To help guide the state’s future transportation research investments, the Minnesota Department of Transportation recently completed a five-year comprehensive strategic plan that looks at streamlining the research governance structure at MnDOT and developing a clearinghouse of information about the agency’s research portfolio to improve decision-making.
MnDOT Research Services, which administers the bulk of the state’s transportation research projects, recently completed a visioning session with agency stakeholders as the first step in implementing the recommendations of the strategic plan, which include:
Establishing agency-wide research strategic priorities
Tracking all of MnDOT’s research expenditures, including those performed outside Research Services
Tracking research investment levels to measure return on investment
Reporting on the outcomes of research projects beyond their life cycle
Identifying the value and impact of research at a topic and program level
In addition to the approximately 175 state, local and multi-state transportation research projects administered and tracked by MnDOT Research Services, several MnDOT specialty offices also invest in their own research to support or guide their work.
In recent years, MnDOT inspection crews have reported loose anchor bolts on many support structures for overhead signs, high-mast light towers, tall traffic signals, and other signs and luminaires. On newly installed structures, many nuts on anchor bolts may loosen in as little as three weeks; on older structures, they may loosen less than two years after retightening.
Federal standards mandate inspections at least once every five years, a requirement that already stretched MnDOT’s resources for managing light poles, traffic signals and 2,000-plus overhead signs. With an estimated 20 percent of loose anchor bolts in MnDOT’s highway system at any given time, crews would have to inspect structures every year to ensure public safety.
This issue is not unique to Minnesota. In a national survey, some states estimate as many as 60 percent of their anchor bolts may be loose. Minnesota, like other states, tightens anchor bolts according to American Association of State Highway and Transportation
Officials (AASHTO) standards. But the standards and procedures for tightening and retightening bolts were insufficient. To develop appropriate specifications, MnDOT needed to know why bolts loosen. The agency also needed improved standards and procedures to ensure that anchor bolts are tightened effectively
What Was Our Goal?
MnDOT decided to undertake a research project to determine why anchor bolts and nuts on sign and luminaire support structures loosen after installation or retightening, and to develop new standards and procedures that ensure proper and lasting tightening of these bolts.
Researchers from Iowa State University examined specifications and procedures for tightening anchor bolts on support structures in Minnesota. They also developed new specifications and instructions to help crews tighten bolts properly and ensure lasting safety of signs and lights in Minnesota’s highway system.
How Did We Do IT?
Researchers conducted a literature search on anchor bolt loosening. Then they surveyed MnDOT maintenance staff on bolt lubrication and tightening practices, and visited sites in Minnesota and Iowa to observe installation and retightening practices.
In the laboratory, investigators studied the relationship of torque, rotation and tension of various bolt diameters and material grades. They found that bolt stiffness, grip length (the distance between the nuts at each end of an anchor bolt in a two-nut bolt system), snug-tight standards, lubrication and verification after 48 hours played a role in effective tightening practices.
To determine the impact of environmental and structural strain on bolt tightness, researchers monitored sign structures in the field and in the lab. They attached strain gages to the bolts and post of an overhead sign near Minneapolis-St. Paul and installed a wind monitor, camera and data logging unit nearby to collect strain and environmental data for four months. In the lab, they instrumented a post and baseplate mounted in concrete to compare current and proposed tightening specifications and practices.
Investigators developed specifications for each bolt size and grade, anchor baseplate dimension and pole size used by MnDOT based on lab and field results. They also created finite element models to analyze future anchor bolt configurations.
What Did We Learn?
Over- and under-tightening contribute to premature loosening of nuts on anchor bolts. While contractors may lack the experience and training to properly use turn-of-nut guidance, AASHTO recommendations poorly serve the bolt sizes and grades used by MnDOT.
AASHTO’s snug-tight guidance neglects certain characteristics of nuts and bolts, and its turn-of-nut direction is provided for only two bolt sizes and two bolt grades. In some cases, these standards may cause the heads of small bolts to break off and may lead to undertightening of large bolts. MnDOT can measure torque in the field but cannot determine tension, making AASHTO’s equation for verifying torque and tension impractical.
