In the last few years, the term soft walls has entered the racing vocabulary, but how much do we really know about them? A better question is, How do they apply to short-track and local track racing? Understanding the physics behind the soft walls (or Energy Dissipating Barrier) provides a better appreciation of their application in motorsports.

There are a few types of soft walls. Some have been in design for more than 10 years, while others have been a reaction to current problems.

Crash energy would be dissipated without the soft wall in place. The key element of the soft wall is where and how quickly the energy is dissipated. Without the soft wall, the energy is dissipated by the crush of the race car and takes the minimum time possible. It is the high crash energy, or impulse, over a short time that causes the most injury to the driver.

With the soft wall in place, the crushing of the race car and the energy-absorber material dissipates the crash energy. The benefit is that the energy absorber (usually foam) is crushed over a large surface area. Increasing both the impact area and the amount of crushable mass will increase the duration of the accident while reducing the kinetic energy of the accident. This combination will provide a less intense impulse felt by the driver.

The standard concept of a soft wall features an inner wall design that is used to dissipate the energy of the car crashing into it. Most of the soft walls in the industry currently installed at Richmond, Indianapolis, Talladega, Phoenix, and Loudon are of the SAFER (Steel and Foam Energy Reduction) style. A group headed by Dr. Dean Sicking at the University of Nebraska-Lincoln's Midwest Roadside Safety Facility designed these walls.

"The total emphasis is on driver safety," says Sicking, professor of civil engineering. "We put in thousands of hours with computer models and on the test track to develop a barrier that would decrease peak forces applied to the car by elongating the impact event, which allows the occupant restraint systems more time to operate optimally and reduce driver injury."

The SAFER walls consist of a tubular steel wall with tremendous bending strength. The bending strength of the wall element will prevent it from wrapping around the front of the car and virtually eliminate the pocketing. The tubular steel is coated on the surface of this barrier with zinc rich paint. The zinc provides a lubricant, which further reduces the friction between the vehicle and the barrier. By reducing the friction, longitudinal deceleration is also reduced. This longitudinal deceleration pulls the car into the barrier, increasing the acceleration of the driver. Behind the tubular steel, the barrier incorporates spaced foam energy absorbers. These absorbers are made from polyethylene foam.

The early versions of the wall had solid sheets of polyethylene behind the steel, but the energy management properties of that design were not satisfactory. After more computer modeling by Sicking and his group, the spaced absorber design was developed. Through testing, this design showed superior energy management properties and reduced the amount of absorber material required.

The cost of this SAFER system is estimated to be a minimum of $175 per linear foot of wall. On longer, sweeping corners, the cost is closer to this figure. On shorter tracks, the tubes will actually have to be rolled to the radius of the racetrack, a procedure that will somewhat increase the cost. As you get to smaller and smaller tracks, the radii become tighter, and cost of the work required to get the tubular steel to fit increases.