Minnesota Department Of Transportation Research Articles

Assessment of In Situ Compactness and Air Void Content of New Asphalt Layers Using Ground-Penetrating Radar Measurements

This paper deals with the possibilities of ground-penetrating radar (GPR)-based quality control testing, which was demonstrated on an experimental road section of a ~220–240 m long Hungarian residential street. The measurements and their assessment aimed to control the prescribed compactness and air void content of newly built asphalt layers. Research has discussed the relationship between the air void content and the dielectric constant of asphalt layers, and provided empirical results for this relationship. We suggest a new logistic model with lower and upper asymptotes instead of the exponential formula often used in the literature. Contrary to this newly developed robust model, existing models are sensitive to extreme dielectric constant values due to the mathematical nature of their exponential function. The results of the new logistic model are compared to those of the Hoegh–Dai (HD) and Minnesota Department of Transportation (MnDOT) models on the basis of a few calibration data points. Through systematic data collection and analysis, the developed robust empirical model demonstrates a significant correlation between the relative permittivity and air void content in asphalt mixes, enabling accurate estimation of the air void content within a ±0.5% margin of error. The air void content can be applied to estimate the asphalt layer modulus. The developed model can be further exploited by utilizing a combination of GPR and drone technology. The “symbiosis” of these technologies can lead to a totally non-destructive imaging system, which can then be applied to environmental monitoring of roads and their surroundings in terms of quality control of asphalt compaction work and the hot asphalt mix behind the compaction roller during pavement construction.

Use of chip seal treatments to mitigate pavement roughness progression in cold regions

ABSTRACT Chip Seals are a type of pavement preservation treatment characterised by its ability to reduce pavement deterioration and restore surface condition. Chip seal performance, like other pavement preservation treatments, depends on several factors such as environmental conditions, traffic level and the condition of the existing pavement structure prior to treatment application. In cold regions, the presence of freeze and thaw cycles promotes the generation of thermal cracks and possible tenting distresses, consequently, pavement roughness has been a prominent parameter to assess treatment performance. The objective of this study was to evaluate the roughness progression on several chip seal configurations in a cold climate region, utilising a set of field performance data from the Pavement Preservation Group Study, a broader research study conducted by the National Center for Asphalt Technology and the Minnesota Department of Transportation’s Road Research Facility. The main findings indicate that chip seals provide a negligible effect on immediate roughness improvement; however, on a long-term basis, they provide a reduction in IRI progression over time. The magnitude of the IRI benefit is dependent on the type of chip seal implemented and the traffic level experienced.

Quality Assurance Methods for Hourly Nonmotorized Traffic Counts

Growing numbers of public transportation and recreation agencies have implemented automated bicycle and pedestrian traffic monitoring programs. To support these initiatives, researchers and agency analysts have developed programs, methods, and measures to ensure data quality. These methods include statistical tests for identifying and flagging outliers and other invalid counts and procedures for imputing or managing missing and censored counts. Because statistics such as annual average daily bicyclists are used frequently in planning and engineering, analysts have focused on validation of daily counts using data from permanent monitors. Procedures for ensuring the validity of hourly counts have not been standardized. This paper presents quality assurance (QA) methods for hourly nonmotorized traffic counts at 115 short-duration and nine permanent monitoring sites on multiuse trails monitored by the Minnesota Department of Natural Resources (MnDNR) and the Minnesota Department of Transportation (MnDOT) between 2016 and 2021. These methods include statistical tests for flagging and censoring invalid hourly counts and procedures for imputing estimates for censored or missing counts. Differences in traffic flow estimates with and without QA are documented, and hourly patterns and factors are presented. Use of quality assurance methods for hourly counts can increase the validity of estimates of nonmotorized traffic.

