All posts by mndotresearch

Adding Snowplow Camera Images to MnDOT’s Traveler Information System

MnDOT installed network dash cameras and ceiling-mounted cameras on 226 snowplows, approximately one-quarter of MnDOT’s snowplow fleet. The cameras, integrated with the onboard mobile data computer and automated vehicle location equipment, automatically captured snapshots of road conditions during plowing. The snapshots were incorporated into several facets of MnDOT’s 511 traveler information system: the desktop and mobile versions of the website and the 511 app. Motorists and MnDOT alike found the project to be valuable, with the up-to-the-minute imagery helping members of the public and MnDOT’s maintenance staff make well-informed decisions during winter storm events.

“The largest barrier to implementation involved the development of the software package for integrating snowplow cameras into the current AVL system. It required a great deal of back-and-forth to get things right,” said oe Huneke, Maintenance Decision Support Systems (MDSS)/AVL Section Manager, MnDOT Office of Maintenance.

“We did research to make sure the cameras did not block drivers’ views, taking state and federal regulations into consideration, and we tested the cameras to make sure they were capturing images at the right resolution,” said Jon Bjorkquist, Maintenance Technology Development/ Implementation Coordinator, MnDOT Office of Maintenance.

What Was the Need?

Reliable information about road conditions during winter weather allows motorists to make informed travel decisions and helps MnDOT responders maintain roads. While meteorological updates on a winter storm and automated status reports on Minnesota’s snowplow fleet are important sources of data, they do not provide visual information about road conditions.

In 2015, a pilot project allowed MnDOT to take road condition pictures from cameras mounted on selected snowplows during winter storms. The system was limited, however. Few snowplows were outfitted with these cam-eras, images were not available to the public, and network infrastructure did not allow for easy scaling. A larger scale program was needed to capture road imagery taken from snowplows across Minnesota and to share the pictures with Minnesota motorists.

What Was Our Goal?

MnDOT sought to install cameras on a sizable portion of MnDOT’s snowplow fleet. In addition to making hardware and network enhancements to collect and compile the image data, MnDOT also set out to make the photos avail-able in near-real-time to its internal maintenance staff and the traveling public.

Camera mounted on the ceiling of a MnDOT snowplow cab.
To capture images of road conditions, MnDOT mounted cameras in the cabs of one-quarter of MnDOT’s snowplow fleet.

What Did We Do?

In 2015 and 2016, MnDOT installed network dash cameras and ceiling-mounted cameras on 226 snowplows, approximately one-quarter of the agency’s total snowplow fleet. The cameras, integrated with the onboard mobile data computer and automated vehicle location (AVL) equipment, automatically captured snapshots of road conditions during plowing. This system included the following key operational features:

  • The dash cameras automatically recorded images whenever the computer-AVL system was on.
  • The cameras recorded an image of the road ahead of the plow.
  • Images were taken once every five minutes and were only retained if the plow was moving at least 10 mph.
  • The cameras were capable of taking operator-initiated snapshots and video clips.
  • Video clips could be classified into three categories: accident, general interest or work zone.

The system sent the plow camera images and metadata (geolocation, plow, camera and conditions) to a MnDOT server upgraded to accommodate the data. MnDOT set a data retention schedule for mobile snapshots and video segments as well as the data server.

Plow images were incorporated into several facets of MnDOT’s 511 traveler information system, including the desktop and mobile versions of the website and the 511 app. Plow images plotted at 10-minute intervals on the 511 maps provided motorists with up-to-the-minute, easily accessible information on road conditions. The images were also incorporated into MnDOT’s internal website called Condition Acquisition and Reporting System.

What Did We Learn?

The project demonstrated the successful integration of various hardware, software and network systems, carrying the road weather imagery step by step from the cameras to the public 511 interface. The project also succeeded in scaling up an earlier, modest effort to furnish snowplows with cameras.

In addition, MnDOT collected input on the value of the cameras from a range of interested parties: the public, snowplow operators and supervisors, and MnDOT management staff.

The public response was overwhelmingly positive, with 319 Facebook users responding to a MnDOT post about the cameras. All the respondents used positive emote icons (“heart” or “thumbs up”). Several members of the public provided responses through Facebook and MnDOT’s “Contact Us” Web page about the value of being able to view actual road conditions, though others expressed concern about the cost of the system.

Surveys of MnDOT snowplow drivers and supervisors and interviews of MnDOT managers revealed that supervisors and managers had a largely positive view of the program as well. Drivers provided mixed reviews. Comments from these groups yielded the following recommendations about implementing a program of this nature:

  • Perform outreach efforts that clearly communicate benefits to achieve broad buy-in from snowplow drivers. Provide training and follow-up instruction on use of the cam-era’s features to encourage drivers to use the manual snapshot and video features.
  • Address drivers’ concerns about privacy (such as “Big Brother is watching”) directly, and understand that these concerns have lessened over time. Supervisors should be advised not to react too quickly to privacy concerns.
  • Address concerns about in-cab distraction by adjusting the system configuration or hardware. This might include making dash camera screens dimmable at the driver’s option, or placing screens and cameras out of critical sightlines.

What’s Next?

This project was a success, with snowplow camera images providing significant benefits to MnDOT staff and the traveling public. Based on this work, MnDOT plans to install camera systems on additional snowplows in the state fleet—as deemed necessary by district management—and to continue displaying snowplow images on MnDOT’s 511 system.


This post pertains to Report 2017-41, “Installing Snowplow Cameras and Integrating Images into MnDOT’s Traveler Information System,” published October 2017.

