Worst motorsports crashes ever

Does anyone here watch any motorsports races? If so, what was the most horrible motorsports crash you've ever seen?

For me, the most horrible motorsports crash I've ever seen was this one in the following video:

YouTube - Michael McDowell Nascar Crash 4-4-08

April 4, 2008. Michael McDowell, a NASCAR Nextel Cup rookie, was performing a qualifying attempt for the 2008 Samsung 500 at Texas Motor Speedway, when his car suddenly lost control and smashed into the wall, causing the car to barrel-roll several times while shedding debris everywhere AND with fire coming out of the engine compartment! But the most shocking thing of all is that he walked away completely unscathed!

What was the worst motorsports crash you've ever seen?

Typically when people talk about the 'worst' crash ever, they mean the 'best'. But if you really want to talk about the worst, it definitely is Ayrton Senna's at Imola 1994.

The crash didn't look bad, but it was enough to kill the three-time World Champion. Despite being champ 4 less times and winning less than half the amount of races than Michael Schumacher, people still acknowledge Senna as the fastest man to have ever stepped into an Formula One car. The loss of Senna was a massive loss for Formula One. His death was the last the sport has experienced. Car safety has improved tremendously since then, so much so that crashes like Robert Kubica's in Montreal in 2007 only kept him out of the cockpit for two weeks.

Here's another one from F1. Same year, but in Australia. David Coulthard almost decapitates Alex Wurz.

The best F1 crash for me was this one. One McLaren goes smacking into the wall on the left and bounces all the way across to the other side of the track, and this causes 10 or so cars behind it to get absolutely munched. Nobody died or was seriously injured, either.

I've seen spectacular wrecks in races at Talladega Superspeedway and Daytona International Speedway, where 20-30+ cars are involved. Such massive wrecks are known as "the Big Ones." They are very common at both tracks, especially the former.

Interestingly, the crashes that are most survivable are the ones that look the worst, such as the violent flips and barrel-rolls after the car goes airborne and upside-down. Some of these wrecks may sometimes cause the car to catch fire. But the ones that are truly the worst are the ones that go head on into the wall. They may not look that bad, but they can be fatal. That is exactly what happened to Dale Earnhardt in his fatal crash on the final lap of the 2001 Daytona 500. He got loose, and massively decelerated from 180+ mph, cutting across traffic at a sharp angle, hitting the wall head on. No fire, no catapulting into the air, and he died instantly of a type of injury known as a basilar skull fracture.

Seven years later, Michael McDowell survives a horrifying crash while using the newly-engineered Car of Tomorrow. He gets loose, hits the wall, catches fire, and barrel-rolls several times. The safety features of the new car, the SAFER barrier (Steel and Foam Energy Reduction), and the HANS device (Head and Neck Support) protected him. The crash was striking similar to the fatal crash of Gordon Smiley, an Indy driver, and was about 10 mph faster than Dale Earnhardt's fatal accident.