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Rollover Resistance

DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 575
[Docket No. NHTSA-2001- 9663; Notice 2]
RIN 2127-AI81
Consumer Information Regulations; Federal Motor Vehicle Safety Standards

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AGENCY:  National Highway Traffic Safety Administration (NHTSA), DOT.
ACTION:  Notice of Proposed Rulemaking
SUMMARY:  The Transportation Recall Enhancement, Accountability, and Documentation Act of 2000 requires NHTSA to develop a dynamic test on rollovers by motor vehicles for the purposes of a consumer information program, to carry out a program of conducting such tests, and, as these tests are being developed, to conduct a rulemaking to determine how best to disseminate test results to the public.  In response, this notice discusses the results of NHTSA's evaluation of numerous driving maneuver tests for the dynamic rollover consumer information program that Congress mandated for the American public beginning in the 2003 model year.  This notice also proposes several alternative methods for using the dynamic rollover test results in the agency’s consumer information for vehicle rollover resistance.  

DATES:  Comment Date:  Comments must be received by [insert date 45 days after publication].

ADDRESSES:  All comments should refer to Docket No. NHTSA-2001-9663; Notice 2 and be submitted to: Docket Management, Room PL-401, 400 Seventh Street, SW, Washington, D.C.  20590.  Docket hours are 10:00 a.m. to 5:00 p.m. Monday through Friday.

For public comments and other information related to previous notices on this subject, please refer to DOT Docket Nos. NHTSA-2000-6859 and 8298 also available on the web at http://dms.gov/search and NHTSA Docket No. 91-68; Notice 3, NHTSA Docket, Room 5111, 400 Seventh Street, SW, Washington, DC 20590.  The NHTSA Docket hours are from 9:30 am to 4:00 pm Monday through Friday.

FOR FURTHER INFORMATION CONTACT:  For technical questions you may contact Patrick Boyd, NPS-23, Office of Safety Performance Standards, National Highway Traffic Safety Administration, 400 Seventh Street, SW, Washington, DC 20590 and Dr. Riley Garrott, NRD-22, NHTSA Vehicle Research and Test Center, P.O. Box 37, East Liberty, OH 43319.  Mr. Boyd can be reached by phone at (202) 366-6346 or by facsimile at (202) 493-2739.  Dr. Garrott can be reached by phone at (937) 666-4511 or by facsimile at (937) 666-3590.

Information Included in Document:

Executive Summary 
Safety Problem
Background
Comments to the Previous Notice
National Academy of Sciences Rollover Rating Study
Choice of Maneuvers for Dynamic Rollover Resistance Tests
Proposed Rollover Resistance Rating Alternatives
Intent to Evaluate Centrifuge Test
Handling Tests
Cost Benefit Statement
Rulemaking Analyses and Notices
Submission of Comments
Summary of Evaluation Test Results

Executive Summary
Section 12 of the “Transportation Recall, Enhancement, Accountability and Documentation (TREAD) Act of November 2000" directs the Secretary to “develop a dynamic test on rollovers by motor vehicles for a consumer information program; and carry out a program conducting such tests. As the Secretary develops a [rollover] test, the Secretary shall conduct a rulemaking to determine how best to disseminate test results to the public.”  The rulemaking must be carried out by November 1, 2002. 

On July 3, 2001, NHTSA published a Request for Comments notice (66 FR 35179) discussing a variety of dynamic rollover tests that we had chosen to evaluate in our research program and what we believed were their potential advantages and disadvantages.  It also discussed other possible approaches we considered but decided not to pursue.  The driving maneuver tests to be evaluated fit into two broad categories: closed-loop maneuvers in which all test vehicles attempt to follow the same path; and open-loop maneuvers in which all test vehicles are given equivalent steering inputs.  Other potential tests using a centrifuge or computational simulation were discussed but not included in our test plan.  This notice discusses the comments we received and the results of our test program to date. 

The TREAD Act calls for a rulemaking to determine how best to disseminate rollover test results to the public, and this Notice of Proposed Rulemaking proposes alternatives for using the dynamic tests results in consumer information on the rollover resistance of new vehicles.  The resulting rollover resistance ratings will be part of NHTSA’s New Car Assessment Program (NCAP). The tests will be carried out and reported to the public by NHTSA.  This program places no regulatory requirements on vehicle manufacturers.  Past NCAP ratings have been developed using a procedure of public notice and comment, but there was no legal requirement to do so since no regulatory requirements were imposed on any party except NHTSA.  Because the dissemination of information will pose no regulatory burden on manufacturers, we provided a brief statement on the potential benefits of this program and no regulatory evaluation.

