ARLINGTON, Va. — A recent series of frontal offset crash tests by the Insurance Institute for Highway Safety included multiple tests of each vehicle, a 2001 Hyundai Elantra (small car) and 2001 Dodge Grand Caravan (passenger van). The manufacturers of these vehicles requested the second tests because they believed the Institute's first tests didn't reflect the same performance as in tests conducted by the companies. In each case, however, the second test revealed new problems.
"In the case of the Grand Caravan, it was a fuel leak, and for the Elantra a late airbag deployment. These findings complicated the crashworthiness evaluations of both vehicles," explains Institute president Brian O'Neill. The Institute conducts frontal offset crash tests at 40 mph. Based primarily on the results of these tests, the Institute evaluates the crashworthiness of passenger vehicles, assigning each vehicle a rating from good overall to poor.
Late airbag inflation and high leg injury measures
compromise Elantra's crash test performance
The Elantra's structural performance in all three of the Institute's offset tests was good, but there were clear indications of leg injury risk plus a late airbag deployment in the second and third tests. These are the problems that led to the car's poor overall crashworthiness evaluation — a worse rating than the previous Elantra design (1996-2000 models), which was rated acceptable overall.
After the first test of the Elantra, Hyundai engineers requested a retest, saying the leg injury measures recorded on the driver dummy in the Institute's initial offset test weren't typical of this car. In the Institute's second test of the Elantra, the leg injury measures were somewhat lower (better) but a new problem was revealed — the Elantra's driver airbag deployed late in the impact (76 milliseconds into the crash compared with 28 milliseconds in the first test). The delay allowed the driver dummy's head to strike the steering wheel, resulting in high head injury forces. In a third test, the airbag again deployed late (64 milliseconds into the crash), indicating that the result of the second test wasn't an anomaly.
"Clearly the airbag sensors in the Elantra aren't recognizing in time the severity of all of the crashes they need to," O'Neill points out.
Fuel leak compromises Grand Caravan's crash test performance
When the Institute conducted the first offset test of the Grand Caravan, there was more intrusion into the occupant compartment than DaimlerChrysler engineers said they had recorded in their tests of this vehicle. When the Institute conducted a second test, there was somewhat less intrusion, although the overall intrusion patterns were similar in both tests. However, a new problem was revealed in the second test: A part on top of the gas tank to which the fuel pump is attached cracked during the impact, allowing fluid to leak from the fuel system (note: a less volatile fluid than gasoline is added to cars' fuel systems in crash tests to allow identification of leaks without the risk of fire). Examination of the gas tank from the Grand Caravan in the first offset test identified a similar problem, even though there wasn't any fuel leakage. Because of these findings, DaimlerChrysler redesigned the part that cracked in the Institute's tests. The third test, which was conducted with the part that will be on a few 2001 model Grand Caravans (those manufactured on or after July 6) and all 2002s, revealed no fuel system leakage nor any evidence of weakness around the redesigned part.
Measurements of occupant compartment intrusion (cm),
2001 Dodge Grand Caravan, 40 mph frontal offset crash test
"The overall performance of the Grand Caravan was similar in all three tests, except for the fuel tank," O'Neill says. "Based on these tests, the 2001 models manufactured before the redesigned fuel systems are rated poor for crashworthiness because of the leak. The 2002 models with the fixed fuel systems and side impact airbags with head protection are rated acceptable."
Structural design is key to good performance
The Institute's frontal offset crash test into a deformable barrier is especially demanding of vehicle structure. The driver side hits the barrier, so a relatively small area of the vehicle's front-end structure must manage the crash energy. This means intrusion into the occupant compartment is more likely to occur than in a full-width test.
"Good structural design is the key to good performance in the offset test," O'Neill notes. "If a car's front-end structure absorbs and manages the crash energy so the occupant compartment remains largely intact, with little or no intrusion, then the dummy's movement is likely to be controlled, and injury measures are likely to be low. In contrast, poor structural design means greater likelihood of poor control of the dummy and high injury measures."
Institute and government crash tests complement each other
The Institute's crashworthiness evaluations are based primarily on results of the frontal offset crash test at 40 mph. Each vehicle's overall evaluation is based on three aspects of performance — measurements of occupant compartment intrusion, injury measures from a Hybrid III dummy positioned in the driver seat, and analysis of slow-motion film to assess how well the restraint system controlled dummy movement during the test.
The federal government has been testing new passenger vehicles in 35 mph crash tests since 1978. This New Car Assessment Program has been a major contributor to crashworthiness improvements — in particular, improved restraint systems in new passenger vehicles. The Institute's offset tests, conducted since 1995, involve 40 percent of a vehicle's front end hitting a deformable barrier at 40 mph. This test complements the federal test involving the full width of the front end hitting a rigid barrier. Both tests are contributing to improvements in crashworthiness — in particular, improved crumple zones and safety cages.
The same 40 mph offset crash test is used to evaluate new cars by the European Union in cooperation with motor clubs and by an Australian consortium of state governments and motor clubs.