Materials and Construction

Selecting Structural Synthetic Fibers for Use in Thin Concrete Overlays

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Lab testing has demonstrated that structural synthetic fibers in thin concrete overlays keep cracks tight and help transfer loads across pavement slabs. A recently released research study, co-funded by the Minnesota Department of Transportation and the Minnesota Local Road Research Board, provides recommendations for selecting fiber types and dosages in pavement design.

What Was the Need?

Concrete pavements usually measure 8 to 15 inches thick. For many of these pavements, designers recommend placing dowel bars at the joints during the pour to assist the transfer of wheel load from heavy commercial and agricultural vehicles across concrete slab joints.

MnDOT has found that dowel bars are not effective in a thin concrete overlay, a 4- to 6-inch layer of concrete over an older pavement. These slabs fracture prematurely around the dowels. Adding structural fibers to concrete offers a potential solution. Used primarily to keep cracks from widening, these fibers consist of pieces of thin synthetic material—polymers, carbon fabric, even steel—mixed into the concrete batch.

Many states do not have formal standards for fiber types or characteristics, dosage rates or other specifications for their use. MnDOT currently uses the approved products list created by Illinois Department of Transportation.

Minnesota road engineers agree that fibers work well in concrete, but how well was unknown. Research was needed to determine the optimal physical characteristics of fibers, the amount that should be mixed in to the concrete, and products currently not on the approved products list that may be effective.

What Was Our Goal?

MnDOT wanted to investigate fiber performance in thin concrete overlays, specifically to help identify fibers that are most appropriate in these overlays and recommend acceptable dosage rates for mixing and placing the thin concrete. MnDOT also needed a test procedure and design recommendations or specifications for using fibers.

“This research looked at fiber performance in terms of load transfer to see if fibers can provide an alternative to dowels in thinner concrete pavements,” Maria Masten, Concrete Engineer, MnDOT Office of Materials and Road Research.

What Did We Do?

Research began with a literature search and a survey of state transportation agencies identified by the American Concrete Pavement Association as leading users of fiber-
reinforced concrete overlays.

Laboratory testing first focused on post-crack performance, relying on ASTM C1609, the nationally recognized testing standard. Investigators tested 10 fibers of various lengths, geometries and stiffness in three dosage levels in concrete, evaluating the impact of fiber properties on post-crack performance.

 

cracked concrete beams with fiber reinforcement
Post-crack performance testing of fiber-reinforced concrete beams shows that after cracking, fibers work to keep cracks from widening.

Testing then turned to joint performance. Researchers used four fibers from the previous lab examination and added a fifth fiber, a synthetic fiber used in MnROAD test cells in 2017, to test load transfer across cracks between sections of fiber-reinforced concrete. Together, the two lab phases tested 11 fibers in 43 concrete mixtures in over 400 samples 10 beams and 10 cylinders each of 30 fiber-reinforced concrete samples for post-crack performance, one plain concrete mix and 12 additional fiber-reinforced mixtures in joint performance testing. Analysis considered post-crack performance, crack width, fiber geometry, dosage, load transfer efficiency and residual strength.

In the final step, researchers analyzed the collected data and developed recommendations for MnDOT.

What Did We Learn?

Results confirmed that fibers help keep cracks and joints tight and improve load transfer across cracks and joints in thin concrete overlays. This research indicated synthetic fibers provide equal or better performance than steel fibers, which are expensive, heavy and difficult to mix. Dosages less than 0.25 percent fiber volume fraction of concrete mixture did not improve post-crack flexural or load transfer efficiency across the joint.

In lab mixing, longer and stiffer fibers tended to ball and mat with greater frequency than shorter fibers, though researchers developed a mixing method that reduces balling and matting. Fiber dosage, stiffness and shape significantly influenced strength. Embossed, twisted and crimped fibers outperformed straight, flat synthetic fibers; longer fibers with larger diameters outperformed shorter, smaller diameter fibers that inhibit workability.

