All posts by Stefanie Toftey

New Project: Tools to improve the durability of asphalt pavements

This research focuses on improving the durability of asphalt pavements by examining emerging technologies, materials, and temperature‑control methods. Recent advancements—such as warm mix asphalt (WMA), polymer modifiers, bio‑binders, and surface treatments that reduce heat absorption—show strong potential for reducing asphalt aging and increasing resistance to thermal cracking. Environmental factors, including pavement shading from trees, have also demonstrated measurable effects on pavement temperature and long‑term performance.

Building on these developments, this project aims to conduct a comprehensive review of existing tools and evaluate two promising approaches in detail: WMA technology and updated asphalt binder specifications. Experimental testing will compare WMA with conventional mixtures, analyzing compaction behavior and low‑temperature cracking resistance using methods such as gyratory compaction and semi‑circular bend testing. Parallel testing of asphalt binders will assess new specification parameters to predict cracking performance more accurately under Minnesota’s climate conditions.

“We are always looking at increasing durability in our pavements,” said Michael Flaagan, county engineer for Pennington County, Minnesota. ”This research gives us additional choices in increasing performance with the potential for cost savings.”

The anticipated outcome is a set of practical guidelines for Minnesota agencies to integrate WMA and improved binder selection into current pavement practices. These strategies are expected to increase pavement lifespan, reduce maintenance costs, lower emissions, and support better decision‑making for agencies with limited budgets. By identifying and validating the most effective tools and materials, the project contributes to long‑term sustainability, cost efficiency, and improved resilience of the state’s asphalt pavement network.

The Objectives:

  1. Conduct a comprehensive literature review of current technologies, materials, and temperature‑control methods that improve asphalt pavement durability.
  2. Evaluate the compaction behavior and low‑temperature cracking resistance of warm mix asphalt (WMA) in comparison with conventional mixtures through laboratory testing.
  3. Assess newly proposed asphalt binder specification parameters using low‑temperature binder tests, including Bending Beam Rheometer (BBR) and Asphalt Binder Cracking Device (ABCD) methods, to better predict cracking performance.
  4. Develop preliminary guidelines for integrating WMA technologies and improved binder selection into Minnesota’s asphalt paving practices.

Project Details:

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Utilizing hydrogen fuel technology for transportation fleets

Minnesota Executive Order 19‑27 and State Statute 16C.135 set ambitious goals for MnDOT to reduce fleet fuel consumption and emissions by 2030 while prioritizing zero‑ and low‑emission vehicle purchases. Hydrogen fuel technology is being explored as a promising option to help meet these requirements without compromising operational needs. The research aims to assess existing and emerging hydrogen applications suitable for MnDOT’s medium‑ and heavy‑duty vehicles, compare hydrogen’s life‑cycle impacts with conventional fuels, and outline potential pathways for converting MnDOT’s fleet to hydrogen technologies.

“The use of hydrogen as a transportation fuel in Minnesota is in its infancy,” said Jed Falgren, P.E., MnDOT’s state maintenance engineer and office director for the Office of Maintenance. “While no commercial hydrogen fuel market exists in Minnesota today, this research will help us identify how we can best leverage the technology if/when it becomes available. Early identification of best practices can help us lower implementation costs in the future, and this continues our effort to identify fossil fuel alternatives that are safe and effective.”

The project anticipates several key benefits, including lower life‑cycle costs, significant reductions in greenhouse gas emissions, and insights into the safety and risks associated with hydrogen adoption. Expected outcomes include evaluating hydrogen‑powered fleet technologies from economic, environmental, and social perspectives, as well as identifying the strengths and limitations of different hydrogen systems. Together, these efforts could help position MnDOT as a leader in sustainable fleet management and support broader adoption of hydrogen infrastructure across Minnesota.

“The transportation strategies of today won’t get us to the Minnesota of tomorrow,” said Beth Croteau-Kallestad, sustainable transportation planning director in MnDOT’s Office of Sustainability and Public Health. “We’re excited to see MnDOT exploring fueling options that support health, reduce emissions and strengthen Minnesota’s future.”

The Objectives:

  1. To conduct a comprehensive survey of existing and emerging hydrogen fuel technologies suitable for MnDOT’s medium‑ and heavy‑duty vehicles.
  2. To evaluate the feasibility of these technologies for MnDOT’s operational needs.
  3. To perform a comparative life‑cycle assessment of conventional fuels versus hydrogen considering economic, environmental, and social impacts.
  4. To develop tentative plans for converting portions of the MnDOT fleet to hydrogen fuel systems.

Project Details:

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Feasibility of LED Solar Street Lighting

The need for this research stems from documented safety benefits associated with roadway lighting and the growing challenges in maintaining traditional, wired lighting systems. While rural locations often face high costs for delivering grid power to remote intersections, recent increases in wire theft has affected communities across Minnesota. These issues highlight the importance of exploring alternative, resilient lighting solutions that can improve safety without relying heavily on conventional electrical infrastructure.

The research process will assess the feasibility of solar‑powered LED roadway luminaires through a combination of laboratory testing, field evaluation, and cost‑benefit analysis. Key activities include analyzing battery performance under cold‑weather conditions, studying how lower illumination levels affect safety and energy use, and examining the practical integration of solar panels and batteries into existing streetlight design. A field implementation at selected sites, including potentially rural intersections or trail locations, will help validate performance and identify operational considerations such as durability, code compliance, and vandalism resistance.

The expected benefits of this work include reduced lifecycle costs, lower environmental impacts, and decreased operational and maintenance demands. Solar‑powered streetlights eliminate the need for grid‑based electricity, reduce wiring infrastructure vulnerable to theft, and offer long‑term savings over a planned service life. Environmental gains are anticipated through reduced energy consumption and lower CO2 emissions, while improved lighting reliability and appropriate illumination levels are expected to support nighttime safety and reduce crash risks statewide.

“This project will provide unbiased, objective research using equipment, methods, and people that would otherwise be unavailable to local government,” said Nick Peterson, city engineer for Saint Paul Public Works. “As a result, Minnesota cities and counties will learn effective strategies for implementing solar-powered street lighting in our cold climate.”

The Objectives:

  1. Test energy storage capacity of Lithium-ion battery under different temperatures. The battery energy storage capacity is a critical component in the feasibility of solar powered LED street lighting in cold northern climates.
  2. Explore the implications of running the streetlights at a lower brightness on power conservation and traffic safety. The balance between the energy demand for street lighting and the traffic safety is critical to an optimized solar powered LED streetlight that has a minimal solar panel and battery size and less effect on the existing streetlight infrastructure design.
  3. Conduct a comprehensive cost-benefit analysis considering material, labor, and maintenance costs for the installation and use of the solar-powered LED luminaire system, along with the benefits, such as the saved utility costs, the avoided costs of nighttime crashes, and the associated environmental benefits, such as the associated reduction of CO2 emissions.
  4. Provide MnDOT with guidelines and specifications on solar-powered LED streetlight implementation details.

Project Details:

  • Start Date: 07/16/2025
  • Estimated Completion Date: 05/31/2027
  • Funding: Local Road Research Board
  • Principal Investigator: Mijia Yang
  • Co-Principal Investigators: Xiangfa Wu and Yao Yu
  • Technical Liaison:  Nick Peterson

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Evaluating and implementing ground penetrating radar for monitoring moisture fluctuations in in-service roads

Moisture fluctuations within pavement foundations—driven by rainfall, freeze–thaw cycles, and groundwater changes—can significantly impact pavement performance, especially on Minnesota’s low volume roads. Traditional moisture measurement methods, such as in place sensors or falling weight deflectometer testing, tend to be costly, intrusive, slow, and offer limited spatial coverage. Ground penetrating radar (GPR), however, provides a faster, non-invasive, and more affordable way to assess subsurface moisture over large areas, making it particularly useful for local agencies with limited resources.