Establishment and Care of Salt-Tolerant Grass on Roadsides

Kentucky bluegrass, the grass species that MnDOT typically uses for roadsides, was sensitive to salt; many installations could not tolerate winter deicing salts and died. Research on salt-tolerant grasses begun in 2009 resulted in MNST-12, a grass mix of fine fescues (with 20 percent Kentucky bluegrass for sod cutting, transport and installation stability) that is more salt-tolerant. MNST-12 was installed at many roadsides sites but by 2013, many MNST-12 installations were not thriving. Research into the reasons for these failures and the ways to best establish and care for MNST-12 revealed that this salt-tolerant grass mix requires a different planting and irrigation regimen than the standard MnDOT protocols that had been used for decades on Kentucky bluegrass. When installed as seed, MNST-12 should be planted in August or September; when installed as sod, it can be laid between May and November if sufficient irrigation is available. MNST-12 roots slowly and needs a particular irrigation regimen in early stages. Moisture replacement of 60 percent of its evapotranspiration rate is sufficient to promote establishment.

“The [highway] construction critical path for program delivery rarely includes a biological requirement for establishing vegetation. For salt-tolerant fescue grasses, planting dates and irrigation regimens matter,” said Dwayne Stenlund, Erosion Control Specialist, MnDOT Office of Environmental Stewardship.

“Basing irrigation approaches on evapotranspiration could reduce water consumption and, ultimately, the cost of establishing areas by sod,” said Eric Watkins, Professor, University of Minnesota Department of Horticultural Science.

Failed Kentucky bluegrass along a roadway
Because of its poor salt tolerance, Kentucky bluegrass has failed at many roadside sites in Minnesota.

What Was the Need?

Minnesota has more than 24,000 acres of green, grassy roadsides, ranging from street terraces to Interstate high-way medians. These roadside environments have many stressors, including heat, drought, insects, weeds, traffic and salt.

MnDOT has traditionally used Kentucky bluegrass for turfgrass, but its poor salt tolerance has resulted in many failed installations. Seed and sod research begun in 2009 produced MNST-12, a salt-tolerant grass mix of mostly fine fescues. By 2013, however, many roadside installations of MNST planted under MnDOT’s standard turf care protocols had failed and the reasons were unclear.

Replacing an acre of failed sod costs up to $25,000. MnDOT needed to learn why the turf failed and find the right methods to establish and care for salt-tolerant grass.

What Was Our Goal?

Researchers sought to assess installations of MNST seed and sod across the state to determine the planting and care practices that resulted in successful establishment or in failure. They also wanted to identify best practices for salt-tolerant turf establishment and care.

What Did We Do?

The study had two phases. In the first phase, researchers identified 16 roadside sites located throughout the state with salt-tolerant turf that had failed or performed poorly. They assessed these sites from July 2013 through 2014, and gathered detailed information about the sites from MnDOT, landscape contractors, sod producers and weather data sites. Information included date and time of installation, sod or seed used, temperature and precipitation at installation, and irrigation and mowing protocols. At each site, researchers also took measurements of ground cover, salinity, temperature, moisture content, surface hardness and depth of soil to top of curb. Soil samples were tested for pH, available phosphorus and organic matter.

Beyond variations in soil moisture, it was unclear whether any other soil aspect promoted the success or failure of site turf. Homeowners at various locations suggested that installation date and supplemental irrigation might have influenced a site’s success.

In the second phase of the study, investigators identified the best management practices for MNST by examining three factors that could influence turf performance:

  • Use of soil amendments during establishment. Researchers examined the effects on MNST performance of seven types of soil amendments, from slow-release fertilizers to various composts, used in trial plots.
  • Timing of seed and sod installations. Subsections of large trial plots at St. Paul and Blaine, Minnesota, were seeded or sodded monthly starting May 1 through Nov. 1. The watering regimens followed MnDOT’s 2014 specifications.
  • Post-installation watering regimens. Researchers planted sod plots of MNST and Kentucky bluegrass in a controlled outdoor area using an automatic sheltering system that protected the test areas when it rained. Irrigation was carefully controlled to test seven watering regimens. Researchers studied turf cover, root growth and shear strength of grasses at the sites.

What Did We Learn?

Soil amendment treatments had little effect on turfgrass performance, whether the plots were seeded or sodded.

MNST planted as seed cannot tolerate the heat and frequent drought conditions of Minnesota’s summers during establishment. Seeding should therefore only occur in August and September. Sod may be laid between May and November, provided there is adequate irrigation.

MNST differs biologically from Kentucky bluegrass and has different watering needs. Root development occurs more slowly and requires a longer period of irrigation during establishment, thriving with moisture replacement between 60 and 100 percent of the evapotranspiration rate. With adequate water, MNST establishes well.

MNST should not be mown until roots are established several inches into the soil profile. Drought-stressed turf should not be mown.

What’s Next?

Revisions to MnDOT’s specifications and guidelines are needed. In addition, MnDOT will need to adjust its previous recommendations for watering MNST-12 sod to ensure a successful installation. Further, guidelines for designers and inspectors must be updated. MNST is a different grass community than Kentucky bluegrass–dominated sods: The perception of what “success” looks like must be changed, and this change can be best accomplished through images. New methods of irrigation will need to be devised and implemented. Providing water only as the plant needs it could result in considerable savings in water and labor over time. Additional studies related to best management practices are pending.


This post pertains to the LRRB-produced Report 2017-31, “Best Management Practices for Establishment of Salt-Tolerant Grasses on Roadsides,” published July 2017. 