Probabilistic cost-based decision-making matrix: IDIQ vs. DBB contracting

Public departments of transportation (DOTs) are increasingly adopting alternative contracting methods (ACMs), such as Indefinite Delivery/Indefinite Quantity (IDIQ) agreements, to shorten project delivery and increase scheduling flexibility. However, the challenge remains to decide when an IDIQ contract would offer better value for money in a project compared to the conventional Design-Bid-Build (DBB) method. This paper proposes an IDIQ project selection framework that incorporates expected construction costs to identify suitable candidate projects. Historical bid data, an alternate cost indexing system, nonlinear regression analysis, and the Monte Carlo simulation technique are used to create and compare IDIQ and DBB probabilistic construction cost estimates. The study demonstrates the effectiveness of the framework using a single-award IDIQ granted through the Minnesota Department of Transportation (MnDOT) and past bidding information for projects awarded between January 2008 and April 2015. Additionally, the paper acknowledges the limitations of the study, including its reliance on MnDOT data, the exclusion of non-cost factors, and the assumption of project homogeneity. The study also provides valuable recommendations for future research to address these limitations and enhance the understanding and practical implementation of IDIQ contracting in the construction industry.

Parameter Study of Financial Analysis for Implementing Solar Photovoltaics Structural Snow Fences

Structural snow fences are known as a cost-effective way to enhance road safety on highways, which, however, are only used during winter, making them “useless” during summer. To increase their cost-effectiveness, Photovoltaics Snow Fences (PVSF) were developed by integrating PV panels with conventional structural snow fences. As part of the feasibility study supported by the Minnesota Department of Transportation (MnDOT), a financial analysis was performed involving many parameters, such as the capital and operating costs of the PVSF system, installation orientation of the panels, discount rates, energy selling prices, availability of incentives, ownership of the PV system, etc. The effects of these parameters on the analysis results were evaluated, where critical (most sensitive) parameters were first identified, and then their quantitative effects on the analysis results were evaluated in terms of Net Present Value (NPV) and Internal Rate of Return (IRR). The results indicate that the real discount rate is the most sensitive parameter in determining the cost-effectiveness of a PVSF project in Minnesota by looking at its NPV, when the benefits, such as Federal Tax Credits, Renewable Energy Certificates, and those associated with the use of snow fences, are considered in the financial analysis. The cost of the PVSF system is the most sensitive parameter for IRR, depending on the ownership of the PV system (by MnDOT or via a Power Purchase Agreement).

Cost–Benefit Analysis of Implementing Solar Photovoltaic Structural Snow Fences in Minnesota

Structural snow fences have been increasingly used in northern regions of the United States. They are known as a cost-effective and efficient technology to prevent snow accumulation on highways and, therefore, improve road safety. Structural snow fences, however, are used only during winter, and to add more value to the structure, an idea to install solar photovoltaics (PV) panels on structure snow fences was first proposed by the Minnesota Department of Transportation (MnDOT), who was interested in looking at the feasibility of integrating structural snow fences with PV panels, called PV snow fences (PVSF). The PVSF would be constructed by replacing the rails between the poles of the structural fences with customized PV panels that have the same dimension as the rail. This arrangement is to ensure that the original function of the snow fences, that is, eliminating blowing and drifting snow on highways, would not be affected. Considering different factors or parameters, such as project size, panel size, installation angle or orientation of the panels, discount rate, energy selling price to a utility company, availability of incentives, ownership of the PV system, etc., a comprehensive cost–benefit model has been established to analyze the pros and cons of different implementation plans. The analysis results show that the longer the length of the PVSF is, the more cost-effective the project is, due to a lower capital cost and increased power generation. A Power Purchase Agreement (PPA) would significantly shorten the payback period in consideration of the key benefits brought through a PPA, including minimal up-front capital costs, lower energy costs, no risk, no upkeep, leveraging available tax credits, and enhancing the value of the property, which is, therefore, more realistic and would be a higher priority for an agency like MnDOT or other state DOTs.

Minnesota Distance-Based Fee Project: Charting a Path Forward

This paper summarizes an innovative demonstration by the Minnesota Department of Transportation (MnDOT) of the distance-based fee (DBF) concept. Fees based on actual road usage, as opposed to fuel consumption, have been explored by numerous states as an alternative transportation revenue source to the motor fuel tax. These approaches rely on the collection of road usage data, and most states have pilot tested approaches reliant on aftermarket devices installed within individually owned vehicles. Private-sector vendors are responsible for managing data collection, fee assessment, and account management. In the near term, the most feasible and scalable option for DBF deployment may be to leverage embedded telematics technologies under a fleet-based reporting and collection approach. MnDOT worked with two shared mobility (SM) providers offering carsharing services in the Minneapolis–St. Paul region. A connected and automated vehicle (C/AV) partner was also included to demonstrate the collection of road usage information from emerging C/AV technologies. The demonstration successfully collected the required information for DBF assessment from the SM and C/AV providers including information necessary to support audits by the Minnesota Department of Revenue. The demonstration showed that the information necessary for assessing and collecting DBF could be obtained from embedded telematics systems and reported by a fleet provider on behalf of all users in that fleet. Although the specific architecture demonstrated would probably need significant adaption for scaling to a national system, it nonetheless provides insights that support development of a broader ecosystem of usage-based charging strategies.