“We studied many varieties of fibers before writing a specification for using fibers in concrete overlays. This is one step forward in understanding fiber’s contribution in concrete pavements or overlays,”  Manik Barman, Assistant Professor, University of Minnesota Duluth Department of Civil Engineering.

Fiber shape had moderate influence on load transfer and displacement in joint performance testing. Dosage levels and crack width strongly affected joint performance. Overall, it was found that fibers can increase the load transfer by 30 percent and can reduce the slab displacement by 50 percent.

Researchers suggest designers use trial batches of mixtures, submitting samples to ASTM C1609 testing and selecting fibers based on joint performance results from this study. Graphs and tables from this study correlate fiber properties with post-crack flexural strength and joint performance to help guide selection and dosage.

What’s Next?

Researchers recommend fibers with high lateral stiffness and irregular cross sections in lengths between 1.5 to 2.5 inches and at dosage levels no greater than 1 percent fiber volume fraction to avoid balling, matting and unworkability of concrete mixtures. MnDOT will issue fiber requirements so manufacturers can then submit products and test results for evaluation by MnDOT in developing a new approved products list for fibers in concrete pavements.

Future research could focus on validating design recommendations in the field; establishing fresh fiber-reinforced concrete mixture parameters by running slump, air content and other tests of fresh mixes; and analyzing life-cycle costs and benefits.

This post pertains to the MNDOT and LRRB-produced Report 2018-29, “Comparison of
Performances of Structural Fibers and Development of a Specification for Using Them in
Thin Concrete Overlays,” published August 2018.

Maintenance Operations, Traffic and Safety

New Training Tools Offer Clear Guidance for Liquid Roadway Treatments

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The Minnesota-led Clear Roads winter maintenance research program has developed a set of training tools—two videos and two quick reference guides—to promote liquid roadway treatments and provide practical guidance for agencies implementing a liquid anti-icing/deicing program.

Many agencies use liquids such as salt brine as anti-icing treatments to prevent ice from forming on roadways. But the application of salt brine as a deicing treatment during or after a winter storm has been slower to catch on. When used in the right conditions, liquid deicing treatments are as effective as granular sodium chloride while using less salt, but liquid-only routes are used by only a minority of winter maintenance agencies. To get the word out about the benefits of using salt brine and other liquids as both anti-icing and deicing treatments, as well as provide practical information about liquid application procedures, Clear Roads initiated this project.

Need for Research

While there is a wide range of information available about the use of brine and other liquids for anti-icing and deicing, there was a need to offer clear, comprehensive guidance in a single resource and to provide training tools for implementation.

A 2010 Clear Roads project helped lay the groundwork for this effort by identifying the parameters for effective implementation of liquid-only plow routes. That project produced a quick reference guide that outlined the conditions when liquid deicing treatments are most effective and provided application rates and implementation recommendations. A follow-up study was needed to update this guidance and to develop tools to facilitate the implementation of liquid-only plow routes.

Maintenance truck applying liquid de-icer on highway

Objectives and Methodology

This project’s goal was to produce a set of training tools—two videos and two quick reference guides—explaining the benefits of liquid-only plow routes, outlining procedures for implementation, and addressing misinformation and misconceptions. The project had two objectives:

• Inform agency decision-makers and the general public about the benefits of liquid roadway treatments while dispelling common myths.
• Provide practical guidance for maintenance managers and plow operators, and for agencies looking to start a liquid-only program.

Researchers began by conducting a literature review of research and practices related to liquid-only plow routes. They then sent an online survey to agencies in 27 states to determine which agencies used liquid-only roadway treatments. The survey yielded 92 responses from state DOTs and county and municipal highway departments. Follow-up interviews with 14 survey respondents gathered information about types of roads where liquid-only routes are used, application rates and material usage, brine making and storage, cycle times and loading times, and public perception and environmental concerns.

Results

Of the 92 survey respondents, 30 indicated that their agency had a liquid-only route. In general, these respondents reported that liquids are more effective than solid deicers in
the right circumstances. Based on the information gathered in the survey, interviews
and literature review, researchers created two videos:

  • A shorter video for agency decision-makers and the general public that discusses the benefits of liquid-only treatments while addressing common misconceptions (particularly misinformation about corrosion and salts in the environment).
  • A full-length video for practitioners that includes information from the short video as well as tips for starting a liquid-only program, discussion of equipment types, and recommended usage parameters and application rates.

