here for crash video
The test uses a crash dummy strapped into a racing seat which is mounted inside a roll cage. The cage is offset thirty degrees, to represent a worst-case load on the head, and attached to a solid steel sled. The sled is accelerated down a set of tracks to a speed of about 35 mph. That may not sound fast, but when the sled slams into a hydraulic piston it comes to a complete stop in about 12 inches (30cm), generating the same force on the driver as a typical stock car crash into a concrete wall.
There is nothing dumb about the dummy. Inside it has sensors which monitor 33 different body reactions including displacements, forces and accelerations. All of these sensors feed information to an on-board computer at rates up to 10,000 times per second. A typical one-half second crash produces 165,000 pieces of data. Three high-speed digital cameras shoot from the front, top and side of the sled. They each record 1,000 frames per second and are synchronized to the data acquisition computer.
All this technology might sound impressive, but it doesn't come close to standing next to the track, watching live, as the sled makes impact. We can't print here what people typically say after witnessing their first crash test.
2006 SAE Motorsports Engineering Conference
#2006-01-3631 contains a collection of performance data for a variety
of head and neck restraints. The paper can be found here.
The comparative graphs contained in that presentation can be found here.