Tag Archives: maintenance

New Tools to Optimize Truck Station Locations

The Minnesota Department of Transportation (MnDOT) has 137 truck stations across the state. These stations house and allow maintenance of MnDOT highway equipment as well as provide office and work space for highway maintenance staff. Within 20 years, 80 of these stations will need to be replaced as they reach the end of their effective life spans. Researchers developed a geographic information system based modeling tool to determine the most effective locations for truck stations in the state. Using data from many sources, a new research study has determined that MnDOT could rebuild 123 stations, relocate 24 on land available to MnDOT and combine two. MnDOT would save millions of dollars using the location optimization alternatives over the 50-year life cycle of a typical truck station.

What Was the Need?

MnDOT operates 137 truck stations, 18 headquarter sites for maintenance operations and over 50 areas for materials delivery. Truck stations are used to house and maintain large highway equipment, and to provide office and work space for highway maintenance staff. Some stations also store materials. 

The average life span of a truck station is 50 years. Within the next 20 years, 80 of MnDOT’s truck stations will need to be replaced. With costly capital replacement imminent, MnDOT has considered measures to optimize truck station locations within its eight state districts, including possibilities of reducing the size of some, increasing others, or combining the facilities of some state and local agencies into new partnerships. Determining the best effective locations for new truck stations could reduce costs for both state and local partners.

MnDOT needed a means of selecting and collecting the most appropriate data for an investigation into optimizing truck station locations. The agency also needed tools such as a computer model to analyze the data. These resources would allow MnDOT to determine the most time- and cost-effective locations for future truck stations. 

What Was Our Goal?

The initial objective of this research project was to collect data about truck service areas, including the quantity of highway equipment and materials capacity, and the materials storage capacity of facilities. This information combined with service route data would allow MnDOT to optimize truck station locations by determining whether facilities should be closed, resized, combined or relocated, and whether other materials storage locations would be necessary. An economic benefit–cost analysis would compare alternatives. 

A map of Minnesota indicates the location of each of MnDOT’s 137 truck stations with a blue square and of major highway routes connecting the stations, also shown in blue.
This project will determine the future of more than half of MnDOT’s 137 truck stations in the next two decades.

What Did We Do?

To determine how other departments of transportation (DOTs) and related agencies have addressed choosing the best locations for facilities, researchers conducted a literature review that included reports from six state DOTs and Australia, Transportation Research Board publications and other research papers. In addition, they consulted the standards developed by MnDOT’s Truck Station Standards Committee. 

Researchers also conducted surveys and interviews of both MnDOT and outside agency stakeholders. 

With many data sets collected for each truck station site, researchers used a geographic information system (GIS) platform to solve a location-allocation problem and a multivehicle routing problem for the truck stations. The problems incorporated such factors as amount of equipment, equipment capacity, storage capacity, material demand for road segments and other information. Estimated costs of operation for each location alternative were compared to present costs of each truck station. 

“Using real-world data, we built GIS models of maintenance operations to determine optimal truck station locations. With expected life spans of around 50 years, truck stations that are optimally located will reduce operating costs and save money for MnDOT and Minnesota taxpayers.” —William Holik, Assistant Research Engineer, Texas Transportation Institute

MnDOT’s Maple Grove Truck Station and Maintenance Center is a new 108,000-square-foot facility.
MnDOT’s truck stations range in size from Class 1 buildings of at least 25,000 square feet to smaller
Class 3 facilities with four or fewer overhead doors.
MnDOT’s Maple Grove Truck Station and Maintenance Center is a new 108,000-square-foot facility. MnDOT’s truck stations range in size from Class 1 buildings of at least 25,000 square feet to smaller Class 3 facilities with four or fewer overhead doors.

What Did We Learn?

The literature review showed that optimizations of facility locations may require a second level of sites, such as strategically placed materials storage depots. Some research also showed that both transportation and facility costs must be considered and that after a certain point, consolidation of stations could cost more as vehicles and staff were required to drive farther to reach them. 

