Editorial

Safer walls, please!

 by Mark Cipolloni
December 29, 1999

Can concrete oval track walls be made safer?  We think they can be.  We owe it to the drivers, their families and to our sport to try! (Note: I originally wrote this article about making oval track walls safer on November 16, 1996 and SpeedCenter published it).


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Introduction
Since auto racing began in earnest in the early 1900’s the sport has witnessed countless fatal accidents and serious injuries, particularly on oval race tracks. The problem is not with oval tracks themselves, but with the inherent high speeds on ovals and the rigid concrete walls which protect the viewing public from an out of control race car(s). We all know what happens when a high speed vehicle strikes an immovable object such as a wall. The driver can be seriously injured.

This past year (1996) alone the following CART and IRL drivers sustained serious or fatal injuries on oval tracks:
Scott Brayton, Alessandro Zampredri, Buddy Lazier, Eliseo Salazar, Stan Wattles, Eddie Cheever, Dan Drinan, Brad Murphey, Tony Stewart, Mark Dismore, Mark Blundell, Scott Goodyear, Paul Tracy and Emerson Fittipaldi (in 1998 and 1999 Greg Moore lost his life on an oval track and spectators were killed at Michigan and Charlotte.  Gonzalo Rodriquez lost his life against a concrete wall as well).

This list only includes Indy Car drivers injured on oval tracks. If you include all other forms of oval track racing, I’m sure the list would number well over 100 in just one year!

It's Time To Do Something About It

In my opinion, the racing community has not done all it can to alleviate this problem. Sure, the cars are much safer today, but racing is about speed. It always has been and always will be. With speed comes very high impact forces when a car hits one of the immovable concrete retaining walls.

To compound the problem, new oval tracks are popping up all over the place with the same unforgiving walls used for the last 75 years. Primarily because of the litigious society we live in, track owners, and the engineers they hire to design them, are so concerned with protecting the viewing public from out of control race cars, they fail to consider alternative wall systems that can protect the fans AND reduce injury to the driver.

Although disheartened by it, the racing community accepts the death and injuries to the drivers because auto racing is dangerous and the drivers know the risk and are willing to take it. I say hogwash! It is time we put our heads together and examine everything we can do to reduce this danger!

To gain a better understanding of this problem let’s first examine the forces involved in a racing accident and then discuss a proposed solution. Try to bear with me through the following Physics lesson. I have tried to put it in layman’s terms. Understanding the physics will help you to understand my proposed solution to this problem.

A Lesson In Physics

The following physics exercise is meant to give you an understanding of the force a car strikes a solid concrete wall with and the forces that a 'soft wall' deal with.  The actual forces the driver feels is a bit more complicated and is directly related to how much 'crush' zone a car has.  In rough terms, a race car needs a crush zone of about 3 feet to keep the 'g' forces a driver feels in the 50 to 60 range, a range thought to be survivable in almost all cases.

An object in motion has kinetic energy. The magnitude of the kinetic energy depends on both the mass and the speed of the object according to the equation:

E = 0.5mv2

where m is the mass of the object and v2 is its speed multiplied by itself. The change in a vehicles energy, ‘delta E’, can be derived from the equation:

‘delta E’ = (m x a)d

where ‘a’ is the acceleration (or deceleration, also known as negative acceleration) applied to the mass, ‘m’, and ‘d’ is the distance through which ‘a’ acts. For an object subjected to a planet’s gravitational forces, the ‘m x a’ portion of the second equation, mass ‘m’ times acceleration ‘a’ is equal to an object’s weight (also known as force), something we all can relate to. Because the acceleration due to gravity on earth is a constant, your weight is a function of your mass, or the amount of matter you are made of. For example, the body of a small person is made up of less matter/mass than a large person. Hence the large person has more matter/mass, and hence more weight (m x a).

When an object is lifted from a surface a vertical force (gravity) is applied to the object. As this force acts through a distance, energy is transferred to the object. The energy associated with an object held above a surface is termed potential energy. If the object is dropped, the potential energy is converted to kinetic energy as it accelerates ‘a’ due to gravity at the rate of 32.17 feet per second squared. The further the distance ‘d’ that object accelerates due to gravity the more energy it gains.

Once an object is no longer accelerating or decelerating it is no longer gaining or losing energy. In other words, a car traveling at a constant velocity has energy equal to the first equation, but it is not gaining or losing energy as per the second equation because ‘a’ = zero. In outer space, that same object has no weight nor energy in the vertical direction because there is no acceleration downward due to gravity. However, it can have kinetic energy if propelled in any direction.

