Reports

MnDOT's Pavement Management Unit conducts a biennial pavement condition assessment of the trunk highway system using an automated video and laser equipped van. The pavement condition data is then reduced to 3 pavement indices, PSR, SR and PQI. This report was based on data collected during 1999 and 2000.

In October 22-24, 2000, 59 leaders from consulting engineering firms, Minnesota Department of Transportation (Mn/DOT) and the Department of Administration gathered in Minneapolis, Minnesota to participate in a workshop to address their fundamental working relationships and the processes related to the consultant program. The workshop was convened by the University of Minnesota's Center for Transportation Studies and sponsored by Mn/DOT and the Consulting Engineers Council of Minnesota. The workshop objective was to discover new ways for Mn/DOT and the consulting industry to expedite the delivery of transportation projects that benefit the public. Leaders in the private and public sector, seeking to address the challenges of the future with fresh approaches and new thinking, met to: Understand the central role of the Consultant Program in the "Big Plan"; Analyze the problems facing government and private users of the Consultant Program; Examine the best practices in Consultant Programs from other state DOTs and lessons they may hold for Minnesota; Develop a blueprint to make the Consultant Program "better-faster-cheaper" and more satisfying to work in. Four groups of Mn/DOT stakeholders, two groups of consulting firms and an administration group were formed to identify issues and challenges in the "as is" consulting process from their perspectives. The major issues and challenges were recorded and reported to the larger workshop. After presentation by other state DOTs on best practices, the group created stretch goals for the consultant program. The next steps in bringing improvement ideas to strengthen the consultant program into action include: Preparation of the Final Workshop Report to be mailed to each participant within three weeks; and A Steering Committee meeting immediately following the workshop to identify goals and dates for the next steps.

Recent advances in flexible pavement design have prompted agencies to move toward the development and use of mechanistic-empirical (M-E) design procedures. This report analyzed seasonal trends in flexible pavement layer moduli to calibrate a M-E design procedure specific to Minnesota. Seasonal trends in pavement layer moduli were quantified using data from the Minnesota Road Research Project (Mn/ROAD) and Long Term Pavement Performance Seasonal Monitoring Program (LTPP SMP) sites located in Minnesota. The relationships investigated were between climate factors, subsurface environmental conditions, and pavement material mechanical properties. The results show that pavement layer stiffness is highly respondent to changes in the average daily temperature and available moisture. Five seasons were used to characterize the seasonal variations in pavement layer moduli for design purposes. Seasonal factors were used to quantify the cyclic variations in the pavement layer stiffness for a typical year. The maximum stiffness of the pavement layers is reached when temperatures are cooler. The hot mix asphalt layer moduli are at a minimum in the summer when temperatures are high. The granular base layer moduli are at a minimum during the early spring-thaw period when excess moisture is unable to drain. Finally, the fine-grained subgrade layer moduli are at a minimum in late spring and summer due to the low permeability and slow recovery of the material. The Integrated Climate Model (ICM) was used in this study to compare predicted data to actual data from Mn/ROAD. It was found that the ICM data compared favorably, however, the ICM was not able to predict the spring-thaw period.

In this study, researchers devised a scheme for calibration of earth pressure cells to observe their response to various loading configurations and to recommend a procedure for field installation. As a result of calibration tests, a field installation procedure was developed. Preliminary field data indicate that soil calibration and placement procedure provide reasonably accurate measurements.

The use of salt as a deicer is common in Minnesota because of its low cost and efficiency, but it causes many problems for highway maintenance staff because of its impact on the adjacent vegetation. Salty soils are not conducive to healthy vegetation growth, and the absence of healthy vegetation along the road may lead to weed control problems, increased erosion, and resulting damage to the pavement structure. The report outlines salt effects on soil, as well as methods to avoid vegetation damage by salt and ice before it occurs and to repair damage. It also contains a list of salt-tolerant grasses and woody plants for use in Minnesota. Preventive methods include selection of appropriate vegetation for conditions; use of salt-tolerant grasses and sods; use of native grasses and wildflowers; effective turf establishment practices; protection of existing vegetation; optimization of salt use; and use of products that are friendly to vegetation. Maintenance methods include irrigation to flush salt from soil; soil treatments; vacuuming and sweeping; rejuvenation (reseeding or aeration) of damaged areas; and design and construction strategies.