Reports of state DOT location optimization efforts were instructive. Iowa DOT noted the need to consider the slow highway speeds of snowplows. This was a critical element for researchers to include in their optimization models as it determines route travel times. Vermont Agency of Transportation highlighted the use of satellite materials depots. Generally, state DOT efforts were confined to small regional issues, unlike MnDOT’s statewide scope.

In interviews with MnDOT and local agency stakeholders, researchers learned about partnerships that already existed between MnDOT and city and county agencies. These partnerships primarily included the sharing of truck stations and sometimes of materials. These partnerships were included in the optimization development.

Researchers optimized the truck station location using a GIS optimization model and separate cost analyses. They developed alternatives for each truck station individually. Each alternative was then analyzed to determine costs and savings over a 50-year life cycle. 

Finally, researchers determined which alternatives could be most effectively executed and their optimum order. They also developed an implementation plan for station relocation and replacement. This modeling was an iterative process: Each optimal location replaced the existing location and became the baseline against which the next station alternative was compared. The result was a comprehensive set of location possibilities for each MnDOT district with multiple alternatives for every truck station, including benefit–cost analyses. Researchers’ optimization solutions determined that 123 truck stations could be rebuilt on-site, 24 could be relocated on land available to MnDOT, and two could be combined. 

“We successfully analyzed all of our truck station and loading locations, determined which were good candidates for potential relocation or consolidation, and developed a data-driven plan of action to save millions of dollars.” —Christopher Moates, Planning Director, MnDOT Building Services

What’s Next?

MnDOT now has the information it needs to effectively implement cost-saving changes in future truck station planning and construction. The agency could use the researchers’ initial recommendations or further employ the GIS modeling tool to examine variations on the results of the project. 

This post pertains to Report 2019-10, “Optimizing Truck Station Locations for Maintenance Operations,” published February 2019. For more information, visit MnDOT’s Office of Research & Innovation project page.

Pothole Patching Study Yields Best Practices Guidance

For most road crews, repairing potholes is an essential and highly visible duty.  Choosing the best or most cost-effective pothole repair method, however, has remained a complicated puzzle.

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.

DecisionTree

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. 

New recommendations aim to help roadside turfgrass thrive

Keeping Minnesota’s roadsides green is about more than just aesthetics—healthy turfgrass can improve water quality, reduce erosion and road noise, and provide animal habitat. However, harsh conditions such as heat, drought, and salt use can make it difficult for roadside turfgrass to thrive.

In 2014, as part of a study funded by the Minnesota Local Road Research Board (LRRB), researchers in the University of Minnesota’s Department of Horticultural Science identified a new salt-tolerant turfgrass mixture that could be used on Minnesota roadsides. But, when MnDOT began using the mixture, called MNST-12, the agency experienced a series of installation failures.

Now, led by Professor Eric Watkins, the research team has identified new best management practices for installing and establishing this type of salt-tolerant turfgrass.  The study, funded by the LRRB, specifically focused on watering practices, soil amendments, and planting date for both seed and sod.

“Newer improved seed or sod mixes like MNST-12 may have differing requirements for successful establishment compared to other species or cultivars that contractors and other turf professionals are more familiar with,” Watkins says. “Since all of these management practices are prescribed—or not prescribed—in the MnDOT specifications, generating data that can inform future specifications is a valuable outcome of this work.”

The study, which was conducted over several years, included experiments on how water should be applied to new MNST-12 turfgrass installations, the use of soil amendments at the time of establishment, and the effect of the seeding or sodding date on the success of a new planting.

Researchers tested turfgrass watering requirements using an automated rain-out shelter. Photo: Matt Cavanaugh

Based on their findings, the researchers recommend these changes to MnDOT specifications:

  • No soil amendments are necessary, but adequate seedbed preparation is important.
  • Seeding is preferred to sodding between August 15 and September 15.
  • Sodding can be permitted throughout the year, but only if the installer is able to supply frequent irrigation.
  • When watering in sod, attention should be given to the species being used and local rates of evapotranspiration (evaporation from both the soil and plant leaves). Sod installers can anticipate using between 100,000 and 170,000 gallons of water per acre to ensure a successful establishment.
  • Sod can be mowed as soon as sufficient root growth prevents an operator from manually pulling up pieces by hand, but it should not be mowed if wilting from heat or drought.

