All posts by mndotresearch

Self-propelled auto-flagger keeps workers out of traffic

Working with a Minnesota manufacturer, researchers developed a moving automated flagger assistance device (AFAD) that signals traffic at work zones. The AFAD is operated remotely by a worker who can stand off the roadway out of traffic.

“Everybody who has used the mobile AFAD has liked it. We love our stationary AFAD unit. These units have really big stop-slow signs—they’re so visible,” said Jeremy Gjovik, Transportation Operations Supervisor, MnDOT District 3.

“The AFAD is a one-of-a-kind device. We were able to basically start from scratch and come up with a device that meets all the needs it was designed for,” said Edward Terhaar, Principal, Traffic Engineering, Wenck Associates, Inc.

Terhaar served as the principal investigator for the study.

What Was the Need?

According to data from the U.S. Bureau of Labor Statistics, 149 roadway workers were killed nationwide from 2003 to 2015 while flagging or directing traffic, and many near misses have been reported with the increase in distracted driving that has come with mobile device use.

In 2014, MnDOT trained over 60 state and district maintenance workers in the use of an automated flagger assistance device (AFAD). The AFAD has been embraced in Minnesota as a highly visible device that effectively directs traffic in stationary maintenance and construction projects while keeping flagging personnel off the road during operation.

The AFAD does not, however, suit moving operations (like pavement crack sealing) because the device requires towing. Engineers at MnDOT wanted to determine if the AFAD could be made into a mobile device that could be operated by a road crew near, but not on, the roadway.

What Was Our Goal?

MnDOT funded this research to develop a self-contained, self-propelled mobile AFAD for use on moving work zone roadway projects.

What Did We Do?

2017-09-p2-imageResearchers met with MnDOT engineers to identify the features that would be required in a moving AFAD. They determined that the device would have to be towable to a construction site with standard towing gear, operable remotely through wired or wireless controls, movable forward and in reverse, and able to use rechargeable onboard batteries.

The research team investigated existing self-propelled devices from the United States, Canada and Australia for moving wheeled objects, large and small, to see if they could be adapted to these needs. No suitable device was found.

After further consultation with the Technical Advisory Panel, researchers approached DJ Products of Little Falls, Minnesota, a company that designs and manufactures devices (including battery-operated devices) for moving trailers, dumpsters, shopping carts and aircraft.

Researchers met with DJ Products in February 2015, reviewed its products and agreed that DJ Products would develop a prototype vehicle on which the AFAD could be mounted. In August 2015, after evaluating and modifying designs, DJ Products hosted a demonstration of the prototype vehicle without the AFAD attached. The research team requested modifications, and in April 2016, the company presented a new self-propelled device with the AFAD attached.

What Did We Learn?

Initial field testing was delayed due to seasonal weather issues and device operating problems that required the replacement of components. In February 2017, a MnDOT operator tested the mobile AFAD on a crack-sealing project on State Highway 71 south of Sauk Centre.

The moving AFAD can be operated with a wired or wireless controller, as well as with controls on a handlebar mounted on the vehicle. Operators must use one remote for moving the wheeled unit, and the remote from the original AFAD for sign messaging. The new device moves forward and backward, can be towed with a standard hitch, and employs onboard batteries and a charger.

Setup and takedown require more effort than conventional flagging, but this effort is not considered cumbersome. The moving AFAD can be operated by one person standing 400 feet or more off the roadway, and the device is large enough to be easily seen and understood by road users.

The new device was used for only one hour initially. The sealing crew was outpacing the moving AFAD because the crack-sealing project entailed few repairs with greater distance between repair locations than is typical of such projects.

What’s Next?

The moving AFAD device can be used as is, and is still being tested by MnDOT. Further modifications will be requested, including enhancement of the battery-powered unit, as it currently requires a battery change to operate through an entire work shift.

Steering and controller design will likely be modified. Currently, the moving AFAD operates like a rear-wheel-drive vehicle and must be steered from its rear-wheel, traffic-facing axle, forcing the remote operator to guide it up the road as if backing up a boat trailer. MnDOT operators may ask that the device be redesigned to be steerable from the traffic-leading end of the vehicle, as if it were pulling the signage up the road, allowing for more intuitive control.

MnDOT personnel would also like to see the device’s controller integrated with the sign controller, eliminating the need for two controllers—one for moving, the other for operating the sign. Nevertheless, the device appears to be a promising option for mobile AFAD use by an operator who need not stand on the road to direct traffic.


