Science Background information
Additional information about the science of crashes is available in the lesson to design a vehicle to safely transport an egg.

Expert information in this section has been provided by:
Rolin E. Barrett, Jr., Ph.D., P.E.
Consulting Engineer and Accident Reconstruction Specialist
Barrett Engineering

Eric Klang, Ph.D.
Director, Undergraduate Program
Mechanical & Aerospace Engineering
Faculty Advisory, Wolfpack Motorsports

Expert: A barrier offers the ability to deform and absorb part of the impact if possible. But you want the barrier not to allow the vehicle to dig into it so to speak. In other words you don’t want the vehicle upon contact with the barrier to suddenly have a reduction in speed along the barrier. So ideally you would make the outer surface of the barrier somewhat slippery as well as the barrier being able to have a spring quality to it.

Interviewer: Let’s talk a little bit about guardrails and I guess describe some of those features and also what happens in that case the guardrail usually does permanently deform.

Expert: The tax payers pay for it with highway and road maintenance However it’s a lot cheaper to have that barrier deformed and be replaced than to repair the person who could be injured badly. The barrier deforming, absorbing the blow is a small price to pay to save the human life or serious bodily harm. The barriers when they are deformed have to be replaced. But again that’s part of their design. They’re intended to do that.

Expert: One of the original versions of breakaway guardrails with energy absorbing terminals involved the use of wood posts as opposed to simply using steel. Wood posts were used many years ago to allow absorption, deflection and then ultimately break away. The ends of the posts have been modified so that they will not protrude or are not as likely to protrude into the passenger compartment. The barrier can still give regardless of whether you hit on the end or you hit along the side.

Interviewer: What are the properties of good and bad barriers on race tracks and public roads?

Expert: Race tracks and public roads share one thing in common about the barrier. The barrier should do its part to both retain the vehicle in the area where the vehicle is supposed to remain, such as on the road surface or on the track surface. And thus keep it away from harming others. As well as lessen the chance that it will harm the occupants of the vehicle. Barriers also should absorb energy from the hit to lessen the severity of the impact.

Interviewer: Are there any difference between barriers of public roads and race tracks?

Expert: Yes. Race track barriers are much more sophisticated. The cost factors involved in trying to make the same barriers for all public roads become prohibitive. Race track barriers are designed for much higher speeds. The speeds on a race track are two to three times the speed of passenger vehicles on the public road. Race track barriers are designed with the idea that the vehicles are going to be traveling around the track in a known direction. Highway barriers have a much more complicated problem because vehicles in the course of an accident may approach the barrier at a very unusual angle. They may approach the barrier nearly perpendicular. After a collision a vehicle may even be knocked backwards in some cases. So the barriers that are used along public highways have to take into a fact the much more complicated nature of the accidents.

Interviewer: How does vehicle speed impact the design of the barriers?

Expert: One of the efforts in recent years with highway barriers has been the use of cables that are suspended above the ground parallel to the travel of the road. These cables have been used as an economical means of providing an energy absorbing barrier that still keeps the vehicles from approach oncoming vehicle lane. The vehicles on a race track are at higher speed. The barriers do need to be ultimately stronger because of the greater energy that’s involved in retaining the cars on the track. However the barriers are doing different jobs. So that accounts for the difference in construction. As far as the effectiveness the race track barriers are better at maintaining a high speed vehicle on the track. And they cost a lot more.

Interviewer: We know there’s a difference in race tracks but also motorcycles need a different kind of barrier so there are certain races and certain racetracks that need certain barriers to be safe Drag races don’t like guardrails because the car can get under the guardrail so it depends.

Expert:: One question I had was thinking about some of the different barriers that people might not even think about at race tracks and on public roads. The other day we talked about Bobby Allison’s wreck at Talladega where the fence kept his car in the racetrack. Two other barriers at the race track are water barrels and Styrofoam blocks.

