Developing Roadway Standards for Ride Quality from the Customer's Perspective

This paper reports the findings of research conducted for the Pennsylvania Department of Transportation (PennDOT) to develop customer-based standards for ride quality on four functional classes of highway: Interstate highways, other national highway system (NHS) roads, secondary roads with average annual daily traffic (AADT) greater than 2,000, and secondary roads with AADT less than 2,000. The field work, in which subjects evaluated the ride quality of predetermined test sections of pavements, was conducted in six Pennsylvania counties to incorporate a variety of settings across the state. These subjective ratings were regressed on international roughness index (IRI) values for each of the four highway classes and revealed a fan-shaped pattern in which motorist satisfaction with ride quality dropped off with increased roughness most sharply on Interstate highways, less so for other NHS roads, and still less for secondary roads. PennDOT's current standards for what constitutes good ride quality for each of the four road types equates closely with the 70% level of motorist satisfaction, whereas the standards for excellent ride quality coincide with the 90% motorist satisfaction level for all but the lower-volume secondary roads. The results also suggest that motorist satisfaction with ride quality is extremely sensitive to IRI in rural settings, moderately sensitive to IRI in urban settings, and less so in major metropolitan suburban areas. This pattern is the reverse for NHS roads, and for secondary roads motorist satisfaction is very sensitive to IRI in rural areas and less so in urban and suburban areas. From these results, PennDOT could consider adopting more ambitious ride quality standards, targeting even higher levels of customer satisfaction. However, adopting such standards would require a careful analysis of the cost implications, which is beyond the scope of the research reported here.