Research Reports

Pedestrian assets, particularly sidewalks, are highly susceptible to aging, adverse weather conditions, and suboptimal construction practices, often leading to rapid deterioration. This deterioration is often ignored due to the widespread misconception that pedestrian assets are low risk, resulting in many deteriorated sidewalks being left untreated or inadequately maintained. A comprehensive deterioration modeling framework that integrates advanced spatial and temporal data sources, advanced data analytics, and predictive modeling would enable infrastructure managers to predict the aging process of pedestrian assets and ultimately prioritize investments, plan maintenance schedules, and allocate budgets efficiently. This project developed assessment frameworks and deterioration models for pedestrian assets that support reliable and informed decision-making regarding funding needs and asset design and maintenance. Various data sources and modeling and analysis procedures were explored, and a pedestrian asset assessment methodology was developed and evaluated. The research demonstrated a scalable and cost-effective approach to assessing sidewalk conditions, providing actionable insights for proactive maintenance. The quantifiable benefits, including construction savings, improved life-cycle costs, reduced risk, and safety enhancements, position this methodology as a valuable tool for sustainable infrastructure management.

This research summary is part of the final deliverable for Report 2024-34, "Pavement Marking Patterns and Widths – Human Factor Study," published in March 2025.

Various broken lane line configurations, marking length and gap between markings, exist across the United States. The normal width of pavement markings and the use of contrast markings with broken lane lines also varies across the country. This project explored how various pavement marking configurations impact observations from drivers during an open road human factors evaluation. The participants drove an instrumented vehicle through test areas with various pavement marking configurations. Participants provided feedback on marking visibility and their preference toward the pavement marking pattern. Participant observations took place during the day and at night. Researchers also conducted a preliminary investigation into the same marking test areas using an advanced driver assistance system (ADAS). The study found that drivers preferred wider broken lane line markings, and broken lane line markings with more marking and less gap than current MnDOT practice. No specific preferences were found for contrast markings. The researchers recommend that MnDOT adopt the 12.5-foot to 37.5-foot broken lane line pavement marking pattern as it is preferred by road users and maintains the current MnDOT 50-foot cycle length. In addition, to skip line and gap dimensions, the research team also recommends MnDOT adopt 6-inch-wide pavement markings as the research results show that not only are 6-inch-wide pavement markings preferred over 4-inch-wide pavement markings by road users, they also offer a safety benefit.

This research summary is part of the final deliverable for Report 2024-27, "Assessment of Travel-Time Reliability and Operational Resilience of Metro Freeway Corridors," published December 2024.

This study estimated and analyzed the travel-time reliability (TTR) and traffic-flow measures of effectiveness (MOE) for 74 directional corridors in the metro freeway network in Twin Cities, Minnesota, from January 2018 to December 2023, for both morning and afternoon peak periods. The network-wide trends for both TTR and MOE indicate that the traffic flows in the Twin Cities freeway network have not reached the pre-pandemic level as of December 2023. The TTR and MOE estimation results were applied to identify a set of the most vulnerable routes in the current network. Further, the preliminary resilience model, developed in the previous phase, was enhanced and applied to determine the operational resilience of 74 directional corridors in the network and a set of the low-resilient routes were identified. The effects of the route-wide geometric configuration on TTR, MOE and operational resilience on individual corridors were also analyzed. The results from this research could provide the basis for geometric and operational improvements of the metro freeway corridors.

This Research Summary is part of the final deliverable for Report 2024-28, "Bridge Pile Repair Using Underwater Fiberglass Reinforced Plastic (FRP) Jacket and Steel Reinforced Grout, published in February 2025.