The kinetic energy of a vehicle hitting a wall is a function of it’s mass (i.e. density), the angle at which it hits, and the velocity in the horizontal direction, and can be represented by the following equation:

E = 0.5m(v sin(t))2

where t = the angle between the vehicle’s center of mass as it impacts the wall, and a tangent to the wall at the point of impact. If we assume an average impact angle of 30 degrees or less, the actual energy of the car hitting the wall is 25% of what it would be head-on (sin 300 squared = 0.25). Therefore, shallow angle impacts tend to be less severe than more direct hits.

We have heard that drivers sustain loads as high as 100 g’s in an accident. 1 ‘g’ is the force equal to one earth’s gravity on your body. 100 g’s would be equivalent to a person lying on you weighing 100 times as much as you. Not a pretty sight I’m sure.

Although the general public is familiar with the term ‘g’ forces in a racing accident, actually gravity has nothing to do with the severity of a crash. The same race car traveling at 200 mph in outer space (and weighing zero) hitting an immovable concrete wall would sustain the same damage as it does here on earth. Gravity acts in the vertical direction. For the most part, a race cars velocity (and energy) is in the horizontal direction. So gravity, or ‘g’ forces are just a way for the average person to understand the magnitude of the force felt by the driver.

Let’s try to explain this in simpler terms. If a bird feather, which is not very dense (i.e. it has almost zero mass), were to impact a wall at 200 mph, it would hit with very little force because it has almost zero energy to dissipate with a mass that's almost nothing. Likewise, an Indy Car traveling at 200 mph has less than 1/2 the energy of a 200 mph NASCAR Winston Cup car to dissipate because it has less than 50% of the mass. That same Indy car has four times as much energy to dissipate at 200 mph than it does at 100 mph because energy is a function of speed squared. To look at it another way, a crashing car would apply a force 4 times as great on a concrete wall at 200 mph than it would at 100 mph.

The trick to driver safety is to dissipate the energy of the vehicle over a distance great enough to allow the drivers body, and the car, to decelerate at a reasonable rate. To exaggerate what I mean let’s use this analogy - if a 200 mph Indy car gradually comes to a stop in 1,000 feet, the driver feels very little ‘g’ forces on their body because the deceleration ‘a’ is very small. If a 200 mph race car hits a wall head on and comes to a stop in the distance it takes for the front of the car to crush against the driver’s body, fatal injury results because the deceleration ‘a’ is very large and the immovable wall exerts an equal and opposing force (i.e. the mass of the car and driver times a very large deceleration ‘a’ against the car and driver, until they stop. The human body can not withstand that amount of force.

However, the key point to understand here is that either the walls will have to crush about 3 feet, or the cars will need crush zones of about 3 feet to keep the 'g' forces the driver feels in the 50 to 60 range (3 feet was derived from knowing the range of speed a race car might hit a wall).  In other words, it's not really the mass of the vehicle that will determine how much 'g' force a driver feels, but the amount of distance the car decelerates over a given time period.  The only real issue with vehicle mass is the design of the vehicles crush zone.  A heavier vehicle will require a stronger, and possibly more complicated crush zone.  Winston Cup car, for example, needs properly designed crush zones, and if they weighed less, the design of that crush zone would be a little easier. The crush zone must work not only in head-on accidents, but in accidents up to about 30 degrees as well.  We will address crush zones in another article and urge NASCAR to start designing them into their cars as soon as possible

So How Do We Make Walls Safer?

An out of control car has a given amount of energy (E) as it approaches a wall. To dissipate that energy we must do one of three things:

1. Reduce the cars mass or velocity so it has less energy to dissipate. We can make the cars with less material but then they will be lighter and the speeds will go up, so scratch that idea. We can limit the horsepower so the cars only go 100 mph, but that would be like driving on the New Jersey Turnpike, so scratch that idea too. However, keeping speeds from increasing much beyond today’s levels would be very prudent.

2. Reduce the deceleration. We can put 10 rows of bundled tires in front of the walls so the car decelerates gradually and comes to a safe stop, however, there would be no track left on which to race.

3. Increase the distance over which the car changes speed by building flexibility into the walls. This is analogous to reducing the deceleration. The current walls DO NOT MOVE. Therefore, the distance over which a car decelerates is, for the most part, zero.

Because the concrete walls are very rigid during the initial impact (the most critical moment), the distance ‘d’ to dissipate the car’s energy, is entirely within the car crushing against the wall. Instead, if ‘d’ were increased by the amount a wall ‘gives’ or compresses, some the kinetic energy of the car could be dissipated by the wall, giving the wall enough time to redirect the car’s energy parallel to the wall where it can be scrubbed off gradually. That is the KEY point to remember.

