A number of factors contribute to the risk of collision including; vehicle design, speed of operation, road design, and driver impairment. Worldwide motor vehicle collisions lead to significant death and disability as well as significant financial costs to both society and the individual.

Many different terms are commonly used to describe vehicle collisions. The World Health Organization use the term road traffic injury, while the U.S. Census Bureau uses the term motor vehicle accidents (MVA) and Transport Canada uses the term "motor vehicle traffic collision". Other terms that are commonly used include auto accident, car accident, car crash, car smash, car wreck, motor vehicle collision (MVC), personal injury collision (PIC), road accident, road traffic accident (RTA), road traffic collision (RTC), road traffic incident (RTI), road traffic accident and later road traffic collision, as well as more unofficial terms including smash-up and fender bender.

Some organizations have begun to avoid the term "accident". Although auto collisions are rare in terms of the number of vehicles on the road and the distance they travel, addressing the contributing factors can reduce their likelihood. For example, proper signage can decrease driver error and thereby reduce crash frequency by a third or more. That is why these organizations prefer the term "collision" rather than "accident".

However, treating collisions as anything other than "accidents" has been criticized for holding back safety improvements, because a culture of blame may discourage the involved parties from fully disclosing the facts, and thus frustrate attempts to address the real root causes.

Motor vehicle collisions can be classified by mechanism. Common mechanisms include head-on collisions, run-off-road collisions, rear-end collisions, side collision, and rollovers.

The definition of a road-traffic fatality varies from country to country. In the United States, for example, the definition used in the Fatality Analysis Reporting System (FARS) run by the NHTSA is a person who dies within 30 days of a crash on a US public road involving a vehicle with an engine, the death being the result of the crash. In the U.S., therefore, if a driver has a non-fatal heart attack that leads to a road-traffic crash that causes death, that is a road-traffic fatality. However, if the heart attack causes death prior to the crash, then that is not a road-traffic fatality.

The definition of a road accident fatality can change with time in the same country. For example, fatality is defined in France as a person who dies in the 6 days (pre 2005) after the accident; in the 30 days (post 2005) after the accident..

A 1985 study by K. Rumar, using British and American crash reports as data, found that 57% of crashes were due solely to driver factors, 27% to combined roadway and driver factors, 6% to combined vehicle and driver factors, 3% solely to roadway factors, 3% to combined roadway, driver, and vehicle factors, 2% solely to vehicle factors and 1% to combined roadway and vehicle factors.

A 1985 report based on British and American crash data found driver error, intoxication and other human factors contribute wholly or partly to about 93% of crashes.

An RAC survey found most British drivers think they're better drivers than non-British drivers. Nearly all drivers who'd been in a crash did not believe themselves to be at fault. One survey of drivers reported that they thought the key elements of good driving were: