Category Archives: research

General research posts.

Materials and Construction, research

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

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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.

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

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.

research, Traffic and Safety

Research finds pedestrian-focused infrastructure can boost safety

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Article reprinted from CTS News, August 12, 2026.

Published MnDOT Report: Behavioral Investigation of Temporary and Permanent Pedestrian Infrastructure

Pedestrian injuries and fatalities have significant personal, societal, and financial impacts, making it crucial to identify effective strategies to improve pedestrian safety. A research project by the UMN’s Human Factors Safety Laboratory (HFSL) evaluated the effectiveness of both temporary (i.e., quick-build) and permanent pedestrian-focused intersection features, such as curb extensions and pedestrian refuge islands. Researchers sought to understand how these features changed pedestrian and driver behavior — and how that affected safety.

Minnesota, in line with nationwide trends, saw an increase in pedestrian deaths between 2013 and 2022 (from 1.55 to 2.33 deaths per 100,000 nationwide). Similar high-income countries generally experienced a decrease in pedestrian deaths in the same period. “This remains a hot-button topic for research in the traffic safety space,” said HFSL research associate Curtis Craig, lead investigator on the project and CTS scholar, in a webinar discussing the research. The project was sponsored by the Minnesota Department of Transportation and the Minnesota Local Road Research Board.

Several unique factors make U.S. roadways especially challenging for pedestrians. “The high incidence of large trucks and SUVs makes it more difficult to see pedestrians, and any impact would be more severe because of the greater mass and geometry of the front grills on those vehicles,” Craig said. “There’s also simply a large preponderance of high-speed, multi-lane roads, which is a high-risk factor for pedestrians and drivers.”

Pedestrian-friendly infrastructure strategies aim to reduce those risks. With guidance from Minneapolis’s Vision Zero 2023–2024 pedestrian safety plan, researchers identified 12 intersections in Minneapolis and St. Paul to study before and after the installation of quick-build pedestrian infrastructure and concrete infrastructure. Quick-build infrastructure includes temporary or plastic features, such as bollards replicating bump-outs and sidewalk extensions. The goal of the study was to compare the safety influence on driver behavior of these quick-build features with those of permanent concrete infrastructure.

The study evaluated a mix of signalized and unsignalized intersections with temporary and permanent infrastructure features in a variety of income areas and with various levels of pedestrian and vehicle traffic. The team recorded driver behavior in pass-through and right-turn intersections. Data was collected in staged and natural pedestrian crossings using both in-person observations and video to record driver speeds, stops, and pedestrian behavior. The video footage was analyzed with the help of artificial intelligence algorithms.

The study found that whether permanent or temporary, the presence of the installations generally improved the rates of drivers stopping for pedestrians and led to a small but significant decline in traffic speeds at intersections. Temporary median refuges reduced the average speeds of drivers in free-flowing traffic at both signalized and unsignalized intersections. Since high driver speed is associated with a higher likelihood of pedestrian fatalities and higher injury severity, this is an especially meaningful benefit, Craig noted.

However, using flexible delineators as temporary curb extensions slightly reduced the likelihood of drivers stopping for pedestrians compared to permanent infrastructure, particularly at signalized intersections. The researchers noted a decline in stopping rates, for right-turning drivers at signalized intersections outfitted with temporary curb extensions, while the permanent, concrete curb extensions appeared to perform slightly better. The researchers speculated that the presence of bollards or other features surrounding the temporary infrastructure created a distraction, or “clutter,” that diverted drivers’ attention away from pedestrians as they navigated the intersection turn. “It’s a more visually complex environment, with more cars and more pedestrians to look out for,” Craig said.

The flexible delineators used cost between $30 and $100 each plus labor for installation, and most intersections require 12 delineators. Meanwhile, permanent concrete extensions cost about $18,000 each (or more if installation requires interaction with the sewage system) and median islands cost as much as $55,000. However, the study emphasizes that fatal pedestrian crashes have a tremendous cost. Beyond devastating personal and societal impacts, researchers point to a 2020 assessment by the U.S. Centers for Disease Control and Prevention that tallied more than $68 million in medical and work-loss costs related to pedestrian fatalities.

No two intersections in the study could be considered identical; the presence or lack of on-street parking, construction, and variations in pedestrian behaviors influenced each crossing. Craig said that future engineering projects considering the use of quick-build infrastructure need to weigh the many variables that define each intersection. Ultimately, when transportation infrastructure prioritizes pedestrians, public safety improves on Minnesota’s streets.

