Research Reports

Part of the challenge achieving maximum field density in subgrade materials is transferring the optimal compaction and moisture content data from laboratory testing to the field. This research investigated the proficiency of four different instruments at accurately predicting moisture contents of three subgrade soils (loam, silt, silty/clay) commonly used in Minnesota roadway construction projects. The four instruments were; DOT600 (moisture content), WP4C dewpoint potentiometer (matric suction), the Button Heat Pulse Sensor (BHPS) (temperature rise vs. moisture content), and an exudation pressure test device. The DOT600 showed a strong correlation between the output period (measured in micro-seconds) and volumetric water content. The WP4C did not accurately measure matric suction for any of the loam, silt or silt/clay soils at suctions below 250 kPa. Published data shows that the matric suction of soils compacted at optimum moisture content is usually in the range of 200 - 300 kPa. The BHPS showed a strong correlation between measured temperature rise and water content but in its current configuration is not rigorous enough to withstand field conditions. The exudation pressure device was applied to soils compacted in a AASHTO T99 mold at various moisture contents. Water was exuded from the packed samples at pressures between 100 and 500 psi corresponding to AASHTO-T99 moisture contents of 10 to 25%. Accurate moisture content readings from any of these instruments may not be as important as a more precise and simple calibration between the measurement units of the instrument and the optimum moisture content determined from the AASHTO T99 test.

This project focused on the enhancement and evaluation of a battery-less wireless weigh-in-motion (WIM) sensor for improved enforcement of road weight restrictions. The WIM sensor is based on a previously developed vibration energy harvesting system, in which energy is harvested from the vibrations induced by each passing vehicle to power the sensor. The sensor was re-designed in this project so as to reduce its height, allow it to be installed and grouted in an asphalt pavement, and to protect the piezo stacks and other components from heavy shock loads. Two types of software interfaces were developed in the project: a) An interface from which the signals could be read on the MnDOT intranet b) An interface through a wireless handheld display Tests were conducted at MnRoad with a number of test vehicles, including a semi tractor-trailer at a number of speeds from 10 to 50 mph. The sensor had a monotonically increasing response with vehicle weight. There was significant variability in sensor response from one test to another, especially at the higher vehicle speeds. This variability could be attributed to truck suspension vibrations, since accelerometer measurements on the truck showed significant vibrations, especially at higher vehicle speeds. MnDOT decided that the final size of the sensor was too big and could pose a hazard to the traveling public if it got dislodged from the road. Hence the task on evaluation of the sensor at a real-world traffic location was abandoned and the budget for the project correspondingly reduced.

A friction measurement system was developed for Polk County and installed on two snowplows in the county's winter road-maintenance fleet. The major components of the developed system were a special instrumented wheel, a pneumatic pressure-controlled cylinder, force-measurement load cell and accelerometers, a data collection microprocessor and a data processing micro-processor. The road friction coefficient was estimated in real-time and was stored on a secure digital card along with the current GPS-sensed location of the truck. The friction coefficient information was also displayed in real-time using LED lights for the operator. Although the basic design of the friction wheel system had been used for several previous years of intermitant testing without showing significant wear, the almost identical installations on the Polk County trucks suffered bearing failures after the first few days of continuous use. The failed bearings were replaced with larger bearings in a more robust mount. Apparently, the system again failed in a few days, but the research team did not learn of this failure until the end of the project. The low budget for the project and the significant travel required to go to Crookston posed major challenges in getting a friction measurement to work effectively for Polk County.

The Federal Highway Administration (FHWA) estimates that 58 percent of roadway fatalities are lane departures, while 40 percent of fatalities are single-vehicle run-off-road (SVROR) crashes. Addressing lane-departure crashes is therefore a priority for national, state, and local roadway agencies. Horizontal curves are of particular interest because they have been correlated with increased crash occurrence. This toolbox was developed to assist agencies address crashes at rural curves. The main objective of this toolbox is to summarize the effectiveness of various known curve countermeasures. While education, enforcement, and policy countermeasures should also be considered, they were not included given the toolbox focuses on roadway-based countermeasures. Furthermore, the toolbox is geared toward rural two-lane curves. The research team identified countermeasures based on their own research, through a survey of the literature, and through discussions with other professionals. Coverage of curve countermeasures in this toolbox is not necessarily comprehensive. For each countermeasure covered, this toolbox includes the following information: description, application, effectiveness, advantages, and disadvantages.

