A Crash Course in Crash-Test Ratings

As a car shopper, you'll want to know if the vehicle you’re thinking about buying is, within reasonable limits, as safe as possible. After all, you’ve most likely heard that the survival rates in car crashes can vary greatly depending on what model you’re in. But to the uninitiated, deciphering crash-test results can be a daunting task. If you decide to plunge deep into researching the matter, you might find a lot of conflicting information — even contradictory test results.

If finding the safest car possible is a priority but you don’t know where to start, there’s still hope of making sense of it all, as well as an innovative new way of seeing that the odds work out in your favor. But first, it helps to know a bit about the tests themselves, what some of the issues are and what makes a vehicle safe.

The Crash Agencies and Tests
In the U.S., there are two main organizations that do crash testing: the National Highway Traffic Safety Administration (NHTSA), an arm of the federal government; and the Insurance Institute for Highway Safety (IIHS), an insurance trade group.

Crash dummies are prepped for a test + click to enlarge

The NHTSA was officially established in 1970 as part of the Highway Safety Act and the result of the series of historically notable highway-safety hearings in 1966. Those hearings led directly to the federal requirement for seatbelts and to the formation of the new-car testing regimen that continues today as the New Car Assessment Program. The agency started the current frontal crash-ratings system in 1994, added side-impact tests in 1997 and has most recently added a static rollover test in 2001 as well as a dynamic “tip-up” rollover test in 2004.

The IIHS was established as a research-based organization in 1969. The organization conducted various crash tests for research on behalf of insurance companies for several decades before devising its own testing program for car shoppers. Since 1995, the IIHS has been conducting frontal offset crash testing for new vehicles and added other tests in recent years, including side-impact testing in 2003 and a new rear-impact test in 2004. The Institute buys vehicles new from dealerships and tests them at its facility in Virginia.

There are just too many models for the agencies to be able to test each one every year, so both agencies only test a small number of vehicles annually — usually either those that have been completely redesigned for that model year, or those that have significant design changes that might affect crash performance.

“The number of cars we test each year is directly related to the amount of money Congress gives us,” said Rae Tyson, spokesman for the NHTSA. “We test as many cars as we can purchase.”

NHTSA crash test + click to enlarge

The agency generally stays away from low-volume specialty cars and high-end vehicles, favoring top sellers and particularly those that are new or ones that have been redesigned. Carrying over results from models that haven’t seen significant revision, Tyson said, the agency provides relevant test data for 80 to 85 percent of the new vehicles sold annually.

The choices the IIHS makes on which vehicles to test each year are “based primarily on which models are redesigned and which groups we need to test,” such as compact SUVs or midsize sedans, according to Russ Rader, spokesman for the IIHS. While the IIHS does like to test similar vehicles together, Rader said that the Institute emphasizes models that are popular or new, testing a total of 70 to 80 vehicles per year.

In the NHTSA testing procedure, crash-test dummies are belted into the driver and front-passenger seats and the vehicle is crashed into a fixed barrier at 35 mph. The dummies have precise instruments onboard to measure forces in the head, chest and legs. After the test, those forces are then analyzed and related to the likelihood of serious injuries for a real occupant.

The federal agency’s side-impact test follows a similar procedure, though with dummies belted into front and rear seating positions. Instead of the vehicle moving, a 3,015-pound barrier is bashed into the side of the vehicle at 38.5 mph to simulate a “T-bone” intersection collision. The NHTSA measures the forces involved but does not consider the likelihood of a head injury.

The NHTSA also conducts a rollover resistance test, which measures how easily the vehicle might roll over in a crash that does not involve another car — for instance, the likelihood that a vehicle might be “tripped” by a curb, guardrail or ditch. Here, the agency relies on two factors in the test: a calculation from measurements at rest, called the static stability factor (SSF), and a dynamic “tip-up” test, which is a sudden driving maneuver on a track under controlled conditions.

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In the IIHS’ frontal offset crash test, a dummy is mounted into the driver’s seat and 40 percent of the total width of the vehicle strikes a barrier on the driver’s side at 40 mph. The barrier is made of deformable aluminum honeycomb, so as to simulate the crash against another vehicle. Tested vehicles are then ranked based on structural performance and the likelihood of occupant injury. The test primarily measures how well the front-end crush zone absorbs energy during a crash and how well the occupant compartment holds together.

The IIHS side-impact test is similar to the NHTSA test, though the impact occurs higher than in the federal test to more accurately simulate a collision from a pickup or SUV. The barrier weighs 3,300 pounds and is impacted at 31 mph. Test dummies used in the side-impact test are the size of a small fifth-percentile female or 12-year-old adolescent to measure the worst-case scenario head injury from the front of the oncoming vehicle. Again, injury measure, intrusion of the vehicle and the motion of the dummies are studied to arrive at ratings.

The IIHS does not test for rollover likelihood, but the Institute is now testing for the likelihood of head or whiplash injury as the result of a rear-end collision — a particular concern for the insurance industry. Here, the organization looks at the geometry of the seat’s head restraint, and the seats are also tested in a situation that simulates a stationary vehicle being struck at 20 mph by a vehicle of the same weight. Forces are measured through a special test dummy, and the geometric and dynamic ratings are combined.

Published 6/23/06