Research Reports

Recycled Asphalt Shingles (RAS) include both manufacture waste scrap shingles (MWSS) and post-consumer tearoff scrap shingles (TOSS). It is estimated that Minnesota generates more than 200,000 tons of shingle waste each year. Recently, a portion of this waste has been incorporated into hot-mixed asphalt (HMA) pavement mixtures. The current technology limits the amount of RAS in HMA to no more than 5 percent by weight. This leaves a lot of underutilized shingle waste material throughout the state. This has prompted MnDOT to investigate other potential uses RAS. One potential use is to improve the performance of gravel surfacing and reduce dust by replacing common additives such as calcium chlorides with RAS. This is especially relevant as gravel sources in Minnesota have been depleted and/or have declined in quality, which has affected the performance of gravel surfacing. These poorer quality fines can increase the amount of dust generated and increase the difficulty of keeping the roadway smooth. Some agencies have used dust control additives to help the performance of these lower quality gravels. Successful implementation has the potential of removing valuable RAS materials from the waste stream to supplement the use of more expensive virgin materials and improve the performance of local roads.

The Twin Cities freeway network is a densely instrumented and growing transportation system. As the Minnesota Department of Transportation (MnDOT) pursues a performance-based management strategy to monitor the health of the network and make planning and management decisions, the data from this vast network is being examined using a variety of methods. To provide MnDOT with timely performance information regarding the Twin Cities freeway network, a streamlined program was developed based on existing and new methodologies. The Highway Automated Reporting Tool (HART) utilizes a user-friendly interface for corridor, date, time, and report selection. Selected data are automatically examined to identify and correct errors and produce 'cleaned' data for use within each report. Using interpolation and autoregressive integrated moving average (ARIMA) techniques, small errors are corrected in place while preserving as much useful data as possible. Larger issues are corrected using an imputation algorithm relies on uses nearby sensors and historical data to create representative replacement data. In this first version of HART, four reports are included: Speed-Based Congestion, Congestion Intensity, Lost and Available Capacity, and Maximum and Total Throughput. The Speed-Based Congestion report matches the existing methodology used to generate the annual Congestion Report.

This report presents a study of the impact lane markings and signing have on driving behavior at a two-lane roundabout located in Richfield, Minnesota. After its completion in 2008, this roundabout sustained a suspiciously high amount of crashes. In response, through this study, engineers experimented with changes in the roundabout's signs and lane markings, as roundabout design regulations are relatively lax and nonspecific in contrast to those for standard signalized intersections. An observational study was conducted that reduced 216 hours of before and after video records of the roundabout into a database of all the violations committed by drivers. Along with the observational data, crash records were analyzed and demonstrated that improper turns and failing to properly yield account for the majority of collisions. The changes implemented in the approaches to the roundabout and specifically the extension of the solid line seems to have reinforced the message to the drivers that they must select the correct lane before approaching the roundabout entrance. Although choosing the correct lane does not directly address yielding violations, it does reduce the occurrence of drivers conducting an improper turn and to some extent reduces the need for a driver to change lanes within the roundabout. The implemented changes produced a 48% reduction in normalized occurrences of improper turns, and a 53% reduction in normalized occurrences of drivers choosing the incorrect lane a month after the changes, while a year later, these reductions were 44% and 50%, respectively.

As a natural extension of University of Minnesota value capture study in 2009, this project demonstrates the application of value-capture strategies to supplement transportation funding for the completion of TH-610 in Maple Grove, Minnesota. Using spatial and regression analysis, we estimate that the completion of TH-610, with two additional exits, would lead to a significant growth in assessed property value, including about $12 million in land value and $5 million in buildings. The growth would result in about $4.3 million in property tax capacity, and about $1 million in annual property tax revenue. With multiple scenarios of hypothetical value-capture designs, we estimate the revenue potential of value capture would range from about $12 million to about $37 million, which could be used to supplement project finance to expedite the completion of TH-610.

A flashing LED stop sign is essentially a normal octagonal stop sign with light emitted diodes (LED) on the stop sign's corners. A hierarchical Bayes observational before/after study found an estimated reduction of about 41.5% in right-angle crashes, but with 95% confidence this reduction could be anywhere between 0% and 70.8%. In a field study, portable video equipment was used to record vehicle approaches at an intersection before and after installation of flashing LED stop signs. After installing the flashing stop signs, there was no change in the relative proportion of clear stops to clear non-stops when minor approach drivers did not face opposing traffic, but the relative proportion of clear stops increased for drivers who did encounter opposing traffic.