Joint performance and faulting of ultra-thin and thin structural-fiber reinforced concrete pavements

ABSTRACT Structural fibers contribute to the overall performance of concrete pavements by mitigating various distresses. To understand the influence of structural fibers on the pavement structural responses and distresses, the Minnesota Department of Transportation (MnDOT) constructed two ultra-thin (3 and 4 in. thick) and three thin (5 and 6 in. thick) fiber reinforced concrete cells along with one plan concrete control test cell at the Minnesota Road Research (MnROAD) facility in 2017. These test cells have 6 ft x 6 ft concrete slabs and were constructed on the granular base layer. While the structural designs of these cells were intended for roads with low to moderate traffic volume, the cells were subjected to accelerated loading to complete the study in a short period of time. This paper summarizes the design and construction of the six test cells and provides a comprehensive discussion on the joint performance behavior and transverse joint faulting trends, emphasizing the influence of the fibers on the abovementioned. It was found that fibers can improve joint performance and decrease faulting in thin concrete pavements. Regarding the ultra-thin pavements, no conclusion was possible to be drawn on the contribution of the fibers.

Safety Evaluation of Changing Speed Limit from 55 mph to 60 mph on Two-Lane, Two-Way Road Segments

This paper describes the efforts to evaluate the safety impacts of increasing the speed limit from 55 mph to 60 mph on selected two-lane, two-way state highway road segments in Minnesota, U.S. An empirical Bayes (EB) before–after analysis was used to estimate crash modification factors (CMFs) for both segments (1,909.11 mi) and intersections (1,722 3-leg and 1,191 4-leg). Aggregate analysis conducted using all the segment and intersection data showed a 2.9% increase in total crashes, a 2.5% increase in injury (KABC) crashes, and a 0.05% reduction in the injury (KAB) crashes. These results—along with before-and-after operating speed data from another study by Minnesota Department of Transportation (MnDOT) (2019) showing that the 85th percentile operating speed remained the same and that the mean operating speeds increased by 1 mph following the speed limit increase—can lead to a conclusion that the speed limit increase from 55 mph to 60 mph had a minor effect on combined segment and intersection crashes or operating speeds. It is important to note that these results are specific to the corridors that were selected by MnDOT for the increase in speed limit; caution must be exercised when extending these to systemwide increases in speed limits in Minnesota or in other states, and when estimating long-term effects of speed limit increases as operating speeds can change over a longer period of time.

Effect of Mill and Thin Overlays on Roughness for Pavements in Cold Climate Locations

Mill and thin asphalt overlays are a popular preservation treatment for asphalt and composite pavements owing to their ability to address a variety of distresses. Their effectiveness depends on different factors such as traffic, climate, and condition of the pavement at the time of treatment, with typical treatment lives ranging from 5 to 12 years. In cold regions, performance in relation to roughness is of particular interest, as factors like frost action and thermal cracking tend to accelerate roughness progression. The objective of this study was to evaluate the effect of thin asphalt overlays on pavement roughness in cold climate locations using a set of field performance data from the Pavement Preservation Group Study, a broader research study conducted by the National Center for Asphalt Technology and the Minnesota Department of Transportation’s Road Research Facility. The findings indicated that treatment application resulted in both short- and long-term benefits. Following construction, a performance jump was obtained, which was greater for pavement sections with higher International Roughness Index (IRI) IRIpre values. This can be interpreted as rougher sections benefiting more in the short term than smoother sections, where the IRI is already low. Conversely, pavements with lower roughness at the time of treatment obtained greater life-extending benefits. This is interpreted as smoother pavements obtaining a greater benefit over time, and reinforces the concept of preserving pavements while in good condition to maximize pavement life. The magnitude of the benefits was also dependent on the type of milling machine used.