This research aims to advance the validation and practical use of GPR for evaluating pavement moisture in real‑world low‑volume road settings. The study includes conducting GPR surveys on test sections equipped with moisture sensors, comparing datasets, and assessing how effectively GPR can identify areas affected by drainage or moisture issues. To support broader implementation, the project also involves creating an automatic detection algorithm capable of identifying moisture variations in unbound pavement layers.

The algorithm will be refined into a user‑friendly software tool featuring modular code, a graphical interface, and documentation. Ultimately, the project will deliver implementation recommendations designed to strengthen decision‑support tools and technical guidelines, helping Minnesota’s transportation agencies more effectively monitor and manage pavement moisture conditions.

“For this research to reach its full potential, participation from local engineers and practitioners is essential,” said Eyoab Zegeye, research operation engineer at MnDOT’s Office of Materials and Road Research. “Based on our encouraging findings, the next step is to evaluate whether this approach could be implemented on real low‑volume roads and develop testing and reporting protocols that can be quickly adopted by local agencies. County and municipal staff have the closest understanding of their road networks, challenges, and resource limitations. Their involvement ensures that the tools developed are realistic, usable, and aligned with real‑world needs.”

The Objectives:

  1. Validate and implement GPR-based pavement moisture assessment methods on low-volume roads.
  2. Evaluate GPR’s ability to efficiently survey large pavement areas and monitor moisture conditions.
  3. Identify pavement sections potentially affected by drainage issues using GPR data.
  4. Conduct GPR surveys on low-volume road test sections equipped with in-situ moisture sensors and compare the results.
  5. Develop an automatic detection algorithm to evaluate moisture variation within unbound pavement layers.
  6. Validate the algorithm and implement it as software with modularized code, a graphical user interface, and a user manual.
  7. Produce implementation recommendations to enhance decision-support tools and technical guidelines for assessing moisture fluctuations in Minnesota’s low-volume roads.

Project Details:

  • Estimated Start Date: 7/16/2025
  • Estimated Completion Date: 6/30/2027
  • Funding: MnDOT and Local Road Research Board
  • Principal Investigator: Halil Ceylan
  • Co-Principal Investigators: Sunghwan Kim
  • Technical Liaison:  Eyoab Zegeye

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Holistic design and selection criteria for unbound geomaterials used in pavement systems

Unbound geomaterials used in roadway base layers strongly influence pavement durability, yet current practices in Minnesota often focus narrowly on gradation and index properties. This research seeks to fill that gap by examining mechanical behavior alongside hydraulic, water retention, and suction characteristics to better understand how these materials perform within real-world environmental and pavement systems.

Pavement base layers serve two essential purposes: providing mechanical support that prevents fatigue, settlement, and rutting, and enabling drainage that protects the structure from elevated pore pressures and freeze‑thaw damage. Although millions of tons of these materials are used annually, past studies rarely consider the full interaction between the base layer, surface conditions, and environmental factors.

The project’s primary goal is to develop a new holistic guideline for selecting unbound geomaterials and designing pavement foundations. By integrating both mechanistic and hydraulic considerations, the long‑term objective is to support a shift toward design approaches that enhance roadway performance while reducing maintenance needs and costs.

The Objectives:

This project aims to develop a new holistic unbound geomaterial selection and pavement foundation design guideline. This will be achieved through the completion of four primary objectives:

  1. Review of current roadway foundation design practices and guidelines of MnDOT and local counties and cities in Minnesota.
  2. Collection and analysis of existing data from the literature on the topic (including the extensive previous work of the research team).
  3. Developing a holistic design and material selection framework that explicitly takes material drainage characteristics, material mechanical characteristics, unsaturated soil mechanics properties, and prevailing environmental characteristics into account.
  4. Extensive laboratory and field testing to demonstrate and verify the new approach.
  5. Evaluating and modifying the pore suction resistance factors and seasonal multipliers used in MnPAVE.

