Science Background information

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

Extending the time of impact during an accident is the focus for many safety devices. In consumer cars, extending the time of impact is the basis of many safety devices such as airbags, seat belts and crumple zones in cars and break-away utility poles and crash cushions on highways.

Extending the time of impact saves lives. A race car is designed so that the car, not the driver, takes the energy from the hit. When a car flips and rolls, it is actually protecting the driver. Blunt, direct, head-on hits have nothing to absorb the energy – except the driver.

The cause of injuries is kinetic energy transfer. Managing kinetic energy is what keeping people safe in crashes is all about. Front crumple zones allow the driver/passenger compartment to slow down more slowly. If this compartment crumples, there is a much greater possibility of significant driver and/or passenger injury.

A driver can suffer a fatal accident at less than 20 mph depending on the car design and type of direct hit.

Interviewer: if you were teaching this lesson what guidance would you give to 8th grade students as they get ready to design their egg transport vehicle?

Rolin: The best thing to do with an egg transport vehicle is to realize that you’ve got to limit the forces on the egg the forces of acceleration on the egg to a certain maximum value. Design a compartment to prevent the egg from contacting a hard feature of the interior. I would make a crumple zone on the outside of the exterior surface of the vehicle to permit the vehicle to absorb some of the blow for the egg prior to the egg transport compartment medium having to do its job.

Interviewer: Well how could you do some of those things?

Rolin: If the transport vehicle is a rigid interior and you have the delicate egg the best thing to do is to place some kind of energy absorbing medium in there. Such as foam or some kind of soft material which will deform and crumple. It does not have to restore after the accident to its original value. It can be something that is a one time use item and just simply deform and crumple and absorb the impact. The idea is to spread out the duration of the impact for the egg and to prevent it from contacting a hard feature.

Interviewer: I guess it’s safe to say that adding vehicle crumple zones would be another methodology.

Rolin: Yes you can then look at the possibility of adding crumple zones or crush zones if you want o call them that. On the exterior of the vehicle, outside of the egg compartment itself. That area can be modified to allow the same extending of the accident duration as well as the ability to limit the peak values felt of shock and acceleration felt by the egg. And the same thing’s true in passenger vehicles.

Interviewer: So what variables make a difference in the success of design? Height? Wheelbase? Track? Distribution of weight?.

Rolin: For an egg transport vehicle the length is the first thing I would consider. The longer the distance in which the egg has to slow down the better you’re going to be. Because for a given speed at which the vehicle impacts a barrier the longer the time you can spread it out the softer you can make the accident for the egg. So to do that you need a longer distance, a greater dimension in which the vehicle can softly crumple up and absorb the impact. The height of the vehicle will make some relevancy because of its height relative to the bumper. So really that’s more like a contour design of it. Also stability as to stay on a track as opposed to rollover and fall off of it. The wheelbase is primarily going to impact the size of the available egg compartment and the room you have to put in cushioning medium. The track of the egg transport vehicle is similar to the height in the sense that it’s going to affect the stability and the distribution of weight. I would think that you would want the heavier part forward allowing the egg to not have a weight behind it forcing it further into the barrier upon impact.

Interviewer: How about the plastic track.

Expert: You want the egg transport vehicle to remain on the test track throughout the duration of the experiment. If the vehicle is not stable or if the test track is not designed to prevent the vehicle to remain on it reasonably so then it will leave the track. And unfortunately the egg will suffer a complicated type of accident.

Expert: As we get this track higher – we actually did a test here at the office. And I used a golf ball as our egg. As the track got higher the car left the track. What design factor could be incorporated to prevent off track excursions

Expert: Strangely enough the test track, the design of the test track is very similar to the design of a roadway. It allows you to see what happens if you don’t design a roadway for the safe posted speed then the vehicles cannot safely travel at that speed and they will leave. As a matter of fact vehicles do leave the roadway commonly in accidents on a regular basis. We have single vehicle accidents occurring when the vehicle cannot safely negotiate the contours of the road. The test track is the same way. You need to treat the test track just like you would treat a roadway. You need to make it so that the changes are smooth and gradual. And that the track banks or contours to allow the vehicle to remain stably on it.

Interviewer: Name three design features for the egg transport vehicle and or its safety compartment you would incorporate if you were doing the lab?

Rolin: If I had to pick three design features for the egg transport vehicle I would say padding the interior, padding the egg transport compartment to prevent the egg from contacting a hard feature of the interior. I would make a crumple zone on the outside of the exterior surface of the vehicle to permit the vehicle to absorb some of the blow for the egg prior to the egg transport compartment medium having to do its job. And then I would design the vehicle to safely remain on the test track and to hit at predictable manner.

