Institute for Transportation

About the research

The density and air void content of asphalt mixtures affect the durability and performance of asphalt pavements. Pavement longitudinal joints typically have a lower density than the mat because they receive less compaction than the center section of the mat for various reasons. The higher air void percentages resulting from lower densities can lead to high permeability and allow water infiltration, which in turn can cause moisture-induced damage and decrease base and subbase support to the pavement, reducing pavement life. Void-reducing asphalt membrane (VRAM) has been used at the longitudinal joints of asphalt pavements to achieve higher densities and prevent moisture infiltration, thereby reducing deterioration at the longitudinal joints. VRAM is applied before the hot-mix asphalt (HMA) layer is placed and migrates into the HMA to fill 50% to 70% of the air voids.

This research evaluated the extent to which J-Band, a VRAM product, increases density and improves performance. Field cores were collected from two sections, one with and one without VRAM. Asphalt mixture performance tests, including disk compact tension and semi-circular bend tests, and push-pull tests were carried out in the laboratory on the field-collected specimens. Volumetric measurements were also taken, and ground penetrating radar was used in the field. It was determined that the pavement sections with VRAM had a lower permeability, higher bond energy, and higher fracture energy than the pavement sections without VRAM.

About the research

The installation and maintenance of pavement markings represents a significant financial investment for local agencies. Local agencies need a mechanism to better understand the value, cost, and need for markings along their roadways to make the best use of available budgets. This project developed a prioritization approach and spreadsheet tool (link provided in box 15) to assist local agencies in meeting this need. Multicriterion decision analysis using the simple additive weighting method was employed to assess the multiple factors/criteria that affect pavement marking decisions. An Excel spreadsheet tool was developed to implement this approach using different pavement marking alternatives, including centerlines, edgelines, centerlines and edgelines, high-visibility markings, and enhanceddurability markings. The criteria considered by the process include project type, County Roadway Safety Plan (CRSP) rating, functional classification, pavement condition, traffic volume, age of current markings, pavement width, preferences for marking costs, desired marking durability, and crash reduction potential. This tool is posted on the Local Road and Research Board (LRRB) website in the “Resources” section at the following URL: https://lrrb.org/ resources/. Factor weights are used to assign a relative importance to each of these criteria for a respective alternative compared to other alternatives. The result is a performance rating score for each marking alternative relative to all model criteria and factors that provide users with information on the relative performance of different marking alternatives in comparison to one another and an estimated project cost for the highest ranking alternative for a site. The highest scoring alternative represents the marking that should be considered for use. Additionally, the tool ranks all sites being evaluated compared to one another based on the highest rating scores from each individual site.

About the research

The objective of this research was to conduct an independent evaluation of winter maintenance performance indicator and LEM data collection and processing practices. The evaluation sought to establish whether the correct data were being collected and if the appropriate analyses were being conducted on the available data. Appropriate analyses means analyses that are able to identify successes and isolate best practices. Once we can distinguish and measure success, management can reward and encourage it elsewhere.

About the research

This project will complete the testing and deployment of an advanced system for forecasting frost on bridges in Iowa by application to four bridges in central Iowa. Our method employs a widely used research and operational numerical model for weather forecasting and includes a bridge-surface temperature balance equation for specific forecasts of bridge surface temperature.

About the research

Pavement marking is an essential component of roadway construction and safety. The markings need to be visible (day and night) so that drivers can quickly identify where the markings are and determine what message is being defined. Good pavement marking provides critical elements to guide drivers on correct road paths, complement road signs that inform and warn drivers, and improve night driving conditions.

This project’s objective was to review existing pavement marking practices by local agencies in Minnesota (material selection, installation, specifications, and contracting procedures) to provide guidance for maintaining good pavement markings, thereby saving money and increasing road safety. The two specific objectives were as follows:

1. Review existing pavement marking practices in local agencies.
2. Develop recommendations for better management of pavement marking through the use of pavement marking management tools and coordination with the Minnesota Department of Transportation (Mn/DOT).

About the research

This project was performed to evaluate the performance of recycled aggregates and large stones used in the aggregate base/subbase layers of pavement systems and provide recommendations regarding pavement design and material selection.

As part of this project, 11 test cells were built at MnROAD to evaluate the impact of recycled aggregates and large stones on the long-term pavement performance via a series of laboratory [permeability, soil-water characteristic curve (SWCC), stereophotography (image analysis), gyratory compaction, and resilient modulus (MR) tests] and field tests [intelligent compaction (IC), falling weight deflectometer tests (FWD), rutting measurements, international roughness index (IRI) measurements, light weight deflectometer (LWD) tests, and dynamic cone penetrometer (DCP) tests]. In addition, a pavement mechanistic-empirical (ME) design approach was used to provide recommendations for designs of pavement systems containing recycled aggregate base (RAB) and large stone subbase (LSSB) layers.