Design Considerations for Embankment Protection During Overtopping Events

Roadways in Minnesota’s Red River watershed are prone to flooding and overtopping, where wide flows of water wash across the surface of the roadway. Repairing the resulting damage to roadway embankments can be costly and time-consuming, requiring lengthy road closures. Protecting roads from destructive scour could significantly reduce the cost and time of repairs after a flood event. Researchers investigated three “soft” design methods using full-scale models and field monitoring, with flexible geogrid mat providing the best erosion protection. Regardless of protection technique, any physical separation from the soil beneath led to failure by creating a pathway for water to follow. Establishing root growth and vegetation would improve the performance of all techniques by anchoring the soil.

“This project developed a fairly complete matrix of useful erosion protection measures that our own staff can implement—techniques that are less elaborate and more cost-effective than hiring contractors,” said J.T. Anderson, Assistant District Engineer, MnDOT District 2.

“This project was a combination of basic and applied science, and is a great example of the university and MnDOT working together successfully to solve problems unique to our geography and climate,” said Jeff Marr, Associate Director, Engineering and Facilities, University of Minnesota St. Anthony Falls Laboratory.

What Was the Need?

Roadways in the Red River watershed are prone to flooding and overtopping, where wide flows of water wash across the surface of the roadway. Downstream scour and erosion of roadway embankments can result in breach or washout of the entire roadway. Repairing the damage caused by flooding and overtopping can be costly and time-consuming, requiring lengthy road closures. Frequent flood events in recent years reinforce the need to protect roadways where flooding is likely to occur.

Raising the roadway to prevent overtopping is not a feasible solution, as flood plain law does not allow moving the problem elsewhere by backing up the water. The most cost-effective option is to allow floodwaters to overtop roadways and to try to protect their embankments from scour. Protecting roads from destructive scour and erosion by developing cost-effective scour prevention measures could greatly reduce the cost of repairs, as well as the time required to reopen the roadway after a flood event.

What Was Our Goal?

The goal of this project was to investigate the effectiveness of slope protection techniques to shield overtopped roadways and their downstream embankments from scour and erosion. A further goal was to use cost-effective methods that could be installed by local agencies instead of contractors. The researchers evaluated several “soft” design methods using an integrated approach of full-scale models and field monitoring.

What Did We Do?

Using the findings from a literature review, the research team developed a field-based program to collect data on the hydraulics associated with full-scale overtopping events. Researchers recorded flood stage at several locations near the Red River during over-topping events and evaluated the failure modes under natural conditions. Annual field monitoring occurred from 2013 through 2016 during overtopping events.

Next, the research team conducted a series of experiments at a full-scale laboratory facility to study the hydraulic and erosional processes associated with overtopping. The facility simulated a transverse section of a roadway and included an upstream water supply, road crest, shoulder and downstream embankment slope.

Photo of sod growing through square mesh plastic geogrid material
Sod is overlaid with geogrid to help stabilize the sod’s root system and soil beneath.

Two slopes were examined in the lab: 4:1 (horizontal:vertical) and 6:1. With bare soil used as a control, three erosion protection techniques were investigated: armored sod hydraulic soil stabilization, turf reinforcement mat (Enkamat) and flexible concrete geogrid mat (Flexamat). All three are alternatives to riprap and other hardscapes, and encourage vegetation to grow through a mat, helping to stabilize the soil and protect the embankment from scour and erosion.

What Did We Learn?

The researchers were able to draw some definitive conclusions from the laboratory experiments:

  • Bare soil with no vegetative cover (the control) is highly susceptible to erosion and is the worst-case scenario. New installations should have established vegetation before the first overtopping event is expected.
  • All three mitigation techniques reduced erosion, but the flexible concrete geogrid mat provided the best protection. Researchers noted that these results describe overtopping that occurred immediately after the protection treatments were installed. Established vegetation and root growth would likely improve the performance of all techniques.
  • Initiation of erosion appears to be linked to small-scale inconsistencies in the soil, erosion control material and placement of the protection technique. Small failures can quickly develop into mass failure of the embankment.
  • Failure occurred in areas where the protection technique physically separated from the surface of the soil and exposed a direct pathway for the water to flow. Inflexible protection techniques were the poorest performers.
  • Common locations for failure were the toe of the slope and the upstream transition from the shoulder to the soil slope, with steeper slopes failing most often.

What’s Next?

No mature vegetation existed on the embankment slope in the laboratory flume, which mimics the post-construction period in the field. Full vegetation is more typical for much of an embankment’s life cycle. Since one of the most important functions of vegetation on a slope is the ability of its roots to anchor soil, further study of these techniques with mature vegetation could provide a better understanding of their effects.

Future studies should include other stabilization techniques as well as the effects of overtopping on frozen and thawing soils, through-embankment seepage or piping, and various soil types on performance of the stabilization technique. Future projects could also evaluate the use of multiple techniques along with the study of anchoring improvements and longevity of the erosion control products.


This post pertains to the LRRB-produced Report 2017-21, “Design Considerations for Embankment Protection During Road Overtopping Events,” published June 2017. NCHRP Synthesis Report 496, “Minimizing Roadway Embankment Damage from Flooding” provides the state of the practice on mitigating damage from overtopping. 

MnDOT Explores the Use of a Unified Permitting Process for Oversize/Overweight Loads

Researchers produced a proof-of-concept for developing a one-stop permitting process that would allow commercial haulers to plan a travel route and secure all required permits from a single source. MnDOT is working to develop a first-of-its-kind, unified permitting process to consolidate the requirements of every jurisdiction in the state into a single, quick-response platform that meets the needs of haulers.

“From a hauler’s perspective, the permitting process can be very cumbersome. Each agency’s application is different as are the general provisions that haulers need to follow,” said Renae Kuehl, Senior Associate, SRF Consulting Group, Inc.

“As carriers, we’re trying to do our due diligence in getting permits. But the current process can lead to significant safety and legal risks,” said Richard Johnson, Transportation Manager, Tiller Corporation.

