“This is a huge tragedy for IndyCar but I hope that out of this tragedy comes some good in terms of improving more in safety, like when Greg Moore died and Dale Earnhardt, and now Dan Wheldon. The innovations that come out from that in terms of improving driver safety need to be kicked up another notch. We hope that is what will happen.” –Paul Tracy
I’m a relatively new Indycar follower. Part of dealing with a series of health crises over the last 18 months was getting rid of electronic baggage: relentlessly negative people, and those who confuse ‘snarky’ with cruel. That left some holes in motorsports content that were happily filled by new friends from the open-wheel world like PopOffValve, OilPressure and SpinDoctor500blog. They introduced me to a new world and a new group of drivers. I immediately picked out Dan Wheldon for his wit, his smile and his ability to communicate what so effectively during his Versus appearances. Over the last couple weeks, I’ve read many words of grief, tribute and, more recently, of thoughts about what happens next.
As a reminder, this blog focuses on analyzing and understanding the science and engineering of racing. Opinions are welcome, but they have to be substantiated by fact and stated respectfully. No ad hominem attacks.
A Brief History of Barriers
The original purpose of barriers around tracks was keeping cars separated from spectators. In addition to concrete walls to prevent the cars from driving off track, debris-spewing accidents necessitated fencing to contain airborne objects. Most fencing was standard-issue chain-link, which is cheap, plentiful, easy to put up and surprisingly strong.
Solving one problem (as so often happens) generated another: while very effective at keeping spectators safe, drivers could be (and were) seriously injured hitting these rudimentary structures. The problem became worse as speeds rose – the kinetic energy of an object increases with the square of its speed. This means a car going 180 mph has nine times more kinetic energy than the same car going 60 mph. When a car comes to a stop, all of its kinetic energy has to be dissipated – transformed into heat via skidding or friction between the brake rotors and the brake pads, for example. The longer the car takes to come to a stop, the less force experienced by the driver.
Concrete walls are simply too unyielding. Springy walls might seem like the answer, but bouncing a car back into the paths of other cars creates other problems. The SAFER (Steel And Foam Energy Reducing) barriers were a huge technical advance because they dissipated the car’s energy via flexing hollow steel square tubing and smushing foam between the tubing and the concrete wall. The SAFER barriers have been one of the most visible technical achievements associated with motorsports.
Photo from: http://www.chainlinkfence-yihang.com/Engineering-Drawings.html
Catchfences pose a slightly different set of problems. They should have the same properties as the walls, but they can’t block the view. In addition to sight, one of the best parts of seeing a race in person is the sound and – if you’re close enough – feeling the wind generated by the cars zooming by. Chain link fence is a good compromise between visibility and protection.
Chain-link fabric is like an elastic metal mesh. It can give in two ways: gentle forces cause the mesh to deform. The diamonds stretch out of shape, but when the force is removed, the fabric springs back to its original shape. The fence can also deform by stretching the wires that make up the mesh. A large-enough force will break the wire, leaving a hole in the fabric.
How much the mesh can stretch depends on how it is supported. If the frame is too big – meaning that there’s a very large area of mesh between supports — the mesh will stretch too much. Vertical poles are used periodically to provide additional strength. How the poles are attached to the mesh is critical, because the attachments allow the load to be shared between the fabric and the poles. The larger the forces, the more robust the links between the poles and the mesh must be.
Photo from: http://jonesinforspeed.blogspot.com/2008_07_01_archive.html
Race track fencing is stouter in just about every way. The mesh is made of larger-gauge wire with higher tensile strength. The links between the poles and the fabric are stronger: In the picture at right, steel cables run horizontally through the mesh and are fixed to the vertical poles using some massive turnbuckle-like fixtures.
Different tracks have different installations. Some have metal tubing running horizontally as reinforcement. One of the pictures below has larger-holed mesh that is attacked to the poles at every possible point.
The SAFER barrier represented a paradigm shift in barriers: a entirely different principle of operation. Catchfence improvements have primarily been via stronger mesh, stronger or a greater number of poles, or better links between the poles and the mesh. But it’s basically the same fundamental design.
The chain-link fence has been institutionalized in motorsports, with governing bodies developing specific standards for debris fencing. These standard tests allow us to compare different types and installations of fences. In the FIA test, a 760-kg (1675 lb) test mass is shot into a fence at a speed of 65 km/h (40 mph) at heights of 1.6 m and 2.5 m (5.25 and 8.2 feet respectively). While 40 mph seems very slow, they’re taking just about the entire mass of an Indy car and concentrating it in a relatively small sphere. A real car would impact over a much larger area and spread out the force.
