Search Content

This report presents the step by step installation and testing procedures developed for the load response instrumentation at the Minnesota Road Research Project (Mn/ROAD). Load response instrumentation measures such parameters as strain, deflection and pressure in the pavement layers from dynamic axle loadings. The test procedures presented were performed immediately before and after paving to check for any gross malfunctioning of lead wires or sensors. The procedures presented do not include any accuracy tests. Initial survivability of the sensors is discussed as are probable causes for failures.

Intelligent compaction (IC) is a roller-based innovative technology that provides real-time compaction monitoring and control. IC can monitor roller passes, vibration frequencies/amplitudes, and stiffness-related values of compacted materials or intelligent compaction measurement Values (ICMV). Various ICMVs have been introduced since 1978. Based on the five levels of ICMV in the 2017 FHWA IC Road Map, the current implementation of ICMV in the United States has been limited to Levels 1 and 2. However, Level 1 and 2 ICMVs fail to meet the FHWA IC Road Map criteria. To achieve the full potential of IC technology, Level 3 and above ICMVs are needed to gain the confidence of agencies and industry and the adoption of IC to soil and base compaction. This project aims to (1) evaluate Level 3-4 ICMV systems against Level 1 ICMV systems for soils, subbase, and base compaction and (2) develop a blueprint for future certification procedures of IC as an acceptance tool. This study also aligns with the goals of the ongoing HWA IC for foundation study and the TPF-5(478) pooled fund study. This final report details the ICMV background, field test efforts, analysis results, and an IC specification framework for compaction acceptance.

Measuring equity in transportation is vitally important to ensure that the transportation network serves the entire community without introducing barriers to access. However, not all methods for assessing transportation equity produce the same results or are appropriate for all scenarios—the analysis methods used should be selected to produce the highest likelihood of determining the most equitable outcomes. This research project synthesizes previous research investigating equity assessments by MnDOT, academia, and industry and leverages these findings in concert with directly collected community experience and staff expertise to achieve the following objectives: (1) establish a detailed understanding of current challenges and needs related to equity assessment in Minnesota; (2) identify or develop assessment methods and equity-focused strategic actions that will improve the likelihood that transportation equity in Minnesota is assessed in a manner that achieves context-sensitive outcomes representative of the communities served; and (3) facilitate the adoption of identified or developed equity assessment methods and complementary strategic actions, including information detailing appropriate use cases, data requirements, and considerations through a bespoke training program.

The introduction of fiber reinforced plastic (FRP) dowels as possible alternatives to the epoxy-coated and stainless-steel dowels, was contemporaneous with a paucity of knowledge of their long-term performance. Although various isolated efforts had examined them on a short-term basis and produced some qualitative results or long-term predictive models, actual long-term performance in service was still unknown and unanalyzed. An experiment at the MnROAD Research facility placed FRP dowels in 2000 in some of the jointed plain concrete pavement (JPCP) panels of test Cell 52 and used epoxy-coated dowels in the remaining panels of this cell. The contiguity of this test cell with Cell 53, a JPCP high-performance concrete cell built in 2008 with stainless steel dowels, and Cell 54, a taconite JPCP cell with epoxy-coated dowels in built in 2004, facilitated a comparative analysis of performance of the 3 dowel types particularly in load transfer efficiency (LTE) and ride quality. The difference in the inception of the cells constrained a performance over time and encouraged a time-series autoregressive integrated moving average (ARIMA) analysis. Projections to 30 years showed that LTE and ride quality of FRP dowels were no different from those of the epoxy-coated dowels and the stainless-steel dowels although Cell 53 was designed and built with thicker concrete (12-in. thick) compared to 7.5-in in cells 52 and 54.