What Was the Need?

Hauling oversize or overweight freight on Minnesota’s roadway system—highways, county roads, township roads and city streets—requires approval by each governing authority along the route. Roadway managers must review hauler travel plans to make sure size and weight limits for vehicles and loads will not endanger roadway facilities, hauler equipment and personnel before issuing the over-size or overweight permit.

Any single hauling route may require permits from multiple roadway authorities, each with different application procedures and response times. Some governing bodies, MnDOT among them, issue these permits online and can turn them around in minutes. Other agencies issue permits by mail, fax or email, which can take several days.

Haulers, however, may not have time to wait for a permit. If equipment breaks down at a loading site, for example, replacement equipment is needed immediately to meet contract deadlines and avoid paying labor costs for idle workers. A construction emergency may also demand large equipment be towed to a site. In situations like these, haulers often make the trip without appropriate permitting, accepting the legal and safety risks.

What Was Our Goal?

To simplify the permitting process, Minnesota local agencies would like to develop an online permitting application process that would allow permit-seekers to determine routes based on their vehicle and load size, and secure all necessary permits at one time. This research, the first phase of a multiphase study, aimed to determine the feasibility of a one-stop, unified permitting process by studying its technological and operational needs and gathering input from various stakeholders.

What Did We Do?

Investigators worked with the Technical Advisory Panel (TAP) and a group of policy experts from county and state agencies, commercial haulers and consultants to identify audiences with a stake in a unified permitting process. During meetings in northern Minnesota and in the Twin Cities area, investigators and TAP members met with key stakeholders: haulers and representatives from industry organizations; seven MnDOT offices (including Freight and Commercial Vehicle Operations, Information Technology, Maintenance and Geospatial Information); Minnesota counties; the City of Duluth; the Duluth-Superior Metropolitan Interstate Council; Minnesota State Patrol; the State Patrol Commercial Vehicle Section; and a county sheriff’s office.

The research team identified the challenges and needs of each stakeholder and organized the concerns according to policy, process and technology. Then they explored solutions that would allow the development of a one-stop permitting process.

What Did We Learn?

Researchers determined that a unified permitting process is feasible. Policy issues include the need to standardize general provisions statewide, such as travel hours, insurance requirements and warning devices such as flagging needs. For example, currently the color of flags and lettering on banners vary from jurisdiction to jurisdiction; well-framed general provisions could make these requirements more uniform to serve multiple jurisdictions. The information required by each governing authority in its permit applications could also be normalized.

Process issues were about workflow. More than 80 percent of hauler requests are repeat-able: A commercial haul may be run on the same route with the same-size load three times a month for four months and may not require a full reapplication each time. Some agencies rely on paper, fax or emails to receive permit requests; others purchase permit-ting software; still others build their own software. These systems could be made more uniform so they could interact and share information among agencies.

Technology issues called for an interoperable system that could bring together geographic information system (GIS) capabilities and regulatory data that could be both received and shared. Mapping data could identify each permit required along a route being developed, and a portal could allow agencies to share information as well as allow permit-seekers to enter information and retrieve permits themselves. A portal could also integrate different software packages while offering information like Minnesota’s Gopher State One Call digging hotline.

What’s Next?

In Phase II of this project, which has already begun, researchers will develop a pilot portal that allows users to create route plans, identify permits needed and apply for all permits in one action. Investigators will test the platform with a three-county group. If this effort is successful, researchers will build a unified permitting process for use within all jurisdictions in Minnesota.

MnDOT is also enhancing its software for handling oversize/overweight permits and carrier credentials. Transportation Research Synthesis 1704 surveyed state agencies about current offerings.


This post pertains to the LRRB-produced Report 2017-26, “Oversize/Overweight Vehicle Unified Permitting Process (UPP) Phase I,” published August 2017. 

Pothole Patching Study Yields Best Practices Guidance

Researchers identified four pothole repair methods suitable for Minnesota: cold mix, hot recycled asphalt, mastic material and mill-and-fill with hot-mix asphalt. They tracked the performance of each method at five sites in northern Minnesota for two years. Using the results from this monitoring period, researchers developed decision trees for selecting an appropriate repair method and best practices for using each method. The decision trees were developed in two formats: as a flowchart that can be used in a maintenance guide and as flash cards that can be laminated and used by maintenance crews for quick reference in the field.

“We wanted to develop a decision tree for choosing the right pothole repair method that could be laminated for use in the field,” said Susan Lodahl, Assistant State Maintenance Engineer, MnDOT Office of Maintenance.

“This project offers help deciding what kind of pothole patch is appropriate for the conditions, including the pothole dimensions, location in the roadway and the season,” said Manik Barman, Assistant Professor, University of Minnesota Duluth Department of Civil Engineering.

What Was the Need?

Repairing potholes is one of the most public of road crews’ duties. Drivers notice cracks and holes, and feel the effects of short-term repairs that kick up gravel as wheels roll over patched holes.

Selecting the appropriate patching method and materials varies depending on several factors, including the size of the pothole and its location on the roadway. Patching methods and materials face seasonal challenges too. In northern Minnesota, asphalt plants shut down for the winter and don’t reopen before March, if then. Potholes that are repaired in cold weather aim for short-term fixes with patches that can be replaced when warm weather returns or when the pavement can be milled and overlaid with hot-mix asphalt (HMA). Road crews have tried applying HMA in winter using various heating systems and in-place recycling methods, but even warm weather patches only offer semipermanent repair.

Whether it’s spring, summer, fall or winter, choosing the best, most cost-effective or durable pothole repair method has remained a complicated puzzle, one that MnDOT would like to help road crews solve.