Overall, this project found that finer recycled concrete aggregate (RCA) material would be preferable to coarser RCA material and a blend of RCA and recycled asphalt pavement (RAP) materials would be preferable to natural aggregate for aggregate base layers. RCA materials provided better performance than the blend of RCA and RAP materials, indicating that RCA materials would be preferable to the blend. For LSSB layers, this project found that geosynthetics would be required to successfully construct thinner LSSB layers. Overall, thicker LSSB layers provided better structural support than thinner LSSB layers both in the short term and the long term.

About the research

Pavement marking is important for safety. Maximizing pavement marking performance in terms of increased retroreflectivity, within limited budget constraints, allows agencies to make better decisions toward providing more effective pavement marking performance on their roadway networks. This research project included conducting a survey of local agencies’ pavement marking practices, mining existing National Transportation Product Evaluation Program (NTPEP) pavement marking data, and developing recommendations for future pavement marking research to support local agency needs.

The NTPEP pavement marking performance data (related to pavement marking products used by local agencies in Minnesota) was analyzed to provide guidance to local agencies in terms of pavement marking material selection based on performance. The objective included determining pavement marking products of interest to local agencies and developing performance metrics for these products based on existing NTPEP data. The analysis performed on the NTPEP included modeling the deterioration behavior as a function of time. Also two-way ANOVAs were performed to compare various performance measures and the impact of different conditions on these measures.

About the research

The final report for this project provides an integrated selection procedure for evaluating whether an existing hot-mix asphalt (HMA) pavement is an appropriate candidate for a bonded concrete overlay of asphalt (BCOA). The selection procedure includes (1) a desk review, (2) coring, (3) visual examination (site visit), (4) additional coring and/or laboratory testing (optional), (5) preparation of preliminary estimates (optional), and (6) a final report with design recommendations.

This project also included an analysis of material testing performed by the Minnesota Department of Transportation (MnDOT) on numerous HMA cores to determine if the performance of existing BCOAs could be correlated to HMA material properties. The results of the laboratory testing were inconclusive. None of the existing HMA material properties tested could be correlated to long-term BCOA performance due to the high variability among the measured parameters within a section, the small number of cores per section, and the fact that the sections investigated exhibited little or no distress that could be attributed to the asphalt layer’s properties. Although no conclusions could be made from the limited laboratory testing, it is fair to say that the BCOAs from these projects were performing as designed.

About the research

The Minnesota Department of Transportation (MnDOT) is investing significant resources in intersection collision warning systems (ICWS) based on early indications of effectiveness. However, the effectiveness is not well documented, and negative changes in driver behavior at treatment intersections may affect drivers overall, resulting in a spillover effect. Moreover, the effectiveness of ICWS may decrease if drivers do not perceive a change in the dynamic messages. Therefore, the objectives of this research were to (1) evaluate driver behavior at mainline and stop-controlled approaches for intersections with and without ICWS and (2) assess the traffic volume range and limits where the system is nearly continuously activated and is likely to lose its effectiveness.

Video data were collected at five treatment and corresponding control intersections, and various metrics were used to compare changes in driver behavior. In general, no negative behaviors were noted for either treatment or control intersections.

About the research

This multi-phase study utilized Second Strategic Highway Research Program (SHRP2) Naturalistic Driving Study (NDS) data to evaluate the impact of traffic control devices in reducing driver speed in work zones. The main advantage to the SHPR2 NDS data is that on-road driver behavior was captured and can be used to evaluate how drivers behave in various situations. The study included four different analyses. The first evaluated where drivers began reacting to various work zone traffic control devices. The second assessed how drivers changed speed upstream to immediately downstream as they encountered various traffic control devices. The third assessed how drivers react when they encounter the back of a queue and the fourth developed speed based on work zone characteristics such as presence of barriers.

The project also includes a toolbox that summarizes information about work zone traffic control devices, countermeasures, and work zone features that have a demonstrated impact on speed in work zones. Features were identified through a survey of the literature. Additional information for some of the features and countermeasures was gained through the various analyses of SHRP2 data conducted through this project. Guidance from the work zone traffic control manuals for various states was summarized when appropriate. Recommendations for use of each feature or countermeasure relevant to addressing speed in work zones was developed by the team and reviewed by work zone experts and the project panel.