Photo from http://www.geobrugg.com/contento/security/English/Home/Debrisfences/CrashTests/tabid/3874/language/en-US/Default.aspx
The photo at left shows the fence working perfectly in terms of what’s being tested: The mesh deforms (a lot!) without breaking. Load is transferred to the poles, with the poles nearest the impact bending. The emphasis, however, is pretty strictly on containment.
With that background, let’s examine some of the theories that have been advanced and see how the science stacks up.
The “It’s Obvious What Went Wrong” Theory
I got a chuckle out of Dean Sicking, inventor of the SAFER barriers and Director of the Midwest Roadside Safety Facility, when I started our conversation by asking him how many people contacted him after the crash and asked him to make a definitive conclusion about the cause of the crash solely the basis of the television video.
Motorsports accidents rarely have a single cause. It is almost always a confluence of events that add up to disaster. Even Sicking, with many years of experience, can’t look at a videotape and positively identify a cause. A formal investigation is in progress. Sicking (who is not part of that investigation) noted that the investigators will use every bit of data they have access to: accelerometers in the cars that measure the forces the cars experience and earpiece accelerometers (which all Indycar drivers wear) that provide data about the forces the driver feels (because the two forces are rarely identical). They will have that information from every driver and car on the track. The team will investigate all of the safety apparel (HANS, firesuits, helments, etc.), in-car video, photos, broadcast video and all of the information from race control. This is a very complicated situation given the number of cars involved and it’s going to take some time to unwind.
The one think Sicking is willing to say definitively is that “It’s too soon to blame the fence”. He has some ideas on how the current catchfence design could be improved – but he politely declined to share those given that he hasn’t had an opportunity to test any of them yet.
The “Inside-Outside” Theory
Photo from: http://markjrebilas.com/blog/?p=6338. Check his website - there are some really great pictures.
A popular theory making the rounds is that the fence at Las Vegas Motor Speedway is unsafe because the vertical support poles are on the inside of the fencing (facing the track). The support poles in the picture at left are on the outside (facing away from the track). In a coincidence perfect for the black helicopter crowd, SMI tracks (like Las Vegas) have the vertical supports inside the fencing, while ISC tracks have supports outside the fencing. Sicking doesn’t think the location of the poles inside vs. outside makes a significant difference. A number of people have advanced the theory that the poles on the inside ‘shred’ the car and that moving them to the outside of the wire mesh would provide a much smoother surface.
I think the picture they have in their minds is of a car traveling along parallel to the fence and hitting the posts as it goes by. If that were the case, then it would be true that having the posts on the outside would be better; however, it’s highly unlikely a car would travel that way.
Most crashes don’t happen parallel to the fence – the car hits with some component of velocity perpendicular to the fence, which makes avoiding hitting a pole virtually impossible given the spacing between the poles.
Sicking says the problem is not whether the poles are inside or outside the mesh, but that they are so close that it is almost impossible for a flying car to hit the fence without hitting one (or more) poles.
The “Close the Cockpit” Theory
It is hard to find any evidence countering the assertion that an open-wheel driver is much more susceptible to injury from a cockpit-first barrier or catchfence hit than a stock car driver. Indy cars have a roll hoop, but it’s a fairly minimal structure and, if compromised, leaves nothing to protect the driver’s head. If you want evidence in support of closed cockpits, consider the two extremely violent crashes experienced by Audi LMP (closed-cockpit) cars at this year’s 24 Hours of LeMans. Both drivers walked away.
While acknowledging that open-cockpit cars are an integral part of Indycar tradition, I don’t think you can escape the conclusion that maintaining that tradition increases the risk to the drivers. Whether that’s an acceptable risk or not, it seems to me, is up to the drivers.
The “Hockey Rink” Theory
Hockey rinks use a clear wall to protect fans from flying hockey pucks (and sometimes from players being slammed against the boards). The Lexan polycarbonate is strong enough to withstand the force of the hockey puck and still allows clear sight lines for the fans. Lexan is used for bullet-proof windows and similar demanding applications. Lexan is also used (and recently mis-used) in the windshields of NASCAR stockcars.
When thinking about forces, the mass of the object, its speed and the time of the hit (how long the two objects are in contact) are important. The record speed for a hockey puck (which weighs about 5.5-6 oz.) is about 106 mph. Race cars, on the other hand, weigh a whole lot more (1600 and 3250 lbs in round numbers for Indycars and stock cars) and travel even faster. I’ve compared on the plot below the kinetic energies (KEs) of a NASCAR stock car, an Indy open-wheel car and a hockey puck. Some values are shown in the table for comparison:
Comparing the kinetic energy of a hockey puck with race cars.
||Kinetic Energy (J)
|NASCAR Stock Car
(The hockey puck is that flat purple line on the graph.)
