A side collision, also called a T-bone accident, is a vehicle crash where the side of one or more vehicles is impacted. These crashes typically occur at intersections, in parking lots, and when two vehicles pass on a multi-lane roadway.

A 2016 study found that, in the EU, side impact collisions were significantly less common than frontal impact collisions, at rates of 22-29% and 61-69% respectively. However, they tend to be much more dangerous. Another report commissioned by the EU in 2015 found that side impacts accounted for roughly 35-40% of passenger fatality and serious injury, as opposed to 55% attributed to head-on collisions. A likely contributor to this fact is the amount of protection offered by the struck vehicle. Even when equipped with the safest cars on the road, these casualties occurred at much lower speeds than in head-on collisions, with passenger fatality and serious injury typically occurring at 50 km/h (~31 mph) in side impact collisions, as opposed to 70 km/h (~43 mph) for frontal impacts. Additionally, side impacts tend to affect more vulnerable areas of the body. While front and rear impacts typically produced the most serious injuries in the lower extremities (legs and feet), side impacts typically resulted in most serious injuries in the head and chest regions.

In 2008, a total of 5,265 (22%) out of 23,888 people were killed in vehicles which were struck in the side in the United States.

For European motorcyclists, side impact is the second most frequent location of impact.

For European cyclists, thorax injuries are associated with side-impact injuries in urban areas and/or at junctions.

In several European countries, such as the UK, Sweden, and France, around one quarter of traffic injuries are produced by side collisions, but accounted for 29 to 38% of injuries which were fatal.

In European vehicle side impact, 60% of casualties were "struck side", while 40% were "non struck side", in 2018.

Fatal casualties count as 50% and 67% in UK and in France, in 2010