A traffic collision, also called a motor vehicle collision, car accident, or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other 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 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.

A number of factors contribute to the risk of collisions, including vehicle design, speed of operation, road design, 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 in 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.
Some organizations have begun to avoid the term "accident", instead preferring terms such as "collision", "crash" or "incident". This is because the term "accident" implies that there is no-one to blame, whereas most traffic collisions are the result of driving under the influence, excessive speed, distractions such as mobile phones or other risky behavior.
Historically, in the United States, the use of terms other than "accidents" had been criticized for holding back safety improvements, based on the idea that a culture of blame may discourage the involved parties from fully disclosing the facts, and thus frustrate attempts to address the real root causes.

A number of physical injuries can commonly result from the blunt force trauma caused by a collision, ranging from bruising and contusions to catastrophic physical injury (e.g., paralysis) or death.

Psychological:
Following collisions, long-lasting psychological trauma may occur. These issues may make those who have been in a crash afraid to drive again. In some cases, the psychological trauma may affect individuals' life can cause difficulty to go to work, attend school, or perform family responsibilities.
A 1985 study by K. Rumar, using British and American crash reports as data, suggested 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. Reducing the severity of injury in crashes is more important than reducing incidence and ranking incidence by broad categories of causes is misleading regarding severe injury reduction. Vehicle and road modifications are generally more effective than behavioral change efforts with the exception of certain laws such as required use of seat belts, motorcycle helmets, and graduated licensing of teenagers.

Traffic collision affect the national economy as the cost of road injuries are estimated to account for 1.0% to 2.0% of the gross national product (GNP) of every country each year. A recent study from Nepal showed that the total economic costs of road injuries were approximately $122.88 million, equivalent to 1.52% of the total Nepal GNP for 2017, indicating the growing national financial burden associate with preventable road injuries and deaths.

Legal consequences:
There are a number of possible legal consequences for causing a traffic collision, including:
-Traffic citations: drivers who are involved in a collision may receive one or more traffic citations for improper driving conduct such as speeding, failure to obey a traffic control device, or driving under the influence of drugs or alcohol. Convictions for traffic violations are usually penalized with fines, and for more severe offenses, the suspension or revocation of driving privileges.
-Civil lawsuits: a driver who causes a traffic collision may be sued for damages resulting from the accident, including damages to property and injuries to other persons. Criminal prosecution: More severe driving misconduct, including impaired driving, may result in criminal charges against the driver. In the event of a fatality, a charge of vehicular homicide is occasionally prosecuted, especially in cases involving alcohol. Convictions for alcohol offenses may result in the revocation or long term suspension of the driver's license, and sometimes jail time, mandatory drug or alcohol rehabilitation, or both.