This Technical Summary pertains to Report 2017-09, “Development of a Moving Automatic Flagger Assistance Device (AFAD) for Moving Work Zone Operations,” published March 2017. 


Previous research:

Seven Pilot Projects to Change Transportation Practice in Minnesota

Roadside fencing that protects endangered turtles, a toolkit for identifying potentially acid-producing rock and a device that could save MnDOT $200 million a year in pavement damage are just a few of the advancements that MnDOT hopes to make in the near future, thanks to seven recently funded research implementation projects.

Each spring, the governing board for MnDOT’s research program funds initiatives that help put new technology or research advances into practice. This year’s picks aim to improve the environment, reporting of traffic signal data, notification of lane closures and the design and quality of pavements.

Here’s a brief look at the projects (full proposals here):

Protecting the Environment and Wildlife

  • To avoid the leaching of potentially acid-generating rock during excavation projects, MnDOT hopes to develop a GIS-based risk-screening tool that identifies areas where PAG rock might be encountered. Guidance will be developed for identifying and handling PAG rock.

Found in bedrock throughout the state – especially northern Minnesota, PAG minerals can release acid upon contact with air or water, a danger to aquatic and human life.

“Anytime we dig, there is the potential to expose this stuff,” said Jason Richter, chief geologist.

  • Reducing roadway access for small animals, including endangered turtles, is a priority for MnDOT and the Minnesota Department of Resources. MnDOT will analyze the effectiveness of different types of small animal exclusion fences tried across the state and develop a standard set of designs for future projects.
Improved Reporting of Traffic Signal Data
  • A centralized hub of traffic signal data could benefit future vehicle-to-infrastructure (V2I) applications and assist with the modeling of transportation project impacts. Methods and tools will be developed for a regional database of intersection control information that extracts data from MnDOT’s recently acquired Central Traffic Signal Control System and soon-to-be adopted Signal Performance Measure application.
Real-Time Notice of Lane Closures
  • In this pilot project, 20 MnDOT arrow board messages will be equipped with technology that automatically reports lane closures on 511 and highway message boards, providing more timely motorist notification.
Longer-Lasting Roads and Improved Quality Control
  • This summer, a new quality assurance device called the Rolling Density Meter will be deployed on several pavement projects, eliminating the need for destructive sample cores.
    “This is the ultimate in compaction control,” said Glenn Engstrom, Office of Materials and Road Research director. If contractors obtain the right level of density when paving asphalt roads, MnDOT could eliminate $200 million per year in premature road failure.
  • In 2018, MnDOT plans to require Intelligent Compaction (a pavement roller technology that reduces workmanship issues) on all significant asphalt projects. A vehicle-mounted mobile imaging device will be piloted that collects necessary supportive roadway alignment data, without the need for survey crews.
  • Upgrades to MnDOT’s pavement design software, MnPAVE, (incorporating recycled unbound and conventional base material properties) will help increase the service life of Minnesota roads.

MnROAD Breaks New Ground

In June, MnROAD, the only cold-weather accelerated pavement testing facility of its kind in North America, begins construction on its third phase of research since 1994, the first time MnDOT has rebuilt in partnership with other states.

Dozens of new experiments are planned along MnROAD’s test tracks in rural Albertville: the high-volume original Interstate-94 westbound (built in 1973), the mainline I-94 westbound (originally opened in 1994) and an adjacent low-volume road closed track.

Six states and numerous  industry partners recently formed the National Road Research Alliance (NRRA) to co-sponsor  the reconstruction.

NRRA-prioritized research will support state and local needs, including effective use of fiber-reinforced concrete, asphalt overlays of concrete pavements, cold central plant recycling and concrete partial depth repairs to name a few.

MnROAD has two 3.5 mile test segments on Interstate 94 and one closed 2.5-mile low-volume road.
MnROAD has two 3.5 mile test segments on Interstate 94 and one closed 2.5-mile low-volume road.

“The advantage of having these test  sections at MnROAD is we can take  bigger risks and push the envelope in terms of mix designs and layer thicknesses for both asphalt and concrete  layers that could not be done on a public roadway,” MnDOT Research Operations Engineer,   Dave Van Deusen said.