This study investigates the perceived safety risks and barriers that might prevent transit and shared mobility services from attracting post-COVID riders in Greater Minnesota. It includes an online survey of Greater Minnesota residents to understand their COVID-related safety concerns and their preferences and perceptions toward existing and potential safety protocols. The survey results show that, during the post-COVID era, driving alone continues to dominate, but desires to use transit and shared mobility modes remain strong. Lack of access, lack of interest, and lack of available better alternatives jointly affect transit-use behavior. Women, people with COVID concerns, urban residents, online shoppers, and transit users are associated with stronger preferences toward COVID safety measures. People with COVID concerns, online shoppers, and transit users are also associated with preferences toward general transit service improvements. We also find that elderly people, hesitant tech users, and transit-dependent users are unlikely to be positively affected by trip-planning tools and contactless payment technology. Furthermore, income and car ownership predict future transit use, and younger age is associated with more interest in carpooling. These results help to inform transit and shared mobility providers about what safety and communications strategies will be most effective in bringing users back.

Two projects dealing with field instrumentation of bridges are described in this report. In the first project, a portable, rugged and multi-purpose bridge instrumentation system was developed. This was accomplished by using fourteen removable instruments and a portable data acquisition. The instrumentation included eight reusable strain sensors and six inclinometers, which allowed load distributions, stresses, and displacements to be measured in steel girder bridges. In the second part of the project the portable data acquisition system was used to measure strains near fatigue critical details in steel bridges to determine stress ranges under both controlled and random traffic. For this part of the project conventional strain gauges were also used. Overall this acquisition and modelling system worked quite well for determining strains and deflections of simply supported bridges under static loadings. A new measurement technique for finding deflections, based on slope sensors, was developed and verified. This technique can now be readily used in bridge evaluation. The system should be extended now to various types of bridges including continuous span, concrete girder, and timber bridges.

A retrofit scheme to widen and strengthen nail-laminated timber bridges was evaluated in this project. The scheme consists basically of laying a second, transverse layer of timbers above the existing deck, and casting a grout layer between the two wood ones to insure good force transfer. An old wood bridge was evaluated before and after it was retrofitted in order to investigate the effectiveness of the retrofit technique. In addition, three laboratory specimens, representing portions of the retrofitted bridge deck (ungrouted and grouted), were tested to investigate the strength and the effects of fatigue on the retrofitted bridge deck, and to evaluate the transverse load distribution of the original and retrofitted bridge deck. An analytical model of the retrofitted bridge deck was also developed utilizing the finite element method, the deflection and transverse distribution results from the model studies were compared favorably with the laboratory results.

Statistical techniques were developed for extracting the most significant features (indicators) from a transit system data base, and classifying proposed and existing transit systems according to the selected features. The data base was constructed by using information from all previous years available by the Mn/DOT, the Census and other sources to be used in classifying transit systems. The data base emphasized the use of raw characteristics of the operating system and the area socioeconomics. The feature extraction was done so that the minimum number of features were extracted that can be used for classifying the transit systems with maximum accuracy. The classification method was designed around the data base and is flexible so that it can use future data to update the data base at minimum cost. The transit system patterns, resulting from the classification method, were identified according to need and performance, and the main characteristics were specified for each pattern. These characteristics and descriptions identifying each pattern determines whether it should be modified. A controlled experiment was required to test the classification method. A randomly selected part of the data was classified by the method, and then the unselected data was treated as a control group for the experiment. After the experiment a percent of misclassifications was calculated

Any proposed traffic management action is essentially a forecast that the action will result in certain traffic conditions, but uncertainty concerning the amount and distribution of traffic demand will introduce random error between what is expected and what actually occurs. This report treats the problem of forecasting whether or not a given set of freeway on-ramp volumes are likely to cause over-capacity demand at some point in the freeway mainline. The main source of uncertainty in these forecasts concerns the freeway's origin-destination matrix, and four different methods for estimating this matrix from loop detector data are evaluated using Monte Carlo simulation. Only the method which explicitly modeled freeway traffic flow produced reasonably unbiased and efficient estimates, and it was concluded that successful estimation must be coupled with a good model of freeway traffic flow.

This Technical Summary pertains to Report 2023-13, “Assessment of Bridge Decks with Glass Fiber-Reinforced Polymer (GFRP) Reinforcement,” published March 2023