Assessment of Asphalt Mixture Disk-Shaped Compact Tension Test Indexes for Reflective Cracking Performance

Abstract Disk-shaped compact tension (DCT) testing is a commonly used low-temperature fracture test to determine the cracking resistance of asphalt mixtures. The current testing specification only considers the fracture energy (Gf) from load-crack mouth opening displacement test data. However, Gf does not directly take into consideration the behavior of the post peak region of the curve, which may indicate the mixture’s ability to resist crack propagation and provide insight into fracture processes (e.g., crack growth velocity). It is possible to have two DCT specimens with similar Gf values but dramatically different load-displacement responses. The main focus of this paper is to make a comparative evaluation of various performance indexes developed for DCT fracture testing with respect to field reflective cracking performance of 10 full-scale asphalt concrete overlay test sections. This study evaluates Gf in addition to three other indexes: fracture strain tolerance (FST), rate-dependent cracking index (RDCI) and a proposed DCTIndex from Minnesota Department of Transportation that considers the post peak load-displacement behavior. An equivalent performance index approach is adopted to make comparisons of test sections with varying overlay structures in terms of thickness and material properties. Results from this study showed there was relatively good agreement between all equivalent laboratory performance indexes in identifying the best and worst performing overlay sections, according to normalized field performance indexes after approximately three years of service. In general, the equivalent FST and RDCI laboratory indexes rank test sections similarly, while equivalent Gf and DCTIndex have comparable ranking.

Basic Installations for Reinforced Concrete Arch Pipe

Beginning in 2018, the precast concrete pipe producers of the Minnesota Concrete Pipe Association (CPA) worked with the Minnesota Department of Transportation (DOT) to update the standards for reinforced concrete arch pipe. The Minnesota DOT standard plates include steel reinforcement areas for both circumferential steel and transverse steel (stirrups) where required. The latest Minnesota DOT standards include pipe classes in accordance with AASHTO M206 (or ASTM C506) as well as some larger sizes and higher strength classes that are not included in the AASHTO standard. The reinforcement designs for these larger sizes were performed in accordance with the 8th Edition of the AASHTO LRFD Bridge Design Specifications and were formulated to encompass the worst of either the loads from the field installation, or the testing loads in three-edge bearing. The three-edge bearing test requirements tended to govern the required steel area for transverse reinforcement. However, the field conditions governed the extent to which the transverse reinforcement needs to extend out from the invert of the pipe.

Relating Ndesign to Field Compaction: A Case Study in Minnesota

High field density helps in increasing the durability of asphalt pavements. In a current research effort, the University of Minnesota and the Minnesota Department of Transportation (MnDOT) have been working on designing asphalt mixtures with higher field densities. One critical issue is the determination of the Ndesign values for these mixtures. The physical meaning of Ndesign is discussed first. Instead of the traditional approach, in which Ndesign represents a measure of rutting resistance, Ndesign is interpreted as an indication of the compactability of mixtures. The field density data from some recent Minnesota pavement projects are analyzed. A clear negative correlation between Ndesign and field density level is identified, which confirms the significant effect of Ndesign on the compactability and consequently on the field density of mixtures. To achieve consistency between the laboratory and field compaction, it is proposed that Ndesign should be determined to reflect the real field compaction effort. A parameter called the equivalent number of gyrations to field compaction effort (Nequ) is proposed to quantify the field compaction effort, and the Nequ values for some recent Minnesota pavement projects are calculated. The results indicate that the field compaction effort for the current Minnesota projects evaluated corresponds to about 30 gyrations of gyratory compaction. The computed Nequ is then used as the Ndesign for a Superpave 5 mixture placed in a paving project, for which field density data and laboratory performance test results are obtained. The data analysis shows that both the field density and pavement performance of the Superpave 5 mixture are significantly improved compared with the traditional mixtures. The results indicate that Nequ provides a reasonable estimation of field compaction effort, and that Nequ can be used as the Ndesign for achieving higher field densities.