Forensic analysis of failed cells
Many old test cells will be dug up.  Before any reconstruction starts, however, each test section that is being reconstructed will receive a final forensic study. This allows researchers a look at each layer to see the distress that has occurred over the years—and make the final analysis of why it failed. There are always a lot of theories on the causes of what actually failed, but until the forensic is performed, there isn’t proof on what happened. These findings will help build longer-lasting pavements in the future.

The bid letting date for this year’s construction is April 28, but plans were made available for contractors on March 31. This should give the projects more exposure and generate more interest. Construction begins June 5 and continues until November 2017.

Focus Areas

  • HMA overlay and rehab of concrete and methods of enhancing compaction – States are looking for longer lasting HMA overlays of concrete. New mix designs were developed to promote long-term performance, including how reflective cracking effects can be minimized through design or other joint treatment.
  • Cold central plant recycling – Other states have used reclaimed asphalt pavement stockpiles into plant mix base course mixes (layers below the wear surface) to effectively recycle these materials in a controlled mix design. How can these layers best be used and what type of surface mix or chip seal can be placed on top?
  • Fiber reinforced concrete pavements – Nationally, states want to get a better understanding of the beneficial use of fibers in concrete pavement layers. Is it worth the cost? How can it be best used in both thin city streets and higher volume roadways? Can it be used in new construction and in concrete overlays? The research will provide the answers.
  • Long-term effects of diamond grinding – Each state has aggregates that have been used in concrete pavements that are considered reactive aggregates. Questions arise as to whether diamond grinding might accelerate deterioration in these pavements. What types of topical sealers can be used to treat the surface after the diamond grinding will also be tested.
  • Early opening strength to traffic – What effect does heavy traffic loading have on the long-term performance of full-depth concrete pavement, as well as fast–setting repairs? Test sections will be loaded by a pickup truck in one lane early enough to produce shallow ruts in the surface. In the other lane, a loaded 18-wheeler will travel over the new concrete immediately after it sets, and then sequentially every six hours up to 30 hours. The long-term effects of these early loadings will then be evaluated.
  • Optimizing the mix components for contractors – What effect do low-cementitious content mixes have on long-term performance and constructability of concrete pavements?  Two low cementitious content mixes will be studied to give agencies a better understanding of cost savings. Can these savings be achieved without significantly affecting long-term performance?
  • Compacted concrete pavement for local streets – Compacted concrete pavement is a form of roller compacted concrete that has a standard concrete pavement surface texture. The RCC industry has been successful in Michigan and Kansas constructing CCP pavement on local streets.  This research will determine if the texture that is accomplished is durable in harsh freeze-thaw climates.
  • Recycled aggregates in aggregate base and larger sub-base materials – States continue to look for effective ways to recycle materials into unbound bases. This research will add to MnROAD’s understanding of recycled bases and what seasonal strength values can be used for advanced mechanistic designs–and how they are affected by size/gradation.
  • Maintaining poor pavements– Road owners continually have less funding to maintain their roadway systems. What practices should be used for stabilizing both hot mix asphalt and Portland cement concrete roadways when longer-term repairs cannot be done due to funding levels?
  • Partial depth repair of concrete pavements – Agencies continually seek improved materials and methods for the repair of concrete pavements. In this study, up to 15 innovative concrete pavement repair materials will be evaluated on the concrete panels of the westbound I-94 bypass parallel to the MnROAD mainline.
  • Thin overlays-Experimenting with very thin overlays could provide a real benefit for a lot the roads currently out there. The premise is that with thin overlays, the ride can be smoother and the life of older roads can be extended.

“We don’t often get to reconstruct random roads these days, and when we do, we have much better specifications for low temperature cracking. By the same token, we have to maintain all those older roads built before we had performance grade binders,” said Dave Van Deusen, Materials and Road Research Lab principal engineer. “We will be doing this makeover on an original section of MnROAD built back in the 90’s.”

In one experiment, there is a head-to-head comparison of thin overlays on two sections of road. One section has a thick base and subbase under the asphalt. The other has a heavy asphalt top with very little base.

Van Deusen says if they can get an extra five years of life out of road using thin overlays, he would be pleased. Often, he admits, he is surprised by how long these “short-term” fixes actually last.

Stay up-to-date on construction by signing up for email alerts at mndot.gov/mnroad.  

A Look at Local Bridge Removal Practices and Policies

Many local agencies in Minnesota lack funding to construct and maintain all the bridges in their roadway network. One way to lower costs is to reduce the number of bridges.

In Minnesota, some township bridges are on roads with low usage that have alternative accesses for nearby residents, but local officials are reluctant to remove the bridges.

