Roadside vegetation is essential for managing stormwater and mitigating soil erosion. Using organic and proprietary amendments to improve the topsoil after road construction projects are completed may help reestablish vegetation more quickly and provide better outcomes.
Continue reading Establishing Post-Construction Roadside Vegetation GrowthTag Archives: MnDOT
Impact of Start Time on Students Walking and Biking to School
To increase the number of students who walk or bike to school, policymakers first need to understand the primary factors that prevent students, parents and caregivers from choosing these travel modes. A look at the factors that influence this decision provided information to address barriers to walking and biking for children and families in Minnesota communities.
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Increasing Service Reliability by Adding a Dedicated Right of Way for Buses
In dense urban areas, public transit is a primary mode of transportation for people to commute to work, complete errands and connect with their community. If transit is not reliable, riders may choose other forms of transportation that could negatively affect riders, transportation agencies and communities. To improve service reliability, MnDOT investigated the use of dedicated rights of way (ROWs) for transit service across route segments within the system.
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Industrial by-products prove sustainable options for managing roadside stormwater
Reprinted from CTS News, March 25, 2025
Roadside soil plays a crucial role in stormwater management. Naturally vegetated roadsides can filter and control runoff, helping to keep pollutants out of bodies of water and minimizing flooding to communities. However, soil left behind from road construction does not adequately support filtration and plant growth unless it’s amended with organic matter—and traditional mixtures for doing so, such as with sand and compost, can be costly and resource-intensive.
To find a more sustainable solution, U of M researchers partnered with MnDOT and the Minnesota Local Road Research Board. Building on previous research, a team led by CTS scholar David Saftner, principal investigator and associate professor in the UMD Department of Civil Engineering, tested sustainable roadside soil mixtures using locally available waste materials and by-products generated from forestry, agriculture, and industrial activities.
In this project, nine materials were selected for testing, including a peat/biochar mix; dredged river sediment; pine and ash sawdust; VersaLime (a by-product of sugar beet processing); lime mud, bottom ash, and degritter (from a pulp and paper mill); and recycled concrete aggregate (RCA). All nine materials proved efficient at removing pollutants, though some were more effective than others. After extensive laboratory testing, the five top-performing materials were selected and used to create three engineered soil blends:
- RCA (80%) and ash sawdust (20%)
- RCA (80%) and peat/biochar (20%)
- Dredge sediment (80%) and degritter (20%)
Field testing of these three engineered soil blends took place in outdoor plots. The team studied infiltration rate, pollutant removal, and plant growth from grass and flower seed. Through a life-cycle assessment, the researchers also evaluated material collection and transport, energy demand, human health and ecosystem impacts, climate change, and water use.
Their research revealed that all three engineered soil blends were effective at capturing and filtering the first inch of excess stormwater runoff, offering a viable alternative to traditional soil mixes. Other key findings:
- Of the engineered soil mixes, organic and coarser materials were better at allowing water to pass through.
- Greenhouse tests showed promising plant growth, while field plots experienced challenges—possibly due to seasonal dryness.
- The dredge sediment and degritter soil mix had substantially higher impacts than the other two soil mixes as well as the most CO2 emissions.
- The RCA and ash sawdust soil mix had the lowest impacts, with the RCA and peat/biochar soil mix producing similar results.
Based on their findings, a design guide was developed for road engineers outlining best practices for using local by-products and waste materials to create engineered soil mixes while still adhering to regulatory standards. These recommendations are designed to be standard, common, and repeatable.
“This was a great project and I’m especially happy with the design guide,” Saftner says. “Determining how to implement new procedures is tougher than using tried-and-true methods. Our hope is that the guide will simplify things for practicing engineers looking for more cost-effective, sustainable, and locally sourced solutions.”
The study results also highlighted many of the benefits of engineered soil mixtures including the reuse of waste materials, reduced spending on sand and compost, lower transportation costs, and fewer environmental impacts of transporting material.
Further research on the reuse of waste materials includes another multi-phased project incorporating biochar. The first phase of that project should be finished this summer, with the second phase kicking off in summer 2026.
—Krysta Rzeszutek, CTS digital editor
Related Resources
- Article: Waste materials go to work as pollutant filter
- Article: Treating stormwater with local by-products reduces road construction costs, minimizes waste
- Re-use of Minnesota Waste Material in Sustainably Design Soils. Part 2
- Reusing Local By-Products to Create Sustainable Roadside Soil
- Re-use of Regional Waste in Sustainably Designed Soils: Part 1
Pavement Markings to Support Automated Vehicles
Automated vehicles (AVs) using advanced driver assistance systems depend on pavement markings to accurately track roadway lanes. While MnDOT continues to ensure human drivers easily and effectively detect and interpret various pavement markings, the agency also wanted to understand marking designs and characteristics that support AV functions. Field observations in different locations, during the day and at night, using different data collection methods allowed researchers to evaluate the impact of various pavement marking properties on AV lane-keeping functions. Results support MnDOT in producing pavement marking guidance that is responsive to changing needs.
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Adding fibers to concrete may help create long-lasting roads
Originally published in CTS News, March 19, 2025
Thin pavements—in which new pavements are constructed over an existing base layer—can be an economical option for low- and moderate-volume roads. However, thinner concrete roads are prone to distress caused by weather and traffic loads. The solution, U of M researchers found, may be to add small synthetic fibers to the concrete.
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Comparing the Effectiveness of No Right Turn on Red Sign Types at Traffic Signals
Preventing right turns on red at traffic signals is a generally effective pedestrian safety measure. But when pedestrians are absent, allowing right turns on red can improve traffic flow. Unlike static signs that prohibit right turns on red, dynamic No Right Turn on Red (NRTOR) signs can be activated when pedestrians are present. Comparing driver compliance with dynamic and static signs indicated that each sign type may have its own benefits.
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Examining Driver Preferences for Lane Line Patterns and Widths
Pavement markings that clearly delineate lanes are important for reducing crashes and improving the safety of drivers. The configurations of these pavement markings—primarily the width and length of the line and the spacing of broken lines—vary from state to state. This project identified driver preferences for pavement marking patterns and widths, which can increase visibility and improve safety.
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Understanding the Performance of Road Base Stabilization Additives
Full-depth reclamation (FDR)—an effective and efficient pavement reconstruction method—can be made even more sustainable by strengthening the road base. Laboratory and field testing of proprietary stabilizers used to amend FDR material illustrated improvements in pavement stiffness and economic benefits over time. New pavement design standards for base stabilizers can guide road engineers in choosing the optimal products for sustainable roads.
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New Project: Roundabouts, J-Turns, etc. – Understanding Their Economic Impacts
Roundabouts and J-turns have consistently shown significant improvements in safety and traffic flow in Minnesota and across the U.S. Still, some community residents and businesses oppose replacing traditional intersections with alternative intersections like roundabouts or J-turns.
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