The Minnesota Local Road Research Board (LRRB) has funded a follow-up study to determine whether a monitoring system it field tested for new drivers, called the Teen Driver Support System (TDSS), affected teenagers’ long-term driver behavior.Continue reading New project: Effectiveness of Teenage Driver Support System
Extreme flooding is a threat to Minnesota’s transportation infrastructure and the safety and economic vitality of its communities. A spate of recent flooding events around the state has demonstrated this and heightened the level of concern. Furthermore, climate change — a factor not traditionally accounted for in the design of the state’s infrastructure — is projected to enhance precipitation and the threat of flooding in coming decades.
Given this, MnDOT is undertaking an effort to better predict the threat flooding poses to its bridges, large culverts and pipes, which may be increasingly called upon to convey higher, more frequent flood flows than they were designed for.
The state transportation research program recently launched a two-year extreme flood vulnerability analysis study, which will develop a methodology for characterizing the vulnerability of the state’s bridges, large culverts, and pipes to flooding.
The effort builds upon the previously completed Flash Flood Vulnerability and Adaptation Assessment Pilot Project (2014), which scored bridges, large culverts, and pipes in MnDOT Districts 1 and 6 for flood vulnerability, allowing detailed assessments of adaptation options for each of their facilities to be prioritized.
This new study, which will be conducted by WSP, aims to develop and test ways to enhance the vulnerability scoring techniques used in the previous study and ensure their applicability throughout the state. Researchers will not actually undertake the statewide assessment, but specify an approach that could be used for it. They will also explore how the outputs of the analysis can be incorporated into MnDOT’s asset management systems. The results of this work will be a clear path forward for MnDOT to use for prioritizing adaptation actions — a key step towards enhancing agency resilience and maintaining good fiscal stewardship.
The primary intent of this study is to develop a methodology for characterizing the flood vulnerability of bridges, large culverts, and pipes statewide. As part of the development process, the methodology will be tested on a limited, but diverse, set of assets across the state. Following a successful proof of concept, recommendations will be made on how the outputs (i.e., the vulnerability scores) can be incorporated into the state’s asset management systems.
By determining which facilities are most vulnerable to flooding through the techniques developed on this project, MnDOT can prioritize where adaptation measures will make the biggest impact, ultimately decreasing asset life-cycle and road user costs. Without the development of assessment techniques, adaptation measures run the risk of being implemented in a more reactive and/or ad-hoc fashion, with less regard to where the biggest “bang for the buck” can be realized.
This project will produce several technical memorandums, and is expected to be completed in early 2021.
Researchers have developed an affordable camera-free curve and lane departure warning system that relies on consumer-level GPS, rather than sophisticated, expensive digital maps.
The technology uses cumulative driving trajectory data from GPS points detected every 100 milliseconds to predict driving path trajectories and compare these to mapped curves and lanes. With further development, the system can be used as an inexpensive smartphone app or retail device to warn drivers of lane drift and approaching curves.
“The goal of the project is to reduce lane departure crashes. We viewed this as a seed project and demonstrated that the system can be successful,” said Victor Lund, Traffic Engineer, St. Louis County.
What Was Our Goal?
The Minnesota Local Road Research Board sought research to develop a camera-free curve and lane departure warning system that uses consumer-level GPS capability without reliance on sophisticated, expensive digital maps.
What Was the Need?
Lane departures and run-off-road crashes cause more fatalities and serious injuries in Minnesota than any other accident type.
Many current warning technologies rely on cameras that identify lane position based on pavement markings. In inclement weather, stripes and pavement markings can be difficult or impossible to identify; markings also wear off over time, reducing visibility even in clear conditions. Camera-based lane departure warning systems are also expensive and generally restricted to newer luxury vehicles, making them inaccessible to the general driving public.
