Tag Archives: LRRB

Environment, research

New Project: Feasibility of LED Solar Street Lighting

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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.

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

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.

Traffic and Safety

Understanding Economic Impacts of Roundabouts and J-Turns

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Roundabouts and J-turns improve safety and road user experiences. While public familiarity and acceptance of these alternative intersections designs increase over time, questions remain regarding economic impacts on nearby businesses. An analysis of roundabouts and J-turns continued to show benefits for road users and no notable negative economic impacts on nearby businesses.

Continue reading Understanding Economic Impacts of Roundabouts and J-Turns →
Policy and Planning

Impacts of Shared Mobility in Transportation Modeling

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Newer modes of transportation—ride-hailing services, car sharing, bike sharing and scooter sharing—impact travel behavior and outcomes such as accessibility, traffic congestion and greenhouse gas emissions. Yet current travel modeling analyses do not adequately incorporate these modes, resulting in inaccurate predictions of their influence. This project integrated shared mobility into traffic modeling for more accurate predictions that local governments can consult to make transportation planning decisions.

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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.

Traffic and Safety

Upstream and Downstream Traffic Calming Benefits of Roundabouts

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Roundabouts have been repeatedly shown to reduce fatal and serious crashes, in part by slowing vehicles as they move through intersections. Less was known, however, about how far those speed-reducing effects extend beyond the intersection itself or how they compare with other intersection types. To better understand these upstream and downstream impacts, MnDOT and local transportation agencies worked with investigators to measure vehicle speeds at roundabouts, signalized intersections and all-way stop-controlled intersections. The results showed that roundabouts provide traffic calming benefits beyond the intersection, supporting their continued use as a safe and effective design alternative.

Continue reading Upstream and Downstream Traffic Calming Benefits of Roundabouts →
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

Preventive Road Sawing and Sealing to Reduce Maintenance Costs

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Asphalt pavements will inevitably begin cracking and require maintenance to preserve an adequate level of service. However, preemptively sawing and sealing roads at prescribed locations can reduce cracking and improve maintenance predictability. To help the state’s transportation agencies better manage pavement deterioration, the Local Road Research Board sought to compare the performance of a lower-cost unmodified asphalt binder using the saw-and-seal method with that of a higher-cost polymer-modified asphalt binder without using saw and seal.

Continue reading Preventive Road Sawing and Sealing to Reduce Maintenance Costs →
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

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  →