This project involved the construction of two long-span, high-strength composite prestressed bridge girders to investigate their structural behavior and the adequacy of American Association of State Highway and Transportation Officials (AASHTO) 1993 provisions for their design. The scope of the research included examining prestress losses, transfer length, cyclic load response, and ultimate flexural strength. The research revealed that prestress losses could not be determined solely from strain gage instrumentation. Foil strain gages attached to the strand cannot measure losses caused by relaxation and drift over time. Vibrating wire strain gages embedded in the concrete cannot account for losses in the prestressing strand before the concrete hardens. Researchers used vibrating wire gage data to measure the prestress losses incurred since the time of strand release. To backcalculate the losses that occur before release, researchers used total prestress losses determined from flexural cracking and crack reopening loads. The measured prestress losses were found to be much higher than those predicted by analytical methods. Prestress losses predicted by AASHTO not only ignore concrete stress before release but also overestimate the high-strength concrete modulus, leading to lower initial losses, and overpredict the creep and shrinkage, leading to higher long-term losses.

This report reviews Manitoba's and Minnesota's Specific Pavement Studies (SPS-5) projects. The studies focus on investigating the performance of hot mix asphalt (HMA) overlays on HMA pavements and involve nine core test sections. The SPS-5 design variables in test sections include a control section (do nothing), amount of preparation of the existing surface (mill, no-mill), overlay thickness (50-mm, 125-mm), and the type of overlay material (virgin, recycle). Researchers plan to study the Manitoba and Minnesota SPS-5 projects, part of the Long-Term Pavement Performance (LTPP) Project, until 2010, when each project reaches the approximate age of 20 years. This project update includes a field review by the authors, a review of the existing monitoring data, and an estimate of the expected performance and cost expectations for upcoming years until 2010. Currently after 10 years all sections, excluding the control section, still are performing well. As a result at this point, researchers recommended the least costly treatment, 50-mm recycled asphalt overlay with no surface preparation, for pavement rehabilitation.

This research project examined mycorrhizal and plant factors involved in roadside reclamatin. The addition of fertilizer did not benefit native prairie plantings and generally is not recommended for use at roadside prairie restoration sites.

This project focuses on the second construction phase of the Minnesota Road Research facility (Mn/ROAD) and evaluates three typical, locally available, surfacing aggregates along with a rollover section from the initial phase for performance. The project results indicate that the adsorption test did not predict the performance of the sections in this experiment. All of the aggregates were characterized as marginal in terms of moisture and frost susceptibility. The sections with the greatest percentage of fines typically performed better than sections with a low percentage of fines. The Minnesota Department of Transportation issued a technical memorandum to change the specification from 0-15% to 8-15% passing the No. 200 sieve for Class 1 surfacing aggregate. The project also compared freezing and thawing rates on the aggregate sections to nearby hot mix asphalt (HMA) sections. Soil at any particular depth froze four to five days before HMA sections. The aggregate sections also thawed at exponential slower rates as depth increased from 11 to 35 days, which means that an aggregate surfaced road will freeze sooner and thaw slower than an HMA surfaced road. This information impacts the management of spring load restrictions and winter load limits.

This report presents a real-time system for pedestrian tracking in sequences of grayscale images acquired by a stationary camera. Researchers also developed techniques for recognizing pedestrian's actions, such as running and walking, and integrated the system with a pedestrian control scheme at intersections. The proposed approach can be used to detect and track humans in a variety of applications. Furthermore, the proposed schemes also can be employed for the detection of several diverse traffic objects of interest, such as vehicles or bicycles. The system outputs the spatio-temporal coordinates of each pedestrian during the period the pedestrian is in the scene. The system processes at three levels: raw images, blobs and pedestrians. Experimental results based on indoor and outdoor scenes demonstrated the system's robustness under many difficult situations, such as partial or full occlusions of pedestrians. In particular, this report contains the results from a field test of the system conducted in November 1999.