What Was Our Goal?

MnDOT funded this research to help road crews choose patching methods that match specific repair conditions. Researchers explored patching tools, materials and methods to identify those most appropriate to specific pothole conditions, road locations and time of year. They also evaluated the effectiveness of different methods based on durability, road safety, ride quality, driver satisfaction and other factors.

A researcher conducts a test on a pothole
A researcher conducts an on-site permeability test to determine how well a pothole repair seals and resists water penetration.

What Did We Do?

Research began with a comprehensive literature search of pothole repair methods in Minnesota and other states. From this search, investigators identified four repair methods that best suit Minnesota: cold mix, hot recycled asphalt, mastic material and mill-and-fill with HMA.

With help from the study’s Technical Advisory Panel, researchers identified five sites in MnDOT District 1 near Duluth, Minnesota, where they oversaw 20 pothole repairs. Investigators monitored these repairs for about two years before assessing the methods and their best applications. Researchers then developed decision trees to help road crews choose the most suitable method for each repair and compiled best practices to provide further guidance.

What Did We Learn?

The best practices describe the best uses of each of the four pothole repair methods along with guidelines for preparing the pothole for repair and placing the patching materials.

Cold-mix patches should be placed only in shallow potholes with depths of 2 inches or less. Deeper potholes should be repaired in two lifts, each compacted with a handheld compactor to prevent dishing or denting when the cold mix settles.

Hot mixes using recycled materials should be avoided. The aged binder slows the heating process, and its fines inhibit the bonding of the new binder and aggregate. The new binder also doesn’t seem to rejuvenate the old, and the patches age more rapidly. When hot mix is used for pothole repair, a handheld compactor is required. Recycling mixers such as the Stepp SRM 10-120 should be used to create virgin hot patch material using asphalt oil and sand or small aggregate.

Mastic material provides a smooth driving surface but appears to dish in potholes along longitudinal cracks because the material lacks the strength to support loads. Mastic should only be used on centerline joints and longitudinal joints along shoulders, where it stays in place. It should not be used in wheel paths.

Mill-and-fill with virgin HMA, when constructed with care, can be effective in eliminating dishing and raveling at the patch-pavement interface. Sufficient tack material must be used, and trucks should not be allowed to drive on the tack. The pothole should be filled with the proper amount of HMA, and the patch must be compacted sufficiently. Failure to carefully apply mill-and-fill can lead to significant deterioration at the patch-pavement interface after about 100 days, which can contribute to additional damage in the distressed area.

Using the findings from this study, researchers developed guidelines for patching method selection, placement, compaction practices and moisture control. They also developed decision trees for selecting the appropriate repair method for conditions. The decision trees are available in two formats: as a flowchart for use in maintenance guides and as flash cards for quick reference by maintenance crews in the field. The final report includes best practices and a step-by-step pictorial guide to patching.

Simple Decision Tree for Comprehensive Field Evaluation of Asphalt Patching Techniques

What’s Next?

The decision trees and best practices developed in this study can be easily combined into a patching guide that, with laminated flash cards, can be distributed to MnDOT road crews around the state. This research could be amplified by repeating the process with more pothole repairs in other areas of Minnesota to increase data for performance evaluation and analysis of best practices.


This post pertains to Report 2017-25, “Comprehensive Field Evaluation of Asphalt Patching Methods and Development of Simple Decision Trees and a Best Practices Manual,” published June 2017. 

Cost-Effective Strategies for Repairing Grout in Post-Tensioned Bridges

Researchers provided recommendations and general guidance to assist MnDOT in developing cost-effective strategies for future investigation and repair contracts of post-tensioned bridges built in Minnesota before 2003. To develop these recommendations, researchers identified grout voids in post-tensioning ducts on two representative bridges, documented strand corrosion and repaired voids by filling them with grout.

“With the guidelines developed in this project, we have a good basis for cost-effectively and efficiently inspecting post-tensioned bridges built before 2003,” said Dustin Thomas, South Region Bridge Construction Engineer, MnDOT Bridge Office.

“From a fiscal perspective, it makes sense to do limited inspections on these bridges before committing additional resources to more comprehensive inspection and repair,” said Mark Chauvin, Associate Principal and Unit Manager at Wiss, Janney, Elstner Associates, Inc.

What Was the Need?

Some concrete bridges in the United States are strengthened using post-tensioning—a method of reinforcing concrete by running steel strands through a hollow plastic or metal duct placed within the concrete element. Tension is then applied to these strands with a hydraulic jack, com-pressing the concrete and creating internal stresses that resist external traffic loads. Post-tensioning improves the durability of concrete and virtually eliminates cracking.

Post-tensioning ducts are filled with grout—a mixture of cement, sand and water that hardens around the steel strands. This practice prevents the strands from corroding if they are exposed to air, water and deicing chemicals.

Grouting materials used in bridges built before 2003 frequently produced voids where grout did not fully fill the post-tensioning ducts or cover the strands. These post-tensioning strands were vulnerable to corrosion, which can lead to deterioration in bridge elements over time. Once transportation agencies and the industry became aware of these issues, they improved their construction practices and began using prepackaged grout materials with additives so that the post-tensioning ducts would be completely filled.

About 40 post-tensioned bridges were built in Minnesota before 2003 that might still require repair. MnDOT commissioned a two-phase project to develop techniques for evaluating these structures. In the first phase of the project, completed in 2012, researchers inspected a representative sample of these bridges and developed a general inspection protocol to guide future investigations. In the second phase, described here, researchers developed additional guidance about grout repairs, as well as the most cost-effective contracting methods for such repairs.

What Was Our Goal?