Currently, the researchers are using the results of this project to develop methods for educating and training stakeholders, including turfgrass installers, on these best management practices. They are also developing systems that could be used by installers in the field to help maximize the success rate of turfgrass installations.

“These best management practices can help limit installation failures and reduce maintenance inputs for future installations, providing both an economic and environmental benefit,” Watkins says.

“The knowledge and improved specifications we gained through this research will allow us to make our contractors more successful, which makes MnDOT successful,” says Dwayne Stenlund, MnDOT erosion control specialist. Because local agencies often rely on these MnDOT specifications as a guide for their projects, they will also benefit from the improved practices.

Stenlund also says the new specifications—especially those related to watering requirements—could allow for a clearer understanding of the true cost and value of turfgrass installation and maintenance work, which could ultimately improve the accuracy of the project bidding process.

In another project, the research team is exploring other turfgrass stresses, such as ice cover and heat. They are also testing additional turfgrass species and mixtures in an effort to continue improving MnDOT specifications for roadside turfgrass installations.

Knowing While Mowing: GPS Keeps Maintenance Workers Out Of the Weeds

As temperatures fall and days get shorter, MnDOT Metro District maintenance workers are wrapping up a season of mowing grass along roadsides and in medians that they hope will prove a little more efficient than in the past.

Thanks to a research project that installed GPS devices in tractor cabs, operators have a better sense of exactly which areas they need to mow and which areas should be left alone. Five Metro District tractors were tested in 2015. This year, more than 40 tractors were fitted with the automated vehicle location (AVL) technology, which includes a GPS antenna, an on-board central processing unit (CPU) and an in-cab screen with a user interface.

Trisha Stefanski, Metro District asset management engineer, expects one of the biggest benefits of the project to be a reduction in herbicide use. Maintenance crews use herbicide to control the spread of noxious weeds that sometimes get spread during mowing operations. Mapping exactly where noxious weeds are, and providing that information to operators on a real-time, in-cab screen and user interface helps them mow around those areas.

“We’re really hoping it will reduce the amount of herbicide that we’re putting on our roadways by 50 percent,” Stefanski said. “We’re not certain that will be the number, but that’s what we’re hoping for. We think just not mowing those areas will not spread as many noxious weeds and so we don’t have to apply as much herbicide.”

Metro District operators, such as Jesse Lopez, give the AVL technology rave reviews.

“Basically you can see what you shouldn’t mow and what you should mow. So, it makes it easy for me. It’s just like playing a game,” Lopez said. “This actually helps me to optimize what my job is. I know exactly where I’m at and where I’m going. I think everyone should use it – absolutely everybody who is in a mowing situation or a plowing situation.”

In addition, the AVL technology helps maintenance supervisors keep tabs on exactly where their operators are in real time. It also helps supervisors complete reports by automatically providing the geographic areas where mowing has been completed.

Stefanski says the project has gone really well, and she hopes collecting more data over another mowing season will show real savings on herbicide use. In the meantime, she is thinking of other ways AVL technology could be applied to maintenance operations.

“What I really like about the project is that we are taking something used in a lot snow plows and a lot of other technologies – cars, other things, maybe UPS uses them – and we’re putting it into maintenance operations,” Stefanski said. “Having it for mowing, we can also use it for smooth pavements. We can also use it for other things in mowing operations.”

Taking the guesswork out of measuring winter operations

Being able to accurately and reliably estimate traffic conditions during snow events is critical to transportation agencies. Typically, state DOTs use measurements such as “time to bare pavement”—based on the visual inspection of plow drivers—to gauge the progress of snow operations. These estimates are limited, however, by the subjectivity and inconsistency of human-based measurements.