Having read the physics lesson above, hopefully you will understand that speed is the major contributor to a vehicles energy. However, this sport is all about speed and engineers will always find a way to make cars go faster. Therefore, number 3 is what I would like to concentrate on. If we increase the ‘give’ of the walls, thereby increasing ‘d’ in the above equation, the deceleration ‘a’ will be less (for a given amount of change in kinetic energy), and hence the force of the wall against the car will be reduced proportionately in those CRITICAL initial milliseconds of impact. If we can reduce the forces of the car against the driver during initial impact, the likelihood of the driver surviving or sustaining only minor injuries will be much greater.

I can tell you that NO wall will ever be 100% safe, but any improvement is better than none. As long as we have 1,500 to 3,000 pound race cars circling a track at speeds near, or above 200 mph, racing will be a dangerous sport.

Safety Is NOT Just About Walls

Safety is not only about concrete walls. It is a total package. The cars and equipment must be as safe as possible. Car, driver’s clothing, and helmet manufacturers must continue to improve the safety of their products. Sanctioning bodies must keep speeds in check and continually improve the rules to make the sport safer, without reducing the excitement that comes with speed. AND we must find a way to improve the safety of the concrete walls. We must improve the overall package.

Goals for A Safer Wall

1. It must reduce the critical initial impact forces on the car and driver.

2. It must still contain the car and protect the fans.

3. We don’t want the wall to ‘catch’ the car. If the wall catches the car, such as an impact attenuator on a highway does, the deceleration will be too great because the distance ‘d’ would be too small to bring it from 200 mph to zero mph. The wall must still allow the car to scrub off speed by skidding along it.

4. It must not be cost prohibitive.

5. We are not as concerned about glancing blows as we are about more direct impacts at 30 degrees or more (head-on being 90 degrees or perpendicular). Therefore, the wall system must work as it does today for glancing blows, but work differently when struck by a car at a more direct angle.

6. It must work for new tracks and existing tracks.

7. It must work for light Indy Cars as well as heavy NASCAR Winston Cup cars.

8. It must be easy to fix during a normal caution period.

9. It must be suitable for traditional advertisements on the inside surface.

10. It must not decrease other aspects of safety, such as propelling a car back into the path of other racing cars.

A Proposed Solution - A Cushioned Wall System

It is time to think of the next generation of crash walls as a ‘system’ of components that work together to perform a function of containing the car, but flexing enough to reduce the danger to the driver.

Bundled tires have worked very effectively on road courses to cushion the impact of a crashing race car. However, speeds on oval tracks are much higher, and if you remember the physics lesson above, the impact force on the car and driver is a function of speed squared. We would probably need tires bundled 10 rows deep to protect a driver as well on ovals as they do on road courses. Oval tracks are not wide enough to accommodate that many rows of tires so we must live with a compromise solution.

With that and the above goals in mind, here is what I propose as a solution. The illustration below represents my initial ideas on what a wall system might look like. It is composed of the existing concrete wall and chain link safety fence, supplemented with one row of bundled tires and gel filled rubber bladders, with a smooth semi-hard plastic or rubber enclosure.



The gel filled bladders supplement the tires in dissipating energy. They can be of varying stiffness to accommodate both light and heavy cars. The plastic/rubber enclosure wall separating the tires from the race car provides for a smooth surface so cars hitting it at a shallow angle can ride along it scrubbing off speed in the process, similar to the way they do today.  This smooth facing is a VERY important part of the 'system' (Note - I feel the tire wall used in RIO has a rubber enclosure that has too high a coefficient of friction which tends to 'grab' the car too much).   However, when impacted at a more dangerous, direct angle, the wall compresses a lot more and dissipates SOME of the energy before redirecting the car along the wall to lose the rest of its velocity/energy. A two foot wide wall that compresses up to, say, 1.5 feet, is not enough to dissipate all the cars energy, but the deceleration force experienced by the driver will be an improvement over an immovable wall in those very early moments of impact.

For new race tracks the designers may want to offset the concrete wall back a little further to accommodate two rows of tires instead of one.

Conclusions

Lets examine if the above wall could meet our goals stated above:

1. Does it reduce the impact forces on the car and driver? Yes, it does. The amount depends on the flexibility of the wall, the mass/weight of the car, its speed and how fast it decelerates, and its angle of impact. The fact that the proposed wall will compress up to 18" or so means that the deceleration forces that sometimes measure 100 g’s at initial impact will be reduced when compared to an immovable wall.

2. Can it contain the car and protect the fans? Yes, the existing concrete wall and safety fencing are still in place. They have proven to have the necessary strength to retain the cars in almost all circumstances.

