The Minnesota Department of Transportation (Mn/DOT) built the Minnesota Road Research Project MnROAD between 1990-1993. The 2.5-mile low volume road and the 3.5-mile mainline consists of a 2-lane roadway that originally contained gravel, hot mix asphalt, and concrete test cells designed for both low volume roads and interstate traffic. The mainline interstate cells are trafficked by public interstate traffic and the low volume road has a Mn/DOT 5-axle tractor-semi-trailer to simulated conditions of rural roads in two load configurations, resulting in the same equivalent axle loads or ESALS. MnROAD is located in a wet freeze zone that has affected both its base and subgrade materials with seasonal frost movements. This movement has slowly deteriorated each test cells ride over time. MnROAD has monitored the frost movements using frost pins and has measured the ride (international ride index - IRI) using high-speed profilers over for the life of the project. This paper investigates the loss of ride from both environmental and traffic loadings and how they have combined to cause the deterioration of ride over the last 10 years at MnROAD. The findings suggest that our current process to develop a mechanistic empirical design is currently missing the fact that seasonal differental frost movements play an important role in pavement performance in northern climates and need to be taken into account. Copyright ASCE 2006.