—Amy Goetzman, contributing writer

Related MnDOT research

Many MnDOT and LRRB projects have looked at pedestrian safety. Here is a sample of them.

Materials and Construction, research

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

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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.

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

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.

Bridges and Structures, research

Evaluating a New Low Slump Concrete for Bridge Decks 

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For over 30 years, MnDOT has used the same low slump concrete overlay mixture to extend the service life of bridge decks. However, MnDOT suspected that changes in the materials used in the mixture over time may have contributed to increased cracking. This project evaluated a new mixture design, with and without glass fibers, to reduce cracking, improve sustainability and lower costs.

Continue reading Evaluating a New Low Slump Concrete for Bridge Decks  →
Materials and Construction, research

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

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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.

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

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.

research, Traffic and Safety

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

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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.

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

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.

research

Innovation at work: Minnesota Mousetrap award winners

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Originally published by the Center for Transportation Studies, July 6, 20205 as Minnesota Mousetrap award winners: Crack Wagon De-Tack Sprayer and Curb Stop Wrench Truck Storage Solution | Minnesota LTAP

Congratulations to the recipients of Minnesota’s 2026 Build a Better Mousetrap awards! All Minnesota submissions were forwarded to the national mousetrap program in June. Awardees from across the country will be chosen by the National LTAP & TTAP Association in four categories.

Minnesota Pioneer Award

The City of St. Cloud’s Crack Wagon De-Tack Sprayer was recognized with the Minnesota Pioneer Award, given to a locally relevant product or tool that is among the first to solve a maintenance problem with a homegrown solution.

Problem: Spraying crack filler typically requires the work of multiple laborers and creates an unsightly mess of toilet paper, which is used for absorbing the sticky residue.

Solution: For $360, City of St. Cloud staff members created a 25-gallon flat-bottom tank that holds water and Dawn dish soap, complete with an attached hose and wand that can be used by one person to apply the solution. This eliminates the need for a follow truck to spray soapy water over the cracks, reducing the number of laborers on the road and amount of toilet paper clean-up. It’s an environmentally friendly solution that benefits both workers and residents.

SMART Transformation Award

The City of Waite Park received the SMART Transformation Award for its Curb Stop Wrench Truck Storage Solution. This recognition is awarded for a locally relevant significant change to any transportation activity or process that is SMART (Specific, Measurable, Achievable, Realistic, and Time-bound) and results in improved efficiencies. 

Problem: City of Waite Park staff members prefer to use crew cab pickup trucks for their work because of the interior storage capacity. But there’s an issue: longer truck cabs mean shorter beds. When storing and transporting materials such as curb stop wrenches, which are around 10 feet long, creative solutions are required.

Solution: The agency constructed a storage apparatus and installed it onto a ladder rack that sits above the truck bed. The device consists of exhaust tubing secured to front and rear plates with u-bolts and is equipped with a locking mechanism built from common gate hardware. The wrenches slide right into the tubes and are secured for transport — a convenient storage solution for just $175.

Honorable mention: City of St. Paul’s Improved No Parking Stake

Problem: City of St. Paul workers were frequently injured while hammering wooden “No Parking” signs into the ground.

Solution: By affixing a metal spike to the bottom of each sign, the signs can easily be pushed into the ground, removing the hazard of hammering entirely. This solution also decreases the sign installation time — an added bonus for staff members.

Learn more about award-winning projects from previous years.

The Minnesota Build a Better Mousetrap Competition is sponsored by the Minnesota Local Road Research Board and administered by MnLTAP.

Materials and Construction, research

Evaluating the Use of Stabilizers on Gravel Roads 

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Gravel roads often experience significant deterioration that requires costly maintenance. To mitigate this deterioration, transportation agencies can apply chemical stabilizers to improve aggregate cohesion. This project examined the mechanical, environmental and economic performance of five gravel stabilizers and three application methods to determine the best options for reducing deterioration.

Continue reading Evaluating the Use of Stabilizers on Gravel Roads  →
Multi-modal, Policy and Planning, research

Integrating travel demand management into transportation planning

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Reprinted from Catalyst, June 22, 2026

Minnesota’s transportation landscape is rich with options designed to get travelers to their destinations safely and quickly. These modes, ranging from commuter bike trails and public transit to rideshares, buses, rail, roads, streets, and highways, are strategically interlinked; improvements or disruptions in one place reverberate across the greater transportation network.