The goal of the second phase of this project was to provide recommendations and general guidance that MnDOT could use to develop cost-effective strategies for future investigation and repair of post-tensioned bridges built in Minnesota before 2003. As part of this project, researchers identified grout voids in post-tensioning ducts on two representative bridges, documented strand corrosion and repaired voids by filling them with grout.

Workers repairing grout voids
Following bridge inspections, about one-third of discovered grout voids were filled using vacuum-assisted or pressure grouting repair techniques.

What Did We Do?

In 2013, researchers inspected three spans on two Minnesota bridges for voids around post-tensioning strands. They began the project by using ground penetrating radar to map the location of the ducts. Once the ducts were located and mapped, researchers used a borescope to visually inspect the duct interiors at locations where voids were likely to be present. When they found voids, they documented the percentage of the duct filled by grout and the extent of corrosion in the post-tensioning strands within the ducts, if any. Following inspection, researchers filled the voids with grout and installed sensors within the voids at two locations to monitor the long-term corrosion of post-tensioning strands.

Using their experience with these repairs, researchers then created guidelines that would help MnDOT develop cost-effective strategies that can be implemented in future post-tensioning duct investigation and repair contracts.

What Did We Learn?

Researchers found voids in 32 percent of inspected ducts. These voids were typically at least 10 feet long and about one-half the diameter of the duct. Although prestressing steel strands were exposed at approximately half of the grout voids, no significant corrosion of the strands was observed at any location. Light to moderate corrosion was usually observed on the inside surfaces of the galvanized metal ducts at grout voids.

The guidelines developed by researchers address:

  • Typical work plans for investigation and repair, including considerations for bridge access and traffic maintenance during inspection and repair.
  • Document review, including bridge design drawings and post-tensioning shop drawings.
  • Visual surveys to identify signs of distress near post-tensioning ducts.
  • Procedures for borescope inspection and remedial grouting repair.
  • Various contract and project approaches for developing specialized inspection and re-medial repair contracts, with a discussion of the advantages and disadvantages of each approach. Using multiple contracts with graduated levels of inspection and repair will most likely provide MnDOT with the best value.
  • Planning-level cost information for seven representative pre-2003 post-tensioning bridges identified by MnDOT to assist in future budget calculations.

What’s Next?

The guidelines developed in this project will provide MnDOT with a framework to solicit and procure similar engineering and construction services contracts for post-tensioning bridges in Minnesota. Researchers recommend exploring additional techniques to more rapidly assess and inspect post-tensioned bridges, including noninvasive investigative methods that do not require drilling holes.


This post pertains to Report 2017-04, “Considerations for Development of Inspection and Remedial Grouting Contracts for Post-tensioned Bridges,” published January 2017.

Tailgate Test Kit Speeds Up Flocculant Choice to Reduce Sediment in Runoff

The Tailgate Test Kit quickly and easily identifies flocculants that reduce turbidity in construction stormwater discharge. The mobile test setup efficiently determines which of the many available products works best for a particular construction site. In this study, 13 product combinations were tested. A short list of five tests was developed, as well as worksheets to aid in calculating the amount of flocculant needed and developing scale-up procedures.

“The Tailgate Test Kit is a cost-effective innovation that will help us determine the flocculant and quantity of product to use in the field and in real time,” said Dwayne Stenlund, Natural Resources Program Coordinator, MnDOT Environmental Stewardship.

“It’s important to add to the body of knowledge in this area,” said Joel Toso,
Senior Water Resources Engineer, Wenck Associates, Inc. “The Tailgate Test Kit is already being used in the field to help both contractors and maintenance workers make decisions.”

What Was the Need?

Stormwater runoff from construction sites often carries sediment from soil erosion, causing the water to become cloudy or turbid. Federal, state and local stormwater regulations prohibit construction sites from discharging water that is too turbid into the environment. Instead, the runoff must be sent to ponds to allow the sediment to settle to the bottom of the pond. The remaining clear effluent may then be discharged from the site.

A worker collects a sample of construction site stormwater runoff in a plastic-lined settling pond while another looks on.
Testing stormwater sediment levels at the construction site allows field crews to begin treating turbid water quickly.

The chemicals in flocculants speed up the sediment settling process by causing the sediment particles to clump together and fall to the bottom more rapidly. A number of flocculating agents are commercially available. The most effective agent for a specific situation is generally deter-mined by testing various flocculants with water samples in a lab. This selection process usually takes one or two days. Only after the appropriate flocculant is selected can the entire pond be treated.

To speed up this process, MnDOT has developed the Tailgate Test Kit, a series of tests that can be conducted in the field to determine the most effective flocculant, as well as the correct amount, for a specific construction site and soil type. What used to take a day or two to process in the lab now can be accomplished by field crews in an hour or two on the tailgate of a truck, enabling workers to begin treating the ponded turbid water much more quickly.

What Was Our Goal?

The overall goal of this study was to build upon the findings of several recent research projects, including “Flocculation Treatment BMPs for Construction Water Discharges” (2014-25), by developing and improving field methods to reduce total suspended sediment from construction stormwater runoff. A specific aim was to create a method for work crews to test water samples in the field using a mobile test toolkit that contains flocculants identified in previous research. Other goals included determining the most effective amount of the flocculant needed, developing the calculations needed for scale-up once the best product is identified and implementing a test for residual unreacted product.

What Did We Do?

To identify a variety of flocculant product types to evaluate with the Tailgate Test Kit, the research team summarized stormwater best management practices from the literature and from other departments of transportation. Since the effectiveness of product types varies depending upon soil and sediment types and environmental conditions, researchers conducted 13 tests of nine flocculant products (alone and in combination) taken from five distinct product classifications: mineral, polyacrylamide, chitosan, bio-polymer and anionic polyacrylamide. They also tested water samples from eight locations in Minnesota to ensure a cross section of representative samples.