Field Density Investigation of Asphalt Mixtures in Minnesota

In a current research effort, University of Minnesota and Minnesota Department of Transportation have been working on designing asphalt mixtures that can be constructed at 5% air voids, similar to the Superpave 5 mix design. High field density of asphalt mixtures is desired because it increases the durability and extends the service life of asphalt pavements. The paper investigates the current situation of field densities in Minnesota, to better understand how much improvement is needed from the current field density level to the desired level, and to identify possible changes to the current mix design to improve field compactability. Field densities and material properties of 15 recently constructed projects in Minnesota are investigated. First, a statistical analysis is performed to study the probability distribution of field densities. Then, a two-way analysis of variance is conducted to check if the nominal maximum aggregate size and traffic levels have any significant effect on field densities. A correlation analysis is then conducted to identify significant correlations between the compactability of mixtures and their material properties. The results show that the field density data approximately obey normal distribution, with an average field density of 93.4% of theoretical maximum specific gravity; there are significant differences in field density between mixtures with different traffic levels; compactability of mixtures is significantly correlated with fine aggregate angularity and fine aggregate gradation of the mixtures.

Real-Time Traffic Flow Forecasting via a Novel Method Combining Periodic-Trend Decomposition

Accurate and timely traffic flow forecasting is a critical task of the intelligent transportation system (ITS). The predicted results offer the necessary information to support the decisions of administrators and travelers. To investigate trend and periodic characteristics of traffic flow and develop a more accurate prediction, a novel method combining periodic-trend decomposition (PTD) is proposed in this paper. This hybrid method is based on the principle of “decomposition first and forecasting last”. The well-designed PTD approach can decompose the original traffic flow into three components, including trend, periodicity, and remainder. The periodicity is a strict period function and predicted by cycling, while the trend and remainder are predicted by modelling. To demonstrate the universal applicability of the hybrid method, four prevalent models are separately combined with PTD to establish hybrid models. Traffic volume data are collected from the Minnesota Department of Transportation (Mn/DOT) and used to conduct experiments. Empirical results show that the mean absolute error (MAE), mean absolute percentage error (MAPE), and mean square error (MSE) of hybrid models are averagely reduced by 17%, 17%, and 29% more than individual models, respectively. In addition, the hybrid method is robust for a multi-step prediction. These findings indicate that the proposed method combining PTD is promising for traffic flow forecasting.

Reliability Analysis of Minnesota’s Unbonded Concrete Overlay Performance

Minnesota Department of Transportation (MnDOT) has studied pavement performance associated with various interventions in the road network. In this study, unbonded overlay, a major concrete pavement intervention known for its long service life, was examined. Curve fitting was performed, including a comparison of the current decay curves with previous patterns toward a default performance curve, stepwise regression to identify performance variables associated with and predictive of remaining service life (RSL), and reliability (Weibull) analysis to examine the reliability and other performance characteristics of unbonded overlay in the Minnesota network. Reliability analysis resulted in a RSL (scale parameter) of 36 years, which was reasonably consistent with the 35.5 year RSL derived from the MnDOT Highway Pavement Management Analysis (HPMA). It also provided evidence that the unbonded overlay displays an end-of-life failure pattern as well as a 7-year threshold time to failure (location parameter). MnDOT’s sigmoidal decay model predicted the same expected service life (35.5 years) as did the Weibull analysis process (35.8 years). Stepwise linear regression showed a positive correlation between the time from the most recent rehabilitation (TTR_MR) and RSL. The other explanatory variables including RQI_Spike and time from original construction to intervention (TTR) were found to be non-significant in the prediction of RSL.

Potential Use of NASA’s Soil Moisture Active Passive Freeze–Thaw Tool to Assist in Minnesota Seasonal Load Restriction Timing

The U.S. encompasses over 4 million roadway miles, with about half of them located in seasonal frost areas. Roads are especially susceptible to damage when the subsurface is saturated with water (i.e., spring thaw). Spring load restrictions (SLR) are important for maintaining the integrity of roads. Routine determinations of road freeze–thaw (FT) state are limited to vertically embedded temperature data probes (TDP). Although TDPs are valuable to departments of transportation for determining SLRs, TDPs only represent individual points within the road network and are costly to install and maintain. Recent updates to spaceborne technology and algorithms made physically based retrievals of FT conditions possible at improved accuracy and temporal resolution (every 3 days) and have potential use for assisting with SLRs. Although instruments such as NASA’s Soil Moisture Active Passive (SMAP) platform cannot resolve individual roads, past comparisons have shown good correspondence with TDPs. The main objective of this study is to provide information on the potential value of NASA’s SMAP FT tool to supplement other methods for making seasonal load restriction decisions. Results are compared against data and protocols by the Minnesota Department of Transportation (MnDOT) at 10 sites in Minnesota, over four winter seasons (2016–2019). Results show that even when a simple criterion is used—the date of the third consecutive thaw from the SMAP afternoon retrieval—those dates typically fell within a week of MnDOT road postings (61% of the time). In addition, SMAP FT typically matches TDP FT states throughout the year (79% of the time).

