Environment, Materials and Construction

Culvert Design Manual Provides Guidance for Accommodating Fish Passage

Leave a comment

Several years of research have culminated in the publication of a culvert design manual that promotes the safe passage of fish and other aquatic organisms, as well as stream connectivity, throughout the state.

“Engineers designing culverts for Minnesota’s diverse ecological regions will benefit from this document, which offers sound guidance from many practicing experts about how to design culverts that allow aquatic organism passage and preserve stream integrity,” said Petra DeWall, former Bridge Waterway Engineer, Minnesota Department of Transportation (MnDOT).

What Was the Need?

Minnesota’s 140,000 miles of roads and approximately 92,000 miles of streams and rivers meet at tens of thousands of places. Culverts are a cost-effective solution to allow traffic to cross over smaller waterways. Historically, culverts have been designed with the safe passage of vehicles in mind. Recently, a state and national appeal for the safe passage of fish and other aquatic organisms, as well as for waterway integrity and connectivity, has influenced culvert design.

A pair of Topeka shiner fish
The Topeka shiner, once found throughout the state, is one species of federally endangered fish in Minnesota that must traverse culverts to survive.

MnDOT has supported many research projects examining fish and aquatic organism passage (AOP) through culverts, and nationally, a number of published resources exist on appropriate design. Because of the variety of ecological regions in the state, the range of culvert geometries and many other factors, no single solution can accommodate AOP through culverts statewide. A comprehensive culvert design guide was needed to inform designers about solutions that can effectively facilitate the movement of fish and other aquatic organisms in Minnesota while maintaining healthy streams.

What Was Our Goal?

The objective of this project was to produce a comprehensive and accessible culvert design guide that could be used by Minnesota practitioners to design culverts for AOP and stream connectivity. The guide would provide the following benefits:

• More efficient culvert design and permitting process for AOP.
• A central definition of typical designs, which would improve contractors’ familiarity with designs and lower construction costs.
• Avoidance of designs that could be detrimental to the natural environment.
• Avoidance of designs likely to lead to roadway damage and need for repairs.
• Fishery improvement through increased stream connectivity.

What Did We Do?

To determine the scope of the guide, researchers worked with experts from the Minnesota Department of Natural Resources (DNR), the U.S. Forest Service and others with knowledge of civil engineering, AOP and stream geomorphology.

They then sought information for the guide from a wide range of authoritative resources. A literature search examined current and past research by the research team and others; guidance documents from federal agencies; guidance from other states; permit requirements from the DNR and other agencies; and databases of fish populations, stream attributes and culvert data. The literature search also sought to reveal gaps in knowledge where further research specific to Minnesota was needed.

Additionally, researchers surveyed a cross section of highway design engineers and managers from MnDOT, county and city agencies, resource agencies and engineering consultants to identify current design practices for AOP and stream connectivity, and the degree of their effectiveness.

What Did We Learn?

The project resulted in the Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts, a thorough guide for culvert designers, hydraulic engineers and others involved in culvert design and construction in Minnesota. Topics addressed in the guide include:

• The need for culvert designs that include AOP and stream connectivity, as well as the current regulatory context.
• An overview of culvert design, categories of design methods that incorporate AOP and waterway connectivity, and a list of best practices.
• Site characteristics, analysis and tools related to energy dissipation, hydraulic analysis for AOP and sediment transport.
• A design method selection chart, information on certain designs and references for further information.
• Further guidance about design issues such as multiple barrel and floodplain culverts, grade control, retrofits and other cost considerations.

What’s Next?

The culvert design guide will be made available to users online. Future considerations for this project include an associated webinar and efforts to coordinate information presented in the guide with expectations and permitting requirements of MnDOT departments charged with culvert creation and implementation. Additional research is underway to assess culverts and fish passage with respect to storm vulnerability and future hydrologic scenarios.

This post pertains to the MnDOT and LRRB-produced Report 2019-02, “Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts,” published January 2019.