To identify possible changes to how redundant and low-use bridges are identified and removed in Minnesota, the Local Road Research Board conducted a transportation research synthesis, “Local Bridge Removal Policies and Programs,” that explores how other states make bridge removal decisions.

Fifteen state DOTs responded to a survey about their processes, with varying levels of state oversight identified for bridge removal decisions. Researchers also examined funding and incentives offered by some DOTs to local agencies for bridge removal, as well as criteria for considering bridge removal.

A literature search of bridge design manuals, inspection manuals and bridge programs was also conducted to identify related policies and programs.

Read the TRS to learn more about the various bridge removal policies and procedures in place in Minnesota and other states.

New Study: Experimental Shear Capacity Comparison Between Repaired and Unrepaired Girder Ends

MnDOT Research Services recently executed a contract with the University of Minnesota to begin work on a research study titled “Experimental Shear Capacity Comparison between Repaired and Unrepaired Girder Ends.”

The research will determine if a bridge repair to the TH 169 Nine Mile Creek Bridge near Edina and Minnetonka was sufficient to restore the original strength of a girder end in shear. Load testing to failure will be conducted on two repaired girder ends and two unrepaired girder ends that will be removed from the bridge. Objectives include a comparison of the failure load between the repaired ends and the unrepaired ends. The test results also will provide some answers to questions on whether shotcrete is a structural repair or if it is just a covering over of deterioration.

Carol Shield, professor at the University of Minnesota’s Department of Civil Engineering, Civil, Environmental, and Geo- Engineering, will serve as the research project’s principal investigator. Paul Pilarski, MnDOT bridge engineer, will serve as the study’s technical liaison.

According to the initial work plan in the contract, the project is scheduled to be completed by the end of March 2018.

Background

Over time, the south bound exterior girder ends on each side of Pier 4 and Pier 26 of the TH 169 Nine Mile Creek Bridge have suffered significant corrosion damage that exposed shear reinforcement, exterior flange prestressing strands, and the sole plate anchorages. Girder ends were repaired in September 201 3 by encasing a 4-foot length of the end using a system of dowels, additional shear reinforcement, and shotcrete. The bridge is scheduled for replacement in 2017.

There is interest in determining if the repair was sufficient to restore the original strength of the girder end in shear. Load testing to failure will be conducted on two repaired girder ends and two unrepaired girder ends that will be removed from the bridge. Objectives include a comparison of the failure load between the repaired ends and the unrepaired ends.

Project Objective

The ability to effectively repair corrosion damaged girder ends extends the useful life of prestressed concrete bridges. These repairs are significantly less expensive than replacing the bridge. Repairing bridges is also beneficial to the traveling public as travel is not interrupted, or interrupted for a significantly shorter time than for bridge replacement. Experimentally demonstrating that the repair restores the girders up to the design strength enhances the safety of the bridge and provides MnDOT with a documented substantiated repair method that can be applied to other bridge girders in a similar state.

Project Scope

When the southbound lanes of the TH 169 Nine Mile Creek Bridge are taken out of service, the contractor will remove four prestressed girders from the structure and deliver the south ends of them to the University’s Department of Civil Engineering Theodore V. Galambos Structures Lab. Two of the girders will have ends that have been repaired. The other two girders will be of the same shear design but will not have been repaired, nor show significant signs of corrosion. Once at the Galambos Laboratory decks will be cast on the girders. One end of each girder will be tested to failure using a setup designed to precipitate a shear failure. Failure loads between the repaired and original undamaged girder ends will be compared. The development of crack patterns under load will also be documented to further understand the behavior of the repair.

Assistance

MnDOT will make arrangements for transportation of the girder ends to the University’s Civil Engineering Building. MnDOT will request that the contractor provide weights of the cut girders prior to delivery. MnDOT will make arrangements with the contractor to take concrete cores from the short end of the cut girders and provide the existing bridge bearing pads. MnDOT will provide calculations for determining the required deck width and concrete strength to avoid a flexural failure.

Infrared Sensing Not Yet Suitable for HOV/HOT Lane Enforcement

Could the same infrared technology that’s used by security firms to detect trespassers be used to spot carpool lane violators? Not yet, says new research sponsored by MnDOT, which shows that to consistently detect passengers through windshield glass, the system would require a laser that might harm people’s eyes.