“We have revised our specs to follow the recommended procedures for anchor bolt tightening. The new tables of verification torque values will be fine for both two-nut and one-nut anchor bolt systems,” says Jihshya Lin, Bridge Evaluation and Fabrication Methods Engineer, MnDOT Bridge Office.
Researchers revised the specifications to require bolt lubrication, establish torque levels for snug-tight and specify turn-of-nut rotation after snug-tight for a range of MnDOT materials:
• Eight bolt sizes, ranging from ¾-inch diameter to 2.5-inch diameter.
• Five bolt grades.
• Nine baseplate thicknesses.
• 12 single- and double-mast pole types.
The new specifications provide torque levels in tables to verify the tightness for each bolt, plate and pole type, eliminating the need to run equations. To assist crews that are installing or retightening anchor bolts, researchers developed guidelines that include a compliance form with a checklist to direct crews through each step of the tightening process and ensure proper tension.
The new specifications and procedures should improve public safety and reduce the traffic control, manpower and equipment expenditures required to respond to prematurely loosened nuts. Continued monitoring of bolts installed and retightened under these specifications over time would help evaluate the new procedures.
A new implementation project is underway that will demonstrate these findings in the field. Researchers will also produce educational videos for training and demonstration to MnDOT personnel and contractors. Video topics will include:
Basic Concepts of Bolt Tightening
New Specified Procedures
Signals and Lighting
Additionally, researchers will provide one or more training sessions with training materials. Materials and videos will be posted on a website developed by the researchers.
This winter, MnDOT snowplow operators will test and document their experience using potassium acetate (KAc) during severely cold weather as a possible alternative to the commonly used deicing material sodium chloride.
MnDOT maintenance staff have used potassium acetate in the Duluth area as a deicing alternative in several locations (Bong Bridge, Blatnik Bridge, I-35 tunnels, and I-35 at Thompson Hill) with anecdotal success. Advantages of KAc include reducing chlorides runoff into water, a lower effective deicing temperature (approximately -20F) than salt or brine, and less corrosion to vehicles and public infrastructure.
KAc will be used on four plows at select locations in the MnDOT District 1 Duluth sub-area. Crews will document the effectiveness of KAc in removing snow and ice pack at temperatures of minus 15 to 20 degrees Fahrenheit and reducing the time it takes plows to achieve and maintain bare pavement during severely cold temperatures.
In addition to evaluating potassium acetate as an alternative de-icing chemical, researchers will develop application guidelines and material handling requirements.
Researchers from CTC & Associates will review the 2018 Transportation Research Syntheses, Field Usage of Alternative Deicers for Snow and Ice Control, and identify any additional information that is publicly available regarding national and international use of KAc as a de-icing and anti-icing agent. The focus will be on successful uses of the material (material concentration and application rates, weather conditions, timing, etc.) by highway agencies or transferable practices by airports.
MnDOT District 1 personnel will conduct field tests of KAc on selected plow routes during the winter of 2018-2019 and document key data about the amount of material used, locations, equipment, storm characteristics, pavement conditions and other elements. Researchers will assist MnDOT with the design of the field study, the creation of a data gathering tools to be used by plow drivers, monitoring of data quality during the study, analysis of data gathered during the winter season, and writing a report presenting the study conclusions.
New research has started that will provide needed guidance for the design of separated bike lanes, which are rapidly growing in popularity. The two-year Minnesota Local Research Board-funded study, which is being performed by the University of Minnesota, will identify the safety, cost and accessibility attributes of different lane designs and produce a technical memorandum with design guidance for transportation planners.
Separated bicycle lanes (SBLs) are a bicycle facility that employs both a paint and vertical element as a buffer between vehicle traffic and bicycle traffic.
In 2016, the City of Minneapolis increased the total mileage of separated bike lanes in the city from 5.4 to 9.4 miles with plans to increase that to 30 miles by 2020. While many other cities around the U.S. are in the process of installing separated bike lanes as part of their non-motorized transportation networks, research about them has not kept pace.
The Federal Highway Administration’s Separated Bike Lane Planning and Design Guide identified several gaps in existing research, including the effects of SBLs on vehicle traffic, the preferred speed and volume thresholds to recommend SBLs, and the differences in safety between one- and two-way SBLs.
