The Minnesota Department of Transportation began construction on the Minnesota Road Research Project (MnROAD) in 1991 and opened the full-scale pavement research facility to live traffic in 1994. Since the time of its construction, MnROAD, the first major test track since the AASHO Road Test of the 1950s and 1960s, has learned a number of lessons on behalf of the greater pavement community. As part of completing the first phase of MnROAD (its first ten years of operation), researchers at the University of Minnesota reviewed the many products of MnROAD’s first phase for a project titled “MnROAD Lessons Learned.” The Lessons Learned Project involved over fifty interviews, three hundred published and unpublished reports, papers, and briefs, and an online survey of pavement professionals. This paper, based on the Lessons Learned Project, presents an overview of MnROAD products of interest at the local, state, and national levels. Furthermore, the paper provides extensive references for these products in the hopes of increasing awareness of MnROAD’s under-publicized contributions to pavement engineering.

Researchers report the number of cycles corresponding to the lower strain rate in a permanent deformation test, known as flow number (FN), as a good asphalt mix stability indicator; however, its variability has limited its implementation. Current procedures for calculating FN rely on data smoothing techniques, which can yield very different values for the same specimen if different moving average periods are used. A new methodology for determining FN is proposed by modeling the permanent strain versus load cycles curve as a continuous function. Data from cold-mix replicate samples were analyzed and compared, and a substantial reduction in FN variability was observed using the proposed methodology. Use of FN to select the data to determine the power model parameters was also evaluated. Results indicate that establishing FN as the upper cut-off point of the data used to fit the power-model produces a slight reduction in parameter estimates variability. Adopting the proposed model could be useful for permanent deformation characterization and as a unifying criterion for selecting the data used for that purpose.

The saturation aging tensile stiffness (SATS) test has been developed to quantify the moisture damage of a range of U.K. asphalt mixtures. In order to combine the effects of moisture and aging, the test is undertaken at an elevated temperature and pressure in the presence of moisture. This paper describes a procedure developed to investigate in detail the effects of aging, pressure, and moisture damage on results from the SATS test. An aging factor has been determined that captures the increase in stiffness modulus due to hardening that occurs at the elevated temperature and pressure. This factor ranges from 1.38 for a dry specimen to approximately 1.2 for a fully saturated specimen. A pressure factor has been determined that captures decreases in stiffness modulus due to pressure. Results show that the pressure factor is lower for the asphalt containing the basic aggregate, indicating a greater sensitivity to pressure compared to the mixture containing the acidic aggregate. The depressurization temperature in the SATS test protocol was reduced from $85\text{to}30°\mathrm{C}$ to minimize this effect. A moisture factor was calculated, which is a measure of the moisture sensitivity of the asphalt mixture. Results showed that the moisture factor was significantly lower for the asphalt containing the acidic aggregate, indicating greater moisture sensitivity.

In this paper, the influence of overloading on the operational life of flexible pavements is discussed, leading to the development of a deterioration model for pavement and a ticketing formulation for overweight vehicles. To conduct this research, a theoretical model is developed for flexible pavements. Using this model, sensitivity analyses are made and the significant parameters that influence the deterioration of pavement under truck loading are investigated. The relationships between the passing loads and the number of allowable load cycles are obtained. These relationships form the basis for further models by which the damage ratios of flexible pavements are assessed and vehicle fines determined. A numerical example is presented to indicate the applicability and practicality of the proposed models.

This paper presents a methodology for modeling pedestrians’ crossing behavior along an urban trip, as well as an algorithm for the estimation of accident risk along the trip. For that purpose, existing models are exploited and further developed. In particular, a nested logit model and a linear regression model are merged and adapted to develop a hierarchical crossing behavior model, allowing for the estimation of a distribution of crossing probabilities on an urban road link among junctions and various midblock locations. The explanatory variables concern a set of directly measurable geometric and traffic characteristics. A second model is then developed for the estimation of the distribution of crossing probabilities along a trip in relation to the distance from the trip origin. Both models were sufficiently validated by means of appropriate surveys. On the basis of these models, a complete framework for the assessment of pedestrians’ crossing behavior in urban areas is developed. Moreover, a set of formulas for the calculation of accident risk along a trip in relation to the estimated crossing behavior of pedestrians is proposed.