A traffic collision, also known as a motor vehicle collision or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other moving or stationary obstruction, such as a tree, pole or building. Traffic collisions often result in injury, disability, death, and property damage as well as financial costs to both society and the individuals involved. Road transport is statistically the most dangerous situation people deal with on a daily basis, but casualty figures from such incidents attract less media attention than other, less frequent types of tragedy. The commonly used term car accident is increasingly falling out of favor with many government departments and organizations: the Associated Press style guide recommends caution before using the term and the National Union of Journalists advises against it in their Road Collision Reporting Guidelines. Some collisions are intentional vehicle-ramming attacks, staged crashes, vehicular homicide or vehicular suicide.

Several factors contribute to the risk of collisions, including vehicle design, speed of operation, road design, weather, road environment, driving skills, impairment due to alcohol or drugs, and behavior, notably aggressive driving, distracted driving, speeding and street racing.

In 2013, 54 million people worldwide sustained injuries from traffic collisions. This resulted in 1.4 million deaths in 2013, up from 1.1 million deaths in 1990. About 68,000 of these occurred with children less than five years old. Almost all high-income countries have decreasing death rates, while the majority of low-income countries have increasing death rates due to traffic collisions. Middle-income countries have the highest rate with 20 deaths per 100,000 inhabitants, accounting for 80% of all road fatalities with 52% of all vehicles. While the death rate in Africa is the highest (24.1 per 100,000 inhabitants), the lowest rate is to be found in Europe (10.3 per 100,000 inhabitants).

Traffic collisions can be classified by general types. Types of collision include head-on, road departure, rear-end, side collisions, and rollovers.

Many different terms are commonly used to describe vehicle collisions. The World Health Organization uses 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" (MVTC). Other common terms 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), and road traffic incident (RTI) as well as more unofficial terms including smash-up, pile-up, and fender bender

Many organizations, companies and government agencies have begun to avoid the term accident, instead preferring terms such as collision, crash or incident. This is because the term accident may imply that there is no one to blame or that the collision was unavoidable, whereas most traffic collisions are the result of driver error such as driving under the influence, excessive speed, distractions such as mobile phones, other risky behavior, poor road design, or other preventable factors.

In 1997, George L. Reagle, the Associate Administrator for Motor Carriers of the Federal Motor Carrier Safety Administration wrote a letter stating that "A crash is not an accident", emphasizing that the Department's Research and Special Programs Administration, the Federal Highway Administration, and the National Highway Traffic Safety Administration had all declared that "accident" should be avoided in their published writings and media communications. In 2016, the Associated Press updated its style guide to recommend that journalists use "crash, collision, or other terms" rather than "accident" unless culpability is proven. The AP also recommends avoiding "accident" when negligence is proven or claimed because the term "can be read as exonerating the person responsible." In 2021, the American Automobile Association (AAA) passed a resolution to replace "car accident" with "car crash" in their vocabulary. In 2022, the traffic management company INRIX announced that "accident" would be removed from their lexicon. In 2023, the National Union of Journalists in the UK published the Road Collision Reporting Guidelines which includes a recommendation that journalists should "Avoid use of the word ‘accident’ until the facts of a collision are known."

The Maryland Department of Transportation's Highway Safety Office emphasizes that "crashes are no accident", saying that "Using the word accident suggests that an incident was unavoidable, but many roadway crashes can be attributed to human error." The Michigan Department of Transportation states that "accident" should be dropped in favor of "crash", saying that "Traffic crashes are fixable problems, caused by inattentive drivers and driver behavior. They are not accidents." In line with their Vision Zero commitments, the Portland Bureau of Transportation recommends using "crash" rather than "accident".