Project Details:

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Design guidance and best practices for the use of light fill for sustainable road construction

Lightweight Fill (LWF) materials—including Tire Derived Aggregates (TDAs), expanded shale/clay, foamed glass, and recycled glass aggregates—show strong potential for sustainable road construction, yet important knowledge gaps remain. Their environmental impacts, long‑term performance, and construction requirements are not fully understood, especially under Minnesota’s freeze‑thaw cycles and high groundwater conditions. Concerns such as leachate production, potential trench settlement, and challenges faced by local road departments highlight the need for further investigation.

This research seeks to address these gaps by reviewing existing practices, evaluating both environmental and mechanical performance, and developing data‑driven recommendations for using LWF materials in road construction. A detailed assessment will help clarify how these materials behave in pavement structures and embankments and how they interact with water‑sensitive environments. A decision matrix will be used to compare LWF materials and support future project planning.

To achieve these goals, the study will evaluate environmental impacts such as leachate risks, analyze long‑term structural integrity, and conduct Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) to assess sustainability and financial feasibility. The research will also develop recommended construction techniques that improve performance and support Minnesota’s climate goals and broader sustainability initiatives.

“Lightweight fill materials show promise for sustainable road construction, and Minnesota looks to learn from what has been done previously,” said Andrew Witter, Sherburne County Public Works Director and County Engineer. “This project will evaluate how these materials behave in local conditions and develop guidance for local counties and cities. The results will help agencies make informed decisions for the benefit of the transportation infrastructure in Minnesota.”

The Objectives:

  1. Document existing research and practices related to LWF materials in road construction.
  2. Evaluate the environmental impacts of LWF materials, focusing on leachate risks and interactions with water-sensitive environments.
  3. Analyze the long-term performance and structural integrity of LWF materials in both pavement structures and embankments.
  4. Compare LWF materials in a decision matrix to guide future project decisions.
  5. Perform Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) to assess the sustainability and financial feasibility of LWF materials.
  6. Provide recommendations to develop construction techniques that optimize the use of LWF materials and align with Minnesota’s climate goals and broader sustainability initiatives.

Project Details:

  • Estimated Start Date: 06/25/2025
  • Estimated Completion Date: 06/30/2027
  • Funding: Local Road Research Board
  • Principal Investigator: Michele Lanotte
  • Co-Principal Investigators: Angela Farina
  • Technical Liaison: Andrew Witter

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Does lowering speed limits reduce driver speeds on urban streets?

In 2019, the Minnesota Legislature passed a law reducing barriers for cities to systematically lower speed limits. The City of St. Louis Park followed this guidance by reducing speed limits in 2021, but initial speed data collected before and 6–8 months after the changes showed little to no short‑term impact. Because driver behavior is habitual and may change slowly, advocates suggest that greater reductions in operating speeds may emerge over time, highlighting the need for repeat monitoring between 2025 and 2027.

This study aims to evaluate whether longer‑term changes have occurred 2–4 years after the initial reductions, while also examining other Minnesota agencies that have implemented or are considering reduced speed limits. The research will gather both measured and anecdotal data, assess “after” speed conditions where needed, and analyze how effectiveness varies based on roadway characteristics and any accompanying speed reduction countermeasures. These efforts address lingering questions about how speed limit changes influence driver behavior and roadway safety over time.

Understanding speed is critical because it directly affects the safety of all road users. According to Minnesota Motor Vehicle Crash Facts 2022, speeding was the leading cause of traffic fatalities, contributing to 130 of the state’s 444 deaths. By identifying agencies that have reduced speed limits, evaluating short‑ and long‑term impacts, and analyzing site‑specific factors, this research will produce guidance to help Minnesota road agencies assess and implement effective speed limit reductions.

“There is renewed interest in lower speed limits on municipal-type streets,” said Victor Lund, traffic engineer with St. Louis County’s Public Works Department. “The objective of this research is to better understand the intersection of speed limit policy, driver behavior and safety, which will result in guidance to better inform policies, practices and speed limits that support safer streets.”

