It takes a lot of speed to mangle a car like this. The oldest kid in the car was 20.
Looking at the site on Google Earth, it looks like this is where John Travolta lives--his house connects to the runway that these stupid kids were on, and Travolta's 707 is plainly visible.
Looking at the scale, it seems like the runway's around 15,000 feet long--a bit shy of three miles. The article says there were "skid marks" at the end, and if the address in the article is right the wreck happened somewhere near the north end of the runway.
So here's my theory:
One kid gets a new BMW and one of his friends says, "Let's see how fast it can go!" The one tiny bit of good sense they have is expended on thinking, "There's a long runway near here. Let's go use that so we don't get caught speeding!"
Once on the runway, they get set up at one end and start off towards the other, pedal to the floor. Only they don't know how long the runway is, and so the driver is startled when he sees the end coming up far too fast. He stands on the brakes, the car flies off the 80-foot embankment, and ends up smashing into a tree 200 feet from the end of the runway, still 15 feet off the ground.
The link to the story shows a hunk of mangled scrap metal; it appears to be the largest single piece of the car remaining, but the car split into several parts upon impact. Three of the occupants were ejected on impact. The police don't know if any of them were wearing seatbelts but--let's face it--in that kind of wreck, safety equipment just no longer matters. The typical seatbelt and air bag system both depend on the car's basic structure remaining intact.
If the thing had landed on flat ground I doubt the kids would have fared any better.
According to my calculations, they hit the tree going about 70 MPH. The runway is 85 feet above ground, they struck the tree 15 feet up, and they traveled 200 feet before striking the tree--all of this is enough information for me to conclude that they fell 70 feet from the moment they left the runway until they struck the tree. It takes slightly more than two seconds for any object to fall 70 feet in Earth gravity, so it took them about that time to traverse the 200 feet between the end of the runway and the tree. Ergo, a speed of about 100 feet per second, or a bit less than 70 MPH.
At 100 MPH they would have fallen only 29 feet before striking the tree 56 feet above ground.
...not that it matters. Dead is dead, and being dead of stupidity still gets you nominated for a Darwin Award.