Brake Testing Methodology Study - Driver Effects Testing

�� DOT HS (Report No. TBD) March 1999 DRAFT Final Report Brake Testing Methodology Study - Driver Effects Testing �� Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 4. Title and Subtitle 5. Report Date Brake Testing Methodology Study - Driver Effects Testing March 1999 6. Performing Organization Code NHTSA/NRD-22 8. Performing Organization Report No. VRTC-87-0441 7. Author(s) Scott A. Johnston and Louis Tijerina, Transportation Research Center Inc, W. Riley Garrott, NHTSA, Dennis A. Guenther, The Ohio State University, and Gary J. Heydinger, S.E.A. Inc 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) National Highway Traffic Safety Administration Vehicle Research and Test Center P.O. Box 37 11. Contract or Grant No. East Liberty, OH 43319 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered National Highway Traffic Safety Administration Technical report 400 Seventh Street, S.W. 14. Sponsoring Agency Code Washington, D.C. 20590 NHTSA/NRD-22 15. Supplementary Notes. 16. Abstract The National Highway Traffic Safety Administration (NHTSA) is exploring the feasibility of developing brake tests to measure brake system performance of light vehicles. Developing test procedures requires controlling test variability so that measured differences between vehicles are more than just experimental noise. Possible sources of uncontrolled variability include environmental conditions, vehicle-to-vehicle differences for a given model, brake system changes with time, test driver differences, test surface friction changes with time, and test surface friction differences between test sites. The objective of this project was to determine the level of variability in stopping distance tests of light vehicles that is due to differences between drivers. 648 stopping distance tests were conducted with three expert drivers in three different cars on wet and dry asphalt with the ABS working and disabled. All four independent factors had a statistically significant effect on the stopping distance. Several interactions of the independent variables were also significant. The largest main effect was the differences between vehicles. The effect of ABS and surface condition and drivers were all fairly small. The interaction between ABS condition and surface was also small but indicated that ABS mattered more on the wet surface. The remaining interactions were also fairly small. In conclusion, this test procedure measured differences between all three vehicles with very high statistical certainty. Unfortunately, this test procedure used a large number of replications and drivers. If the goal for a brake test program is only to distinguish large differences in braking performance, fewer replications and drivers would be needed for each vehicle tested. 17. Key Words 18. Distribution Statement brake testing, ABS, driver effect Document is available to the public from the National Technical Information Service Springfield, VA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified Form DOT F 1700.7 (8-72) Reproduction of completed page authorized i This document has been prepared under the sponsorship of the United States Department of Transportation, National Highway Traffic Safety Administration. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Department of Transportation or the National Highway Traffic Safety Administration. The United States Government assumes no liability for its contents or use thereof. If trade or manufacturers’ names or products are mentioned, it is only because they are considered essential to the object of the document and should not be construed as an endorsement. The United States Government does not endorse products or manufacturers. The testing performed in this study was for methodology development. The vehicles tested were used vehicles leased from local automobile dealerships or vehicles owned by the National Highway Traffic Safety Administration. The performance of these vehicles may not be indicative of new vehicles. ii TABLE OF CONTENTS Page LIST O F T ABLES ......................................................... iv LIST O F F IGURES .......................................................... v 1.0 INTRODUCTION .......................................................1 2.0 T EST M ETHOD ........................................................2 2.1 T he V ehicles a nd P reparation ..........................................2 2.2 I nstrumentation a nd D ata C ollection ..................................... 2 2.3 T est C onduct ......................................................3 2.4 T he D rivers .......................................................4 2.5 E xperimental D esign ................................................5 2.6 P rocedure ........................................................7 2.7 D ata R eduction ....................................................8 3.0 R ESULTS .............................................................9 3.1 D ata A nalysis ......................................................9 3.2 T aurus P roblems ..................................................26 4.0 C ONCLUSIONS .......................................................29 APPENDIX A T est V ehicle I nformation .........................................33 APPENDIX B S as C ode a nd O utput ...........................................37 LIST O F R EFERENCES ....................................................47 iii LIST OF TABLES Page Table 2 .1 - - Test V ehicles ...............................................2 Table 2 .2 - - Partial T est M atrix ...........................................6 Table 2 .3 - - Run O rder f or D river 1 ........................................7 Table 3 .1 – O utliers i n t he D ata ..........................................12 Table 3 .2 – M eaning o f S ymbols U sed i n C omputational F ormulas ................ 17 Table 3.3 – Split-Plot Factorial Design F-statistic Calculations3 .................. 18 Table 3.4 -- Sums of Squares for Split-Plot Factorial Design3 ....................19 Table 3.5 – Significance Tests of Main Effects and Two-Way Interactions on Natural Log Transformed S topping D istance D ata ......................................21 Table 3 .6 – G reenhouse-Geisser C onservative F -Test ..........................24 Table 3 .7 - - Multiple C omparisons o f L og T ransformed S topping D istance D ata ..... 25 Table 3 .8 – 9 5% C onfidence I nterval F rom R eplications 1 -4 a nd R eplication 5 ....... 29 iv LIST OF FIGURES Page Figure 3 .1 – S hortest S topping D istance I n E ach T est C ondition a nd R eplication ..... 10 Figure 3 .3 – H istogram o f N atural L og T ransformed S topping D istance D ata ....... 11 Figure 3 .2 – H istogram o f C orrected S topping D istance D ata ...................11 Figure 3 .4 - - Main E ffects P lot f or C orrected S topping D istance D ata ............. 13 Figure 3 .5 – T wo-Way I nteraction P lot o f C orrected S topping D istance D ata ....... 15 Figure 3 .6 – T aurus B rake P ad ...........................................27 v 1.0 INTRODUCTION The National Highway Traffic Safety Administration (NHTSA) is exploring the feasibility of developing brake tests to measure brake system performance of light vehicles. Random variability in brake testing can be quite large for light vehicles. Developing brake system performance tests requires controlling test variability so that measured differences between vehicles is more than just experimental noise. Possible sources of variability include environmental conditions, vehicle-to-vehicle differences for a given model, brake lining conditioning, test driver differences, test surface friction changes with time, test surface friction differences between test sites. In 1997, eleven vehicles were tested at NHTSA’s Vehicle Research and Test Center (VRTC). The goals were to evaluate various brake system performance measures and to quantify the levels and sources of variability associated with the measures1. In 1998, a second test program was conducted to further explore brake testing variability. The objective of this program was to determine the level of variability in stopping distance tests of automobiles that is due to differences between drivers for a variety of conditions. VRTC conducted tests with three expert test drivers in three different cars on wet and dry asphalt with the anti-lock brake systems (ABS) working and disabled. This report documents that test program. 2.0 TEST METHOD 2.1 The Vehicles and Preparation VRTC leased three used late model cars for testing. The vehicles were commonly available small, medium, and large passenger cars. All the vehicles were equipped with four wheel disk brakes and ABS. A list of the vehicles tested is shown in Table 2.1. Complete information on the vehicles can be found in Appendix A. 1 Table 2.1 -- Test Vehicles Vehicle Category Vehicle ABS Supplier Test Weight Small Automobile 1995 Chrysler Neon Allied Signal 1234 kg Mid-Size Automobile 1996 Ford Taurus Bosch 1710 kg Large Automobile 1997 Lincoln Town Car ITT 1941 kg VRTC rebuilt each vehicle’s brake system with new original equipment brake linings, brake rotors, and tires.

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