The Objectives:

  1. Identify local agencies in Minnesota that have implemented reduced speed limits or may consider implementation along with any speed reduction countermeasures that have been implemented with the reduced speed limits.
  2. Evaluate the short-term and long-term effects of speed limit reductions implemented in Minnesota through the collection and analysis of speed data.
  3. Assess how these effects vary based on site characteristics or speed reduction countermeasures that were implemented in coordination with the reduced speed limit.
  4. Based on the findings, develop a summary document to aid Minnesota road agencies in assessing potential speed limit reductions.

Project Details:

  • Estimated Start Date: 06/25/2025
  • Estimated Completion Date: 06/30/2027
  • Funding: MnDOT and Local Road Research Board
  • Principal Investigator: Peter Savolainen
  • Co-Principal Investigators: Tim Gates
  • Technical Liaison: Victor Lund

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Are Current Rigid Pavement Roundabout Designs Working in Minnesota?

As roundabouts become more commonplace in Minnesota, the role they play in the improvement of traffic flow and safety increases. Although rigid roundabouts were originally designed with the assumption that they would behave like rigid pavements on motorways, their performance can be affected by the unique traffic patterns and stresses they experience. The irregular shapes of their concrete slabs face distinct braking, stopping, accelerating, and drainage conditions, which increase the likelihood of cracking and other forms of pavement distress. Heavy trucks navigating sharp curves add additional strain. While concrete pavements are generally durable, pavement wear is greatly affected by elements characteristic of roundabout design.

This research seeks to evaluate and improve the performance of concrete roundabouts in Minnesota, with the aim of extending their service life and increasing their overall effectiveness. The project will start with a comprehensive field survey throughout the state, collecting information on different roundabout designs and documenting the types and levels of pavement distress present. The data will be analyzed to identify performance trends and gain a clear understanding of each design’s advantages and shortcomings. In addition to the field investigation, the study will conduct an in-depth structural review of factors such as joint spacing, dowel bar placement, slab geometry, and drainage features.

Using insights from both the field observations and structural analysis, researchers will propose design strategies to improve the durability of Minnesota’s roundabouts. These recommendations have the potential to strengthen roundabout design practices and contribute to a safer, more dependable transportation system.

“With the rapidly growing number of concrete roundabouts being constructed throughout Minnesota, it is important that we monitor their performance and adjust our design methodologies to ensure that the traveling public can utilize them safely, while maximizing the investments spent on their construction and maintenance,” said Thomas Burnham, research operations engineer with MnDOT’s Office of Materials and Road Research. “This research project is set up to accomplish these goals.”

The Objectives:

  1. To measure rigid pavement roundabout performance for various traffic loads and design features.
  2. Using pavement system performance data, identify any design changes that could minimize maintenance.
  3. Create state-of-the-art guidelines and recommendations for improving the design, function and lifespan of concrete roundabouts in Minnesota.

Project Details:

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Can Enhancing Color on Dynamic Message Signs Improve Clarity and Safety?

The majority of MnDOT’s dynamic message signs (DMS) are equipped to produce full color/full matrix messaging. Current signage regulations refer to retroreflective colors for static signs, but MnDOT aims to extend and modify existing standards and guidelines by exploring differences between static signs and DMS.

This research will systematically explore and optimize the use of different colors and color-coding schemes in DMSs to resemble the retro-reflectivity of static signs and examine how legibility, visibility, and effectiveness can be improved. Optimizing DMS colors to mimic retroreflective static sign colors and adapting them to myriad environmental conditions, MnDOT can realize reduced driver distractions, improved information comprehension, and increased safety. The project will also support improved decision-making processes by providing evidence-based guidance for future standards and practices for MnDOT beyond.

A pilot study will be conducted to assess the recommended color settings against benchmark real-world conditions. Empirical data on the new configurations will measure their performance, confirm their effectiveness and identify any adjustments required prior to broader implementation.

“Not all color is created equal! As illustrated in the three graphics below, federal standards for reflective sheeting and striping, NEMA standards for colors, and the triangle of visible light LED lights can produce do not correspond,” said Terry Haukom, senior engineer with MnDOT’s Regional Transportation Management Center. “This variance has caused the signage industry to display colors that meet federal standards but do not look correct to the human eye. In addition to exploring this incongruity, our research is focused on understanding and comparing what typical travelers understand and expect when viewing traffic information on the web, and whether the travel time numbers displayed on our signs can give drivers a better understanding of the travel time to the listed destination if it was displayed with a color scheme that leveraged web-based maps.”