To complement the videos, researchers created two 2-page quick reference guides—a Start-Up Reference Guide to help agencies gain buy-in for a liquid-only program and a Technical Reference Guide with more detailed usage parameters, application rates and general tips.

“To effectively get the word out about liquid-only road treatments, there was a need to put the right message in front of the right audience in a compelling way and to dispel myths and misconceptions. These guides and videos do just that,” said Project Co-Champion, Scott Lucas, Ohio Department of Transportation.

The videos and quick reference guides communicate key information about liquid-only routes, including:

  • Appropriate use: Liquids are especially effective during light snowfalls and at milder temperatures. Agencies also use liquids to loosen packed snow for plowing; during high winds when granular salt may blow off the roadway; and as anti-icing treatments before freezing rain.
  • Benefits: Liquid deicing treatments use less salt, which leads to cost savings and reduced environmental impact. Liquids begin to work immediately, and they stay on the roadway (no bounce or scatter).
  • Misconceptions: Liquid applications of salt brine do not cause more corrosion damage to vehicles than granular salt. Granular salt must dissolve into brine on the roadway in order to melt snow and ice, so either approach exposes vehicles to salt brine. Corrosion inhibitors can help; some studies show they are more effective with liquids than solids.

Benefits and Further Research

The videos give transportation agencies modern communication tools to help target specific audiences: The shorter video is more appropriate for social media distribution and sharing, while the longer video is more useful for agency staff training and cross-agency communication. Both the quick reference guides and the videos will help agencies garner support for liquid-only programs and provide practical guidance for
implementing them.

This post pertains to Liquid Roadway Treatments: Informational and Training Videos, published November 2018. The full report, videos and final presentation can be accessed at 16-06: Training Video for the Implementation of Liquid-Only Plow Routes.

Maintenance Operations, Traffic and Safety

New system underway to determine road recovery time during snow events

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Researchers at the University of Minnesota Duluth (UMD) have developed a system that can use highway loop detector traffic flow and weather data to determine when road conditions have recovered from a snow event. Currently, the Minnesota Department of Transportation (MnDOT) relies on snowplow drivers to estimate when roads are back to normal. The new system aims to relieve drivers of that burden and increase overall fleet efficiency.

In two previous MnDOT-funded projects, UMD researchers looked at using data from loop detectors along with weather station data to develop an automated system that determines normal condition regain time (NCRT) based on changes in traffic flow patterns. The goal is to improve the accuracy of road condition estimates and give dispatchers a big-picture view of traffic flow.

2018-01-p1-image
A line drawing showing a rectangular closed wire loop approximately 6 feet long and 4 feet wide on a road lane beneath the pavement surface. The loop is attached by a length of wire to data collection equipment on the roadside.

“This is a shift to different criteria,” says John Bieniek, Metro District maintenance operations engineer at MnDOT. “The bare lane regain time is now based on judgments from plow operators on the highways and phone calls to dispatchers. We could use the new system to quickly direct trucks to harder-hit areas within and between stations as they are needed.”

The latest project, led by UMD civil engineering professor Eil Kwon, transformed a previously developed computer model into a user-friendly, integrated computer system. The system includes a data management module, a module for target detector station identification and speed recovery function, an NCRT estimation module, and a map- based user interface that allows dispatchers to generate the estimated NCRT for a specified area. Dispatchers and supervisors can also use the interface to assess traffic flow variations, assign plows, and generate reports for past snow events.

The team tested the new integrated system on data gathered from I-494 and I-694 during two snow events in 2015 and 2016. Results show the system was able to successfully generate NCRTs that met or exceeded the accuracy of estimates by maintenance personnel.

“The system developed in this research can provide consistent and objective estimates of the NCRT by utilizing the traffic flow data that are currently available from the existing detection systems in the metro area,” Kwon says.

