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This paper considers ground vehicle lateral/directional stability which is of primary concern in traffic safety. Lateral/directional dynamics involve yawing, rolling and lateral acceleration motions, and stability concerns include spinout and rollover. Lateral/directional dynamics are dominated by tire force response which depends on horizontal slip, camber angle and normal load. Vehicle limit maneuvering conditions can lead to tire force responses that result in vehicle spinout and rollover. This paper describes accident analysis, vehicle testing and computer simulation analysis designed to give insight into basic vehicle design variables that contribute to stability problems. Field test procedures and results for three vehicles are described. The field test results are used to validate a simulation model which is then analyzed under severe maneuvering conditions to shed light on dynamic stability issues.

This paper presents test methods and modeling procedures for identifying the directional handling characteristics of vehicles over the full maneuvering range from straight running to limit cornering and/or braking. The test procedures are designed to validate steady-state and dynamic response performance. The model parameters are derived from simple static tests of vehicle properties and tire parameters identified from tire machine tests. Current steady-state field test procedures validate the model response under cornering only conditions. Model analysis then extrapolates vehicle response under combined cornering and braking conditions. Some discussion is devoted to potential braking in a turn transient testing for more complete model validation.

A significant aspect of trailering safetyis the ability of a combination vehicle to stop with the same effectiveness as the tow vehicle alone. This paper describes the operation of electric and surge brake systems and presents analytical equations which can be used to predict stopping distances of these combinations as well as those trailers having no brakes. Comparisons are then made to full scale brake performance tests with seven different trailers. Problems are discussed and recommendations for a trailer-alone brake test procedure are given.

This paper provides approximate factors, measurement techniques, and test procedures that can be used to determine trailer stability. The recommended performance metric is damping ratio, or an equivalent cycle to half amplitude which is evaluated, via a pulse-steer procedure, at some reference speed. A minimum damping ratio criteria of 0.15 at 55 mph is suggested and compared to the results of recent full scale tests. The approach is useful in selecting a minimum value of hitch load (for various weight tow cars) that will insure a minimum acceptable level of trailer stability at highway speeds.