If you want to understand the debate about "soft walls" and concrete retaining walls in auto racing, think about bullets.
If a bullet hits a hard surface at a slight angle, say 20 degrees, it ricochets. The energy is channeled in another direction and lessened. But if it hits straight on, the bullet is flattened. Enormous energy is concentrated right then and there.
Imagine being a tiny passenger inside the bullet, and you understand the good and the bad of concrete retaining walls in racing.
Now, imagine that the bullet hits a "soft wall"--so-called because it's made of materials that dissipate the energy of crashes away from drivers' bodies. But if the bullet hits at even at a slight angle, it doesn't ricochet. It tends to get caught in the material, concentrate energy then and there, and cause damage to the material and the bullet.
In racing, the "bullet" is the car and the "material" is the soft wall.
There Are 'Snags'
That's the biggest unsolved problem with soft walls. If a material--be it rubber, polyethylene or high-density Styrofoam--contracts enough to cushion the blow of a crash satisfactorily, then the point of impact tends to pocket, acting "like a catcher's mitt," says engineer John Pierce, chief designer of the energy dissipation system generally considered furthest along in development.
That pocketing "snags" or "catches" the crashing car.
"That snagging is of great concern for two reasons," says John Melvin, an expert in racing safety. "One is that the snagging actually will be stopping the vehicle, and therefore adding to the crash energy. The other is, it could redirect the car in a violent way so that it interacted with other cars."
In other words, "You don't want something that's going to act as a spring to shoot the car across the track"--and possibly into the line of onrushing traffic, Pierce says.
Concrete retaining walls have been in use since the first Indianapolis 500, in 1911. They actually were considered state-of-the-art replacements for other types of barriers even through the 1970s and into the '80s. They surround every major American oval track but two--and those tracks, at Dover, Del., and Long Pond, Pa., have walls made of boiler-plate steel, just as unforgiving as concrete.
Concrete walls, though deadly in blunt impacts, usually redirect crash energy in a desirable way--that is, cars hit with glancing blows. The cars then continue to move generally in the direction in which they were traveling before the crash occurred.
To avoid creating new problems while solving old ones, any suitable new soft wall must allow this forward movement to continue after impact. Stopping the car completely and instantaneously would cause even higher concentrations of energy into the car itself--and, far more important, into a driver's body.
In racing, "there's a lot of contact with the [concrete] wall that's at a very slight angle," says Gary Nelson, NASCAR's chief technical officer. "Just a scrape. If the wall is soft at all, I think it would literally grab hold of the car and cause it to stop suddenly.
"Ninety-nine percent of contact with the [concrete] wall at a typical race is not even reported. It's just, 'A car scrapes the wall, the side of the car was flattened, the crew hammered it out, and it went back out a few minutes later.'
"Well, each of those would be a serious accident [with soft walls] in our opinion."
NASCAR Winston Cup cars weigh 3,400 pounds, more than twice as much as Indy cars. So a stock car, crashing at the same speed as an Indy car, produces far more energy, by a formula of physics: Mass times velocity equals energy. Thus, soft walls strong enough to absorb and withstand an Indy car hit aren't necessarily strong enough to deal effectively with a NASCAR hit.
An Overdue Idea
Despite some concerns about soft walls, there are so many designs so near fruition that track owners and sanctioning bodies are being forced rapidly toward a decision: Either they want to spend the money to develop and construct soft walls, or they don't.
Pierce's Polyethylene Energy Dissipation System (PEDS) is being tested at the University of Nebraska's auto-crash test center, with funding from the Indy Racing League and its parent, Indianapolis Motor Speedway.
"I think 25 years from now, we'll look back and say, 'Gosh, I can't believe they raced with concrete walls,' " says former NASCAR driver Ricky Craven, whose career was ruined by one.
In the first practice for the first Winston Cup race at posh new Texas Motor Speedway near Fort Worth in 1997, Craven's car slammed hard against the concrete retaining wall. Still hampered by the lingering effects of the concussion he suffered that day, Craven was held out of races by his Hendrick Motorsports team. He later was released from his contract, and he hasn't had a competitive ride since.