Minnesota Department Of Transportation Research Articles

Mineralogical and microscopic evaluation of coarse taconite tailings from Minnesota taconite operations

Eighteen coarse taconite tailings samples were collected in 2000–2001 from five western Mesabi Range taconite (iron ore) operations located in northern Minnesota, i.e., EVTAC, Hibbing Taconite (Hibtac), USX Minntac, Ispat Inland (Minorca), and National Steel Pellet Company (NSPC), to test their physical, geological, chemical, and mineralogical properties [Zanko, L.M., Niles, H.B., Oreskovich, J.A., 2003. Properties and aggregate potential of coarse taconite tailings from five Minnesota taconite operations, Minnesota Department of Transportation, Local Road Research Board, St. Paul, MN, Report No. 2004-06 (also as Natural Resources Research Institute technical report, NRRI/TR-2003/44)]. The goal was to assemble a body of technical data that could be used to better assess the potential of using a crushed taconite mining byproduct like coarse tailings for more widespread construction aggregate purposes, primarily in roads and highways. An important part of the mineralogical assessment included X-ray diffraction (XRD) analyses and microscopic (polarized light microscopy, scanning electron microscopy, and transmission electron microscopy, i.e., PLM, SEM, and TEM, respectively) evaluation of the size and shape (morphological) characteristics of potentially respirable microscopic mineral particles and fragments. Quantitative mineralogy, based on XRD analyses, showed that the dominant mineral in all samples was quartz (55–60%), followed by much smaller amounts of iron oxides, carbonates, and silicates. Specialized microscopic analyses and testing performed by the RJ Lee Group, Monroeville, PA, on both pulverized (−200 mesh, or 0.075 mm) and as-is sample composites showed that no regulated asbestos minerals or amphibole minerals were detected in the western Mesabi Range samples. A small number (26) of non-asbestos and non-amphibole mineral cleavage fragments/mineral fibers were detected by SEM out of 1000 fields analyzed, but most were identified as minnesotaite and talc, silicate minerals common to the Biwabik Iron Formation. Amphibole minerals, absent in coarse tailings samples from the five western Mesabi Range taconite operations, were present in a single eastern Biwabik Iron Formation sample collected in 2003 for Lake County from the Cliffs Northshore operation in Silver Bay, MN. Importantly, the Superfund Method for the Determination of Releasable Asbestos in Soils and Bulk Materials [United States Environmental Protection Agency (USEPA), 1997. Superfund method for the determination of releasable asbestos in soils and bulk materials, EPA 540-R-97-028, U.S. Environmental Protection Agency, Washington], as modified by Berman and Kolk [Berman, D.W., Kolk, A.J., 2000. Modified elutriator method for the determination of asbestos in soils and bulk materials, Revision 1: Submitted to the U.S. Environmental Protection Agency, Region 8, May 23, 2000] failed to generate any protocol fibers, i.e., fibers longer than 5 μm and thinner than 0.5 μm, from either the western coarse tailings samples or the single eastern Biwabik Iron Formation sample. The combined findings suggest coarse tailings and other taconite mining byproducts should be treated with the same common sense safety and industrial hygiene approach practiced for all mineral-based materials that have the potential to generate respirable dust.

I-394 MnPASS High-Occupancy Toll Lanes

The I-394 MnPASS express lanes opened in May 2005 as Minnesota's first high-occupancy toll (HOT) lane project. The MnPASS lanes were opened by the Minnesota Department of Transportation (Mn/DOT) after a decade of study, outreach, and education that garnered political and community support for a demonstration project on value pricing in the state. Mn/DOT staff and their project partners faced new challenges when the Minnesota governor and legislature authorized the adaptation of the I-394 high-occupancy vehicle (HOV) lanes to HOT lanes, and Mn/DOT leadership sought to implement the project as soon as possible. Without any existing toll roads in Minnesota, the team faced the challenge of delivering a project that was both publicly and politically supportable and technically sound. This paper discusses the expectations and issues addressed by the project team and community task force during the planning process, and the actual results achieved during the first year of operation of the I-394 MnPASS lanes.

