mobile phone while driving. Many jurisdictions now restrict or outlaw the use of some types of phone within the car. Recent research conducted by British scientists suggests that music can also have an effect; classical music is considered to be calming, yet too much could relax the driver to a condition of distraction. On the other hand, hard rock may encourage the driver to step on the acceleration pedal, thus creating a potentially dangerous situation on the road.Cell phone use is an increasingly significant problem on the roads and as the U.S. National Safety Council compiled more than 30 studies postulating that hands-free is not a safer option, because the brain remains distracted by the conversation and cannot focus solely on the task of driving.
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