The purpose of this project was to develop methodologies for monitoring non-motorized traffic in Minnesota. The project included an inventory of bicycle and pedestrian monitoring programs; development of guidance for manual, field counts; pilot field counts in 43 Minnesota communities; and analyses of automated, continuous-motorized counts from locations in Minneapolis. The analyses showed hourly, daily, and monthly patterns are comparable despite variation in volumes and that adjustment factors can be used to extrapolate short-term counts and estimate annual traffic. The project technical advisory panel made five recommendations: (1) MnDOT should continue and institutionalize coordination of annual statewide manual bicycle and pedestrian counts; (2) MnDOT should improve methods for reporting results of field counts and explore web-based programs for data reporting and analysis; (3) MnDOT should lead efforts to deploy and demonstrate the feasibility of new automated technologies for bicycle and pedestrian counting, focusing on new technologies not presently used in Minnesota; (4) MnDOT should begin integration of non-motorized traffic counts from existing automated, continuous counters in Minneapolis into its new databases for vehicular traffic monitoring data; and (5) MnDOT should work with local governments and explore institutional arrangements for (a) establishing a network of permanent, automated continuous monitoring sites across the state and (b) sharing and deploying new technologies for short-duration monitoring to generate traffic counts that provide a more comprehensive understanding of spatial variation in nonmotorized traffic volumes.

At-grade trail crossings have frequently been the sites of bicycle, pedestrian, and snowmobile crashes in Minnesota and throughout the nation. To date, many resources exist for use in the design of trails and intersections, such as the MnDOT Bikeway Facility Design Manual, while guidelines of traffic control at roadway-trail crossings are covered in the MN MUTCD. Resources on comprehensive guidance for safety treatments at roadway-trail crossings, however, are limited. The goal of this document is to synthesize best practices observed statewide in Minnesota and nationally in order to provide engineers and other transportation professionals with guidance on safety treatment applications at trail crossings. Following discussion of principles of user-friendly trail-crossing designs, this document provides a toolbox of categorized treatments which are widely used in the U.S. with discussion on each treatment. Importantly, a decision tree-based treatment selection methodology is developed for fast look-up and selection of appropriate treatments based on the conditions at a particular trail crossing. These conditions include urban/rural setting of the crossing, number of lanes of the crossed roadway, whether the crossed roadway is divided or undivided, the speed limit and average daily traffic (ADT) of the crossed roadway, and whether the crossing is a midblock or parallel path crossing. Each end node of the decision tree leads to a specific toolbox in table form containing all appropriate treatments for the conditions of the study trail crossing. Final treatments for the study site can be simply chosen from the table, combined with site-specific requirements and engineering judgment.

The practices in this guide provide an overview of the current general state of the practice in Minnesota relating to the design, and operation of pedestrian- and bicycle-related factilites.

Conservation and reuse of resources is a necessity in achieving sustainability across the globe. In recent years, construction and demolition debris including bricks has appeared in stockpiles around Minnesota. The objective of this research project was to investigate the possibility of putting the brick to beneficial use as aggregates for base courses in pavements. This would help to conserve natural stone aggregate and also recycle the brick instead of dumping it as waste in a landfill. In addition, contractors could save money by being able to reuse locally available material. MnDOT is already quite progressive in its use of recycled materials and allows the use of recycled concrete aggregates, recycled asphalt pavement, and recycled glass in base and surface courses. Based on current literature review, Minnesota may become a pioneer in the use of recycled brick aggregate as well. There are many different types of clay bricks including structural bricks (both commercial and residential), pavers, and refractory bricks. The structural bricks and pavers will also vary from region to region. The bricks used in Minnesota are of the highest quality available because they have to meet severe weathering requirements. Structural brick accounts for the largest amount of brick manufactured. In this project, samples of various types of bricks were tested. The main tests conducted were the Los Angeles Rattler to assess abrasion properties and the magnesium sulfate soundness to evaluate freeze-thaw durability. In addition, basic engineering properties such as specific gravity and absorption were determined.

Tire Derived Aggregate (TDA) is referred to in this report as rough shreds, shreds, and tire chips of various sizes. The potential uses discussed herein include TDA as lightweight fill, retaining wall backfill, insulation layer, drainage layer, and capillary moisture break. Other uses exist; however, they are beyond the scope of this report. This report summarizes the results of numerous studies regarding the environmental concerns of using TDA both above and below the ground water table. The summary provides general observations based on the literature review performed, comments on the current state of the practice regarding the use of TDA for highway applications, and information on additional resources.

This project addressed several MnDOT critical issues and strategic directions: easing congestion and improving mobility by making multi-modal transit options more easily accessible. It did so by extending the Cyclopath bicycle route-finding system to support multi-modal routes that combine cycling and transit. This required extensions to the route-finding algorithm - to combine biking and transit appropriately - and user interface - to let users express modal preferences and enhance the visual presentation of routes, e.g., to mark mode shifts. We used the Graphserver open-source software to as the routing engine; by building on existing software, we reduced development effort. We conducted interviews with a number of multimodal transit users to guide the design of the user interface.