Rebirth of Chip Sealing in Minnesota

Chip sealing is a common form of pavement preservation used by most cities and counties and by the Minnesota Department of Transportation (MNDOT). MNDOT, working in partnership with the Minnesota Local Road Research Board, was able to rejuvenate the chip seal program in Minnesota. Efforts to improve the performance of chip sealing as a pavement preventive maintenance treatment are discussed. The discussion covers chip seal design, aggregate characteristics, and training efforts, and the successes of MNDOT, counties, and cities are documented.

Low-Volume Road Performance Related to Traffic Loadings at Minnesota Road Research Project

The Minnesota Department of Transportation built the Minnesota Road Research Project (MnROAD) between 1990 and 1993. The low-volume road consists of a two-lane roadway that originally contained hot-mix asphalt (HMA) and portland cement concrete (PCC) test sections. Each of these test sections is trafficked by a controlled five-axle tractor-semitrailer. The trucks have two different load configurations, resulting in the same equivalent single-axle loads (ESALs) over time. The first configuration consists of a legally loaded 80,000-lb (80-kip) truck that runs on the inside lane 4 days per week, and the second configuration consists of an overloaded 102,000-lb (102-kip) truck that runs on the outside lane 1 day per week. The field performances of the different MnROAD test sections over time resulting from the different loading applications are compared. As expected, the thermal cracking performance of HMA was not affected by the traffic loadings, because it is a distress caused by the environment. Similarly, the ride quality of both HMA and PCC pavements was not noticeably different between the two lanes. However, rutting and fatigue cracking of asphalt pavements and faulting of PCC pavements were more severe in the lane with the 80-kip truck than they were in the lane with the 102-kip truck. The higher number of repetitions at a lower load level in the 80-kip lane produced more distress than did the lower number of repetitions at a higher load level in the 102-kip lane. The data presented show that the concept of ESALs may not be appropriate for mechanistic–empirical design procedures.

Methodology for Selection and Development of TransXML Schemas

NCHRP Project 20-64, TransXML, solicited the development of standard, public domain extensible markup language (XML) schemas for the exchange of transportation data as well as the creation of a framework for the development, validation, dissemination, and extension of current and future schemas. The methodology used for the selection and development of the initial set of TransXML schemas ensured their consistency, cohesiveness, and usefulness. Data flow diagrams of the design and construction process had previously been developed for the Minnesota Department of Transportation. They articulate steps in the design process as well as the flow of data between these steps. The diagrams were analyzed to discover candidate data flows that if supported by standardized XML schemas, could improve the design and construction process. The content and structure of the data identified were then modeled with unified modeling language (UML) class diagrams–roughly one UML package per data flow. Consensus of interested parties was achieved through the project website, including specific agreement on data elements and their associations. For each element, relevant attributes were decided, along with their cardinality and data type. For associations, relationship types, cardinalities, and roles were established. Diagrams for each area were compared to achieve consistency and to identify common elements, the latter being extracted into separate UML packages. XML schemas were then developed, based on the UML packages. The geography markup language (GML) was used as the framework for the schemas, building on predefined GML elements and following GML rules for developing application schemas. Sample applications were developed to demonstrate how the schemas support the data flows.

Girder Differential Deflection and Distortion-Induced Fatigue in Skewed Steel Bridges

The prevalence of fatigue cracking in steel bridge girders due to out-of-plane web distortion motivates development of procedures to evaluate the effects of distortional fatigue. In a previous study sponsored by the Minnesota Department of Transportation (Mn/DOT) the frequency and magnitude of distortional stresses on a typical skewed, steel bridge with staggered, bent-plate diaphragms were assessed. The results revealed a diaphragm deformation mechanism that causes distortional fatigue in the girder web gap, leading to simple, accurate estimates of fatigue stress if bridge properties and differential vertical deflection between girders are known. In the present study, linear finite element models are used to represent composite steel bridges and identify bridge parameters that influence relative deflection of adjacent girders. Parameters found to have a significant effect on differential deflection include girder spacing, angle of skew, span length, and deck thickness. These results are incorporated in a simple procedure that is intended for use in management schemes for skewed, steel-girder bridges, with staggered, bent-plate diaphragms, susceptible to web gap distortional fatigue.

