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.
Minnesota’s next round of transportation research projects will attempt to solve these and other questions facing the state’s transportation community. The Transportation Research and Investment Group, which governs MnDOT’s research program, and the Minnesota Local Road Research Board, which represents cities and counties, recently met and selected 21 transportation research projects for funding in fiscal year 2018.
“The selected research studies, which typically take one to three years to complete, will address some of the most major policy, environmental and maintenance dilemmas facing transportation practitioners,” said Linda Taylor, director of MnDOT Research Services & Library.
Below is a list of the selected projects, with links to associated need statements. Final project scopes will become available once contracts are approved. For further information, go here.
To mark Earth Day 2016, MnDOT Research Services is taking a glance at five stellar examples of current research projects at MnDOT that involve pollution control, wetland mitigation, road salt reduction and new ways of recycling pavement.
Soil carried away in stormwater runoff from road construction sites can pollute lakes and rivers.
Stormwater settling ponds provide a place for this sediment to settle before the water is discharged into local bodies of water. However, since stormwater ponds have limited space, a mechanism is needed to remove clean water from the pond to prevent the overflow of sediment-laden water.
MnDOT-funded researchers designed temporary stormwater ponds with floating head skimmers that can remove clean water from the surface of the settling pond, using gravity to discharge water into a ditch or receiving body.
The study, which was completed in spring 2014, identified five methods for “skimming” stormwater ponds that can improve a pond’s effectiveness by 10 percent. MnDOT researchers also created designs for temporary stormwater ponds on construction sites with the capacity to remove approximately 80 percent of suspended solids.
These designs will help contractors meet federal requirements for stormwater pond dewatering. Researchers also determined how often a pond’s deadpool must be cleaned, based on watershed size and pool dimensions.
Stormwater can pick up chemicals and sediments that pollute rivers and streams. Roadside drainage ditches, also known as swales, lessen this effect by absorbing water. But until recently, MnDOT didn’t know how to quantify this effect and incorporate it into pollution control mitigation measures.
In a study completed in fall 2014, researchers evaluated five Minnesota swales, measuring how well water flows through soil at up to 20 locations within each swale.
A key finding: grassed swales are significantly better at absorbing water than expected, which may reduce the need for other, more expensive stormwater management practices, such as ponds or infiltration basins.
This could save MnDOT and counties significant right-of-way and construction costs currently expended on more expensive stormwater management techniques.
Road salt is used for de-icing roadways during winter months, but can have a negative impact on the environment.
This research, which was just approved for funding through the Minnesota Local Road Research Board in December 2015, will investigate the reduction in road salt application during winter months that can be attained with permeable pavements, while still providing for acceptable road safety.
Some initial investigations (see previous study) suggest that road salt application can be substantially reduced, even eliminated, with permeable pavement systems. The proposed research will investigate this hypothesis more thoroughly, and further document the reduction in road salt application that can be expected with permeable pavement.
Road construction in northeast Minnesota often causes wetland impacts that require expensive mitigation. However, borrow areas excavated for road construction material can be developed into wetland mitigation sites if hydric vegetation, hydric soils and adequate hydrology are provided. Fourteen wetland mitigation sites were constructed north of Virginia, Minnesota along the U.S. Trunk Highway 53 reconstruction project corridor and evaluated for wetland. The sites were established with the goal of mitigating for project impacts to seasonally flooded basin, fresh meadow, shallow marsh, shrub swamp, wooded swamp, and bog wetlands. All but one of the sites consistently meet wetland hydrology criteria.
The sites contain a variety of plant communities dominated by wet meadow, sedge meadow, and shallow marsh. Floristic Quality Assessment (FQA) condition categories for the sites range from “Poor” to “Exceptional.”
According to the research report published in March 2016, these sites have shown the potential for creating mitigation wetlands in abandoned borrow pits in conjunction with highway construction. Adaptive management, particularly water level regulation, early invasive species control, tree planting, and continued long-term annual monitoring can make mitigation sites like these successful options for wetland mitigation credit.