Another goal of the project was determining a data-derived definition of normal traffic flow for snow-cleared roadways. As part of this effort, researchers found that traffic resumed free-flow conditions after roads were cleared, but always at a slightly slower speed than on normal, dry roads. Researchers then developed a process to determine the “wet-normal” free-flow speed at each detector station based on the traffic flow pattern during a given snow event.

So far, the system has only been used with data from past snow events and has not generated results in real time. Going forward, MnDOT plans to fund additional work that will incorporate big data tools to allow the system to operate in real time—as storms happen—to improve roadway snow operations.

This article originally appeared in CTSs Catalyst Newsletter, May 2018 and pertains to Technical Summary 2018-01TS. The full report, “Development of a Road Condition Recovery Time Estimation System for Winter Snow Events” 2018-01, published January 2018, can be accessed at mndot.gov/research/reports/2018/201801.pdf.

Bridges and Structures, Maintenance Operations, Policy and Planning

New measure allows comparison between bridge and pavement conditions

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Transportation planners lack a method to directly compare bridge and road conditions. In a new MnDOT-funded study, University of Minnesota researchers have proposed a Percent Remaining Service Interval (PRSI) measure that can uniformly assess the condition of bridges and pavements, enabling planners to make the most efficient use of preservation and improvement funding.

A nighttime view of workers and heavy equipment at a road construction site
Planners would like a condition measure similar to RSL that could be used to compare and prioritize needs for highway and bridge construction.

“Both the MnDOT Bridge Office and the Materials and Road Research Office have very good management systems in place,” says Mihai Marasteanu, a professor in the Department of Civil, Environmental, and Geo- Engineering (CEGE) and the study’s principal investigator. “There is a good potential to develop a new common metric that both offices could use.”

What Did We Do?

To begin developing this new measure, researchers conducted a literature review of current methods used in asset management and life-cycle cost analysis. The review of bridge research focused on performance measures and life expectancy assessment methods, while the study of pavement literature concentrated on performance measures as well as on the use of road service life measures.

Next, the research team, which included civil engineering bridge professor Arturo Schultz, surveyed both bridge management staff and pavement management staff from state transportation agencies. Team members then analyzed the asset management practices of MnDOT’s Office of Bridges and Structures and Office of Materials and Road Research to identify methods for assessing service lives and rehabilitation needs and to highlight the similarities and differences in approaches.

Based on the findings from the survey and analysis, researchers suggested the new method of PRSI that would serve both pavement and bridge needs and offered guidelines for the next steps in developing and implementing a unified PRSI procedure.

“Ultimately, funds for guardrail repairs are drawn from the same purse that pays to fill a pothole or repair a deck joint,” Marasteanu says. “With PRSI, planners could target average values across systems to optimize life-cycle costs and pursue an even distribution of PRSI values to make planning consistent from year to year.”

What’s Next?

In the next phase of the project, researchers will work with the pavement office to identify relevant data for calculating PRSI for pavements. “In addition, we plan to identify the time and costs required to reach the evenly distributed configuration of PRSIs necessary for planning consistency, assess how preservation activities impact funding efficiency, and calculate recommended metrics for asset sustainability,” Marasteanu says.

This article originally appeared in the Center for Transportation Studies’ Catalyst Newsletter, October 2018. The full report, published July 2018, can be accessed at “Remaining Service Life Asset Measure, Phase I,” .

 

 

Policy and Planning, Research

Implementation of Research Strategic Plan Underway

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Coverpage of Research Services Strategic PlanTo help guide the state’s future transportation research investments, the Minnesota Department of Transportation recently completed a five-year comprehensive strategic plan that looks at streamlining the research governance structure at MnDOT and developing a clearinghouse of information about the agency’s research portfolio to improve decision-making.