High-Occupancy Toll Lane Innovations: I-394 MnPASS

The Minnesota Department of Transportation (Mn/DOT) has implemented the state’s first optional toll lane project, called the I-394 MnPASS, in the Minneapolis-St. Paul metropolitan area. This project, which opened in May 2005, converts the high-occupancy vehicle (HOV) lanes on I-394 into high-occupancy toll (HOT) lanes, allowing solo drivers the opportunity to pay an electronic fee to bypass congestion. The lanes remain open to HOV use at no charge, including transit riders, car pools, and motorcyclists. I-394 MnPASS is the first tolling project that prices a facility directly adjacent to general-purpose lanes, separated only by a double-white-stripe buffer. Several HOT-lane innovations have been introduced to reduce project development time and costs, to improve operations, and to enhance enforcement.

Part 2: Pavements: Impact of Increasing Roadway Construction Standards on Life-Cycle Costs of Local Residential Streets

With increasing damage due to the combination of increasing traffic load applications, adverse climate, and increasing frequency of trench cutting and patching associated with utility work, residential streets are requiring more frequent, extensive, and costly maintenance and rehabilitation (M&R) to maintain adequate levels of serviceability during pavement design life. Increased cost of M&R and eventual reconstruction are an added burden on already limited city budgets. To rectify this situation, city managers and engineers are looking at enhancing current structural design standards for residential streets to increase their load-carrying capacity. With an increase in load-carrying capacity, it is hoped that frequency of M&R will be reduced and the design life of such pavements will be extended. However, adopting a higher design standard has significant cost implications. The question then becomes, Will the expected increase in initial cost be offset by the significant decrease in M&R costs and corresponding increase in pavement life that will delay eventual reconstruction? The Minnesota Department of Transportation (DOT), on behalf of the Local Road Research Board, initiated a study to evaluate the impact of enhancing residential street pavement design standards to accommodate greater axle loads on life-cycle costs. The primary focus was to compare the life-cycle costs of residential streets designed using Minnesota DOT's 5- to 7-ton and 9- to 10-ton design standards. The study concluded that life-cycle cost for the 5- to 7-ton and 9- to 10-ton design standards was not significantly different at the 95% significance level.

Impact of Increasing Roadway Construction Standards on Life-Cycle Costs of Local Residential Streets

With increasing damage due to the combination of increasing traffic load applications, adverse climate, and increasing frequency of trench cutting and patching associated with utility work, residential streets are requiring more frequent, extensive, and costly maintenance and rehabilitation (M&R) to maintain adequate levels of serviceability during pavement design life. Increased cost of M&R and eventual reconstruction are an added burden on already limited city budgets. To rectify this situation, city managers and engineers are looking at enhancing current structural design standards for residential streets to increase their load-carrying capacity. With an increase in load-carrying capacity, it is hoped that frequency of M&R will be reduced and the design life of such pavements will be extended. However, adopting a higher design standard has significant cost implications. The question then becomes, Will the expected increase in initial cost be offset by the significant decrease in M&R costs and corresponding increase in pavement life that will delay eventual reconstruction? The Minnesota Department of Transportation (DOT), on behalf of the Local Road Research Board, initiated a study to evaluate the impact of enhancing residential street pavement design standards to accommodate greater axle loads on life-cycle costs. The primary focus was to compare the life-cycle costs of residential streets designed using Minnesota DOT's 5- to 7-ton and 9- to 10-ton design standards. The study concluded that life-cycle cost for the 5- to 7-ton and 9- to 10-ton design standards was not significantly different at the 95% significance level.

Implementation of Spring Load Restrictions Using a Deflection-Calibrated Thaw Index