Though in-vehicle technology for the public usually falls outside the research interests of the Minnesota Department of Transportation and the Minnesota Local Road Research Board, the agencies have been funding development of lane departure warning technologies to improve driver safety. GPS technologies offer an intriguing path to consumer-level lane departure warning systems.
High-level GPS can be accurate to the centimeter level, but access is restricted and use is expensive. These systems also rely on accurate, lane-level roadway mapping, an elusive data set with high access costs.
What Did We Do?
Researchers began with a literature search of the uses of standard GPS receivers in lane departure and navigation. The research team then developed an algorithm for travel direction that uses standard GPS in a straight road lane departure system to determine driving trajectories at accuracy levels suited to safe driving needs.
Investigators adapted a publicly available digital mapping platform to the same algorithm to identify navigational points along curves and develop the curve lane departure warning system. The team enhanced standard safe distance methods to consider driver reaction time in determining when approach warnings should be issued.
Researchers then brought the two developmental stages of the system together with a warning system that identifies vehicle speed, curvature characteristics and safe speed limits, and calculates distance for driver response times to issue an audible warning to drivers on lane drift and a text warning of when and how much to reduce speed as the vehicle approaches a curve.
For project testing and demonstration, investigators programmed the algorithm into a device with a built-in GPS receiver, connected it to a laptop for messaging and conducted driving tests on Rice Lake Road and on Interstate 35 near Duluth.
“From a technical point of view, this approach works. We developed a warning system with standard GPS that everyone has in a phone or vehicle. This is a lifesaving technology in a sense,” said Imran Hayee, Professor, University of Minnesota Duluth Department of Electrical Engineering.
What Did We Learn?
Finding no research on development of consumer-grade GPS for lane departure purposes, the research team adapted previous work on the relative accuracy of GPS readings from a MnDOT study on wearable GPS for work zone safety.
Researchers adapted a consumer-level GPS device to acquire data at 10-hertz frequency, which yields a GPS position point of 2.7 meters if a vehicle is driven at 60 mph.
The system calculates lane trajectory from cumulative readings and detects turns or drift. The curve warning system plots trajectories and compares these with open-source digital maps with road-level (rather than lane-level) accuracy to anticipate curves.
In road testing, the system issued audio warnings for every one of the approximately 200 lane changes, including curves. For curve warnings, the system scanned for curves at least half a mile ahead and calculated the vehicle’s speed and the distance to a curve to issue a timely text warning of the curve ahead and an advisory speed limit. Additional messages were issued when the vehicle was on the curve and when the curve had ended.
False alarms—warnings issued when the vehicle was not departing its lane—occurred in 10 percent of the tests, usually on sharp curves. Further adjustment of the algorithm and additional testing reduced false alarms significantly as the system accumulated data over multiple uses of the same roadway.
Investigators filed a patent for the technology and will continue to develop the system. Further refinement of reference road direction information will improve accuracy and safety; the research team has developed a new project to employ vehicle-to-vehicle dedicated short-range communication technology to expand road direction reference data. The system will then need to be adapted for a consumer-level device or a smartphone app for use in any vehicle.
This post pertains to the LRRB-produced Report 2018-34, “Development and Demonstration of a Cost-Effective In-Vehicle Lane Departure and Advanced Curve Speed Warning System,” published December 2018.
Researchers for the Minnesota Department of Transportation have developed a new travel-time reliability measurement system that automates the process of gathering and managing data from multiple sources, including traffic, weather and accident databases, to generate travel-time reliability measures and reports for the metropolitan freeway network.
What Was the Need?
Improving traffic efficiency has become a key goal of traffic operations managers. In heavy traffic periods, MnDOT’s Regional Transportation Management Center (RTMC) coordinates with Minnesota State Patrol and MnDOT Maintenance Services to detect and quickly respond to freeway incidents in the Twin Cities. The RTMC works with the Freeway Incident Response Safety Team to assist and remove stranded vehicles using MnDOT emergency road service trucks. RTMC also updates real-time road condition information on its 511 traveler information system.
