Tag Archives: Local Road Research Board

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.

Updated stormwater guide reflects new research, experience

Reprinted from Catalyst, December 16, 2024

Effective stormwater management is essential for maintaining healthy urban environments, but it requires consistent monitoring and maintenance to prevent costly failures—something that municipalities across the state have struggled with for years.

At a recent CTS webinarAndy Erickson, research manager at the University of Minnesota’s St. Anthony Falls Laboratory and CTS scholar, guided more than 160 attendees through recent changes made to the Minnesota Stormwater Inspection and Maintenance Resource Guide. The original guide, published in 2009, has been revised to incorporate more than a decade’s worth of field applications, research, and practical experience. The updated resource aims to improve the inspection, operation, and maintenance of stormwater management practices across the state, providing practitioners with essential tools to optimize stormwater management and increase cost-effectiveness.

Stormwater management is crucial for controlling urban runoff, and systems such as green infrastructure and low-impact development reduce pollution before stormwater is sent to lakes, rivers, and streams. However, these systems require regular upkeep to remain effective, and maintenance challenges arise from their passive nature and logistical issues in large urban areas. One key problem is the lack of on-site staff for monitoring and making the proactive inspections vital for preventing failures. Regular maintenance can reduce costs by avoiding the need for major repairs, but municipalities may still struggle to stay within their maintenance budgets, as funding for upkeep is often inadequate compared to the cost of new infrastructure.

“Since there are no operating staff on-site to see when these things fail or see what’s causing them to fail, we have to be proactive in our inspections,” Erickson said. That means inspectors must travel multiple times to locations spread out across the metro region—which significantly increases costs. “Depending on the size of the practice, your total maintenance cost might become more than your original construction cost within five years of the life of that practice,” he said. 

The 2024 update to the Minnesota Stormwater BMP Maintenance Resource Guide aims to address this issue by offering detailed instructions for inspecting and maintaining various stormwater systems. The updated guide includes inspection checklists in the form of fillable PDF documents. These checklists should streamline the inspection and documentation process and help inspectors assess site conditions, including vegetation health, erosion, and drainage performance. And the forms can be easily updated and reused, providing a practical tool for ongoing stormwater management. “The forms are not static, but rather are intended to serve as a resource that can be used and adapted to fit a jurisdiction’s particular needs,” Erickson explained.

Following items from the checklist, the guide provides specific maintenance recommendations based on inspection findings, including how to address issues such as erosion, vegetation dieback, and structural failures. 

“You can go through these to really home in on what maintenance is needed and when the maintenance is needed,” Erickson said.

The updated Minnesota Stormwater BMP Maintenance Resource Guide is now available online for download.

—Emma McIntyre, CTS communications intern

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