The City of Ottawa, Canada, uses a Dynaflect to monitor the change in pavement strength during the spring thaw at 11 test sites selected to represent its arterial road network. As the average deflection of the sites approaches a threshold value, load restrictions are publicized by signage and advertisements in local newspapers. The restrictions remain in effect until deflections decrease below the threshold value. Local police equipped with portable weigh scales enforce the restrictions. The goal is to allow for the shortest possible restriction period and still ensure that the road infrastructure is protected. However, the decision to implement load restrictions is traditionally made too late, because prediction of thaw progression between weekly deflection testing is difficult. The city's pavements are occasionally subjected to full-load hauling during the initial and most critical portion of the thaw period. To predict the onset and progression of the spring thaw better, the thaw index (TI) was used in addition to deflection testing. The TI (as calibrated separately by the Minnesota Department of Transportation and Manitoba Transportation and Government Services, Canada) was analyzed to determine whether it would predict the same implementation date as did deflection data. Results suggested that calibration factors provided by either agency are sufficiently accurate in the Ottawa environment but the Manitoba calibration is slightly more precise. Future investigation will involve use of surface curvature index, as well as direct temperature measurements from the city's Road Weather Information Systems.

Accelerated Loading Testing of Stainless Steel Hollow Tube Dowels

The use of dowels in rigid pavements to provide adequate load transfer is a common practice in current pavement design. Since the use of deicing salts in cold climates results in significant deterioration of dowels, the need to optimize performance and reduce pavement life-cycle cost prompts the need for alternatives to common round steel dowel bars. These alternative dowels must be able to withstand corrosion while providing adequate long-term load transfer performance across jointed slabs. Results are presented of the accelerated loading of two jointed test pavement specimens that incorporate one of two types of dowels: a stainless steel hollow tube dowel or an epoxy-coated solid steel dowel. The accelerated loading of these test specimens was accomplished courtesy of the second generation of the Minnesota Accelerated Loading Facility (MinneALF-2), a 10-year-old joint project between the Minnesota Department of Transportation and the University of Minnesota that allows for the realistic simulation of repeated truck loading of concrete pavement joints. For this study, each specimen was subjected to 10 million 9-kip loading cycles. Deflections between jointed slabs were measured with linear variable differential transformers, and the load transfer efficiency (LTE) for each case was calculated from these measurements. Although the LTE for the stainless steel hollow tube dowels was lower than that for the epoxy-coated dowels, the results suggest that the stainless steel tubes are capable of providing a sufficiently high long-term LTE for concrete pavement joints. At the same time, the stainless steel hollow tube dowels considerably reduce the risk of joint deterioration due to dowel corrosion.

Comprehensive Evaluation of New Integrated Freeway Ramp Control Strategy

A new integrated ramp control strategy, recently deployed by the Minnesota Department of Transportation in the Twin Cities metropolitan area, is evaluated. This strategy, stratified zone metering (SZM), takes into account real-time ramp demand and queue size information and aims to strike a balance between two competing objectives: improving freeway efficiency and preventing excessive ramp delays. In this study, the SZM strategy was compared to the earlier ZONE metering strategy as well as to the no-control alternative. Comprehensive metrics were generated through rigorous microsimulation to assess critical aspects of the strategy's performance. The evaluation results are consistent with qualitative field observations and confirm that SZM strategy improves freeway efficiency when compared with the no-control alternative, reduces freeway travel time and delay, improves freeway speed, smooths freeway flow, and reduces the number of stops. More important, excessive queue spillbacks and ramp delays were significantly reduced under SZM control when compared with the earlier ZONE metering strategy. However, the nonrestrictive metering rates under SZM may cause the freeway proper to be overloaded; this leads to compromised freeway performance as compared with the more restrictive ramp control. This is especially true for heavy traffic demands, when higher ramp volumes are allowed on the freeway.

Rural Expressway Intersection Surveillance for Intersection Decision Support System

More than 30% of all vehicle crashes in the United States occur at intersections; these crashes result in nearly 9,000 annual fatalities, or approximately 25% of all traffic fatalities. Moreover, these crashes lead to approximately 1.5 million injuries per year, accounting for approximately 50% of all traffic injuries. In rural Minnesota, approximately one-third of all crashes occur at intersections. AASHTO recognized the significance of rural intersection crashes in its 1998 Strategic Highway Safety Plan and identified the development and use of new technologies as a key initiative to address the problem of intersection crashes. A study of 3,700 rural Minnesota intersections showed that right-angle crashes account for 36% of all rural intersection crashes. Approximately 50% of crashes at intersections that have higher than expected crash rates are right-angle crashes. Further investigation also found that poor gap selection is the predominant causal factor in these crashes. To address the problem of poor gap selection, the University of Minnesota and the Minnesota Department of Transportation have a rural intersection decision support (IDS) system under development. When deployed, it will provide a driver with the additional information needed to make correct decisions concerning the available gap. The surveillance component of a rural IDS system is described. The surveillance system uses sensors, processors, and a communication system to determine the intersection “state,” including location, speed, acceleration, lane of travel, and vehicle classification (where necessary) of each vehicle in the surveillance zone. This state information will determine when to activate alerts and warnings.