3. Does the wall still allow the car to scrub off speed by skidding along it? Yes, although the wall system compresses, the rubber tires and gel filled bladders have a natural tendency to rebound, albeit very slightly. At the same time, the semi-hard, smooth plastic enclosure allows a car to skid along the face of the wall, not caught by it. Because the enclosure around the tires prevents the car from snagging them, it reduces the chance of the car decelerating too fast.

4. Is the wall overly expensive? It’s hard to say. How do you put a price on a drivers life? The materials to construct the wall - used tires, gel, semi-hard plastic, rubber gel filled bladders are all readily available and easily manufactured. If mass produced, the cost can probably be kept reasonable. The construction of the wall is straightforward and can be done by a good contractor. Think of all the old tires that won’t end up in some landfill polluting our environment. Most importantly, all components proposed for this system would be designed to be maintenance free except during a very severe impact where the plastic enclosure may break and need replacing, or the tires and gel bladders may have to be retied together.

5. Does the wall system work as a traditional wall for glancing blows, but work differently when struck by a car at a more direct angle? Yes, the proposed wall can be designed to have enough stiffness and rebound to guide a car hitting it at a glancing blow, yet compress when impacted at a more direct angle. The semi-hard plastic enclosure wall also helps to distribute the forces over a larger number of tires behind it. As the wall is impacted, the enclosure wall, bundled tires, and gel-filled bladders would compress as a unit, and help to then guide the car parallel to it as it scrubs off additional energy.

6. Does it work for new tracks and existing tracks? Yes, the wall can be retrofitted to any existing concrete wall or new wall. Approximately 2’ to 3' of track width will be lost in a part of the racing surface outside the traditional racing groove.

7. Does it work for light Indy Cars as well as heavy NASCAR Winston Cup cars? By adjusting the size and viscosity of the gel filled rubber bladders, the overall wall system stiffness can be adjusted to accommodate light and heavy vehicles. Additional computations are required to determine the ideal overall stiffness of the wall system for any given race car.

8. Is it easy to fix during a normal caution period? Yes, extra prefabricated sections of wall (assume 6’ sections) can be on hand to replace any section(s) of wall damaged during an accident. It may take a couple of extra minutes, but a crew trained to fix the wall should be able to do so in a reasonable amount of time. The wall should reform itself completely after a mild impact just by nature of the tires returning to their original shape. Therefore, for minor brushes with the wall, no maintenance should be required.

9. Is it suitable for traditional advertisements on the inside surface? Yes, the semi-hard plastic enclosure can be a plain white surface that can accommodate painted or stick-on advertisements.

10. Does it decrease other aspects of safety? It should not. Because of the wall’s flexibility, one might argue that it will act like a spring and propel a car back onto the track in the path of other cars. That happens anyway, depending on the angle at which the car strikes the traditional concrete wall. The ‘rebound’ spring constant of the proposed wall system shown above would be low, thereby, reducing the rebound force of the car back onto the track. For glancing blows it should have little effect. Further studies should be done to determine if this is of concern.

The Next Steps

1. Give me your opinions of this proposal. I welcome all comments and suggestions to improve the preliminary design. I will work with anyone willing to continue the pursuit of safer race tracks.

2. CART, NASCAR or one of the track owners should finance the final engineering design and development of engineering drawings of a cushioned wall system.

3. As part of the final design, work out details of transitioning the wall where turns meet straight-aways. In these areas it is anticipated that the existing concrete wall may need to be reconstructed for a length of approximately 100’.

4. Construct a ‘cushioned’ wall at one track for testing.

5. Evaluate the performance of the cushioned wall by testing it in one or more races.

6. Modify the wall system design based on results of the testing.

7. If successful, the sanctioning bodies can then require that all oval track owners install cushioned wall systems on existing tracks within two to three years. The financial hardship to the track owner can be offset by financial incentives from the sanctioning body. However, the cost of the proposed wall system is estimated to be fairly low, and it is only required in the turns.

I have taken the time to write this paper in an attempt to make this sport safer. I call on everyone involved, the promoters, the sanctioning bodies, the car owners, the fans, and especially the drivers, to do something. It is not an easy problem to solve, but if we can save one life, or one seriously injured driver, it is worth it.

It will take money, determination, ingenuity, and most of all, the willingness to stop saying the sport is dangerous - live with it. However, we owe it to the fans, the teams, the drivers, and most of all the spouses and children who endure the grief of a lost or seriously injured driver, to do something about the inherent danger of our existing wall systems.

Go to our forums to discuss this article

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