MnDOT already extends the lives of some old concrete highways by paving over them with asphalt instead of tearing them up. Now MnDOT hopes to add a third life for these old concrete roads by using a process called cold in-place recycling to re-use that existing asphalt pavement when it reaches the end of its life.
Cold in-place recycling (CIR) uses existing pavements, without heat, to create a new layer of pavement. It involves the same process of cold- central plant mix recycling (which is being employed by MnDOT for the first time on two shoulder repair projects this year), but it is done on the road itself by a train of equipment. It literally recycles an old road while making a new road.
CIR has been in use in Minnesota for 20 years, but only with hot-mix asphalt (HMA) over gravel roads. The purpose of a new study, which was approved for funding in April 2016, is to validate Iowa’s promising new practice using CIR on bituminous over concrete.
In this research project (see proposal), MnDOT will use cold-in-place recycling to replace the asphalt pavement on a concrete road and then evaluate it for several years, comparing it also with control sections.
Along with the potential of a better service life, the cost of CIR is much lower than new hot mix asphalt (HMA). Therefore, a 20-percent to 30-percent price reduction per project may be realized.
MnDOT’s latest crop of transportation research projects have been identified. This year, researchers were asked to pay special attention to how their work could benefit the public and be put into real-world practice.
MnDOT’s Transportation Research Innovation Group (TRIG) and the Minnesota Local Road Research Board recently announced their Fiscal Year 2017 funding awards after hearing proposals from researchers at multiple universities. The two bodies chose 20 research proposals totaling about $2.9 million that will study new and innovative approaches to improving the environment, making transportation systems safer, improving construction methods and operating in more cost-effective ways.
According to MnDOT Research Management Engineer Hafiz Munir, MnDOT Research Services made some key changes to its annual requests for proposal that will help ensure research makes a difference to the agency’s bottom line. This year, researchers were asked early on in the proposal process how they would quantify their results, what benefits the research could achieve and how their research could be implemented in the future.
“Now we’ll be able to track those metrics and that will help MnDOT not only quantify the potential benefits of the projects, but also implement the results,” Munir said. “The bottom line is that we will be able to not only save money, but also improve the way MnDOT does business.”
Several of the 20 newly funded projects deal with improving transportation safety, Munir said, and many others are focused on implementing cost-saving practices, innovations and new technologies.
The projects approved in December 2015 will do the following:
Create an inexpensive GPS-based system that alerts the driver when a motor vehicle deviates from a lane or approaches a curve. (Project summary)
Find out whether a smartphone app can effectively warn drivers about upcoming roadway curves. (Project summary)
Determine whether different types of roadway turfgrass are better suited for specific regions of the state. (Project summary)
Create a comprehensive design guide for fish-friendly culverts. (Project summary)
Determine how social media can be used to engage diverse community groups within the state. (Project summary)
Investigate the performance of the state’s first glass fiber reinforced polymer (GFRP) reinforced bridge deck, slated for construction in 2016. (Project summary)
Develop signage recommendations to slow high-speed traffic as it approaches roundabouts. (Project summary)
Gather truck reliability data, identifying truck bottlenecks and providing potential mitigation solutions for regular congestion areas. (Project summary)
Determine why anchor bolts are becoming loose on overhead signs, light towers and other support structures — and how to prevent it. (Project summary)
Establish a system and smartphone app for accurately capturing and reporting data about intrusions into work zones. (Project summary)
Develop an advanced sensor system to estimate long-term and dynamic vertical displacements on the I-35W bridge. (Project summary)
Investigate the necessity of pavement markings on low-volume roads and develop an approach to prioritize pavement marking projects. (Project summary)
Compare the performance of different structural fibers in thin concrete overlays. (Project summary)
Evaluate four performance test methods that predict the cracking behavior of asphalt mixes. (Project summary)
Investigate the link between transportation investment and job creation, and analyze transportation investments, business patterns and socioeconomic data in Minnesota counties. (Project summary)
Refine a taconite-based pothole repair compound, and develop a low-cost mechanized system to mix and place it in large quantities.(Project summary)
Investigate how much road salting can be safely decreased with the use of permeable pavements. (Project summary)
Evaluate the use of iron-enhanced check dams for capturing phosphate and toxic materials from roadway runoff. (Project summary)
Improve accessibility calculation capabilities and understanding of travel behavior by integrating data about highway bus operations, park-and-ride facilities, and urban parking costs. (Project summary)
Investigate the concept of estimating traffic volumes from mobile device samples to collect traffic data inexpensively. (Project summary)
Munir said the next steps for these projects this spring include creating technical advisory panels, finalizing project work plans and preparing contracts. Some projects could begin early, depending on available funding and project-readiness. By the time Fiscal Year 2017 begins on July 1, funding will be available to begin all 20 projects.