Duration of Spring Thaw Recovery for Aggregate-Surfaced Roads

Low-volume roads in regions susceptible to freezing and thawing periods are often at risk of load-related damage during the spring thaw. Reduced support capacity during this period results from excess melt water that becomes trapped above underlying frozen layers. Many agencies place spring load restrictions (SLRs) during the thaw period to reduce damage to roadways. The period of SLRs set forth by the Minnesota Department of Transportation is effective for all flexible pavements; however, experience suggests that many aggregate-surfaced roads require additional time relative to flexible pavements to recover strength sufficient to carry unrestricted loads. An investigation was performed to improve local agencies’ abilities to evaluate the duration of SLR on aggregate-surfaced roadways. This was accomplished through seasonal measurements of in situ shear strengths, measured with the dynamic cone penetrometer, on various Minnesota county routes. In situ strength tests were conducted on selected county gravel roads over the course of 3 years. Strength levels recorded during the thaw-weakened period were compared with fully recovered periods that typically occur in late spring or summer. Results indicate that aggregate-surfaced roads generally require 1 to 3 additional weeks over that required by flexible pavements to reach recovered bearing capacity.

Accelerated Loading Testing of Stainless Steel Hollow Tube Dowels

The use of dowels in rigid pavements to provide adequate load transfer is a common practice in current pavement design. Since the use of deicing salts in cold climates results in significant deterioration of dowels, the need to optimize performance and reduce pavement life-cycle cost prompts the need for alternatives to common round steel dowel bars. These alternative dowels must be able to withstand corrosion while providing adequate long-term load transfer performance across jointed slabs. Results are presented of the accelerated loading of two jointed test pavement specimens that incorporate one of two types of dowels: a stainless steel hollow tube dowel or an epoxy-coated solid steel dowel. The accelerated loading of these test specimens was accomplished courtesy of the second generation of the Minnesota Accelerated Loading Facility (MinneALF-2), a 10-year-old joint project between the Minnesota Department of Transportation and the University of Minnesota that allows for the realistic simulation of re...

Comprehensive Evaluation of New Integrated Freeway Ramp Control Strategy

A new integrated ramp control strategy, recently deployed by the Minnesota Department of Transportation in the Twin Cities metropolitan area, is evaluated. This strategy, stratified zone metering (SZM), takes into account real-time ramp demand and queue size information and aims to strike a balance between two competing objectives: improving freeway efficiency and preventing excessive ramp delays. In this study, the SZM strategy was compared to the earlier ZONE metering strategy as well as to the no-control alternative. Comprehensive metrics were generated through rigorous microsimulation to assess critical aspects of the strategy's performance. The evaluation results are consistent with qualitative field observations and confirm that SZM strategy improves freeway efficiency when compared with the no-control alternative, reduces freeway travel time and delay, improves freeway speed, smooths freeway flow, and reduces the number of stops. More important, excessive queue spillbacks and ramp delays were signi...

Part 1: Low-Volume Roads: Climatic and Seasonal Effects on Pavements and Safety: Implementation of Spring Load Restrictions Using a Deflection-Calibrated Thaw Index

The City of Ottawa, Canada, uses a Dynaflect to monitor the change in pavement strength during the spring thaw at 11 test sites selected to represent its arterial road network. As the average deflection of the sites approaches a threshold value, load restrictions are publicized by signage and advertisements in local newspapers. The restrictions remain in effect until deflections decrease below the threshold value. Local police equipped with portable weigh scales enforce the restrictions. The goal is to allow for the shortest possible restriction period and still ensure that the road infrastructure is protected. However, the decision to implement load restrictions is traditionally made too late, because prediction of thaw progression between weekly deflection testing is difficult. The city's pavements are occasionally subjected to full-load hauling during the initial and most critical portion of the thaw period. To predict the onset and progression of the spring thaw better, the thaw index (TI) was used in addition to deflection testing. The TI (as calibrated separately by the Minnesota Department of Transportation and Manitoba Transportation and Government Services, Canada) was analyzed to determine whether it would predict the same implementation date as did deflection data. Results suggested that calibration factors provided by either agency are sufficiently accurate in the Ottawa environment but the Manitoba calibration is slightly more precise. Future investigation will involve use of surface curvature index, as well as direct temperature measurements from the city's Road Weather Information Systems.

