Vehicles often rotate during traffic collisions due to impact forces or excessive steering maneuvers. In analyzing these situations, accident reconstructionists need to apply accurate deceleration rates for vehicles that are both rotating and translating to a final resting position. Determining a proper rate of deceleration is a challenging but critical step in calculating energy or momentum-based solutions for analytical purposes.
In this research, multiple empirical tests were performed using an instrumented vehicle that was subjected to induced rotational maneuvers. A Ford Crown Victoria passenger car was equipped with a modified brake system where selected wheels could be isolated. The tests were performed on a dry asphalt surface at speeds of approximately 50 mph. In each of the tests, the vehicle rotated approximately 180 degrees with the wheels on one side being completely locked. During each run, the vehicle driver prevented steering input by maintaining control of the steering wheel. With respect to data acquisition, the Crown Victoria was equipped with a GPS system capable of monitoring positional changes at 10 Hz. Then, following each run, the actual path of the vehicle was documented by measuring residual tire marks with a robotic total station.
Some analysts use computer simulation or reconstruction software to determine the speeds of vehicles involved in collisions. Other practitioners may be limited to more simplistic tools to evaluate this type of problem. Most of these methodologies use the friction circle or ellipse concept to model the tire forces as slip angles change throughout a vehicle's trajectory. This research was designed to explore the relationship of a simplified model with actual test data. Data analysis showed that the simplified model employed herein provided a reasonably accurate methodology to predict the departure speeds of the vehicle through its respective trajectories.