Research Reports

This Technical Summary pertains to Report 2023-22, “Impact of Speed Limit Changes on Urban Streets,” published June 2023.

This Technical Summary pertains to Report 2022-31, “Establishing a Repeatable Method for Presenting Non-Traditional Traffic Treatments to Maximize Stakeholder Support,” published June 2023

A novel infrastructure design known as the J-turn intersection reduces the risk of serious and fatal crashes at thru-STOP intersections through decreasing points of conflict at an intersection by restricting crossing movements from the minor road. Despite their demonstrated safety efficacy, J-turns have not been met with uniformly positive support. In this research, we first examine novice driver baseline attitudes and driving behaviors on J-turns using a driving simulator study. Results demonstrate that critical errors are decreased with driving exposure to the J-turn; however, attitudes toward J-turns are not improved by exposure alone. A series of studies then evaluates the efficacy of various messaging strategies and educational materials on improving attitudes toward J-turns. The findings from these studies identify that the use of both educational materials and persuasive and customized messaging strategies is an effective method for increasing acceptance of J-turns across diverse resident populations (i.e., rural, suburban, and urban) and among stakeholders in Minnesota. This work demonstrates the importance of the role of proactive educational programs and community initiatives in promoting the acceptance and buy-in toward novel roadway treatments, such as J-turns, among diverse drivers, communities, and stakeholder groups.

This report analyzes how state-funded highway improvement projects in the seven county Twin Cities metropolitan area affected businesses in adjacent Census Tracts. We first identify demographic factors associated with the temporal and financial prioritization of some projects over others, finding that the per capita income of a Census Tract is associated with it featuring more heavily prioritized highway improvement construction. We then turn to the effects of highway improvement construction and operation, using results from the previous analysis to account for endogeneity of improvement timing. While we find largely null results of highway improvement on sales, employment, establishment counts, and turnover for both single-establishment and multiple-establishment firms, we also find that pooling data masks several sources of effect heterogeneity. Specifically, we find that single-establishment firms experience negative sales effects from construction when tracts are affected only by infrastructure replacement projects (improvements that do not affect traffic operations, i.e., a bridge replacement). Furthermore, negative sales and employment effects occur after construction is completed for single-establishment firms in urban areas and in tracts affected by longer bouts of construction. Meanwhile, in suburban areas, some modest gains accrue to multiple-establishment firms. These results suggest that regional planners need to account for potential externalities from highway construction on particularly nearby small business establishments

A pile-supported embankment constructed on TH 241 near St. Michael, MN was instrumented with 48 sensors, including strain gages on the piles and on the geogrid, as well as earth pressure cells and settlement systems near the base of the embankment. Pile supported embankments are relatively novel structures employed largely at bridge approaches and highway expansions where soft soils would otherwise lead to unacceptably large differential settlements. The structure typically consists of a number of capped piles, well-compacted gravel, and one or more layers of geogrid reinforcement above the piles. Analyses of the data suggest that the redistribution of the embankment load to the piles occurs within and above the so-called load transfer platform, a 1 m layer of geogrid reinforced gravel. Arching seemed to take place within the embankment, such that the stress at the top of the platform was concentrated above the piles.

Storm-water runoff from the Woodbridge neighborhood of the City of Shoreview had previously been managed through culverts and other hydraulic structures. In adherence to the Clean Water Act, many watersheds instituted limits to the percentage of storm water that may be allowed into certain lakes and rivers. To minimize this run-off and the associated impacts and in accordance with the City’s sustainable design policy, the City of Shoreview built the Woodbridge neighborhood local roads using pervious concrete pavements in 2008. Pervious concrete pavements exhibit high hydraulic conductivity and high sound absorption coefficient in local or low volume roads. They also provide cost savings through the minimization of hydraulic structures.

St. Louis County performed two HMA reconstructions on portions of County State Aid Highways during 2004 and 2005; CSAH 4 south of Biwabik, and CSAH 16 east of US Highway 53. The county saw differences in initial cracking performance and identified the two roads as potential research sections in 2005. Both projects were HMA reconstructions consisting of two 12-ft driving lanes with 6-ft shoulders. 24 in. of select granular modified (less than 7 percent passing the #200 sieve) was placed above the natural soil, followed by 6 in. of class 5 base material, and 5.5 in. of bituminous pavement. The bituminous pavement was constructed as 2.5 in. base lift, 1.5 in. binder lift, and 1.5 in. wear course lift. The recycled Asphalt Pavement (RAP) for the two projects all came from CSAH 16 millings. Bituminous mixtures were designed using Marshall MV criteria. This study is a continuation of Report 2009-15, "Best Practices for RAP Use Based on Field Performance."

Micro-milling provides an innovative way to rehabilitate asphalt pavements. Micro-milling uses a milling drum with more teeth and a tighter lacing pattern to create a smoother surface than the traditional milling process (about 3 times the teeth than regular milling heads). The smoother surface provides a better surface for thin overlays, ultra-thin bonded wearing course (UTBWC), chip seals, and microsurfacing.

This Technical Summary pertains to Report 2023-31, “Evaluation of Slurry Spreaders and Plows (Underbody, Wing and Two-Way Reversible),” published August 2023.

MnDOT evaluated five pieces of new winter maintenance equipment: two slurry spreaders, an underbody scraper, a true-float wing plow and a two-way reversible plow. For Winter 1 of the evaluation program, all equipment was acquired, installed, and field-tested in MnDOT District 2. For Winter 2, a data collection program was developed to capture quantitative data on how well the equipment worked in District 2, compared side by side against comparable routes with traditional spreaders. Winter 1 and 2 field testing of the three types of plow equipment allowed operators to fix operational problems and led participants to agree that MnDOT should continue to use such equipment and acquire more. MnDOT participants did not reach consensus on whether to continue to use or buy more of the two slurry spreaders. Data analysis showed that they performed comparably to traditional slurry spreaders in terms of road regain time and salt use when they were operational. Issues included equipment height, causing loading and maintenance worker safety concerns; equipment weight, reducing how much material could be loaded in the truck; difficulty in setup; equipment not operating as expected; and difficulty obtaining vendor parts and getting vendor support. These issues led to the cancellation of a third winter of testing in a different district. It was suggested that the equipment might better suit MnDOT’s needs by mounting it on a boxless truck.