A handful of county highway department employees in the Rochester area gathered recently at the Olmsted County Public Works Service Center for a presentation and live demonstration by University of Minnesota Research Fellow Brian Davis about his team’s work involving light detection and ranging – or LiDAR.
“LiDAR is like radar, but with light,” Davis said. “It gives you information about what’s around the sensor.”
Davis and his fellow researchers have outfitted a sedan with special LiDAR equipment and other technology that is capable of capturing a 360-degree, 3-D view of a scene in real time.
“We use the car as a test bed,” Davis said. “We have a lot of different types of sensors on the car that we use for the different projects that we’re working on. Right now we have a LiDAR sensor on top. Sometimes we have a high-accuracy GPS receiver in there. We have a cellular modem. We have a handful of inertial sensors. So it’s a lot of different stuff that we use to cater to the application.”
For his presentation, Davis showed the attendees some of the data his team had already collected.
“We showed a handful of pre-collected data at a handful of intersections around Rochester and Minneapolis,” Davis said. “What it shows is the point cloud collected by the sensor – just the raw point cloud with no post-processing done. In that information you can see people moving through it, cars moving through it, buses and light rail trains.”
After the presentation, Davis led the group to the parking lot for a close-up look at the technology and how it collects data and displays that data in real time. Le Sueur County GIS manager Justin Lutterman was among those who could envision possible applications for LiDAR.
“It’ll be interesting to see where this can go,” Lutterman said. “I’m sure the private industry will take off with this and emergency management, or the sheriffs and ambulances, would appreciate this kind of technology on their vehicles for a situation they might have to recreate. Roads and traffic designers would be able to monitor their resources, pavements, traffic counts and things like that.”
Over the coming months, researchers will gather more data to develop a workshop for county personnel interested in learning more about LiDAR and how it can be applied in their transportation systems.
“The next steps for this project are to collect some data with the car at intersections. Then we can use that information to fine tune our algorithms,” Davis said. “What the algorithms are going to do is take that raw data and give us useful information, like the number of cars, or the time a car passes through an intersection. That all feeds into the workshop we’re developing. The workshop is going to be for county GIS workers, traffic engineers and county engineers who are interested in learning about these technologies.”
In the search for a quieter rumble strip, Minnesota may have found a winner in California.
California’s standard rumble strip design outperformed Minnesota’s and Pennsylvania’s in a comparison study along a rural highway near Crookston, Minnesota. (Read the recently published report.)
“California’s rumble strip still gave significant feedback to drivers, but it was significantly less noticeable outside the vehicle,” said engineering consultant Ed Terhaar, who performed a noise analysis with acoustical engineer David Braslau on behalf of the Minnesota Local Road Research Board.
Although they serve as an effective warning to drivers, rumble strips can cause unwanted noise when a vehicle drifts over a centerline or edgeline.
Both the LRRB and the Minnesota Department of Transportation, which is sponsoring a companion study, are interested in finding a new design that still captures the driver’s attention, but minimizes the sound heard by neighboring residents.
