I found this description of the video on a computer website:

Computerworld - A dramatic Web-based video depicting four deaths caused by a young driver who was texting at the wheel has provoked a debate over the best ways to curb distracted driving in the U.S.
Some experts favor more laws banning texting while driving, while others favor technology that disables wireless service in a moving vehicle. However, psychologists see a valuable place for dramatic presentations like the latest graphic video produced by police in Wales, arguing that such tools can have an impact in educational settings, especially on young drivers.
The four-minute video, produced by local police in Gwent, Wales, has gone viral, attracting more than 1.5 million views on YouTube alone. YouTube has restricted viewings to those over 18 because of the bloody, graphic nature of the video; it's also requiring people to register before viewing it, although the video has been posted at the Gwent police Web site and elsewhere without restrictions. However, YouTube's restrictions have worked inconsistently, sometimes requiring a registration and other times not.
In a statement on its site, the Gwent police department said it is hoping the video can be used in schools across the U.K. to deter texting while driving. The Gwent police helped facilitate the filming of the video, including the auditions of 300 teenagers from Wales, "because we want to stop ALL drivers, but particularly young and new ones, from causing accidents," the statement said.
In the video, a teenage girl named Cassie Cowan texts on her cell phone while driving with two other girls. Her vehicle crosses the middle of the road, colliding head-on with an oncoming car. The two cars careen off the road, the girls exchange glances with bloodied faces, then a third car violently strikes Cassie's car in the side.
Much of the video is devoted to the aftermath at the scene, including Cassie screaming at her apparently dead friend, and footage of victims in another car, including an infant and a young girl, who asks why her parents won't wake up.
NBC's Today show broadcast portions of the video and questioned an advertising executive about the effectiveness of such a disturbing public service announcement in the ongoing debate over texting and driving.
Today noted that the dramatization is too graphic to be fully shown on most U.S. television stations, but the video has provoked some experts to debate the most effective means of curbing texting, which is already illegal in 17 states and the District of Columbia.