Travel demand management (TDM) is an approach to transportation planning that encourages more efficient travel through a combination of mode choice and infrastructure design. This “big picture” approach centers the specific needs of local communities to create viable options for people to shift away from single-occupancy vehicles for at least some trips. Among the benefits of more efficient road use are improved congestion and air quality and reduced costs for road maintenance and construction.

A UMN research study led by Kaitlyn Denten, infrastructure policy researcher at the Institute for Urban and Regional Infrastructure Finance within the Humphrey School of Public Affairs and a CTS scholar, aimed to investigate how TDM strategies can best be integrated into highway construction projects.

In Minnesota, two factors are bringing the TDM approach to the forefront. The Transportation Greenhouse Gas Emissions Impact Assessment (Minn. Stat. §161.178 [2025]) is now part of highway construction and reconstruction projects. This statute requires projects to meet state greenhouse gas (GHG) and vehicle miles traveled (VMT) goals by either modifying the project, halting the project, or offsetting the GHG and VMT created by the project. 

Additionally, the Metropolitan Council, through its 2023 Regional Travel Demand Management Study Action Plan, recommended that a study be conducted to identify how TDM strategies could be incorporated into all phases of highway construction. The Met Council’s goal is to improve commuting, meet climate objectives, and reduce or delay the need for costly highway expansion projects.

In response to the Met Council’s recommendation, the UMN research team first conducted a nationwide scan to identify best practices for integrating TDM into highway projects. Examples in Colorado, California, New Jersey, Delaware, and Washington show how local, state, and federal transportation agencies and other entities coordinated to better understand local travel patterns and solve complex challenges. The scan revealed how TDM has been used to inform planning and policy, improve design and construction, encourage mode choice, and manage demand or emergency situations.

The researchers also studied Minnesota examples. The 2007 collapse of the I-35W Bridge in Minneapolis diverted 140,000 daily commuter trips. MnDOT, the Met Council, and regional stakeholders created travel alternatives from the time just after the collapse through the bridge’s reconstruction, which was completed in September 2008. TDM strategies included new transit services, fare subsidization, teleworking programs, and expanded park-and ride facilities.

In Duluth, a more northern expanse of Interstate 35W became a “mega project” between 2010 and 2012. During this time, 3 bridges and 12 miles of roadway pavement were replaced, shoulders and safety features were added, and intelligent transportation systems components were installed for emergency communications. TDM strategies helped facilitate communications between local and state entities, transit services, and the MnDOT construction teams to improve travel alternatives and ease the flow of traffic during this prolonged disruption.

TDM is becoming a more defined and important part of future transportation planning. “Ultimately, integrating TDM into highway projects enhances travel options and creates modal choices for travelers,” Denten says. “This reduces delay during peak times and improves safety and efficiency for construction crews. It can also remove the need for travel and push travel to non-peak times. Further, holistic TDM approaches for highway construction projects could lead to more efficient transportation systems and perhaps delay or remove the need for a highway project in the first place.”

The study offers best practices to help policymakers, planners, engineers, and local officials within the Metropolitan Council and beyond incorporate TDM into their projects. These strategies provide opportunities to shape policies and projects that respond to unexpected and intermittent challenges while supporting Minnesota’s long-term goals of reducing highway construction costs, climate impacts, and travel disruptions.

This research project was sponsored by the Applied Research in Transportation (ART) Program, which addresses time-sensitive research questions in a 6- to 12-month timeframe. CTS and the Minnesota Department of Transportation contributed initial funding to launch this pilot program in 2024, with the Metropolitan Council joining in 2025. To reinforce the applied nature of the program, ART projects must directly address a current process, document, or policy need with an initial focus on sustainability in transportation and climate change impacts. 

—Amy Goetzman, contributing writer

Environment, research

Reducing Phosphorus Pollution from Ponds

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Ponds and historic wetlands are essential for preventing excessive phosphorus from reaching downstream waters. These systems remove solids, nutrients, metals and hydrocarbons from stormwater runoff as particles settle to the bottom. However, low oxygen levels in the water can cause phosphorous to be released from bottom sediments. This project examined the effectiveness of strategies to limit that release and reduce negative downstream impacts.

Continue reading Reducing Phosphorus Pollution from Ponds →