Polk County tests
Terhaar and Braslau’s research showed that Minnesota and California’s designs produce a similar level of interior noise. Although external decibel levels are not that different from each other either, Minnesota’s rumble strip has a considerably stronger tone that can be heard further away.
“California’s sound is less sharp, less intrusive and less noticeable,” Braslau said. “Minnesota’s has a really sharp peak. So while the absolute sound level of California’s isn’t all that much lower, its perception is less.”
Testing was performed using three different vehicles – a passenger car, pickup truck and semi-trailer truck – at three different speeds – 30, 45 and 60 miles per hour.
In general, Pennsylvania’s rumble strip had both a quieter interior and exterior sound than California’s and Minnesota’s.
Like Pennsylvania, California’s rumble strip has what is called a sinusoidal design – a continuous wave pattern that’s ground into the pavement (it’s the style commonly used in Europe and has been called a “mumble strip” because it’s quieter). The main difference between the two is that California’s wave length is 14 inches, while Pennsylvania’s is 24 inches.
Minnesota’s design is much different than the sinusoidal pattern used by the other two states.
“It’s not a continuous wave – it’s basically chunks of pavement taken out at certain intervals with flat pavement in between. It’s more of an abrupt design, whereas California and Pennsylvania’s are more continuous and smooth,” Terhaar explained.
The next step for researchers is to test variations of the California rumble strip design at MnDOT’s Road Research Facility (MnROAD).
The 8-inch rumble strip tested in Crookston is the typical edgeline design used by Polk County, but it was found to be too narrow for semi tires, so MnDOT will look at wider designs in its follow-up study. Researchers will also look at the impacts to motorcyclists and bicyclists, as well as the California rumble strip’s centerline striping capability.
A new tool developed by the Local Road Research Board helps cities and counties assess how much increased heavy vehicle traffic affects local roads.
Researchers created an analysis method and corresponding spreadsheet tool that city and county engineers can use to calculate the impact of heavy vehicles on asphalt roads beyond what was planned in the original pavement design.
The information will help agencies optimize services, such as garbage collection, for the least amount of damage. It will also help agencies better plan roads in new developments, as well as redesign existing roads that are nearing the end of their lives.
Lack of Data
Heavy trucks cause local roads to deteriorate more quickly than passenger vehicles, but it is challenging to quantify the impacts, especially for areas where traffic was not forecast at the time a road was designed.
Many local engineers in Minnesota have requested information about the impact of heavy vehicles in light of new construction, commercial distribution facilities and hauling routes. This information is needed to assist in local road planning and maintenance.
In a newly completed study, investigators developed two methods for calculating heavy vehicle impact:
Calculate the additional bituminous material (and associated costs) that would have been required to construct the pavement had the heavy truck traffic been predicted when the pavement was designed.
Calculate the portion of a pavement’s design life, measured in equivalent single-axle loads (ESALs), consumed by unanticipated vehicles.
“Before this project, there wasn’t an easy way for an engineer to determine how much a specific truck was going to decrease the life of a road,” said Deb Heiser, Engineering Director, City of St. Louis Park.
Whereas previous research has calculated the impact of extremely heavy vehicles over the short-term (typically the course of a construction project), this project calculates the impact of long-term increases in traffic from vehicles that are heavy, but still mostly within normal legal weight limits.
The tool can be used for a single street segment or an entire road network. Users can also compare current situations with proposed ones to evaluate the impact of potential changes in heavy traffic levels.
Replacing traffic signs at the right time is an important science.
Waiting too long can endanger lives and expose an agency to a lawsuit. But replacing traffic signs prematurely could cost a single city tens of thousands of dollars per year.
If fully implemented, new recommendations developed by MnDOT and the Local Road Research Board (LRRB) could save public agencies as much as $41 million over three years by helping them better manage their signs and meet new federal requirements on retroreflectivity without replacing signs prematurely. Here’s how:
At a purchase price of $150 to $250 a piece, plus $20 per year for maintenance, the cost of an unnecessary traffic sign adds up. (Maintenance costs involve replacing signs that have been vandalized, knocked down, or that no longer meet required levels of retroreflectivity.)