MnDOT Research Services, which administers the bulk of the state’s transportation research projects, recently completed a visioning session with agency stakeholders as the first step in implementing the recommendations of the strategic plan, which include:

  • Establishing agency-wide research strategic priorities
  • Tracking all of MnDOT’s research expenditures, including those performed outside Research Services
  • Tracking research investment levels to measure return on investment
  • Reporting on the outcomes of research projects beyond their life cycle
  • Identifying the value and impact of research at a topic and program level

In addition to the approximately 175 state, local and multi-state transportation research projects administered and tracked by MnDOT Research Services, several MnDOT specialty offices also invest in their own research to support or guide their work.

Bridges and Structures, Maintenance Operations, Traffic and Safety

Improved Specifications for Tightening Anchor Bolts on Signs, Luminaires and Traffic Signals

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In recent years, MnDOT inspection crews have reported loose anchor bolts on many support structures for overhead signs, high-mast light towers, tall traffic signals, and other signs and luminaires. On newly installed structures, many nuts on anchor bolts may loosen in as little as three weeks; on older structures, they may loosen less than two years after retightening.

Federal standards mandate inspections at least once every five years, a requirement that already stretched MnDOT’s resources for managing light poles, traffic signals and 2,000-plus overhead signs. With an estimated 20 percent of loose anchor bolts in MnDOT’s highway system at any given time, crews would have to inspect structures every year to ensure public safety.

This issue is not unique to Minnesota. In a national survey, some states estimate as many as 60 percent of their anchor bolts may be loose. Minnesota, like other states, tightens anchor bolts according to American Association of State Highway and Transportation
Officials (AASHTO) standards. But the standards and procedures for tightening and retightening bolts were insufficient. To develop appropriate specifications, MnDOT needed to know why bolts loosen. The agency also needed improved standards and procedures to ensure that anchor bolts are tightened effectively

What Was Our Goal?

MnDOT decided to undertake a research project to determine why anchor bolts and nuts on sign and luminaire support structures loosen after installation or retightening, and to develop new standards and procedures that ensure proper and lasting tightening of these bolts.

Researchers from Iowa State University examined specifications and procedures for tightening anchor bolts on support structures in Minnesota. They also developed new specifications and instructions to help crews tighten bolts properly and ensure lasting safety of signs and lights in Minnesota’s highway system.

How Did We Do IT?

Researchers conducted a literature search on anchor bolt loosening. Then they surveyed MnDOT maintenance staff on bolt lubrication and tightening practices, and visited sites in Minnesota and Iowa to observe installation and retightening practices.

In the laboratory, investigators studied the relationship of torque, rotation and tension of various bolt diameters and material grades. They found that bolt stiffness, grip length (the distance between the nuts at each end of an anchor bolt in a two-nut bolt system), snug-tight standards, lubrication and verification after 48 hours played a role in effective tightening practices.

To determine the impact of environmental and structural strain on bolt tightness, researchers monitored sign structures in the field and in the lab. They attached strain gages to the bolts and post of an overhead sign near Minneapolis-St. Paul and installed a wind monitor, camera and data logging unit nearby to collect strain and environmental data for four months. In the lab, they instrumented a post and baseplate mounted in concrete to compare current and proposed tightening specifications and practices.

Base of an overhead sign that shows large bolts
Researchers attached strain gages to the bolts and the mast of a new overhead sign. Installers followed new procedures and specifications to tighten the bolts so that investigators could evaluate the effectiveness of the new standards.

Investigators developed specifications for each bolt size and grade, anchor baseplate dimension and pole size used by MnDOT based on lab and field results. They also created finite element models to analyze future anchor bolt configurations.

What Did We Learn?

Over- and under-tightening contribute to premature loosening of nuts on anchor bolts. While contractors may lack the experience and training to properly use turn-of-nut guidance, AASHTO recommendations poorly serve the bolt sizes and grades used by MnDOT.

AASHTO’s snug-tight guidance neglects certain characteristics of nuts and bolts, and its turn-of-nut direction is provided for only two bolt sizes and two bolt grades. In some cases, these standards may cause the heads of small bolts to break off and may lead to undertightening of large bolts. MnDOT can measure torque in the field but cannot determine tension, making AASHTO’s equation for verifying torque and tension impractical.