Duration of Spring Thaw Recovery for Aggregate-Surfaced Roads

Low-volume roads in regions susceptible to freezing and thawing periods are often at risk of load-related damage during the spring thaw. Reduced support capacity during this period results from excess melt water that becomes trapped above underlying frozen layers. Many agencies place spring load restrictions (SLRs) during the thaw period to reduce damage to roadways. The period of SLRs set forth by the Minnesota Department of Transportation is effective for all flexible pavements; however, experience suggests that many aggregate-surfaced roads require additional time relative to flexible pavements to recover strength sufficient to carry unrestricted loads. An investigation was performed to improve local agencies’ abilities to evaluate the duration of SLR on aggregate-surfaced roadways. This was accomplished through seasonal measurements of in situ shear strengths, measured with the dynamic cone penetrometer, on various Minnesota county routes. In situ strength tests were conducted on selected county gravel roads over the course of 3 years. Strength levels recorded during the thaw-weakened period were compared with fully recovered periods that typically occur in late spring or summer. Results indicate that aggregate-surfaced roads generally require 1 to 3 additional weeks over that required by flexible pavements to reach recovered bearing capacity.

ISO 19133 Tracking and Navigation Standard

Most information maintained by a department of transportation (DOT) includes a physical location to specify where the data apply. Most often, this location is described with a linear referencing method (LRM). Because no single method is best for all applications, multiple methods are often used in each DOT. Engineers use stationing to locate construction items. Transportation data administrators may use mile point to locate roadway characteristics. Safety officers often use reference markers to locate crashes. TRB has stated that location can serve as an integrating concept for assimilating data from multiple sources. Until now, there were no standards for linear referencing methods; they vary between databases and between DOTs. Consequently, it has been difficult to integrate data from numerous sources by using locations with disparate formats. A new ISO standard should help remedy this situation. The ISO 19133 tracking and navigation standard includes a package for linear reference systems. It generalizes how linear locations are specified to enable translation between locations from different methods. It is based on the generalized model for linear reference, an abstraction of the NCHRP 20-27 conceptual model. According to the standard, locations are formalized as position expressions composed of a method of measurement (LRM), a linear element along which the measure is made, and the measurement itself. Locations can be on the linear element or offset laterally to either side. This paper explains the standard, how it was derived, and its implementation at the Minnesota DOT in its location data manager project.

ISO 19133 Tracking and Navigation Standard: 6.6 Linear Reference System Standard

Most information maintained by a department of transportation (DOT) includes a physical location to specify where the data apply. Most often, this location is described with a linear referencing method (LRM). Because no single method is best for all applications, multiple methods are often used in each DOT. Engineers use stationing to locate construction items. Transportation data administrators may use mile point to locate roadway characteristics. Safety officers often use reference markers to locate crashes. TRB has stated that location can serve as an integrating concept for assimilating data from multiple sources. Until now, there were no standards for linear referencing methods; they vary between databases and between DOTs. Consequently, it has been difficult to integrate data from numerous sources by using locations with disparate formats. A new ISO standard should help remedy this situation. The ISO 19133 tracking and navigation standard includes a package for linear reference systems. It generalizes how linear locations are specified to enable translation between locations from different methods. It is based on the generalized model for linear reference, an abstraction of the NCHRP 20-27 conceptual model. According to the standard, locations are formalized as position expressions composed of a method of measurement (LRM), a linear element along which the measure is made, and the measurement itself. Locations can be on the linear element or offset laterally to either side. This paper explains the standard, how it was derived, and its implementation at the Minnesota DOT in its location data manager project.