“Some vendors have proposed significant investments in sensing technology for HOV/HOT lane enforcement,” said Nikos Papanikolopoulos, Professor, University of Minnesota Department of Computer Science and Engineering. “This research demonstrated that it’s not safe, so the tests saved a lot of money and protected the well-being of drivers.”

“Development is still continuing in the industry, so we will cautiously evaluate sensing technologies as they come along,” said Brian Kary, MnDOT Freeway Operations Engineer. “This research gave us a solid base of knowledge about what we’ll be looking for and what we need to avoid.”

Papanikolopoulos served as the research project’s principal investigator, and Kary served as technical liaison.

What Was the Need?

High-occupancy vehicle/high-occupancy toll (HOV/HOT) lanes have gained popularity in recent years as a way to address highway congestion in urban areas. However, enforcing the provisions that either prohibit or charge a toll to single-occupant vehicles in HOV/HOT lanes can be challenging. Currently, enforcement is handled by law enforcement officers, but this is a labor-intensive process that can’t catch every violator and can create a traffic safety hazard.

Obtaining technology to assist officers with enforcement is a goal for MnDOT and many other agencies that operate HOV/HOT lanes, and several manufacturers are working to develop enforcement cameras. But this has proven to be a difficult task. Window tinting and glare from sun-light can thwart common sensing technologies like video cameras and microwave radar (commonly used in speed limit enforcement). Previous research using near-infrared sensors has shown promise, but none has produced completely successful results.

This study tested Honeywell’s Tri-Band Infrared (TBI) sensor, which was originally used to automatically detect intrusions at high-security entrance gates. In addition to a black-and-white camera and an illuminator, the TBI has two co-registered near-infrared cameras. The system takes advantage of the fact that human skin reflects infrared light much more effectively at wavelengths below 1400 nanometers. The TBI’s infrared cameras are sensitive to different wavelengths, one below and one above that threshold, and fusing the images from these two cameras makes silhouettes of faces more prominent.

What Was Our Goal?

The goal of this project was to evaluate whether the TBI sensor is suitable for HOV/HOT lane enforcement applications.

Illuminator
Infrared lasers helped the TBI sensor detect people through glass, but they also pose a danger to eye safety.

What Did We Do?

Investigators first tested the sensor outdoors on oncoming vehicles with known positions that ranged from 25 to 140 feet from the sensor. These tests demonstrated that the sensor had limited ability to penetrate modern vehicle glass, possibly because the system’s illuminator component was ineffective.

Investigators purchased two infrared lasers providing illumination at wavelengths of 1064 nanometers and 1550 nanometers to increase the TBI sensor’s ability to detect people through windshield glass. Then they conducted indoor tests to compare the impact of these illuminators with that of the original illuminator: With a test subject holding front passenger windows from several manufacturers in front of his face, the lasers were aimed at the subject while the TBI attempted to detect him.

Finally, investigators conducted outdoor tests using the TBI to detect people in three test vehicles from the front and the side under both sunny and cloudy conditions. These tests were conducted both without illumination and with the aid of high-power incandescent spotlights modified to output infrared light, and with the sensor at several different distances from the vehicles.

What Did We Learn?

The indoor tests demonstrated that when aided by supplementary illuminating lasers, the TBI sensor was capable of detecting humans through commonly manufactured vehicle window glass.

However, to achieve successful results, these lasers must operate with high power in a narrow range of wavelengths. Despite operating outside the visible spectrum, they can damage human eyes when operating at the necessary power level to enable effective detection through glass. While investigators conducted this project’s indoor tests with adequate protection, there is currently no way to ensure safe usage of the lasers in real-world applications.

In the second outdoor tests, the unilluminated sensor successfully detected a passenger only once out of 24 attempts. With illumination, the sensor successfully detected people in some cases, particularly when there was no direct sunlight or reflective glare. One surprising discovery was that high-band (above 1400 nanometers) infrared light penetrated window glass more consistently, even though the low band had more spectral energy.

What’s Next?

Due to safety concerns about using the illuminating laser at a high enough power to penetrate all windshield glass, the system is not suitable for HOV/HOT lane enforcement. There is some indication that sensor technology has improved since the release of the TBI, and MnDOT will continue to monitor industry developments, but it has no current plans to pursue using infrared cameras for this application.

The technology may be suitable for other sensing applications that do not require high-power illumination. For example, the sensors might be useful in systems that provide information to drivers in real time, such as applications that identify available truck parking spaces in rest areas or that alert drivers to the presence of workers in work zones.