“We have revised our specs to follow the recommended procedures for anchor bolt tightening. The new tables of verification torque values will be fine for both two-nut and one-nut anchor bolt systems,” says Jihshya Lin, Bridge Evaluation and Fabrication Methods Engineer, MnDOT Bridge Office.

Researchers revised the specifications to require bolt lubrication, establish torque levels for snug-tight and specify turn-of-nut rotation after snug-tight for a range of MnDOT materials:

• Eight bolt sizes, ranging from ¾-inch diameter to 2.5-inch diameter.
• Five bolt grades.
• Nine baseplate thicknesses.
• 12 single- and double-mast pole types.

The new specifications provide torque levels in tables to verify the tightness for each bolt, plate and pole type, eliminating the need to run equations. To assist crews that are installing or retightening anchor bolts, researchers developed guidelines that include a compliance form with a checklist to direct crews through each step of the tightening process and ensure proper tension.

What’s Next?

The new specifications and procedures should improve public safety and reduce the traffic control, manpower and equipment expenditures required to respond to prematurely loosened nuts. Continued monitoring of bolts installed and retightened under these specifications over time would help evaluate the new procedures.

A new implementation project is underway that will demonstrate these findings in the field.  Researchers will also produce educational videos for training and demonstration to MnDOT personnel and contractors.  Video topics will include:

  • Basic Concepts of Bolt Tightening
  • New Specified Procedures
  • Signals and Lighting
  • Overhead Signs

Additionally, researchers will provide one or more training sessions with training materials.  Materials and videos will be posted on a website developed by the researchers.

This post pertains to Report 2018-27, “Re-Tightening the Large Anchor Bolts of Support Structures for Signs and Luminaires,” published August 2018.

 

 

Maintenance Operations, Traffic and Safety

New Project: Potassium Acetate As a Salt Alternative

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This winter, MnDOT snowplow operators will test and document their experience using potassium acetate (KAc) during severely cold weather as a possible alternative to the commonly used deicing material sodium chloride.

MnDOT maintenance staff have used potassium acetate in the Duluth area as a deicing alternative in several locations (Bong Bridge, Blatnik Bridge, I-35 tunnels, and I-35 at Thompson Hill) with anecdotal success. Advantages of KAc include reducing chlorides runoff into water, a lower effective deicing temperature (approximately -20F) than salt or brine, and less corrosion to vehicles and public infrastructure.

KAc will be used on four plows at select locations in the MnDOT District 1 Duluth sub-area. Crews will document the effectiveness of KAc in removing snow and ice pack at temperatures of minus 15 to 20 degrees Fahrenheit and reducing the time it takes plows to achieve and maintain bare pavement during  severely cold temperatures.

In addition to evaluating potassium acetate as an alternative de-icing chemical, researchers will develop application guidelines and material handling requirements.

Project Scope

Researchers from CTC & Associates will review the 2018 Transportation Research Syntheses, Field Usage of Alternative Deicers for Snow and Ice Control, and identify any additional information that is publicly available regarding national and international use of KAc as a de-icing and anti-icing agent. The focus will be on successful uses of the material (material concentration and application rates, weather conditions, timing, etc.) by highway agencies or transferable practices by airports.

MnDOT District 1 personnel will conduct field tests of KAc on selected plow routes during the winter of 2018-2019 and document key data about the amount of material used, locations, equipment, storm characteristics, pavement conditions and other elements. Researchers will assist MnDOT with the design of the field study, the creation of a data gathering tools to be used by plow drivers, monitoring of data quality during the study, analysis of data gathered during the winter season, and writing a report presenting the study conclusions.

Watch for new developments on this project.  Other Minnesota transportation research can be found at MnDOT.gov/research.

Bicycling, Traffic and Safety

New Project: Guidance for Separated/Buffered Bike Lanes With Delineators

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New research has started that will provide needed guidance for the design of separated bike lanes, which are rapidly growing in popularity. The two-year Minnesota Local Research Board-funded study, which is being performed by the University of Minnesota, will identify the safety, cost and accessibility attributes of different lane designs and produce a technical memorandum with design guidance for transportation planners.