The use of water barrels is really more a low speed application. The use of the concrete and steel and some times an absorbing material barriers that are used on the track right off of the track themselves. Those are intended to withstand higher impacts. The big difference here is that the race track has to constrain all of the parts of the vehicle to the track surface. The highway barriers primarily just keep the vehicle on the surface as best they can. But if a wheel comes off and goes down a grassy hill it just doesn’t matter as much. There are no spectators sitting close by the highway hopefully.I was just thinking of a couple other barriers just of interest that I’ve seen at different tracks. The Indy Racing League developed softer walls and a majority of the oval tracks used that system. I think about those particular designs and why they’re much better. At certain tracks I saw NASCAR and other racing leagues use Styrofoam blocks. And actually put Styrofoam block on the track. And some tracks use tires on road courses. But every time somebody hit the Styrofoam blocks they exploded. The Styrofoam barrier worked but led to long caution flags.

Expert: One key thing to keep in mind with any safety device or any device intended to protect an egg simply in an egg transport vehicle is that you’re ultimately constrained by cost. You have to be reasonable. You want to do as much as you can but within a reasonable cost. If the cost is too high for the given vehicle the public can’t afford to buy it and use it. And if the road’s maintenance is too high or the road barrier system is too costly then very few roads will be built using that system. So we do have to be reasonable within cost. But we try to maximize what we can do for those dollars.

Interviewer: So why don’t they put air bags in race cars or in barriers around the track?

Expert: Airbags surrounding the track in problem areas may be difficult to maintain and employ properly in an accident. There are some technological issues at this time. Airbags in race cars, I would not be surprised to see them at a future point. But they already have many safety systems and restrain systems that are excellent. So airbags would have to make a new and different contribution.

Interviewer: You say though that one of the big differences between a race car and a private car would be seatbelt use? The race drivers know the seatbelts save lives. So that system works. The reason we have airbags in passenger cars is that people did not use their safety belts

Expert: Yes I would. Seatbelt usage among professional drivers is 100 percent. They know from both experience and from their training that the seatbelt will save their life more often than not. The seatbelt is the one device that is most likely to help them out during an accident. Airbag is a device that can offer some improvement for the types of accidents where it’s designed to deploy. But you really find the seatbelt is again the most efficient general use device for safety.

Interviewer: What are the most common mistakes/faults in designing barriers for tracks and public roads?

Expert: If I had one big criticism I would say that they’re not tall enough. A lot of places along the roads you find that there’s an increased potential for the cars to leave the road, which will enhance the severity of the accident. I’d like to see barriers used much more broadly. So I would like to see the height of the barriers increased. The other problem I see with the barriers and this is a very unusual problem is that some cars with sloped contours on their hoods and front ends that allow them to actually slide over the top of the barrier.

Expert: I think that while the race cars are designed to survive a severe accident, they’re ultimately designed for better protection of the driver. They have rigid interiors that tend not to deform. So it’s supposed to keep a rigid passenger zone around the driver so as to not crush the driver. Passenger cars don’t often don’t have this design. Passenger cars are more susceptible to compromising passenger space in a severe accident. However in minor accidents the passenger cars do offer some crumple zone protection.

Crashes during races can cause serious injury and death. When Dale Earnhardt, Sr., crashed into the barrier at Daytona in 2001, the force with which he hit the wall was not as great as other accidents that he and other drivers have had. However, how he hit the wall made it a fatal crash. According to Liz Allison in her book The Girl’s Guide to NASCAR, “a car takes a direct hit and then tumbles or moves back down the track is far worse than a car that tumbles and then hits the wall. Think if it this way: if you throw a rubber ball at a wall, it comes back hard; but if the ball bounces, then hits the wall, it doesn’t hit as hard because it absorbs a little of the energy with each bounce, rather than taking the full impact. With a race car, the idea is for the car (not the driver) to take the energy from the hit. When a car flips and tumbles, it is actually protecting the driver. Blunt, direct hits have nothing to absorb the energy - - except the driver.”

Safety innovations haven’t been limited to the race cars. Retaining walls and catch fences at race tracks have all been refined and modified through the years to help in protecting the drivers and spectators.

The barriers along the wall are rigid yet are mounted on shock absorbers. The idea is to act as a pad. To minimize chance of injury and car damage in the event of an accident, the barriers are designed to slow down the car by cushioning and bouncing the car. The barrier actually is intended to redirect the car. To let it ride up and then have gravity bring it back down. All of this takes time. And time in an accident is good. It gives the car a chance to reduce its speed. Serious injuries occur when cars are stopped suddenly. Barriers are designed to keep a car from getting up underneath it or behind it.