Interviewer: What are the elements of design for any car? And what is its purpose

Expert:When you design a passenger car you’re designing it to fill a certain role. Maybe that passenger car is supposed to haul a family. Maybe it’s supposed to haul a given product. Or perhaps it’s just for general family use, general transportation by an individual. And so you’re constrained by motor vehicle regulations about the design. You’re also constrained by the size of lanes and other traffic devices. So the design of a passenger car begins with regulations and with the common design or roadway.

Interviewer: What is more important for young kids to understand about accidents?

Expert: The best thing that kids can learn about accidents is that most accidents are the result of driver error. And so take your time. Just make sure that you’re safe and you do things in the proper systematic way that you learn in driver education. But most accidents are the result of either being in too much of a hurry or taking a chance when it’s just not necessary. And then comes the vehicle safety after those factors.

Interviewer: What are important safety rules about driving a car?

Expert: One of the biggest causes of accidents that I experience at my work has been noticing that people drive too closely. Or they drive too fast for existing conditions. For example if there’s a heavy fog or a driving rainstorm you want to slow down. And if you have any doubt about the driving conditions allow for more space between you and any vehicles that may be ahead of you.

Interviewer: Statistics about accidents. When do accidents happen? Who has the most accidents and why do most occur?

Expert: There are different causes of accidents. And the statistics do reflect those. They usually reflect the greater number of accidents when there are more vehicles on the road simply because there is a greater chance. The other issue is times of day when drivers may be tired or otherwise distracted. These are common problems for drivers such as a distraction within the vehicle or they’re simply driving when they shouldn’t be driving.

Statistically most accidents are by younger drivers. And that’s due to inexperience. Although some accidents occur due to drivers who are no longer physically able to operate the vehicle safely. But the younger drivers still dominate most accidents just because of a lack of opportunity to learn about the vehicle and about driving safety.

Interviewer: What if we got off this just briefly and ask what statistics are most commonly associated with design of the car.

Expert: I’ve seen instances where for example with a police car the suspension was improperly designed. That’s very rare. There are some occasions when a vehicle does have a flaw. Maybe there is the ability for a steering or break failure to occur. But this is a very remote possibly. You’re talking about a few times out of a thousand. But if you’re talking about maintenance, yes maintenance does increase the – poor maintenance or a lack of maintenance increases the likelihood of an accident. That definitely is a factor. But most vehicles are quite well designed and are thoroughly tested before they ever reach the public.

Interviewer: What can people do to reduce accidents?.

Rolin: Again one of the most important things to reduce an accident is to simply allow for greater distance between you and other vehicles. As well as to reduce speed when driving conditions worsen.

Interviewer: What is the ultimate restraint system and/or combinations of systems for safety in passenger vehicles.

Expert: A compartment to prevent the egg from contacting a hard feature of the interior. I would make a crumple zone on the outside of the exterior surface of the vehicle to permit the vehicle to absorb some of the blow for the egg prior to the egg transport compartment medium having to do its job

Interviewer: Ok. How do these two differ from the optimum system?

Rolin: We would like to have people packaged in cars like we package eggs for transport. But it’s not practical to do that. So we have to find something that blends in with every day needs. And the current system of seatbelts and airbags do an excellent job. For the near future we’ll see an expansion of the airbag concept to cover other types of accidents than have previously been covered. We’ve seen them go from a simple head on type of protection to side protection and now rollover protection. I think we’ll see some small extensions of that. And we’ll also see the electronics, which activate the airbag systems to be more precisely controlled for each specific accident scenario.

Interviewer: Air bags eventually around the drivers legs in NASCAR?.

Expert: Not very likely. There’s a combination of the cost efficiency. What does it deliver for the amount of extra cost? Also it may impair control of the vehicle by the pedals. It may knock the feet free of the pedals. However one big advancement we can expect is to see multiple use airbags. So that if you’re hit in a collision and then another vehicle comes along seconds or minutes later and collides with you you’re protected from that as well.

Interviewer: I’d like to stay on this for a second more. We have talked about the protection during the crash. What is happening to help prevent the crash in the first place?

Expert: Recently we’ve seen innovations from manufacturers that provide the ability to avoid an accident or to predict an accident. Some of these use radar and they use a system whereby when another vehicle or an object comes within a certain distance the car either takes some measure on its own such as applying the brakes and now there is even some ability to steer. And then of course they prepare the supplemental restrain systems such as the airbags.

Expert: I’d also like to mention another factor. The stability control systems. Because these systems attempt to avoid an accident by anticipating a problem. They measure the path of the vehicle and compare it to the vehicle’s heading. And if the vehicle is not properly oriented for safe driving then the vehicle’s systems will attempt to correct it by applying the brakes, steering or some combination.

Interviewer: So would you say then that would be more the optimum to have all of these systems you know where you have accident avoidance?

Rolin: Yes definitely these things are coming together. The combination is – enhances the safety more than the sum of their individual contributions. One other facet that people have not really talked about much until recently has been the effect of vehicles and pedestrians. And so some systems will be added to vehicles in the near future that should help alleviate injury to pedestrians. Should an accident occur?