Background

Separated bicycle lanes (SBLs) are a bicycle facility that employs both a paint and vertical element as a buffer between vehicle traffic and bicycle traffic.

In 2016, the City of Minneapolis increased the total mileage of separated bike lanes in the city from 5.4 to 9.4 miles with plans to increase that to 30 miles by 2020. While many other cities around the U.S. are in the process of installing separated bike lanes as part of their non-motorized transportation networks, research about them has not kept pace.

The Federal Highway Administration’s Separated Bike Lane Planning and Design Guide  identified several gaps in existing research, including the effects of SBLs on vehicle traffic, the preferred speed and volume thresholds to recommend SBLs, and the differences in safety between one- and two-way SBLs.

Despite safety being a major concern with SBLs, the guide states that “there are no existing studies that have satisfied best practices for analyzing the safety of SBLs.” The guide goes on to caution that even in cases where research on the safety or operational effects of SBLs does exist, “much of the highest quality research comes from outside the U.S.” The FHWA guide also lists cost as a gap in knowledge about SBLs, saying “few benchmarks exist for separated bike lane costs, which vary extensively due to the wide variety of treatments and materials used.”

This research project will provide a thorough synthesis of current research and guidelines and a comprehensive analysis of the impacts of different midblock bike lane designs to help Minnesota-based agencies make data-driven design and planning decisions. Design variables include delineator type and spacing, land and buffer widths, and one- vs two-way bike lanes. Impacts that would be evaluated include installation, maintenance, and user costs as well as safety and facility usage.

Two lane road with bicycle lanes on both sides of the road with cars on the road and cyclists in the bike lanes.

Objective

When considering installing SBLs, many aspects including impacts on both bicycle traffic and other types of traffic (pedestrians, passenger cars, delivery trucks, etc.) must all be considered. However, much of this information is unavailable. By providing a comprehensive repository for the relevant data on the numerous SBL design options, this project will allow engineers and policy-makers to make more informed decisions regarding bicycle infrastructure installations and improvements. Access to this sort of hard data will aid in the process of performing will aid in the prioritization of options for bike facilities thereby reducing the waste of funds on unneeded or unaffordable projects.

Scope

The tasks of the research project include:

  • Conduct a thorough literature review to identify any gaps in the current research.  Examples of this might include the effects of SBLs on all road users, frequency of bicycle and vehicle violations for various SBL designs, recommended speed and volume thresholds for installation, the costs associated with SBLs, or the differences in safety between one- and two-way SBLs.
  • Conduct research such as observational field studies, crash record analysis, synthesis of the results of other studies, road user surveys, review of previous project budgets, bicycle facility repair record analysis, municipal records of complaints and violations, or some combination thereof.
  • Develop a list of options for the design of multi-modal facilities and the respective impacts of those options based on findings from the field studies. This could include maintenance costs, user costs and safety impacts.

By providing transportation planners, engineers, and other practitioners new information on the impacts likely to be associated with different designs, the practitioners will be in a better position to both choose among designs and mitigate potential adverse effects of those designs. The list of design options and associated impacts will be summarized in a technical memorandum with a more thorough presentation in the project final report.

Watch for new developments on this project.  Other Minnesota transportation research can be found at MnDOT.gov/research.

Materials and Construction, Policy and Planning

New Project: Development of Pavement Condition Forecasting for Web-based Asset Management for County Governments

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Many counties have incomplete roadway inventories, but lack asset management programs, which are often cost-prohibitive and require advanced technical training and staff to maintain. The Upper Great Plains Transportation Institute at North Dakota State University (NDSU), has developed a low-cost asset inventory program called the Geographic Roadway Inventory Tool (GRIT). The program, which is currently available to North Dakota counties, will be offered to all Minnesota counties following further development and testing by the Minnesota Local Road Research Board.

Background

NDSU created the asset inventory program as the first step for asset management to allow local roadway managers to document and understand their existing infrastructure using the latest mobile technology and Geographic Information System technology.

The goal of the research study is to expand the program to include roadway forecasting based on the American Association of State and Highway Transportation Officials(AASHTO) 93 model with inventory, pavement condition and traffic forecasting data.

