Figure 2i. Graphics presented to focus groups – 3 level system expressed with words
important than 4 ½ stars.
Most participants felt three rating levels was too few. Very few felt that 10 rating levels was appropriate. Most thought it was too much information and unnecessary.
The findings of this research will help NHTSA to develop appropriate and useful rollover ratings and consumer information in the future. NAS has recommended that the agency provide the public with additional rating levels in order to allow better differentiation of rollover risk between vehicles. While clearly there are improvements to be made in how rollover resistance and ratings are explained and made useful to the consumer, there does not seem to be any basis in our research to date for deviating from stars or from the five rating levels presently being used. However, for consumers who desire more information than just star-ratings, we will provide detailed information on each vehicle on the web-site. Consumers will also be able to differentiate between vehicles through use of the internet based bar-graph data that tested positively, and through other as yet undeveloped presentations.
VIII. Intent to Evaluate Centrifuge Test
The test device for the centrifuge test is similar in concept to a merry-go-round. A person seated at the edge of the merry-go-round feels a lateral force pushing him or her away from the spinning surface that increases with the rotational speed of the merry-go-round. The centrifuge device test shown in Figure 3 consists of an arm attached to a powered vertical shaft. At the end of the arm is a horizontal platform upon which the test vehicle is parked. As the vertical shaft rotates, the parked vehicle is subjected to a lateral acceleration that can be precisely controlled and measured. The basic quasi-static measurement is the lateral acceleration at which the parked vehicle experiences two-wheel lift. The outside tires are restrained by a low curb so the measurement is independent of surface friction, and the vehicle is tethered for safety to prevent excessive wheel lift. This test method was suggested by the University of Michigan Transportation Research Institute (UMTRI) both in comments to our notice about the present rollover resistance ratings and more recently in the context of the TREAD Act. As discussed in Section III, the quasi-static centrifuge test was also recommended by GM, Honda, CU and Advocates as a possible improvement on SSF to measure general rollover resistance. The test method is directed primarily at tripped rollover, which UMTRI noted accounts for all but a small percentage of rollovers.
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