Materials and Construction

Selecting Structural Synthetic Fibers for Use in Thin Concrete Overlays

Leave a comment

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

Report recommends ways to reduce snowplow operator fatigue

Leave a comment

Snowplow operators face harsh driving conditions and must also deal with fatigue and drowsiness. A recent multi-state research project identifies factors that cause driver fatigue in snowplow operators and recommends cost-effective solutions to help reduce it.

Clear Roads – a winter maintenance research initiative – surveyed 33 member states to gather data on snowplow operators’ experiences with fatigue. More than 2,000 snowplow operators from 23 Clear Roads states responded.

Nearly all the respondents (94 percent) reported feeling fatigue at some point while operating a snowplow during winter weather events. The majority of vehicle operators (59 percent) reported their shifts of 8 to 16 hours included both daytime and nighttime segments. Smaller proportions reported that they worked primarily during the day (22 percent) or primarily at night (18 percent).

Survey results also indicated that more experienced operators were more prone to fatigue, and those who worked shifts lasting longer than 16 hours reported significantly higher levels of fatigue.

Based on the results and analysis, researchers ranked the in-cab and external equipment that caused fatigue. The top four equipment-related sources of fatigue were bright interior lighting, standard windshield wipers, misplaced or insufficient auxiliary lighting, and old or uncomfortable seats.

Among the non-equipment-related sources of fatigue, the most commonly reported factor was silence (lack of music or talking), followed by length of shift, lack of sleep, and insufficient breaks.

Snowplow on a snowy highway

Using the same ratings, researchers developed a list of recommended actions that can be implemented by agencies to decrease driver fatigue. The recommendations were based on a comparison of each solution’s costs (equipment costs and potential risk of adversely affecting fatigue) and benefits (effectiveness in reducing operator fatigue).

Among the researchers’ equipment-related recommendations, the most cost-effective called for adding:

  • A CD player or satellite radio to deliver music or speech, preventing short-term fatigue.
  • Dimmable interior lighting to reduce reflections on the windshield and windows, providing better visibility.
  • Dimmable warning lights to reduce back-reflected light from the warning lights, lowering visual distraction.
  • Snow deflectors to reduce the amount of snow blown on the windshield, providing better visibility.
  • Heated windshields to reduce snow and ice buildup on the windshield, providing better visibility.

Non-equipment solutions included encouraging adequate breaks, limiting shifts to 12 consecutive hours when feasible, developing a fatigue management policy, encouraging a healthy lifestyle, and designating dedicated rest locations for operators.

According to the report, both the equipment-related and non-equipment-related solutions provide easy and quick corrective actions that agencies can implement immediately to increase the health and safety of snowplow operators.

Learn More:

Clear Roads is a multi-state winter maintenance research initiative. This article originally appeared in the September issue of the LTAP Technology Exchange.

Education, Environment, Maintenance Operations, Traffic and Safety

Pilot Program Promotes Benefits of Snow Fences

Leave a comment

A new program piloted in western Minnesota to increase snow fence use among private landowners has been so successful that MnDOT is looking at rolling it out statewide.

The University of Minnesota’s Center for Integrated Natural Resource and Agricultural Management worked with MnDOT District 8 staff for more than a year to develop and test a snow fence outreach program that could be used by MnDOT district offices.

“After our training, we saw a 300 percent increase in the number of standing corn rows, and that was on the initiative of a few people in the maintenance group. We’d like to spread the training to other districts,” said Dean Current, Director, University of Minnesota Center for Integrated Natural Resource and Agricultural Management.

Background

Living snow fences are natural vegetative barriers that trap blowing snow, piling it up before it reaches a road, waterway, farmstead or community. It could include leaving a few rows of corn or hay bales along the road side, or even temporary fencing.

MnDOT has about 3,700 sites that are suitable for snow fences. It estimates that if 40 percent of problematic sites had snow fences, the state could save $1.3 million per year in snow management costs. Despite the cost, safety and environmental benefits, private landowners have shown limited interest in the program. An effective outreach program was needed along with strategies for identifying MnDOT personnel who could promote the practice and recruit landowners to the program.