Despite safety being a major concern with SBLs, the guide states that “there are no existing studies that have satisfied best practices for analyzing the safety of SBLs.” The guide goes on to caution that even in cases where research on the safety or operational effects of SBLs does exist, “much of the highest quality research comes from outside the U.S.” The FHWA guide also lists cost as a gap in knowledge about SBLs, saying “few benchmarks exist for separated bike lane costs, which vary extensively due to the wide variety of treatments and materials used.”
This research project will provide a thorough synthesis of current research and guidelines and a comprehensive analysis of the impacts of different midblock bike lane designs to help Minnesota-based agencies make data-driven design and planning decisions. Design variables include delineator type and spacing, land and buffer widths, and one- vs two-way bike lanes. Impacts that would be evaluated include installation, maintenance, and user costs as well as safety and facility usage.
When considering installing SBLs, many aspects including impacts on both bicycle traffic and other types of traffic (pedestrians, passenger cars, delivery trucks, etc.) must all be considered. However, much of this information is unavailable. By providing a comprehensive repository for the relevant data on the numerous SBL design options, this project will allow engineers and policy-makers to make more informed decisions regarding bicycle infrastructure installations and improvements. Access to this sort of hard data will aid in the process of performing will aid in the prioritization of options for bike facilities thereby reducing the waste of funds on unneeded or unaffordable projects.
The tasks of the research project include:
Conduct a thorough literature review to identify any gaps in the current research. Examples of this might include the effects of SBLs on all road users, frequency of bicycle and vehicle violations for various SBL designs, recommended speed and volume thresholds for installation, the costs associated with SBLs, or the differences in safety between one- and two-way SBLs.
Conduct research such as observational field studies, crash record analysis, synthesis of the results of other studies, road user surveys, review of previous project budgets, bicycle facility repair record analysis, municipal records of complaints and violations, or some combination thereof.
Develop a list of options for the design of multi-modal facilities and the respective impacts of those options based on findings from the field studies. This could include maintenance costs, user costs and safety impacts.
By providing transportation planners, engineers, and other practitioners new information on the impacts likely to be associated with different designs, the practitioners will be in a better position to both choose among designs and mitigate potential adverse effects of those designs. The list of design options and associated impacts will be summarized in a technical memorandum with a more thorough presentation in the project final report.
Many counties have incomplete roadway inventories, but lack asset management programs, which are often cost-prohibitive and require advanced technical training and staff to maintain. The Upper Great Plains Transportation Institute at North Dakota State University (NDSU), has developed a low-cost asset inventory program called the Geographic Roadway Inventory Tool (GRIT). The program, which is currently available to North Dakota counties, will be offered to all Minnesota counties following further development and testing by the Minnesota Local Road Research Board.
NDSU created the asset inventory program as the first step for asset management to allow local roadway managers to document and understand their existing infrastructure using the latest mobile technology and Geographic Information System technology.
The goal of the research study is to expand the program to include roadway forecasting based on the American Association of State and Highway Transportation Officials(AASHTO) 93 model with inventory, pavement condition and traffic forecasting data.
Existing input data from GRIT, such as pavement thickness, roadway structural information and construction planning information, will be spatially combined with current Pathway pavement condition and traffic data from MnDOT to automatically forecast the future condition and age of roadways using the AASHTO 93 model. This forecasting model will then allow roadway managers to use this information with comprehensive GIS web maps to prioritize roadways in construction schedule or multi-year plans.
The additional information contained in the pavement forecast system will allow county roadway managers to prioritize projects that can benefit from lower cost pavement preservation activities and understand how long roadways can last before a high cost reconstruction must take place. The online GIS output maps will also enable the public to see what projects will be conducted on a year-to-year basis.
The research team will work with Beltrami, Pope, Faribault, Pennington, and Becker counties and the city of Moorhead in Minnesota to research, develop, test and implement an additional forecasting function of the existing asset management program. This will be done using the AASHTO 93 empirical model to calculate a future pavement serviceability rating (PSR) based on the existing pavement structure and age, forecasted traffic and the latest pavement condition. While existing pavement structure and age information will come from data entered into the GRIT program by counties, processes and procedures will be researched and developed to automatically access pavement condition and traffic data from MnDOT and geospatially combine it with inventory data.