This Technical Summary pertains to Report 2017-05, “Sensing for HOV/HOT Lanes Enforcement,” published February 2017. The full report can be accessed at mndot.gov/research/reports/2017/201705.pdf. 

I-35W ‘Smart Bridge’ Test Site Uses Vibration Data to Detect Bridge Defects

By analyzing vibration data from the I-35W St. Anthony Falls Bridge, MnDOT is working to develop monitoring systems that could detect structural defects early on and ultimately allow engineers to improve bridge designs.

“With data spanning several years, the I-35W St. Anthony Falls Bridge offers a unique opportunity for investigating the environmental effects on a new concrete bridge in a location with weather extremes,” said Lauren Linderman, Assistant Professor, University of Minnesota Department of Civil, Environmental and Geo-Engineering. Linderman served as the research project’s principal investigator.

“This project gets MnDOT closer to using bridge monitoring systems in combination with visual inspection to help detect structural problems before they affect safety or require expensive repairs,” said Benjamin Jilk, Principal Engineer, MnDOT Bridge Office. Jilk served as the research project’s technical liaison.

2017-01-bridge.png
Completed in 2008, the I-35W St. Anthony Falls Bridge has a smart bridge monitoring system that includes hundreds of sensors.

What Was the Need?

In September 2008, the I-35W St. Anthony Falls Bridge was constructed to include a “smart bridge” electronic monitoring system. This system includes more than 500 sensors that continuously provide data on how the concrete structure bends and deforms in response to traffic loads, wind and temperature changes. Transportation agencies are increasingly interested in such systems. As a complement to regular inspections, they can help detect problems early on, before the problems require expensive repairs or lead to catastrophic failure. Smart bridge systems can also help engineers improve future bridge designs.

The smart bridge system on the I-35W St. Anthony Falls Bridge includes accelerometers, which provide data on the way the bridge vibrates in response to various stimuli, including structural damage. Vibration-based monitoring has the advantage of allowing damage to be detected at any location within the bridge rather than only at the specific locations where measuring devices have been placed.

However, it can be difficult to use vibration monitoring to detect damage when vibration is masked by the bridge’s natural response to traffic loads, wind, temperature changes and other environmental conditions. A crack in a bridge girder, for example, can produce a vibration signature similar to one produced by a change in beam length due to variations in temperature or other causes. Consequently, since 2008 MnDOT has conducted a series of projects using data from the St. Anthony Falls Bridge to establish a way to distinguish anomalous data indicating a structural defect or damage from background “noise” associated with other causes.

What Was Our Goal?

This project sought to develop a method for analyzing accelerometer data from the I-35W St. Anthony Falls Bridge that would show how the bridge naturally vibrates due to traffic, wind and other environmental conditions. With this fingerprint of the bridge’s natural vibration, engineers would have a baseline against which to measure anomalies in the data that might indicate structural damage.

What Did We Do?

A large amount of data has been collected from the bridge since its construction. To establish the vibratory fingerprint for the bridge, researchers examined the frequencies and shapes (or modes) of bridge vibration waves. The method they used to identify the data segments needed for the fingerprint was to evaluate the peak amplitude of bridge vibration waves and their root mean square (RMS), a measure of the intensity of free vibration.

The researchers applied this method to the vibration data collected on the I-35W St. Anthony Falls Bridge between April 2010 and July 2015, calculating the average frequencies for four wave modes and determining how they varied with the bridge’s temperature. They also calculated the way frequencies changed with the bridge’s thermal gradients, or variations in temperature between parts of the structure.

What Did We Learn?

The methods developed in this project were successful in establishing a fingerprint for the way the I-35W St. Anthony Falls Bridge vibrates due to environmental conditions, and a way to evaluate changes in vibration over time indicative of structural damage or other factors.

Researchers found that the ratio of peak signal amplitude to RMS in bridge vibrations was a strong indicator of data that should be analyzed, and was evidence of a large excitation followed by free vibration. By themselves, peak amplitude and RMS cannot distinguish between ambient free vibration and forced vibration.

Researchers were able to use this method to successfully analyze 29,333 data segments from the I-35W St. Anthony Falls Bridge. This analysis revealed that as temperature increases, the natural frequency of vibration tends to decrease. The magnitude of this change, they concluded, must be related not just to the elasticity of the bridge but also to other factors such as humidity. However, temperature gradients within the bridge did not appear to have a significant effect on the natural frequencies of the structure.

