This paper describes and compares three methods of estimating the static rollover threshold of passenger cars and light trucks. The Static Stability Factor (SSF), Side Pull Ratio (SPR), and Tilt Table Ratio (TTR) “metrics” are described and methods of measuring each are presented. The comparison of the three metrics is limited to the accuracy, repeatability, and ease of the measurements, and does not attempt to compare their ability to predict real world rollover accident involvement.
The results of the comparison have shown that the three metrics are very closely related. Based on this, the rollover accident predictive power of each metric is expected to be similar. However, the ease and accuracy of the TTR measurement make it the most useful of the three.
DURING THE 1980's, the use of light trucks and multi-purpose vehicles for basic transportation increased considerably. By 1990, domestic full-size pickup trucks were regularly among the top five passenger vehicles sold. The increase in the use of light trucks and multipurpose vehicles as transportation corresponds with the increase in the frequency of rollover accidents.
Many studies have been performed to attempt to correlate vehicle characteristics with rollover frequency. A fairly comprehensive list of references can be found in [1]*. Some of these studies have concluded that vehicle size and/or type correlate with vehicle rollover frequency in single vehicle accidents. Many studies have also found correlation between a vehicle's Static Stability Factor (as defined below) and vehicle rollover frequency. In addition, other static rollover threshold estimation metrics have been proposed.
This paper will describe and compare three static rollover threshold estimation metrics: Static Stability Factor (SSF), Side Pull Ratio (SPR), and Tilt Table Ratio (TTR). The comparisons are based on the ease and repeatability of each measurement, but not on the measurements ability to predict the likelihood of a rollover accident.