Now, new research sponsored by the MnDOT and led by University of Minnesota Duluth civil engineering professor Eil Kwon aims to take the guesswork out of assessing traffic conditions during winter weather events.

“Dr. Kwon’s research on a new approach to snow and ice performance reporting is exciting,” says Steve Lund, state maintenance engineer and director of the Office of Maintenance at MnDOT. “For quite a few years, MnDOT snowfighters have been reporting their performance through a visual review of the roadway conditions. Our snowfighters have a tough job—automating the performance reporting will remove that task from their duties. Also, looking at traffic returning to a ‘normal’ condition is truly the ultimate goal or outcome measure, and where we want to go.”

In the first phase of this project, researchers developed a prototype process that uses data on traffic speed, flow, and density collected by loop detectors in the Twin Cities metro area to estimate the point at which traffic patterns return to normal—an indicator that the roadway surface has “recovered.” In the newly published second phase, researchers further analyzed the traffic flow patterns during snow events under normal and snow conditions and refined the earlier prototype into a traffic-data-based measurement process for snow operations.

“We found that by comparing the variation patterns in traffic flow during a snow event with those during normal weather conditions, we could successfully identify the recovery status of the traffic flow at a given location,” Kwon says.

Based on their findings, the researchers developed a new process to identify the Normal Condition Regain Time (NCRT)—as an alternative to the traditional “time to bare pavement” measurement used to gauge the progress of maintenance operations during a winter weather event.

One advantage of the new process is that it can reflect how road surface conditions affect traffic flow differently during day and night periods. “Nighttime traffic flow patterns are substantially different from those during daytime periods,” Kwon says. “We identified normal traffic patterns separately for daytime and nighttime conditions to account for these differences in estimating the recovery status.”

Future research plans include the development of an operational version of the NCRT estimation system that can be used on a daily basis to analyze and improve snow operations, and the creation of an online version that can be used for coordinating snow operations in real time.

“There is a lot of potential to use these findings to make snow operations even more effective and efficient,” Kwon says. “For example, the analysis of the relationship between the NCRT measures and operational strategies such as plowing start time and methods could help further refine MnDOT’s winter maintenance strategies.”

For more information, download the technical summary (PDF) or the project’s final report.

Video Demonstration: Robotic Message Painter Prototype

In the above video, University of Minnesota-Duluth Associate Professor Ryan Rosandich tests a prototype of a robotic arm he developed to paint messages and markings on roadways. He calls the machine “The MnDOT Robot.”

During a test run in October 2015, the MnDOT robot painted a right-turn arrow and the word “ahead” on pavement at MnDOT’s Pike Lake station in Duluth.

Rosandich hopes commercial companies will show an interest in further developing his proof-of-concept technology into something that road authorities can use regularly to make work easier, faster and safer for their employees.

Companies interested in commercializing this technology can contact Andrew Morrow at amorrow@umn.edu.

Editor’s Note: The paint used in the above demonstration was diluted due to the cold weather at the time of the demonstration and does not reflect the condition of the paint expected in a typical application.

Road Surface Monitors Could Help Reduce Salt Usage

MnDOT is testing a mobile road condition monitor that uses infrared technology to detect hazardous ice, snow or wet conditions without even touching the pavement.

Maintenance crews hope the device, called the High Sierra Surface Sentinel, could help them better determine when it’s time to apply salt when they’re plowing. The mobile sensor reports air temperature, surface temperature and road friction data.

“The biggest reason we’re looking at this is for the friction reading,” said MnDOT Salt Solutions Coordinator Joe Huneke. “Typically, when operators are patrolling their route and the road looks like it’s getting icy, they’ll err on the side of caution and apply salt — and it may not need it.”

The device being tested by snow and ice crews in northern Minnesota would also provide real-time surface weather conditions. Currently, plow operators and supervisors must enter road conditions into a computer or relay them by phone, a time-consuming process that operators are not always able to perform in a timely manner.

