Vehicular suicide is the use of a motor vehicle to intentionally cause one's own death. Suicide by carbon monoxide poisoning may be attempted by running the engine in an enclosed garage, or by piping the exhaust gas into the driver's compartment with a hose, but catalytic converters required for air quality regulations eliminate over 99% of carbon monoxide produced.
Intentional traffic collisions may be a chosen method of suicide where speed limits are high enough to produce fatal deceleration. Modern cars have high rates of acceleration and can easily reach very high speeds in short distances, while most cannot protect occupants in frontal impact collisions exceeding 70 km (43 mi) per hour. Motor vehicles are ideal self-injurious or self-destructive instruments for persons intent upon camouflaging their suicidal motivation from others, because widespread use of the word accident implies traffic collisions are unintentional. The percentage of suicides among the tens of thousands of people killed annually in United States traffic collisions is unknown because suicides are often misclassified as accidents if no suicide note is found. Considering the large number of suicides by other methods, it would be remarkable if vehicles were less used as a convenient method of self-destruction avoiding insurance and religious complications.
The probability and severity of traffic collisions may be increased by suicidal behaviors including drunk driving and speeding. These risky driving behaviors are associated with depression as contributing factors to vehicular suicide. Impact velocity may be maximized by exceeding speed limits or by maneuvering into a head-on collision with a heavier and less maneuverable vehicle like a bus or semi-trailer truck. Crash investigators found head-on collisions with heavier vehicles were a more common suicide method than the single vehicle crashes sometimes assumed to be more typical. These suicidal collisions may kill or injure others.
Aside from use for premeditated suicides, as commuters spend more time driving, vehicles may be available at the instant of a momentary and temporary impulse towards self-destruction fueled by road rage. Suicides comprise nearly two-thirds of the 33,000 annual gun deaths in the United States. Motor vehicles remain widely available while gun control reduces access to firearms. The percentage of traffic fatalities which are suicides appears to be increasing with time.
Understanding the fraction of traffic fatalities attributable to suicide is important because many traffic safety measures are unlikely to influence suicides. Unmeasured suicides in empirical data used to evaluate traffic safety measures will result in systematic underestimation of effectiveness for non-suicidal road users.
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