A significant number of school bus stop-arm violations occur every day throughout the country. In Minnesota, violation and citation data suggests these incidents are grossly underreported and underenforced due to a time-consuming reporting and enforcement process. This project examined current processes and recommended improvements to encourage higher rates of reporting and enforcement.
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Testing Recycled Plastics in Asphalt and Concrete Pavement Mixes
Addressing the increasing need for pavement materials coincides with an increasing supply of plastic waste. Incorporating recycled plastic into aggregate for transportation infrastructure is of growing interest. Testing plastic waste material in both asphalt and concrete pavement mixtures revealed promising results and the need to explore long-term performance and durability.
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Evaluating the Friction of Pavement Markings and Colored Pavement
Pavement markings make travel safer for all road users. However, the material used for retroreflectivity can be slicker than the surrounding pavement. To maximize the safety of bicyclists, motorcyclists and pedestrians, MnDOT and local agencies explored the friction values of different marking materials. Project results produced valuable information on relative friction between pavement and marking materials and, importantly, identified effective testing tools to evaluate and compare products.
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Utilizing Recycled Tires to Treat Stormwater
Repurposing old tires as tire-derived aggregate (TDA) is a stormwater management practice that could retain phosphate in underground treatment systems and prevent it from reaching the soil, surface waters and groundwater. However, chemicals from the TDA may leach into the soil and water sources. This project identifies the environmental impacts and cost-effectiveness of deploying TDA to manage stormwater in Minnesota cities and counties.
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Enhancing Safety for Pedestrians and Bicyclists at Roundabouts
Compared to traditional intersections, roundabouts have been proven to decrease serious crashes. However, because drivers yield rather than stop upon entering roundabouts and at crosswalks, public concerns about pedestrian and bicyclist safety remain. Research and field evaluations into driver yielding and speed behaviors generated insights to guide local transportation agencies and MnDOT to further enhance pedestrian safety at roundabouts.
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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
Refining Max-Pressure Traffic Signal Control to Improve Traffic Flow
Effective traffic signal control technologies facilitate optimal traffic flow and travel time. Building on previous research, this project made significant progress toward field implementation of a novel adaptive signal control technology. This research phase demonstrated the max-pressure traffic signal algorithm can successfully integrate into Hennepin County traffic signal hardware and respond to changing traffic conditions in real time, providing confidence to move to the next step and test the system in the field.
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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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New Project: Best Practice for Oversized/Overweight Vehicles
As hauling practices change for waste collection, mining and other industries, local transportation agencies are receiving more permit requests for oversize or overweight trucks. These larger vehicles can have significantly greater impacts on pavements than passenger vehicles.
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Crossroads 