This document contains the results of Task D, Best Practices Guidelines for the Culvert Repair Best Practices, Specifications and Special Provisions Guidelines Project. These guidelines will provide guidance to Minnesota Department of Transportation (MnDOT) engineers in making better decisions on culvert repairs. New materials specifications, special provisions, and standard details will ensure adherence to standardized practices and increase the effectiveness and longevity of repairs. Focus is on repair of centerline culverts of 24 inches to 72 inches in diameter. This Task D document contains the best practices guidelines for replacement, rehabilitation and repair methods for deteriorating culverts. An overview of replacement methods is provided. Rehabilitation and repair methods are discussed in more detail. The methods discussed are the most common culvert rehabilitation and repair methods identified during governmental and industry surveys conducted during Tasks A and B. The final list for inclusion in this guideline was chosen by the authors and the Technical Advisory Panel (TAP). Special provisions and standard details were prepared for the following methods: paved invert, cured-in-place pipe liner (CIPP), sliplining culvert pipe, centrifugally cast concrete culvert lining, spall repair, joint repair, and void filling outside the culvert.

State departments of transportation around the country are exploring ways to quantify benefits of transportation research, especially in light of a trend toward performance-based outcomes, as seen in the MAP-21 federal transportation legislation. MnDOT initiated this project to conduct the following tasks: review and document practices in place at State DOTs from around the country; determine best practices that have the most potential for implementation by MnDOT; and recommend key milestones/steps for MnDOT to quantify the benefits of its research results.

The degree of modal split in the United States has continued to change with increased use of non-motorized modes. To accommodate a variety of users, context-sensitive solutions are being pursued. Such solutions call for the sharing of right-of-way by multiple user groups with different and often competing demands. Traditionally, the needs of vehicular traffic have been prioritized as evident in many current design standards. This research focuses on developing guidance for design decisions to best balance the competing needs and accommodate all expected roadway users. Non-standard design solutions, often associated with complete streets, were investigated in two major contexts. The first involved a comprehensive review of the current-state-of-the-practice in design standards, complete streets, and associated legislation in Minnesota and nationally. Second, a detailed analysis of 11 'complete street' study sites was conducted. The study primarily focused on evaluating changes in safety and operations between the periods before and after implementation. Differences in the characteristics of the study sites and varying degrees of changes and improvements conducted at each site prevented an aggregate quantification of the implications of complete street improvements across all sites, and specific recommendations for changes in design standards. Nevertheless, the analysis of complete street designs implemented at the 11 study sites suggest that changes made to these study sites did not result in adverse safety or operational impacts. Therefore, providing flexibility and modification to the State Aid Design Standards in the context of complete streets and conditions specified in this research appears to be a reasonable consideration.

Complete streets is emerging as an influential movement in transportation planning, design, and engineering. This guidebook, with accompanying case studies, explores the variety of ways in which complete streets is conceptualized and institutionalized by various jurisdictions. It offers practical and applicable insights for jurisdictions in Minnesota and elsewhere. The research focused on best practices in 11 locations across the nation: Albert Lea, Minnesota; Arlington County, Virginia; Boulder, Colorado; Charlotte, North Carolina; Columbus, Ohio; Dubuque, Iowa; Fargo-Moorhead, North Dakota/Minnesota; Hennepin County, Minnesota; Madison, Wisconsin; New Haven, Connecticut; and Rochester, Minnesota. The guidebook is informed by an analysis of multiple data sources from each jurisdiction. The authors conducted a review of key documents (e.g., plans, policies, design guidelines), site visits, photo documentation, and in-depth interviews with more than 100 key informants. Six best practice areas emerged through the analysis: (1) framing and positioning, (2) institutionalizing complete streets, (3) analysis and evaluation, (4) project delivery and construction, (5) promotion and education, and (6) funding. The six best practice areas are described in detail and illustrated by examples from the case locations. The guidebook concludes with an appendix of complete streets case reports that offer additional details about each of the 11 case jurisdictions.

The objective of this project was to render the Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR) road assessment methods accessible to field engineers through a software package with a graphical user interface. The software implements both methods more effectively by integrating the complementary nature of GPR and FWD information. For instance, the use of FWD requires prior knowledge of pavement thickness, which is obtained independently from GPR.