Items used in the freezing point determination test (ASTM D1177)
Combining road salt with common additives such as corrosion inhibitors, anticaking agents, cold temperature modifiers, thickeners and friction enhancers can increase the effectiveness of the deicer, allowing it to work more quickly or remain on the pavement longer.
To determine how well mixed salt products perform at lower temperatures and inform transportation agencies’ winter maintenance decisions, this Clear Roads project tested eight solids and prewet solids to evaluate the influence of additives on chloride-based deicer performance, including the freezing point or eutectic temperature, ice-melting capacity using the rocker test and pavement friction.
Download the final report and two-page brief: CR 22-03 – Effects of Additives in Deicing Salts at Lower Temperatures, February 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.
Field plots adjacent to the Natural Resources Research Institute parking lot were used to test the infiltration capacity, pollutant removal, and vegetative support capabilities of the soil mixtures.
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.
Since October 2022, five self-driving shuttle vans in Grand Rapids, Minnesota—with onboard operators for safety—have offered free, on-demand rides as part of the Minnesota Autonomous Rural Transit Initiative (goMARTI). This pilot project is a collaborative effort between multiple stakeholders and partners to conduct a first-of-its-kind demonstration of self-driving shuttles in a rural setting.
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.
Agencies selecting a new or replacement storage system for their liquid deicers have a lot to consider, such as safety, environmental impacts, and cost-effectiveness.
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.
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.
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.
Originally published in Catalyst, February 19, 2025
Transit service planning has traditionally focused on peak trips and the needs of “rush hour” commuters rather than off-peak travel. Often, off-peak trips are taken by shift-based essential workers and those who cannot or do not drive. The COVID-19 pandemic further underscored the need for a closer examination of these trips to improve social equity.
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.
Crossroads 