What’s Next?

MnDOT will continue to collect data from the bridge as it ages to further understand its behavior. This will provide an opportunity to determine how anomalies in vibration data correspond to cracking and other forms of structural distress. Ultimately, MnDOT hopes to use this bridge monitoring system in combination with visual inspection both to detect problems in bridges earlier and to develop better bridge designs. Researchers are also currently working on a follow-up project, Displacement Monitoring of I-35W Bridge with Current Vibration-Based System, to determine the effects of temperature on the bridge’s dynamic and long-term vertical displacements, which can be used to monitor the bridge’s stiffness, connections and foundations.

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This post pertains to Report 2017-01, Feasibility of Vibration-Based Long-Term Bridge Monitoring Using the I-35W St. Anthony Falls Bridge, published January 2017. 

MnDOT shares knowledge at national research conference

MnDOT employees are sharing knowledge and displaying leadership in Washington this week by delivering presentations and conducting meetings at the nation’s preeminent transportation conference.

trbThe Transportation Research Board (TRB) 96th Annual Meeting held Jan. 8-12 at the Walter E. Washington Convention Center in Washington, D.C., is expected to draw more than 12,000 transportation professionals from around the world. According to its website, the 2017 event scheduled more than 5,000 presentations in more than 800 sessions and workshops addressing topics of interest to policy makers, administrators, practitioners, researchers, and representatives of government, industry, and academic institutions. TRB’s 2017 annual meeting theme is “Transportation Innovation: Leading the Way in an Era of Rapid Change.”

“Every year when TRB holds its annual meeting, MnDOT’s strong presence at the event is a reminder of our state’s commitment to top-notch transportation research,” said Linda Taylor, director of MnDOT Research Services and Library.

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Brad Larsen (left), MnPASS Policy and Planning Program Director, speaks with a conference attendee during a poster session this week at the Transportation Research Board Annual Meeting in Washington, D.C. Larsen was one of two dozen MnDOT employees invited to deliver presentations at the national transportation research event.

The following is a roundup of MnDOT employees who were invited to deliver presentations and participate in key committee meetings along with their presentation topics and committees (not all staff may have attended the conference; however, due to limited funding or availability):

Kenneth Buckeye, Financial Management

Thomas Burnham, Materials & Road Research

Kathryn Caskey, Transportation System Management

Shongtao Dai, Materials & Road Research

Dan Franta, District 7

Timothy Henkel, Modal Planning & Program Management 

Kyle Hoegh, Materials & Road Research

 Bruce Holdhusen, Transportation System Management

 Santiago Huerta, Metro District

Bernard Izevbekhai, Materials & Road Research

Brad Larsen, Metro District

Rita Lederle, Bridges

Francis Loetterle, Passenger Rail

Dean Mikulik, Materials & Road Research (student worker)

Mark Nelson, Transportation System Management

Steven Olson, Materials & Road Research

David Solsrud, Modal Planning & Program Management 

Trisha Stefanski, Modal Planning & Program Management 

Joel Ulring, State Aid for Local Transportation

Jennifer Wells, Bridges

Benjamin Worel, Materials & Road Research

Charles Zelle, Commissioner

10 Ways Transportation Research Keeps Minnesotans Moving in the Winter

As the first big snow and ice storms sweep through parts of Minnesota today, we’d like to remind you of some of our great winter weather research studies. Here’s a list of some of this winter-related research from MnDOT and the Local Road Research Board:

Living snow fences

Living snow fences are trees, shrubs, native grasses, wildflowers, or rows of corn crops located along roads or around communities and farmsteads. These living barriers trap snow as it blows across fields, piling it up before it reaches a road, waterway, farmstead or community. Through multiple research efforts, MnDOT continues to advance its practices for living snow fences. Willow plants, which are which are inexpensive and fast-growing, are a new form of snow fence. MnDOT has also developed a tool that allows the agency to better offer a competitive payment to farmers.

Related studies:

Permeable pavement

According to recent studies, researchers believe Minnesota could eliminate salt usage on low-volume local roads by switching to permeable pavements. Permeable pavements — pavements that allow water to seep through them — have been studied in some Minnesota cities, and a research project is currently underway to further investigate how much salt reduction can be expected.