The Objectives:

  1. Standardize the emitted colors from MnDOT’s DMS according to NEMA TS4 and MUTCD specifications, ensuring they match the retroreflected colors of static signs and align with current LED capabilities
  2. Document the public’s perception of optimum color if different from standards based on human factors feedback
  3. Document the public’s perception of dark pixel around graphics on emitted colors on DMS
  4. Research and document the public’s perception of emitted colors on DMS compared to static sign messages, and explore the incorporation of web-based travel time map colors to enhance visibility and clarity, especially with colors like amber

Project Details:

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.

New Project: Understanding How Parking Space Requirements Affect Vehicle Miles Traveled

Minimum parking requirements were established in the mid-20th century to mitigate increased motor vehicle congestion but have the potential to contribute to urban sprawl, hinder development, and curb incentives for drivers to choose alternative travel modes. Eliminating or reducing these requirements can help remove excess parking supply, increase alternative modes such as transit ridership, reduce vehicle miles traveled (VMT), and enhance economic productivity. Decreasing VMTs directly mitigates emissions by reducing car travel distances and many VMT reduction strategies hold additional benefits such as increasing accessibility and reducing traffic congestion.

VMT reduction also plays a significant role in Minnesota’s efforts to reduce greenhouse gas emissions from the transportation sector. New legislation passed in 2023 requires reducing VMT up to 20% per capita by 2050. The impacts of parking space requirements or long-term benefits and challenges associated with modifying or removing these requirements have not been studied in Minnesota. This project will investigate, document, and advance the understanding of minimum parking requirements in Minnesota and the region and their impact on VMT reduction.

Researchers aim to establish recommended values based on differing types of land use and community context, e.g., urban, suburban, and rural within Minnesota. Specifically, this project will examine the long-term benefits and challenges presented by reducing and/or removing currently established parking space requirements with new or redevelopment projects, and opportunities for parking space reallocation with existing uses.

“This research aims to fill a critical knowledge gap, will modernize minimum parking requirements reduce vehicle miles traveled, and provide communities with more flexible land‑use options,” said Mark Vizecky, state aid operations engineer, State Aid for Local Transportation at MnDOT.

The Objectives:

  1. Perform literature reviews of historical and current practices, policy and requirements regarding parking space requirements in Minnesota and the Upper Midwest and of current best practices regarding parking space requirements and the impact parking has on land use and travel behavior.
  2. Interview local agencies and the League of Minnesota Cities to gain insight into current parking space practices, policies, and requirements across Minnesota.
  3. Conduct an online survey of business stakeholders to assess the potential economic impacts of parking policy changes regarding customer behavior, business density, operating costs, opportunity cost and sunk cost, and accessibility.
  4. Conduct a travel behavior and mode choice survey using a diverse group of daily commuters from Minnesota’s urban, suburban, and rural communities to understand the influence of parking policies on traveler behavior.
  5. Analyze survey responses using discrete choice modeling to develop utility equations for different parking requirements, which will help predict mode shifts and associated VMT reductions.
  6. Utilize travel demand model data from eight metropolitan planning organizations in Minnesota to assess how changes in parking requirements could impact VMT reduction.
  7. Analyze the sensitivity and data requirements for a parking space requirement that will be effective for local use and develop a toolkit for local municipalities to assess parking needs and the economic impacts of parking policies in local communities.

Project Details

  • Start Date: 06/02/2025
  • Estimated Completion Date: 04/30/2027
  • Funding: Local Road Research Board (LRRB)
  • Principal Investigator: Kakan Dey
  • Co-Principal Investigators: Subasish Das, Ali Zockaie
  • Technical Liaison: Mark Vizecky

Details of the research study work plan and timeline are subject to change.

To receive email updates about this project, visit MnDOT’s Office of Research & Innovation to subscribe.