While the TREAD Act calls for a rulemaking to determine how best to disseminate the rollover test results, the development of the dynamic rollover test is simply the responsibility of the Secretary.  Based on NHTSA’s recent research to evaluate rollover test maneuvers, the National Academy of Sciences’ study of rollover ratings, comments to the July 3, 2000 notice, extensive consultations with experts from the vehicle industry, consumer groups and academia, and NHTSA’s previous research in 1997-8, the agency has chosen the J-turn and the Fishhook Maneuver as dynamic rollover tests.  They are the limit maneuver tests that NHTSA found to have the highest levels of objectivity, repeatability and discriminatory capability.  Vehicles will be tested in two load conditions using the J-turn at up to 60 mph and the Fishhook maneuver at up to 50 mph.  Both maneuvers will be conducted with an automated steering controller, and the reverse steer of the Fishhook Maneuver will be timed to coincide with the maximum roll angle to create an objective “worst case” for all vehicles regardless of differences in resonant roll frequency.  The light load condition will be the weight of the test driver and instruments, approximating a vehicle with a driver and one front seat passenger.  The heavy load condition will add additional 175 lb manikins in all rear seat positions.

The National Academy of Sciences recommended that dynamic maneuver tests be used to supplement rather than replace Static Stability Factor (the basis of our present rollover resistance ratings) in consumer information on rollover resistance.  This notice proposes two alternatives for consumer information ratings on vehicle rollover resistance that include both dynamic maneuver test results and Static Stability Factor.  The first alternative is to include the dynamic test results as vehicle variables along with SSF in a statistical model of rollover risk.  This is conceptually similar to the present ratings in which a statistical model is used to distinguish between the effects of vehicle variables and demographic and road use variables recorded for state crash data on a large number of single vehicle crashes.  The National Academy of Sciences demonstrated the tight confidence limits that can be achieved using a logistic regression model for this purpose.  Such a model would be used to predict the rollover rate in single vehicle crashes for a vehicle considering both its dynamic maneuver test performance and its Static Stability Factor for an average driver population (as a common basis of comparison).

Under the first alternative, the “star rating” of a vehicle would be based on the rollover rate in single vehicle crashes predicted for it by a statistical model.  The format would be the same as for the present rollover ratings (for example, one star for a predicted rollover rate in single vehicle crashes greater than 40 percent and five stars for a predicted rollover rate less than 10 percent).   The present rollover ratings are based on a linear regression model using state crash reports of 241,000 single vehicle crashes of 100 make/model vehicles.  We are proposing to replace the current rollover risk model with one that uses the performance of the vehicle in dynamic maneuver tests as well as its SSF to predict rollover risk.  The performance of a vehicle in dynamic maneuver tests is simply whether it tipped-up or not in each of the four maneuver/load combinations.  The lowest entry speed of maneuvers that caused tip-up will also be used if it improves the predictive fit of the model.  In order to compute a logistic model of rollover risk, it is necessary to have large number of state crash reports of single vehicle crashes to establish rollover rates of vehicles for which the dynamic maneuver test performance and SSF are known.  The agency is performing dynamic maneuver tests on about 25 of the 100 make/model vehicles for which we have SSF measurements and substantial state crash data.  We believe this approach will ensure that the assigned NCAP ratings for rollover resistance correlate to the maximum extent possible with real-world performance.  However, since the agency has not finished testing these 25 vehicles, we cannot yet say what the actual coefficients of the model relating dynamic maneuver test performance and SSF to predicted rollover rate will be.  We are asking for comments on the validity of this concept only in this notice.      

The second alternative is to have separate ratings for Static Stability Factor and for dynamic maneuver test performance.  Dynamic maneuver tests directly represent on-road untripped rollovers.  The dynamic maneuver test performance would be used to rate resistance to untripped rollovers in a qualitative scale, such as A for no tip-ups, B for tip-up in one maneuver, C for tip-ups in two maneuvers, etc.  Here again the results of ongoing dynamic testing of vehicles with established rollover rates would guide the establishment of a qualitative scale.  A statistical risk model is not possible for untripped rollover crashes, because they appear to be relatively rare events and they cannot be reliably identified in state crash reports.  The current Static Stability Factor based system would be used to rate resistance to tripped rollovers.  Again we are asking for comments on the usefulness and validity of this concept in this notice.  Until our testing of the 25 vehicles is finished, we will not know what particular NCAP rating will be assigned to a make/model under either of these two alternatives.

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