Existing input data from GRIT, such as pavement thickness, roadway structural information and construction planning information, will be spatially combined with current Pathway pavement condition and traffic data from MnDOT to automatically forecast the future condition and age of roadways using the AASHTO 93 model. This forecasting model will then allow roadway managers to use this information with comprehensive GIS web maps to prioritize roadways in construction schedule or multi-year plans.

Geographic Roadway Inventory Tool

Objective

The additional information contained in the pavement forecast system will allow county roadway managers to prioritize projects that can benefit from lower cost pavement preservation activities and understand how long roadways can last before a high cost reconstruction must take place. The online GIS output maps will also enable the public to see what projects will be conducted on a year-to-year basis.

Project scope

The research team will work with Beltrami, Pope, Faribault, Pennington, and Becker counties and the city of Moorhead in Minnesota to research, develop, test and implement an additional forecasting function of the existing asset management program. This will be done using the AASHTO 93 empirical model to calculate a future pavement serviceability rating (PSR) based on the existing pavement structure and age, forecasted traffic and the latest pavement condition. While existing pavement structure and age information will come from data entered into the GRIT program by counties, processes and procedures will be researched and developed to automatically access pavement condition and traffic data from MnDOT and geospatially combine it with inventory data.

With pavement forecast information, county roadway managers will be able to better understand which roadways will deteriorate first and which will benefit from more effective, low-cost maintenance programs rather than full-depth reconstructions. The model will not forecast suggested future projects or project costs, but rather just output the future condition of the roadways on a yearly basis. The AASHTO model can be applied for both flexible and rigid pavement sections.

Watch for new developments on this project.  Other Minnesota research can be found at MnDOT.gov/research.

Maintenance Operations

New Project: Guide for Converting Severely Distressed Paved Roads to Unpaved Roads

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Local agencies are increasingly looking at converting low-trafficked paved roads to gravel at the end of their life span to make budgets stretch. However, agencies have few resources to guide them in this process.

The Minnesota Local Road Research Board recently approved funding for a guidebook on effective practices for converting severely distressed paved roads to unpaved roads. The document will help engineers select roads for conversion, safely conduct conversions and communicate the rationale to the public. No such published document currently exists.

Montana State University researchers has been hired to develop the guidebook based on needs the research team previously identified in the National Cooperative Highway Research Program’s Synthesis 485, “Converting Paved Roads to Unpaved. The guidebook, anticipated to be published in late 2019, will include flowcharts that guide practitioners through decision-making processes. A companion webinar is also planned.

The guidebook will be divided into chapters, which will cover:

  • Methods to determine if a road is a candidate for conversion and determine the existing road materials and condition.
  • Methods to convert a road from paved to unpaved.
  • Methods to assess the life-cycles cost of construction and maintenance of the unpaved road.
  • Tools to effectively inform and communicate with the public
  • Safety implications of converting a severely distressed paved road to an unpaved road.

Background
While low- volume roads are typically identified as having an annual average daily traffic (AADT) of less than 400, roads that are appropriate candidates for conversion will typically have an AADT of less than 150.

These roads are often used by agricultural and extraction industries or to access homes and recreational areas. The type of road users, traffic patterns and vehicle types are all factors that need to be considered in the decision to unpave a road. Other factors include road condition, safety, agency maintenance and maintenance capabilities, as well as a life-cycle cost comparison of maintenance options (continued maintenance of the deteriorating road, rehabilitation of the paved road or conversion to an unpaved surface).

According to the research team, very limited information is available about converted roads, and what information is available often comes in the form of newspaper articles and anecdotal accounts of road conversions.

The document will serve as a formal and peer-reviewed information source. The use of the guide and acceptance of the practice of converting from paved to unpaved surfaces (unpaving) where warranted will provide a case for the acceptance of road conversions as another low-volume road management strategy.

Watch for new developments on this project.  Other Minnesota research can be found at lrrb.org and MnDOT.gov/research

 

Minnesota transportation research blog