In a case study of townships in Stevens County, Minnesota, researcher Howard Preston found that nearly a third of traffic signs were not required and served no useful purpose. The average township has 180 signs, which results in an annual maintenance cost of $3,600. The average county has 10,000 signs — an annual maintenance cost of $200,000.
Public agencies could save a collective $26 million* just by removing unnecessary or redundant signs from the field, Preston said. A traffic sign maintenance handbook developed by the LRRB and MnDOT guides agencies through that process.
Traffic signs have more life in them than the typical 12-year manufacturer’s warranty, Preston said. But how often agencies replace them varies throughout the state.
Whereas small municipalities may replace signs on an individual basis through spot-checking for retroflectivity, MnDOT has a schedule. Each of the agency’s 400,000 signs is replaced within 18 years of installation.
Preston found that MnDOT could safely extend the service life of its signs to 20 years, which would save an estimated $1.3 million within the first few years of implementation.
Assuming (in lieu of a research-backed benchmark) that local municipalities would likely start replacing signs around the 15-year mark to ensure compliance with the federal law, Preston estimates that townships, cities and counties could avoid a collective $6 million in unnecessary costs per year just by adhering to the minimum 20-year replacement schedule recommended by the study.
Agencies are required by federal law to have a method in place for ensuring that signs maintain adequate retroreflectivity. A replacement schedule based on science is one way; regular physical inspection is another.
Researchers, who consulted other state’s studies and also examined signs in the field, determined that the life of the modern sign in Minnesota is at least 20 years.
It’s possible that traffic signs actually retain their retroreflectivity for 30 years or more, but further study is needed since sheeting materials on today’s traffic signs haven’t been deployed long enough to know, researchers say.
Minnesota’s transportation research governing boards put a new emphasis on financial benefits when selecting next year’s round of transportation research projects.
MnDOT’s Transportation Research Innovation Group (TRIG) and the Local Road Research Board announced their Fiscal Year 2016 funding awards this week after hearing proposals from researchers in several states. They selected 20 research proposals hall-marked by novel approaches to improving the environment, increasing transportation safety, improving construction methods and boosting the bottom line.
“We asked the principal investigator to present the safety and financial benefits up front, and how they can be implemented to improve the transportation system and economic viability of Minnesota,” said MnDOT Research Management Engineer Hafiz Munir. “We’re making a point early in the process to identify those potential benefits, quantify them and document them in our tracking system.”
Researchers will test new technology that could make crack-free pavements; find better, faster and less expensive ways to reclaim roads; and even explore how to use waste material from road construction projects as part of the landscaping to absorb water runoff.
Links are provided below to brief descriptions of each of the projects:
A revised handbook offers Minnesota cities and counties the latest tips on how to meet new sign retroreflectivity requirements, as well as the 411 on sign maintenance and management – everything from knowing when it’s time to remove a sign to creating a budget for sign replacement.
“The life cycle of traffic signs, from installation to replacement, is a pretty complex issue and it can be a challenge to get your arms around,” said Tim Plath, Transportation Operations Engineer for the city of Eagan. “This handbook really boils it down into some basic concepts and also gives you the resources to dig deeper if necessary. It’s a good resource to have at your fingertips.”
This handbook updates a previous version issued in 2010, to include new FHWA retroreflectivity and maintenance and management requirements and deadlines.
“Maintenance/management of a large number of signs can potentially be an administrative and financial challenge for many local road authorities,” explained Sulmaan Khan, MnDOT Assistant Project Development Engineer.
Here’s a video demonstration of a sign life reflectometer (the Gamma 922), another resource MnDOT has available for local government agencies. Cities, townships or counties may borrow the reflectomer by contacting the Office of Materials and Road Research, (651) 366-5508.