Tag Archives: Minnesota

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.

Materials and Construction, research

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

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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.

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

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.

Environment, Maintenance Operations, research

Goats can play a role in multi-pronged restoration of buckthorn-invaded woodlands

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Reprinted from MnLTAP News, May 4, 2026

Goats are increasingly being used in efforts to manage invasive common buckthorn in Midwestern woodlands. New research demonstrates when and how they are best used.

Continue reading Goats can play a role in multi-pronged restoration of buckthorn-invaded woodlands →
Environment, research

New Project: Engineering Post-Construction Soil Composition to Support Resilient Stormwater Management

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Post-construction soils can produce much higher stormwater runoff rates than pre-construction or typical vegetated soils. Poor soil conditions can hinder the establishment of vegetation and carry large volumes of runoff, sediment, and nutrient loads to local waters. Organic soil amendments (composts) may support post-construction vegetative growth by boosting soil structure, nutrient availability, and water holding capacity.

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

This research aims to define targeted pre-construction soil health baselines, determine optimized design and field implementation inputs that return soils to baseline health indices using organic amendments, and identify how these inputs can benefit transportation requirements and resilient stormwater treatment.

The results may facilitate the quantification of benefits provided through soil health restoration and the development of implementable guidance for roadside soil health restoration techniques.

“This research project will help us understand how implementing soil health practices can improve the performance of roadside vegetation establishment resulting in MnDOT being able to close out construction contracts and stormwater permits sooner,” said Warren Tuel, Natural Resources Program Coordinator with MnDOT’s Office of Environmental Stewardship. “There are also significant potential stormwater benefits of soil health practices including increased infiltration, improved treatment of pollutants present in highway stormwater runoff. The improved management of stormwater will result in improved water quality of runoff from MnDOT highway systems resulting in greater protection of the many water resources here in Minnesota.”

The objectives are:

  1. Evaluate resilience to water availability through organic amendment (e.g., compost) addition through greenhouse stormwater experiments
  2. Optimize amendment loadings based on resilience
  3. Develop a “recipe” for improving the health of poor soils based on soil health measurements, by amending the soil with compost or other organics

Project Details

  • Start Date: 05/16/2025
  • Estimated Completion Date: 06/30/2027
  • Funding: MnDOT
  • Principal Investigator: Bora Cetin
  • Co-Principal Investigators: Angela Farina
  • Technical Liaison: Warren Tuel

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.

Aviation, research

Research assesses roles and impacts of Minnesota’s local airports

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Reprinted from Catalyst, January 22, 2025

To better understand how Minnesota’s small public airports affect their local economies, researchers from the Transportation Policy and Economic Competitiveness Program (TPEC) at the University of Minnesota’s Humphrey School of Public Affairs chose three to profile from across the state. They shared their findings at the 2024 CTS Transportation Research Conference in a presentation highlighting the complex roles and community impacts of local airports.

The profile study built on a 2018 TPEC project that explored the value of airfreight networks for Minnesota’s medical supply chain. In addition, the researchers aimed to update information from a 2019 Minnesota Department of Transportation (MnDOT) study that examined the economic impact of 126 of the state’s 133 public airports.

“We were prompted by questions from several stakeholders, including TPEC advisory board members, to see if there were any travel changes or other impacts from the COVID-19 pandemic or high levels of inflation that had happened since those other studies were completed,” said Frank Douma, director of state and local policy and outreach at the Humphrey School’s Institute for Urban and Regional Infrastructure Finance (IURIF) and the project lead. The research team also included Barbara Rohde, IURIF researcher and licensed pilot, and Audrey Clark, an urban/regional planning graduate student.

Data for the three airport profiles was gathered through interviews with airport and city officials in February and May of 2024.

Granite Falls Municipal Airport

Plane mounted at entrance to Granite Falls Airport

Unique among the three airports studied, the Granite Falls Municipal Airport in west central Minnesota receives no federal funding and attributes its ongoing success to the support of MnDOT and the local business community. A primary user for this 152-acre, one-runway airport is one of the biggest energy and ethanol firms in the Midwest—Fagen, Inc. The company hosts visitors from all parts of the US who travel to Granite Falls in corporate jets for meetings and tours.

The airport is also an active UPS hub—vital for supporting local resident and business needs—and draws tourists with a local bi-annual airshow held in association with the Fagen Fighters WWII Museum that showcases a collection of working aircraft from the era.  

Mankato Regional Airport

“It may be a surprise to some, but the Mankato Regional Airport is the second busiest in the state, following Minneapolis-St. Paul International,” Douma said of the airport located in south-central Minnesota. 

Most of the operations on the airport’s two runways support and serve student pilots; North Star Aviation, a major US flight school, trains 700 aviation students who log more than 40,000 flight hours annually.  “As a person who has taken many flight school lessons, I was so impressed,” said Rohde. “These kids fly until 11 at night to get their time in.” The school provides a direct recruitment pipeline to Minneapolis-based Sun Country Airlines.

The airport also serves the area’s retail, agriculture, and health care industries, which include:

  • A 450,000-square-foot Walmart Distribution Center that opened in 2015 and is undergoing a major expansion.
  • Veterinarians who board planes every morning to travel the country for swine testing.
  • Mayo Clinic helicopters, based here to take advantage of the central location.

Roseau Municipal Airport

Ten miles south of the Canadian border, Roseau Municipal Airport mostly serves the Polaris company’s 1,500-employee manufacturing facility, ferrying executives and researchers across the US from the airport’s single paved runway. Additionally, the airport focuses on supporting community development and health care access with medevac transportation.

Conclusions and next steps

Local airports contribute significantly to the economic competitiveness, community pride, and identity of the Minnesota cities that host them, the researchers found. However, the nature of those contributions is different for each airport, encompassing transportation links, business facilitation, tourism, and emergency services.

A subgroup of TPEC advisory board members recently formed to further expand this research and seek national, state, and institutional partnerships.

—Jacqueline Bass, CTS program editor

Related resources

Policy and Planning, research

Rural Needs, Statewide Answers: Demographics, Health Care Access, and Community Engagement

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Monday, May 13, 2024, 9:00–11:30 am, In Person

Join CTS for their annual all councils meeting to explore topics related to CTS’s 2024 theme of Rural Needs, Statewide Answers: Improving Transportation for All Communities.

The event is free to attend, but registration is required. Please register by Friday, April 26. 

Continue reading Rural Needs, Statewide Answers: Demographics, Health Care Access, and Community Engagement →
Policy and Planning, research

New revenues needed to fill transportation funding gap

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What’s next in transportation?

The Future of Mobility series collects the perspectives of top U researchers and other national experts. In 17 articles, the authors scan the horizon and reflect on critical transportation topics. Each article recommends action steps for public officials and policymakers.

Continue reading New revenues needed to fill transportation funding gap →