“If we can implement our blowing snow control program more consistently, we can help reduce crash severities, improve operational efficiencies due to snow and ice control measures, and improve the mobility of the public,” said Dan Gullickson, Snow Control Program Administrative Coordinator, MnDOT Office of Environmental Stewardship.

How Did We Do It?

In January 2016, investigators surveyed MnDOT District 8 employees to gauge their understanding of snow fences as well as their approach to working with landowners to implement blowing snow control measures. The investigators studied survey responses to assess awareness of and interest in promoting the use of snow fences and grading to reshape road environments for snow and erosion control. They also examined snow fence programs from around the country, identifying types of snow fences used and characteristics of programs that successfully recruit landowner participation.

A permanent snow fence along a rural highway.
A permanent snow fence along a rural highway.

Results from these efforts were used to design an outreach program that was presented to District 8 staff. In January 2017, investigators surveyed the staff to evaluate the training and redesign the program accordingly. Finally, investigators evaluated market values of various snow fence designs.

What Was the Impact?

Initial survey results identified two relevant types of district personnel: maintenance and program delivery staff. Maintenance staff involved in plowing and road care interact more with landowners than do program delivery staff, who design or redesign roadways and may be involved in acquiring land for snow fences. Though tailored for each group, all training described the MnDOT blowing snow control program and its implementation, the role of snow fence coordinators, operational benefits and awareness of how promotion of the program fits within the scope of an employee’s duties.

Keys to the success of snow fence programs around the country include strong relationships and direct communication with local landowners, funding, landowner interest in conservation and public safety, and observable benefits.

A follow-up survey showed marked improvement in staff knowledge of the program and willingness to promote it. Landowner participation grew from four sites to 15 in the year after training, due mostly to maintenance staff participation. Survey respondents suggested potential program improvements such as more program champions; outreach in spring and summer at community and farmer gatherings as well as at local and state fairs; and a clearer understanding of how program promotion fits within job responsibilities.

The market study demonstrated that nonliving snow fences, though the most expensive option for MnDOT, offer the largest benefit per acre. Landowners seem to prefer living snow fences and standing corn rows. MnDOT may wish to raise the annual payment for all living snow fences.

What’s Next?

Considerations for MnDOT include implementing the training program in other districts, further defining central and district staff roles in snow fence promotion and implementation, incentivizing snow fence champions, developing more outreach material and maintaining relationships with landowners.

A new project currently under way aims to further expand these efforts.

This post pertains to Report 2017-42, “Expanding the Adoption on Private Lands: Blowing-and-Drifting Snow Control Treatments and the Cost Effectiveness of Permanent versus Non-Permanent Treatment Options.” Related research can be found by searching “snow fences” under “Projects” at MnDOT.gov/research.

 

Maintenance Operations

Researchers Dig Deeper into AVL/GPS Use in Winter Maintenance Operations

Leave a comment

The Minnesota-led Clear Roads winter maintenance program has profiled six state agencies’ experience with automatic vehicle location (AVL) and GPS in winter maintenance fleets to share best practices with other cold weather states. Strong support by these agencies drives robust use of the technologies for location tracking, asset monitoring and planning for future storms.

AVL and GPS have been widely embraced in winter maintenance operations by transportation agencies around the country. But tracking vehicle locations for operational and safety reasons only scratches the surface of these systems’ potential uses. Many agencies also use AVL/GPS to collect extensive data for planning, operations, safety and inventory tracking to improve efficiency and response strategies.

Need for Research

AVL and GPS have been used in winter maintenance operations for several years. While most agencies use AVL/GPS for tracking vehicle location, the technologies offer operational, safety, inventory and planning applications, as outlined in a 2016 Clear Roads synthesis report. How agencies actually employ these automatic data collection technologies has remained less well-known.

Objectives and Methodology

The goal of this project was to explore agencies’ experiences and best practices in planning, implementing and using AVL/GPS technologies for winter maintenance activities. The investigation began with a survey of state and selected metropolitan transportation agencies about their level of commitment to AVL/GPS implementation and the data the agencies collect, use and share.