What Did We Learn?

Using the results from these tests, the research team developed a short list of five tests that could be conducted in the field and incorporated in the Tailgate Test Kit. The five tests represent a range of flocculant product classifications and reduce the time required to complete the tests.

The team also prepared worksheets with mixing and dosing guidance to help users identify the most effective amount of product to achieve the target turbidity goal. Finally, the team developed scale-up procedures to aid in using test results to determine full-scale dosing rates on-site and procedures for testing new flocculant products.

The researchers investigated four methods for testing residual flocculant to detect any unreacted product in a sample. A preferred method was not identified during the course of this research but would still be a desirable research outcome.

What’s Next?

Next steps for this research effort include field implementation and new product evaluation.

First, investigators recommend developing a training module and field guide for using the Tailgate Test Kit to encourage implementation of the mobile kit throughout the state. If users understand how it works and how to use the test results for scale-up calculations, they will be more likely to use it.

Second, the product list should be kept current by testing additional flocculant products. It may also be beneficial to create a category for flocculants on the MnDOT Approved/Qualified Products List.

Finally, methods to identify residual and unreacted flocculant product need to be developed. If excess flocculant product is used in field tests, the residues will eventually have to be collected and removed for disposal. Minimizing the excess flocculant used at construction sites is desirable.


This post pertains to Report 2017-32, “Tailgate Test Kit for Determining Appropriate Sediment Reducing Chemicals and Dose Rates,” published July 2017. 

New Project: Protecting RICWS and DMS From Wind Damage

MnDOT recently entered into a contract with the University of Minnesota (UMN) to complete a research project to keep wind from damaging rural intersection conflict warning signs (RICWS) and other digital message signs (DMS).

The project is titled “Understanding and Mitigating the Dynamic Behavior of RICWS and DMS Under Wind Loading.” Lauren Linderman, assistant professor at UMN’s Department of Civil, Environmental and Geo-Engineering, will serve as the principal investigator. Jihshya Lin of MnDOT will serve as technical liaison.

“This project will find out the behavior of the DMS and RICWS under AASHTO defined design loads and develop the retrofitting system to avoid the experienced problems that will improve the public safety, reduce the maintenance cost and minimize impact to the traffic,” Lin said.

Background

RICWS have exhibited excessive swaying under wind loads, leading to safety concerns regarding failure of the support structure at the base. It is believed the heavy weight of these signs has brought the frequency range of these systems too close to that of the wind excitations. There is a need to investigate the wind-induced dynamic effects on these sign structures and to propose modifications to the systems to reduce the likelihood of failure. There is also interest in investigating the dynamic behavior of the DMS, particularly the loads on the friction connection.

This research project involves a field investigation to determine the structural performance of these two types of sign structures. Laboratory tests using a towing tank facility and a wind tunnel will be performed on scaled models and opportunely modified models to improve performance and minimize unsteady loads.

The outcome of this project is expected to develop an understanding of the RICWS and DMS sign structures and to provide modifications to improve the structural performance of the RICWS sign structures while maintaining the crashworthy requirements. The results will help to ensure the uninterrupted service of these sign structures, which are important to public safety.

 

Project Tasks

  • Task 1A: Development of Field Instrumentation Plan and Instrumentation Purchase
  • Task 1B: Experimental Determination of Load Effects and Dynamic Characteristics of Post Mounted DMS in Field
  • Task 2A: Development of Numerical Models to Investigate Post Mounted DMS Sign Demands and Fatigue
  • Task 2B: Validation of Numerical Models to Investigate Post Mounted DMS Sign Demands and Fatigue
  • Task 3A: Investigation of Design Loads and Relevant Fatigue Considerations for DMS
  • Task 3B: Analysis of Design Loads and Anticipated Fatigue Life of DMS
  • Task 4: Experimental Determination of Dynamic Characteristics of RICWS in Field
  • Task 5: Development and Validation of Numerical Models to Investigate RICWS Signs
  • Task 6: Numerical and Experimental Investigation of Drag and Vortex Shedding Characteristics of RICWS Signs Using Scaled Models
  • Task 7: Numerical and Small-Scale Experimental Investigation of Modifications to RICWS Sign Panel to Reduce Effects of Vortex Shedding
  • Task 8: Numerical and Analytical Investigation of Noncommercial Means to Damp Motion of RICWS Blankout Sign Structure
  • Task 9A: Research Benefits and Implementation Steps Initial Memorandum
  • Task 9B: Research Benefits and Develop Implementation Steps
  • Task 10: Compile Report, Technical Advisory Panel Review and Revisions
  • Task 11: Editorial Review and Publication of Final Report

The project is scheduled to be completed in March 2019.

Reducing Driver Errors at Two-Lane Roundabouts

Researchers studied driving behavior at four multilane roundabouts to better understand the relationship between traffic control designs and driver errors. Data collected showed that certain traffic control changes decreased turn violations but failed to eliminate yield violations. Researchers were unable to identify long-term solutions for improving roundabout design and signage, and recommended further research to improve the overall safety and mobility of multilane roundabouts.

“Even though the study did not provide a silver bullet on how to prevent crashes at multilane roundabouts, it did create an efficient tool to analyze and quantify driving behavior data,” said Joe Gustafson, Traffic Engineer, Washington County Public Works.

“This study has advanced our knowledge in multilane roundabout safety and is one step closer to providing much needed improvements to roundabout design guidance,” said John Hourdos, Director, Minnesota Traffic Observatory, University of Minnesota.

What Was the Need?

