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Protecting Pedestrians Through Vehicle Design

(updated May 5th, 2009)

Although it may seem like a rare occurrence, a pedestrian being hit by a car is not really that unusual. In the U.S., 4,654 pedestrians were killed in motor vehicle collisions in 2007, while pedestrian accidents comprise about 11 percent of motor vehicle deaths annually, according to the Insurance Institute for Highway Safety (IIHS). The good news is that pedestrian deaths are declining, in part because vehicle designs have changed to reduce injuries when a car and pedestrian collide.

While significant advancements in vehicle occupant safety have been made in recent years, some automakers are now also putting the focus on people outside the vehicle, in part because regulations overseas, particularly in Europe, require such designs. With an increasing number of vehicles sold globally (as opposed to only in one country or region of the world), it makes good economic sense to build vehicles to meet as many different governmental standards as possible.

Bodies Flying
In order to design vehicles to cause less injury to a pedestrian in a collision, engineers and researchers spend time reviewing real-world crash data, using computer simulations of crashes and performing actual crash testing with full dummies and test devices, called impactors, that represent portions of dummies' bodies (such as a leg or a head).

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Statistics show that most pedestrians are struck by the front of a vehicle, but what happens in the crash varies widely depending on several factors, including the type of vehicle, its speed and the height of the pedestrian. The result is a multitude of scenarios that makes studying these accidents challenging.

For example, when a vehicle hits a pedestrian who is crossing the street, the vehicle's bumper and the front edge of the hood generally strike the person. A taller vehicle, such as an SUV, means impact higher on the body, while increased speed of the vehicle means the pedestrian will likely be propelled up over the hood. But it's not even as "simple" as that, according to Douglas Longhitano, a senior engineer at Honda R&D Americas, Inc., who has spent his career focused on safety research and received the U.S. Government Award for Engineering Excellence for his work in pedestrian protection in 2007.

"When someone is crossing the street as they are hit, their body will move forward or backward depending on the way their leg is positioned, since they are usually in a walking stride, not standing still," explains Longhitano. "If the driver hits the brakes, the person typically ends up on the ground in front of the vehicle, but if the driver doesn't brake, the person continues to hit an exterior mirror and land on the driver or passenger side of the vehicle."

Changes to Vehicle Design
To respond to this wide range of scenarios, automakers began addressing pedestrian accidents decades ago by focusing on the obvious vehicle features that could cause harm. Protruding hood ornaments, for example, were embedded in the grille or designed to collapse on impact, while exterior mirrors are now mounted on springs. Even a styling feature such as recessed door handles has helped reduce pedestrian injury.

In recent years, vehicle design has focused on making subtle changes to the front end of the vehicle that aren't obvious to consumers. One example is changing the way that the fenders, hood and windshield wipers are attached, so their performance strength is maintained but they can easily collapse when impacted by a pedestrian. Vehicles from Acura, Honda, Infiniti, Lexus, Nissan, Toyota, Volkswagen and Volvo among others have these types of features.

Hood design and engine compartments have also received many subtle design changes. Today the vast majority of vehicles sold in the U.S. have braces supporting the hood that crush when they are impacted from above, such as by a person's head. In addition, a plastic engine cover serves to soften the impact, as does increased space between the hood and the cover. Beginning in 2001, Volvo, for example, decided it needed 3 inches of deformable space between the hood and engine in its new vehicles for pedestrian safety. As a result, when it came time to decide between two V8 engines for its XC90, one engine was ultimately rejected for the sole reason that it protruded into the company's 3 inches of required space.

One key area still challenging engineers in most U.S. vehicles is the front bumper. For vehicles in Europe and Asia (where there are many more pedestrian collisions and governmental standards regulating them), bumpers are designed with larger crush space and with different supports for the plastic bumper cover in order to reduce leg injury. Unfortunately, these "softer" bumpers don't perform well in the 5-mph bumper test conducted by the Insurance Institute for Highway Safety (IIHS) to assess repair costs, so they generally aren't used on vehicles in the U.S.

Another issue with bumper design for U.S. vehicles relates to the front airbag sensors that are located in the bumper. "Because of the sensor location, it can be difficult to address pedestrian safety and still have the sensors effectively trigger the front airbags, particularly in low-speed collisions," explains Max Gates, spokesman for the Chrysler Group. One way to provide added pedestrian protection while still performing well in the IIHS bumper test is by adding high-density foam behind the plastic bumper cover, a method used on all Toyotas.

Looking Ahead
Automotive engineers and researchers, as well as experts from the safety and medical fields, continue to study vehicle-pedestrian collisions, developing other ways to reduce pedestrian injury while still maintaining a high level of safety for the vehicle's occupants. Honda continues to be a leader in this area of research, with the development of its POLAR-II dummy, the only dummy currently in existence that can measure pedestrian impact. The company uses the dummy to perform computer modeling of pedestrian impacts and lends it to other automakers and industry groups for testing.

One vehicle design we may see on future U.S. models is a pop-up hood system, which would lift the hood a few inches in the area closest to the windshield, effectively giving a larger cushion of space underneath it in the event of a pedestrian impact. This feature is currently in use on some Hondas and Nissans in Europe and Japan, though there are no plans as yet by either company to bring this feature to the U.S.

It's likely that the future design changes we see on vehicles in the U.S. will be driven by safety standards overseas. Both Japan and Europe recently instituted more pedestrian safety standards and the European Union has even more stringent standards set to go into effect in 2010.

While this area of safety may seem slow going, it's Longhitano's opinion that it is so complex it simply can't be rushed. He says, "Understanding [vehicle-pedestrian collisions] is very complex. Every time we do a study, we learn 10 other side things we never expected. Those things in turn raise even more questions, requiring more research."

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