Reducing wind-induced vibrations of road sign structures through aerodynamic modifications: A computational pilot study for a practical example

In this article, we illustrate the potential of aerodynamic modifications of road signs to reduce wind-induced vibrations. Using a real-world sign structure operated by the Minnesota Department of Transportation, we focus on two modification variants, one based on the simple removal of secondary panels and one based on the addition of drag reducing rear extensions to the main panel. Our main analysis tool is a computational fluid dynamics framework based on the finite element method, which is validated against experiments with a scaled sign model that were conducted in the towing tank and the wind tunnel of the St. Anthony Falls Laboratory. We demonstrate computationally that aerodynamic modifications constitute an effective way of reducing the vibration amplitude in the example structure for head wind at the average operating wind speed. The present study can be seen as a first step towards establishing the use of aerodynamic devices for road sign structures.

Nondestructive Full Coverage Asphalt Stripping Detection Using 3D Radar

Since subsurface stripping extent is important for maintaining the road network, Minnesota Department of Transportation (MnDOT) uses forensic measures such as coring. The destructive nature and lack of coverage provided by this accepted method makes finding nondestructive methods for detecting stripping of in situ asphalt pavements an important need for MnDOT and many other agencies. Stripping between hot mix asphalt layers can cause premature failure of pavements. Knowledge of the lateral location, depth and extent of stripping can affect the timing and type of pavement preservation, maintenance, or rehabilitation. This paper reports on use of a DX1821 antenna to collect data at a frequency step of 20 MHz ranging from 50 MHz to 3050 MHz with a dwell time of 7.52 μs using a GeoScope Mk IV control unit on a full-scale asphalt pavement constructed at the National Center for Asphalt Technology (NCAT) test track with built-in stripping. Signals from the known stripped and non-stripped locations were used to evaluate statistical and energy based approaches. It is shown that a maximum energy ratio method, an approach that has been successfully applied to acoustic emission applications in the past, can improve signal clarity for stripping detection using ground penetrating radar (GPR). These results are confirmed using highway speed measurements at the Minnesota Road Research Facility with core validation.

An investigation on perpetual asphalt pavements in Minnesota

Asphalt Pavement Alliance (APA) created the Perpetual Pavement Award program in 2001. This program requires that the roadway has at least 35 years of service at the time of award and had experienced no structural failures. In addition, the program limits candidate roadways to those that have not received more than 100 mm of new asphalt nor have been resurfaced at a frequency exceeding 13 years. Minnesota Department of Transportation (MnDOT) currently owns the record for the most award winners and has received an award every year from 2002 through 2017. This study reviews all the award-winning roadways in Minnesota to determine common material, design factors and considerations which may have contributed to the roadways extended life, often exceeding 50 years, despite the harsh Minnesota climate. For these projects, all the available information and any pertinent supporting information were reviewed. Findings from this review showed that a combination of many different factors including large-scale subgrade correction, utilizing non-frost susceptible base and subbase materials, bituminous treatment of the granular layers, utilization of prime coat, and staged construction may have contributed to the outstanding performance of these award-winning roadways. In addition, a more in-depth analysis was performed on the four project locations within the Minnesota Metro District. To further investigate and characterize these sites, coring and hand auger borings were performed in cracked and un-cracked areas along with Dynamic Cone Penetrometer (DCP) test which the results indicated that the in-situ materials were strong in all the projects. The cores were then used to measure thicknesses, densities, asphalt contents, extracted gradations, and also to perform resilient modulus testing at low and intermediate temperatures. Resilient Modulus testing showed that the asphalt mixtures from different projects perform differently at intermediate temperatures, but this difference is much less pronounced at low temperatures. This could be one reason for the similar long-life behavior of these pavements, as they have been subjected to the low temperature condition in a substantial portion of their service life in the state of Minnesota.