Investigators worked closely with Clear Roads to identify levels of usage of the technologies. Then they selected six agencies that represented various commitment levels, interviewed staff from each agency and gathered relevant documents about agency use of AVL/GPS. Using the information obtained during the interviews, researchers prepared case studies of each agency and recommendations for other agencies to further implement and utilize the technologies.

AVL/GPS hardware installed below and behind the seat in a snowplow
AVL/GPS hardware in this Sawyer County, Wisconsin, snowplow mounts below and behind the seat—a secure position that does not inconvenience the operator.

Results

Twenty-seven of the 38 agencies that responded to the survey reported using AVL/GPS to automatically collect winter maintenance data, while 36 of the 38 agencies indicated plans to add or expand use of the technologies in the future. Based on feedback from these agencies, researchers developed three levels of AVL/GPS use and categorized agencies according to the appropriate level.

Tier 1 agencies employ AVL/GPS for basic location tracking or monitoring. Utah DOT has mounted AVL/GPS behind the dashboard of every snowplow and incident maintenance truck (vehicles that assist stranded motorists on Utah’s roads and highways) in its fleet. The system connects with plow position sensors, tracks idling time and traveling speed, and reports plow locations on a publicly accessible website.

Tier 2 users add basic data collection, equipment integration and system reporting features to Tier 1 usage, often in concert with other technologies. Washington State DOT’s Tier 2 usage integrates AVL/GPS with spreader controllers, plow position sensors, and air and pavement temperature sensors in 80 percent of its fleet to track material use, road weather and operational analysis data. Michigan DOT integrates AVL/GPS with spreaders, plows and dashcams in 94 percent of its fleet to track vehicle location, vehicle diagnostics and material use, and to use for operational analysis and information sharing with the public.

Tier 3 agencies conduct complex data collection, integration and reporting activities with AVL/GPS as part of a suite of instruments and applications that collect and transmit data to users, the agency and, in some cases, the public. Colorado DOT (100 percent of its fleet), Nebraska DOT (33 percent) and Wisconsin DOT (53 percent) link AVL/GPS to data collectors, plows, spreader controllers, pavement and air temperature controllers, and other equipment. Each agency tracks vehicle location, material use, treatment recommendations, vehicle diagnostics and data for operational analysis, among other uses. Colorado and Wisconsin DOTs share data with a maintenance decision support system; Colorado DOT also shares information with the public.

Keys to success with AVL/GPS include obtaining full organizational and financial support from agency management, piloting the system with vendors and operators to identify objectives for use, providing operators with training that emphasizes the technologies’ operational and safety benefits, involving agency mechanics in installation, and using the system data for real-time adjustments to maintenance and resource-allocation strategies.

“The recommendations were very constructive— everything from planning and decision-making to how to best collect data and use it for performance measurement,” said Project Champion, Patti Caswell, Oregon Department of Transportation.

Benefits and Further Research

The final report offers information that will be useful to prospective and current adopters, describing best practices in AVL/GPS planning and implementation, procurement, installation, training, data collection and utilization, and operations and maintenance.

Future research may evaluate methods for integrating technologies from various manufacturers into a cohesive, operational system. Turnkey options remain limited, and integrating sensor, camera, data collection and GPS presents a number of technical challenges. Related study may evaluate communication terminology for uniform data
sharing between agencies. Follow-up research could also identify the costs and benefits of AVL/GPS to quantify the value of these technologies to users.

Connected vehicle technologies, which use roadside units to communicate with other roadside units and wirelessly with vehicles, offer potential applications for real-time data collection and sharing among plow operators and other stakeholders. The relative value and ability to implement such systems may warrant research and comparison to
AVL/GPS.

This post pertains to Strong Agency Support, Multiple Applications Drive AVL/GPS Use , published October 2018. The full report and presentation can be accessed at  Project 16-01, Utilization of AVL/GPS Technology: Case Studies.

Maintenance Operations, Traffic and Safety

New Training Tools Offer Clear Guidance for Liquid Roadway Treatments

Leave a comment

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

1 Comment

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

Leave a comment

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

Leave a comment

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

Leave a comment

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.

 

 

Minnesota transportation research blog