Roundabouts have been shown to improve overall in-tersection safety compared to traditional traffic signals. However, noninjury crashes are sometimes more frequent on multilane roundabouts than on single-lane roundabouts due in part to driver confusion. Common driver errors such as failing to yield and turning violations on multilane roundabouts have contributed to an increase in noninjury crashes.

Given the benefits of improved mobility, traffic throughput and injury reduction of multilane roundabouts, reducing the noninjury crash rate at multilane roundabouts is important to facilitating their use by Minnesota cities and counties. Identifying solutions to reduce common driving violations would be more sustainable than the current practice of converting multilane roundabouts back to single-lane roundabouts.

In a previous study on a two-lane roundabout in Richfield, Minnesota, researchers demonstrated that traffic control  changes could reduce some of these driver errors. However, more data was needed to support study results. Understanding driver behavior and improving traffic control devices are key factors in designing safer multilane roundabouts.

What Was Our Goal?

With limited research on modern multilane roundabouts, the Minnesota Traffic Observatory sought to collect more data to evaluate the correlation between traffic control design features and collisions. Instead of conducting manual observations, researchers used an innovative video analysis tool to collect and process recorded videos of driving behaviors at test sites. Based on the analysis, they attempted to identify driver behaviors and error rates to help reduce noninjury crashes at multilane roundabouts.

What Did We Do?

The research team selected four multilane roundabouts in Minnesota — two in Mankato, one in Lakeville and one in St. Cloud — to observe undesirable driving maneuvers. At each roundabout site, researchers mounted video cameras at key locations to record one to two weeks of driving behavior. Only one roundabout could be observed at a time because only one set of specialized video equipment was available.

The raw videos were processed to produce a data set for analysis. Researchers used TrafficIntelligence, an open-source computer vision program, to automate extraction of vehicle trajectories from the raw footages. They used the same software to correct any errors to improve data reliability. The resulting clean data from the recorded videos were supplemented with historical crash frequency data reports obtained from the Minnesota Department of Public Safety. Collectively, data from both sources allowed researchers to thoroughly investigate the frequency and crash types from the four roundabouts. A statistical analysis of the data revealed that turn violations and yield violations were among the most common driving errors.

Researchers also looked at how violation rates vary with the roundabout’s location and relevant design features. Based on these findings, researchers proposed signage and striping changes to reduce driver errors at the two Mankato test sites. After the changes were implemented, they collected additional video data.

What Did We Learn?

This study provided one of the most comprehensive analyses to date of driving behavior at multilane roundabouts. Researchers were successful in finding solutions for reducing turn violations, but they were unable to identify solutions for yield violations despite the vast amount of data.

Minor differences in the design at each roundabout presented specific challenges. The analysis focused on how each varying design feature impacted driving behavior. Proposed traffic control changes such as extending solid lines between entrance lanes, adjusting the position of yield signs and adding one-way signs successfully decreased turn violations. However, data from before and after traffic control changes showed an insignificant impact on decreasing yield violations. Importantly, the study produced a list of ineffective traffic control methods that can be eliminated from future studies, saving engineers time and money.

The TrafficIntelligence tool was crucial in efficiently processing and cleaning large amounts of raw video. With improvements made to the software program, the tool should be an asset to future research on roundabouts and to other studies requiring observations of driving behavior.

What’s Next?

The traffic control changes that were successful at reducing crashes at two-lane roundabouts should be implemented by traffic engineers. In particular, large overhead directional signs or extended solid lines between entrance lanes should be installed to help reduce turning violations. The analysis method used in this study could also be used for a robust before-and-after evaluation of future modifications to traffic control devices.

Additional research could further scrutinize the data already collected, and researchers recommend that more data be collected to examine additional traffic control methods and other intersection design elements to improve the overall safety and mobility of two-lane roundabouts. This research could also serve as an impetus for the study of numerous roundabouts in a pooled fund effort involving several states.


This post pertains to the LRRB-produced Report 2017-30, “Evaluation of Safety and Mobility of Two-Lane Roundabouts,” published July 2017. A webinar recording of the report is also available.

MnDOT Chooses EasyMile for Autonomous Shuttle Bus Project

ST. PAUL, Minn. – The Minnesota Department of Transportation chose EasyMile, a France-based company specializing in driverless technology, to lead its autonomous shuttle bus pilot project. MnDOT announced in June it will begin testing the use of an autonomous shuttle bus in a cold weather climate.

“We’re excited to partner with EasyMile to help MnDOT test autonomous technology,” said Jay Hietpas, MnDOT state traffic engineer and project manager. “Their expertise will help us learn how these vehicles operate in a winter weather environment so we can advance this technology and position MnDOT and Minnesota as a leader.”

EasyMile, which has a location in Colorado, has conducted driverless technology cold weather tests in Finland and Norway. Minnesota will be their first cold weather test site in the U.S. EasyMile will use its EZ10 electric shuttle bus that has already transported 160,000 people more than 60,000 miles in 14 countries. The shuttle was tested in various environments and traffic conditions. During these tests, the shuttle operated crash-free.

The shuttle operates autonomously at low speeds on pre-mapped routes. It can transport between six and 12 people.

Initially, it will be tested at MnROAD, which is MnDOT’s pavement test facility. Testing will include how the shuttle operates in snow and ice conditions, at low temperatures and on roads where salt is used.

Testing is scheduled to start in November and go through February 2018. The shuttle will also be showcased during the week of the 2018 Super Bowl.

Hietpas said 3M will also be a partner in the project so the company can research various connected vehicle concepts including sensor enhancement and advanced roadway safety materials. When optimized, these materials would aid in safe human and machine road navigation.


Read more about the autonomous shuttle bus pilot project:


Related MnDOT research: