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Research and DevelopmentSafety Performance Standards
15 May 01, page 1
Dr. W. Riley GarrottPat Boyd
National Highway Traffic Safety Administration
May 15, 2001
A Progress Report on Development of a Dynamic Rollover Rating Test
A Progress Report on Development A Progress Report on Development of a Dynamic Rollover Rating Testof a Dynamic Rollover Rating Test
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Presentation Overview• Background• Dynamic Rollover Testing Issues
• Planned Testing– Testing Overview
– Test Vehicles
– Initial Test Maneuvers
• Preliminary Rollover Rating Ideas• Current Status
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Background
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Rollover Crash Statistics
• 10,142 people were killed in light vehicle rollovers during 1999 (FARS)– 8,345 were killed in single-vehicle rollovers– 80 % were not wearing a seat belt– 55 % of occupant fatalities in light, single-
vehicle crashes involved rolloverª 46 % of fatalities for passenger carsª 63 % of fatalities for pickup trucksª 60 % of fatalities for vansª 78 % of fatalities for sport utility vehicles
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Rollover Crash Statistics
• 27,000 serious injuries per year due to light vehicle rollovers (NASS, 1995 – 99 average)– 19,000 in single vehicle crashes
• 253,000 light vehicle rollovers per year (NASS, 1995 – 99 average)– 205,000 in single vehicle crashes
– 178,000 occurred after vehicle had left roadway
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NHTSA Action to Prevent Rollover
• NHTSA includes rollover resistance ratings as part of its New Car Assessment Program– Ratings based on Static Stability Factor (SSF)
ª SSF equals one-half of a vehicle’s Track
Width divided by its Center of Gravity Height– Ratings range from one to five stars
– Rating program official as of January 12, 2001
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NHTSA Action to Prevent Rollover
• Rollover resistance ratings based on SSF are controversial– Some believe that the influence of vehicle
factors on rollover is so slight that vehicles should not be rated for rollover resistance
– Others believe that SSF is a useful predictor of rollover but should be supplemented by dynamic driving tests
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Response to Controversy About SSF
• Congressionally-mandated National Academy of Sciences’ study to assess validity of SSF based rollover resistance ratings and to compare SSF to dynamic tests
• TREAD Act requirements for dynamic rollover resistance ratings
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Requirements of TREAD Act
• SEC. 12. Rollover Tests. No later than 2 years after enactment, the Secretary shall: (1) develop a dynamic test on rollovers of light vehicles for the purposes of a consumer information program; and (2) carry out a program of conducting such tests. As the Secretary develops a rollover test, the Secretary must conduct a rulemaking to determine how best to disseminate test results to the public.
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Response to TREAD Act• Met with representatives of several organizations
to gather ideas– Alliance of Automobile Manufacturers
– Consumers Union
– Daimler-Chrysler (next week)
– Ford Motor Co.
– Nissan Motor Co.– Toyota Motor Co.
– University of Michigan Transportation Research Institute
• Received useful suggestions about dynamic testing approaches
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Dynamic Rollover Testing Issues
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Dynamic Rollover Testing Issues
• Maneuver(s) to use for rollover ratings• Ensuring that cannot get good rollover
rating by degrading vehicle handling– By putting tires with poor traction on a vehicle,
can prevent two-wheel lifts in these maneuvers
– Safety may be degraded because cannot turn as sharply
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Dynamic Rollover Testing Issues
• Use of two-wheel lifts as safety-relevant measure– Minor two-wheel lifts may not be safety issue– Requiring major two-wheel lifts may cause test driver
safety problems
• Outrigger effects– Must have for safety, prevention of test surface damage
– How do they change a vehicles rollover propensity?
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Dynamic Rollover Testing Issues
• Tire wear– How much testing can be performed on a set
of tires before wear effects become significant
• Tire debeading– What to do if tires debead while performing
rollover rating testing
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Dynamic Rollover Testing Issues
• Longer-term repeatability– Effects of weather of results
ª Summer versus winter– Changes to the same test surface with time
• Reproducibility– Effects of testing on different test surfaces
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Planned Testing
Phase IV of NHTSA’s Light Vehicle Rollover Research
Program
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Phase IV Rollover Research
• Comprehensive test program designed to build on earlier NHTSA efforts, suggestions received from interested parties
• Attempts to take comprehensive look at identified issues
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Overall Phase IV Plan• Rating System Development Testing 1 – Spring 2001
• Hot Weather Effects Testing – Summer 2001
• Outrigger Effects Testing – Summer 2001• Tire Wear Effects Testing – Summer 2001
• Rating System Development Testing 2 – Fall 2001
• Fully Automated Vehicle Controller Testing – Fall 2001
• Rating System Development Testing 3 – Fall 2001
• Cold Weather Effects Testing – Winter 2002• Rating System Development Testing 4 – Spring 2002
• Surface Effects Round Robin – Spring and Summer 2002
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Test Vehicles• Four Sport Utility Vehicles:
– 2001 Chevrolet Blazer (no YSC)
– 2001 Ford Escape (no YSC)– 1999 Mercedes ML-320
ª YSC enabled
ª YSC disabled
– 2001 Toyota 4Runnerª YSC enabled
ª YSC disabled
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Test Vehicles• Each vehicle will be tested in multiple
configurations:– Nominal vehicle
– Raised center of gravity height
ª Weights placed on roof above c.g. so as todecrease SSF by 0.05
– Modified handling
ª Load to GVWR, load as far to rear as
possible, larger or smaller tires
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Test Maneuvers• Testing broad array of maneuvers during
Phase IV
• Two broad categories– Open-loop. Handwheel steering angle is
specified function of time
ª Characterization Maneuvers
ª J-Turns with and w/o Pulse Brakingª Some Fishhooks
ª Open-Loop Pseudo DLC
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Test Maneuvers
• Closed-loop. Handwheel steering angle varies according to actions of vehicle– Driver closes feedback loop
ª Double Lane Changes
– Instrumentation closes feedback loopª Fishhook with Roll Rate Feedback
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Test Maneuvers
• Characterization Maneuvers– Pulse Steer – As per Phase II
– Sinusoidal Sweep – As per Phase II– Slowly Increasing Steer – As per Phase II
– Slowly Increasing Speed – Improved version of Phase II maneuver
– Response Time Tests – 0.2 g and 0.5 g severity J-Turns at 50 mph. Performed with straight and curved (0.3 g) lead-in
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Test Maneuvers
• J-Turn Maneuvers– J-Turn – As per Phase II
– J-Turn with Pulse Braking – Improved Phase II maneuverª Improvements to Phase II maneuver
discussed in earlier presentation
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Test Maneuvers
• Fishhook Maneuvers– Fishhook 5 – Improved Phase II Fishhook 1
– Fishhook 6 – Fishhook with roll rate feedbackª Idea discussed in previous presentation
– Nissan Fishhook – Fishhook using Nissan technique for determining timing
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Test Maneuvers
• Double Lane Change Maneuvers– Ford DLC – Perform closed loop DLC per
Ford’s procedure. Use Ford’s path-correction technique to calculate limit behavior
– VDA (Modified Moose Test) DLC
– Consumers Union Short Course DLC
– Open Loop Pseudo-DLC – New maneuver being developed by VRTC
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Planned Phase IV Testing
• Have received many valuable suggestions about Phase IV testing– Comments greatly appreciated!
• Encourage additional suggestions– May revise Phase IV research plan in response to
comments
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Preliminary Rollover Rating Ideas
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Rollover Resistance Score
• Star Ratings derived from a vehicle’s Rollover Resistance Score
• Rollover Resistance Score quantifies vehicles performance in tests– Would go from 0 to 100 (100 = best)
• Table relates Rollover Resistance Scores to Star Ratings
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Rollover Resistance Score
• Composed of multiple parts:– Handling Score
– Limit Maneuver Score– Suggestion made by speaker at National
Academy of Sciences meeting:
Include Static Stability Factor!
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Current Status
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Current Status• Test vehicles purchased and instrumented• Testing in progress
– Vehicle characterization and limit maneuver testing underway
• Request for Comment to be published soon– Comments on this work are appreciated!
• NHTSA will review comments received– May revise Phase IV research plan in response to
comments