MnDOT and RTMC measure delay and congestion on the metropolitan freeway system, reporting the data in annual reports like the 2017 Congestion Report. While useful, this data offers little predictive value on its own. MnDOT’s metropolitan freeway system features 4,000 loop detectors that transmit traffic data every 30 seconds; this data informs the congestion and delay reports.
Correlating this data with locations on the freeway system and various operating conditions, such as weather and traffic incidents, is time- consuming. But the data could be used to systematically evaluate traffic delays and develop strategies to mitigate congestion.
What Was Our Goal?
In this project, investigators sought to develop a system for automatically accessing weather, crash and traffic data to assess travel-time reliability—the variability in travel times for any given route. Travel-time reliability measures are becoming the key indicators for transportation system operations and management.
What Did We Implement?
Investigators developed a new travel-time reliability measurement system (TTRMS) that integrates different types of data (such as weather, traffic, incident, work zone and special event) acquired from multiple sources and automatically produces various types of travel-time reliability measures for selected corridors following user-specified operating conditions and time periods.
“Travel-time reliability is another way of looking at congestion and at strategies for making it more tolerable. It used to take several hours, even days, to process travel-time reliability data. The TTRMS processes it in minutes,” said Brian Kary, Director, MnDOT Regional Transportation Management Center.
How Did We Do It?
Investigators began by developing a detailed design of the TTRMS architecture—its modules, their functions and their interactions. The team then developed a work-zone data input module, where detailed lane configurations of a given work zone can be specified.
Developers designed a travel-time reliability calculation module as the core of the new system that can automatically access MnDOT’s traffic data archive, its incident database and the National Oceanic and Atmospheric Administration’s weather database. It can also accept a set of input data for work zones, such as lane-closure periods and locations. The reliability calculation module was then integrated with user interfaces and reporting modules. Finally the integrated system was tested with the real data gathered in 2012 and 2013 from Interstates 35E and 35W, U.S. Highway 169 and State Highway 100.
What Was the Impact?
The system generated accurate travel-time reliability measures for the test periods and given operating conditions. In particular, the output measures were automatically generated in both table and graphical formats, thus saving traffic engineers significant amount of time and effort.
The TTRMS includes map-based interfaces, which provide administrators and general users with substantial flexibility in defining corridors, specifying operating conditions and selecting types of measures depending on the purposes of applications.
To test the new system’s performance, the research team used the TTRMS to evaluate traffic strategies deployed for the February 2018 Super Bowl in Minneapolis. Two weeks before the event, reliability was low for the freeway system serving the football stadium. During the week of the Super Bowl, MnDOT and the Department of Public Safety aggressively managed traffic incidents to keep traffic moving, and reliability rose substantially despite the increase in tourist traffic. In the days immediately after the Super Bowl, operational strategies returned to normal levels, and reliability fell to previous levels. Results suggest that aggressive incident management during this exceptionally high-volume regional event enhanced traffic efficiency.
Further enhancements to the TTRMS should include automating inputs for work zone data, such as lane closures, changes in work zone locations and time periods. Future research could help traffic operations prioritize resources and develop short-term and long-term freeway improvements, including studies of bottlenecks and the freeway network’s vulnerability and resilience for natural events and large-scale incidents.
This post pertains to Report 2018-28, “Development of a Travel-Time Reliability Measurement System,” published September 2018.
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.
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.
- Identification and Recommendations for Correction of Equipment Factors Causing Fatigue in Snowplow Operations (Clear Roads, Nov. 2017) (LRRB/MnDOT 2017-31, July 2017)
- “Truckers disregarding sleep apnea treatment show greater crash risk,” CTS Catalyst (Apr. 2018)
Clear Roads is a multi-state winter maintenance research initiative. This article originally appeared in the September issue of the LTAP Technology Exchange.
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.
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.
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.
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.
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.
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.
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
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.
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.
“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.
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.
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.
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.
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.
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.