Modern asphalt mixtures are usually a combination of various materials from different sources, including reclaimed asphalt pavement (RAP) and recycling agents (RAs), and are used to attain sustainable growth. However, the lack of a well-established method for determining compatibility between various sources and types of virgin binder, aged binder within RAP, and RAs has been a major impediment in current asphalt material selection and specification. Therefore, the objective of this study was to evaluate various binder and mixture testing methods to characterize the compatibility between complex components of asphalt mixtures, specifically from the perspective of assessing their cracking performance. The primary evaluation consisted of laboratory-prepared materials that used three RAP sources, three asphalt binders (one PG 58–28, two PG 64–22), and two RAs (petroleum-based and bio-oil-based) for both binder and mixture characterization. The binder tests consisted of rheological characterization using the dynamic shear rheometer (DSR) and thermal analysis using the differential scanning calorimeter (DSC), whereas the mixture tests included complex modulus (E*), semi-circular bend (SCB), and disk-shaped compact tension (DCT) tests. The results indicated that the rheological characterization of asphalt binder and mixture may not adequately capture the incompatibility between virgin binder, RAP, and Ras. However, binder DSC analysis and mixture fracture tests have shown promising results for evaluating the compatibility of various mixture components. Therefore, the findings of this study provide agencies with a framework to select the most compatible component materials from various sources for their projects.

This study explored the feasibility and acceptability of using stay in-place fiberglass reinforced plastic (FRP) jackets and underwater steel reinforced grout for timely bridge piling repairs in Minnesota without dewatering. One of the goals of the project was to determine the current state of practice to this corrosion repair and inspection by researching other projects using similar repairs and to develop a survey to other departments of transportation to gather their experience with this type of repair. Another goal was to document the entire repair process on bridge 9462. Two different products, Five Star PileForm F Jacket and grout system and Denso SeaShield FX-70 and grout system, were installed, and contractor feedback was collected during the installation. This type of repair had a very limited impact to the surrounding area compared to a cofferdam-type repair. In fact, the repair was practically invisible to the drivers on the bridge and boaters were able to pass under the bridge while repairs were taking place. The contractor preferred the Denso product due to the jacket being stiffer, which made the jacket want to shut, since visibility in the water was zero. The jacket’s seam was easier to line up. Both products had identical installation steps, and both seemed to be a viable alternative to bridge pile repairs based on the performances from other projects found during the research.

We envisioned a project—a future—where the community is at the forefront of planning and implementation of new technology. Technologies are often developed by select companies and universities, and then tested in communities. Instead of leading with a solution, Community Driven CAV started by understanding community needs and assets, and then creatively explored ways that connected and automated technologies could address them. We wanted the community to drive what technology and use cases we plan for, develop and test. We sought to upturn the usual way of doing business to create a stronger and more equitable transportation future. First the project team conducted three community listening sessions to understand the community’s transportation challenges. Next a workshop with community members and technical experts was held to discuss how CAV technology could potentially help address the identified transportation challenges. This work resulted in potential demonstration concepts for the Creative Enterprise Zone and a Community-Driven Planning Framework, which can be used by others looking to do community led planning.

Asphalt milling is an essential construction activity. It requires concentrated high-intensity applications of force to the existing pavement to remove the asphalt material. The impact that the induced stresses have on the pavement below the mill line is unknown. Consequently, selected milling parameters rarely consider the impact the milling may have on the remaining layers. This study evaluates milling parameters to provide an enhanced understanding of their impacts on the layer directly below the mill line. Five parameters were evaluated and include the time between milling and post-mill overlay construction, existing pavement structure, temperature while milling, depth of milling relative to layer interface, and rotor speed. Pre- and post-milling cores were collected adjacent to each other and evaluated for physical and mechanical properties. The measured properties of the pre- and post-milling cores were statistically compared to determine the impact of milling operations on the integrity of the asphalt concrete immediately below the mill line. Based on the results from this study, it was determined that leaving milled pavement exposed for longer periods of time or milling at cooler temperatures can cause a decrease in the strength of the layer below the mill line and a decrease in the expected pavement life of the new pavement structure. The depth of milling or changing the rotor speed while milling did not have significant impacts on the layer directly below the mill line. In consideration of the results of this study, research with a wider variety of pavements and milling conditions is warranted.