Even if we consider that the time of the hit for the hockey puck could be, say, 100 times shorter than that for the cars, we’re still talking about factors of hundreds or more in terms of the force the wall would have to sustain. Lexan is simply not up to the job. You could try a composite – a combination of two materials that produces properties superior to either. For example, you could reinforce Lexan with steel cable — or even carbon nanotubes; however, you would still need an unrealistic thicknesses of material and it would be very expensive to encircle an entire mile-plus-long track with it. Economically and practically, this isn’t a reasonable solution.
The “Just Keep the Car on the Ground” Theory
This seems like a very simple approach: The best way to prevent car-catchfence collisions is to keep the cars from hitting above the SAFER barriers, which means keeping them from leaving the ground. The new car is designed to decrease the wheel-locking problem that contributes to propeling cars into the air; however, Sicking suggests that the rear wing angle needs to be investigated as another contributor to the problem.
“Angle of attack” refers to the angle between a wing and the oncoming air. In a racecar, the angle of attack determines downforce and drag. Sicking says that the way the wing is run now – pretty close to flat – provides huge downforce and very little drag. The problem, he suggests, is that when the car gets a little bit off the ground, the angle of attack of the rear wing actually encourages the car to continue rising. Increasing the angle decreases downforce and adds drag, which prevents the drivers from running wide open the whole way and discourages the car from lifting. Sicking suggests that increasing the horsepower would also help.
It seems to me there’s a safety issue anytime a driver doesn’t have throttle response. Have you ever been in a rental car trying to enter the expressway (or pass a truck) and you’ve got your foot all the way down on the gas but the car just isn’t going any faster? Not a good feeling. Throttle response gives a driver additional control and additional control is always a good thing.
The “Pack Mentality” Theory
Cars moving at high speeds give drivers very little time to react. Cars moving in close proximity to each other also decrease the margin of error allowed the driver.
The phrase you hear on the Indycar TV broadcasts is “A football field per second” (which is about 204 mph). Those of us who aren’t race car drivers may not appreciate how fast that is. Since most of us don’t have access to a 200-mph car and a track, Sicking sugests heading out to your local high school football field. Park a car at one end and, when you reach the other end, turn around imagine that (one second later) that car is right on top of you.
When cars are moving together at similar speeds, there isn’t actually much danger because their relative speeds are very small; however, the minute one car slows down, the relative speed jumps and the drivers have to responds. From SportsScience to accident reconstruction experts, there is overwhelming evidence that racecar drivers have extremely good reaction times. But even a 99th-percentile reaction time won’t keep you from hitting something if you’re too close to it.
The “We’ll Try Harder and Make Racing Safe so that We Never Lose Another Driver” Theory
Dave Moody touched on this on his Sirius Speedway radio program – he asked whether the Indycar drivers should have been expected to get back in their cars and race after a fatal accident. He suggested that maybe the sport is more humane today and we don’t expect people to ‘buck up’ in the face of tragedy like they did ‘back in the day’.
I have a slightly different take: ‘Back in the day’, more drivers died. People steeled themselves because it was more likely than not that someone would die during a season. Racing has become so much safer, and we’ve had so many fewer accidents that perhaps we have forgotten that this is still inherently dangerous. Getting in a racecar is a calculated risk. When you look back at the old days — tire testing by having drivers run through nails and tacks at high speed — you marvel at the risks drivers willingly accepted. We’ve minimized many of those risks, and a lot of lives have been saved as a result. But there is still a risk that what happened on that tragic Sunday at Las Vegas will happen again. I worry that younger drivers – especially those who have never lost a colleague in an on-track incident – feel an unwarrented invincibility (for themselves and others) that leads to less than prudent moves on the track. But even with everyone on their best behavior, the motorsports sanctioning bodies could implement every innovation we have and that could still not be enough.
Racing is not 100% safe. It never will be.
The “We Owe it to Dan” Theory
At the risk of saying this the wrong way, one of the side effects of the reduced number of serious accidents is that we don’t have a lot of data on those types of accidents. Understanding how to prevent accidents like this requires that we understand the accidents. Many others have put it more eloquently: We owe it to Dan — and all the other drivers — to learn from this tragedy and to make changes. Those changes will not ensure that no driver ever dies on a racetrack, but everything we do will decrease the number of drivers who do make that ultimate sacrifice.
In the second part of this series, I’ll explain how we could do that.