Related studies:

Traffic recovery during winter storms

MnDOT’s Metro District developed a way to automatically determine when to stop plowing a highway after a snow storm. The method involves measuring traffic flow to determine when road conditions have recovered. Current practice calls for maintenance workers to visually inspect traffic lanes. The automated technique could potentially be more accurate and save time and costs.

Related study:

Salt and other deicing chemicals

Minnesota winters are no joke, and Minnesotans still need to get wherever they’re going despite harsh snow and ice conditions. That’s why MnDOT is constantly researching new and improved versions of salt and other deicing chemicals to keep roads safe at the least amount of damage to lakes, rivers and groundwater.

Related studies:

Snowplow blades

A couple years ago, MnDOT snowplow operators in southwestern Minnesota invented an experimental plow that uses the wind to cast snow from the road without impeding traffic or the operator’s view. This winter, MnDOT intends to test multiple types of snowplow blades as part of a larger research project comparing types of deicers.

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Snowplow technology

While a lot of research has been done on the plow itself, MnDOT hasn’t forgotten to invest in research to improve in-cabin snowplow technology as well. Some of the great technology recently developed to assist snowplow drivers, includes a driver assist application that a MnDOT plow driver used last winter to navigate a storm and rescue stranded motorists. The agency is also studying equipment factors that can cause fatigue in snowplow operators.

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Salt-resistant grasses

When the snow melts every spring, the damage salt does to roadside grass is obvious. That’s why researchers have spent years looking into developing and implementing salt-tolerant grasses on roadside settings. The result of this effort has been the introduction and use of salt-tolerant sod and seed mixtures that are made up primarily of fine fescue species. MnDOT is also studying how chlorides are transported within watersheds in order to better focus efforts to reduce deicer usage in  areas where it will have the biggest environmental impact.

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Cold-weather cracking prediction test

MnDOT has developed a test that can tell whether a contractor’s proposed asphalt mix will cause the road to crack in the winter. Building roads using better asphalt mixes leads to less cracking and fewer potholes. The test is expected to save the state about $2 million per year.

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Pedestrian snow removal

It’s not all about cars and trucks. Minnesotans still ride bikes and walk in the winter. That why MnDOT assembled a comprehensive review of existing practices and policies from other states, as well as a summary of valuable publications that could be referenced while developing a new policy.

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Maintenance Decision Making

MnDOT research led to the development of a Maintenance Decision Support System and related components provide real-time, route-specific information to snow plow drivers, as well as recommended salt application levels. These recommendations have reduced chemical usage while still achieving performance targets for snow and ice clearance.

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Partner States Get First Look at Minnesota Road Experiment

Walking along a half-mile segment of Co. Rd. 8 near Milaca last month, materials engineers from around the country got a first look at a shared test site for pavement preservation.

Nearly 60 one-tenth mile sections of Co. Rd. 8 and nearby Hwy 169 were recently treated with various combinations of fog seals, chip seals, crack seals, scrub seals and microsurfacing and a number of thin overlays. Data will be collected from these experimental test roads for three years and compared with the results of a similar experiment in Alabama, where the same test sections were also built on a low- and high-volume roadway, to see which techniques are the most effective for preserving road life.

“Evaluating pavement performance in both northern and southern climates will provide cost-effective solutions that can be implemented nationwide,” said Ben Worel, MnROAD operations engineer.

Photo of Barry Paye, Wisconsin DOT chief materials engineer; and Tim Clyne, MnDOT Metro District materials engineer.

From left, Barry Paye, Wisconsin DOT chief materials engineer, and Tim Clyne, MnDOT Metro District materials engineer, participate in a discussion about future road research needs. Photo by Shannon Fiecke

Nineteen states, which are co-funding the study through MnDOT’s road research facility (MnROAD), were in town Oct. 26-27 for a joint meeting with the National Center for Asphalt Technology in Auburn, Ala. In addition to touring test sections built this summer near Milaca and at MnROAD’s permanent test track in Albertville, the group reviewed preliminary research results and discussed ideas for new experiments.

MnROAD began two joint research efforts with NCAT last year to advance pavement engineering issues that affect both warm and cold climates. In addition to determining the life-extending benefits of different pavement preservation techniques, the partnership has also built test cells to evaluate which asphalt cracking prediction tests best predict future pavement performance. This second study will help state DOTs improve the quality of asphalt mixes, so roads hold up better through harsh winters, leading to less thermal cracking and fewer potholes.

Click here to learn more about the MnROAD-NCAT partnership.