The biggest potential benefit, however, is lower salt consumption.

“Sometimes you get a light cold snow event where it might look like there’s a little ice on the road, but, in fact, you have good friction numbers and you don’t need salt. Once you put chemical down, you’re committed to it,” Huneke said.

District 1 snow and ice crews are evaluating the unit pictured below for its accuracy and effectiveness in determining slippery conditions. It will be compared with another device tested in District 3 that also uses infrared technology to determine how slippery the road is, and technology being tested in District 6 that uses gravitational force to determine the road surface friction.

MnDOT it testing a mobile surface condition sensor that provides real-time surface weather condition of roadways.
MnDOT it testing this mobile road condition sensor, which provides real-time surface weather condition of roadways.

Related Research

MnDOT’s Office of Maintenance has its own research program designed to let maintenance personnel test innovative ideas to keep our roads smooth, snow-free and safe. They even put out a monthly bulletin featuring new ideas and technologies. (You can find the back issues here.)

Other winter maintenance research projects are featured in MnDOT’s 2011-2013 Maintenance Operations Research Report  (PDF, 9 MB, 98 pages)

MnDOT Plow Drivers Invent New, Hybrid Plow Design

If the plow pictured above looks like two different plows welded together, it’s because they are.

Minnesota Department of Transportation snow plow operators in southwestern Minnesota have invented an experimental plow that uses the wind to cast snow from the road without impeding traffic or the operator’s view.

Manufactured for MnDOT by Fall Plows, the plow incorporates half of a traditional bull-dozer style plow with half of a Batwing-style plow.  It eliminates the large “ear” on the driver’s side of a Batwing style plow that can stick out into oncoming traffic during center-line snow removal.

Half of the reversible batwing-style plow, pictured at left, was combined with half of the reversible bulldozer-style plow, pictured at right.
Half of the reversible batwing-style plow, pictured at left, was combined with half of the reversible bulldozer-style plow, at right.

District 8 Willmar Maintenance Supervisor Dennis Marty said he was looking for a reversible-style plow that could be used in the heavy winds and reduced visibility from blowing snow that are prevalent in western Minnesota.

When drivers are plowing against a northwest wind in rural Minnesota, the snow coming out of the chute will sweep across the truck and blind drivers, so operators needed a plow with a reversible system so they could throw the snow with the wind.

While an express plow with chutes on both ends (batwing-style), pictured above at left, was great for throwing snow to the right, when snow plow drivers took it down narrow two-lane roads, the plow stuck 2.5 feet into the oncoming lane and its big barrel partially blocked the headlights and the operator’s view.

So operators tried a regular one-way plow (pictured below), which resembles a funnel laid on it side, and put it on a reversible system that would allow operators to turn the plow both directions, so it could throw snow to the right or the left. However, this plow couldn’t blow snow high enough to the left, so snow piled in the left traffic lane.

One-way reversible plow.
One-way reversible plow.

Marty said he spent four to five years looking for a plow that combined the batwing and bull-dozer designs, but he couldn’t find anything sturdy and maintenance-free enough. Finally, he and Maintenance Research Program Administrator Ryan Otte sat down with Falls Plows in Little Falls, Minnesota and asked the company to build one.

The plow will be useful on low-volume roads that have little traffic during the middle of the night, which allows plow operators to cast the snow with the wind.

The Willmar office began using the experimental plow last winter and will be replacing all of its plows with it. Snow plow drivers from other areas of the state have been so impressed that at least two other maintenance districts have also ordered them.

Related Research

MnDOT’s Office of Maintenance has its own research program designed to let maintenance personnel test innovative ideas to keep our roads smooth, snow-free and safe. They even put out a monthly bulletin featuring new ideas and technologies. (You can find the back issues here.)

Other winter maintenance research projects are featured in MnDOT’s 2011-2013 Maintenance Operations Research Report  (PDF, 9 MB, 98 pages)