Evaluation of Ride Equation Using Current Profiler Systems and New Sensor Technology

This report describes the research performed to evaluate the current ride equation used by the Texas Department of Transportation (TxDOT). The existing equation for determining Present Serviceability Index (PSI) from measured profile is based on ride measurements obtained from a rating session conducted in the late 1960s. Since its original development over 30 years ago, a number of changes have occurred that require a re-evaluation of the current equation. These include such things as changes in vehicle design, and the switch from the predominantly large automobiles to the smaller and more fuel efficient mid-sized and compact cars of today. Additionally, TxDOT has changed the PSI reporting interval from 0.2¬to O.I-mile. The current ride equation is considerably different from the original equation used by TxDOT for estimating PSI from profile data obtained with the Surface Dynamics Profilometer (SDP). The original model was developed from a rating session that was held in the late 1960s. In that rating session, the profile of each section was measured and various statistics computed. Included in these statistics were the amplitudes and wavelengths, or spectral estimates that make up the road profile. The first model related these estimates to the ride ratings. Since the time this first equation was developed, several modifications were made. The first occurred in the early part of the 1980s, at which time a model was developed that would include a better relationship for calibrating the less expensive Mays Ride Meter. About 1995, a model was developed that related the PSI from the profile measurements to the International Roughness Index, or IRI. This model was later refined in 1996 and is in current use today.