With pavement forecast information, county roadway managers will be able to better understand which roadways will deteriorate first and which will benefit from more effective, low-cost maintenance programs rather than full-depth reconstructions. The model will not forecast suggested future projects or project costs, but rather just output the future condition of the roadways on a yearly basis. The AASHTO model can be applied for both flexible and rigid pavement sections.
Local agencies are increasingly looking at converting low-trafficked paved roads to gravel at the end of their life span to make budgets stretch. However, agencies have few resources to guide them in this process.
The Minnesota Local Road Research Board recently approved funding for a guidebook on effective practices for converting severely distressed paved roads to unpaved roads. The document will help engineers select roads for conversion, safely conduct conversions and communicate the rationale to the public. No such published document currently exists.
The guidebook will be divided into chapters, which will cover:
Methods to determine if a road is a candidate for conversion and determine the existing road materials and condition.
Methods to convert a road from paved to unpaved.
Methods to assess the life-cycles cost of construction and maintenance of the unpaved road.
Tools to effectively inform and communicate with the public
Safety implications of converting a severely distressed paved road to an unpaved road.
While low- volume roads are typically identified as having an annual average daily traffic (AADT) of less than 400, roads that are appropriate candidates for conversion will typically have an AADT of less than 150.
These roads are often used by agricultural and extraction industries or to access homes and recreational areas. The type of road users, traffic patterns and vehicle types are all factors that need to be considered in the decision to unpave a road. Other factors include road condition, safety, agency maintenance and maintenance capabilities, as well as a life-cycle cost comparison of maintenance options (continued maintenance of the deteriorating road, rehabilitation of the paved road or conversion to an unpaved surface).
According to the research team, very limited information is available about converted roads, and what information is available often comes in the form of newspaper articles and anecdotal accounts of road conversions.
The document will serve as a formal and peer-reviewed information source. The use of the guide and acceptance of the practice of converting from paved to unpaved surfaces (unpaving) where warranted will provide a case for the acceptance of road conversions as another low-volume road management strategy.
Water is being drawn out of the state’s aquifers faster than it is being replenished, so public agencies like MnDOT are increasingly interested in figuring out how to reduce water usage.
A two-year research project underway at MnDOT is investigating how the agency can re-use wastewater at its safety rest areas and truck-washing stations. In addition to preserving groundwater, MnDOT hopes to reduce utility and septic system costs.
MnDOT owns and operates over 1,000 buildings, including 68 safety rest areas, 137 truck stations, 18 regional/headquarters maintenance sites and 15 weigh stations and truck scales.
These facilities either discharge their wastewater to a subsurface sewage treatment system or a wastewater treatment plant.
Researchers from the University Of Minnesota’s Onsite Sewage Treatment Program have been hired to investigate the potential avenues for wastewater re-use at MnDOT. They will consider when re-use makes sense from a regulatory, environmental, economic and management perspective; recommend the most appropriate applications for reuse and identify any challenges with implementation.
Potential benefits include:
Preserve ground and drinking water for potable drinking.
Reduced life-cycle costs in areas where low-producing wells could meet drinking water needs while reused wastewater could be used for toilet flushing and equipment wash-down.
In areas with municipal water, lower water utility costs.
Increased longevity of septic systems due to decreased loads.
As the state, counties, or cities construct new facilities or upgrade existing ones, this research will provide insight into what options are readily available to reduce water consumption and improve water efficiency. If these types of reuse systems are demonstrated by MnDOT, then they could lead to usage by other properties across Minnesota.
The city of Shoreview, Minnesota was on the right track when it took the unusual step of paving a residential neighborhood with pervious concrete to help control stormwater and pollutant runoff into a nearby lake, according to a recently released seven-year performance study.
Typically used for parking lots and sidewalks, porous paving material allows stormwater to filter through the pavement and an aggregate base into the soil rather than run off the pavement and drain into storm sewers.
Shoreview bucked convention by using pervious concrete in a traffic application — low-volume, low-speed roads in the Woodbridge neighborhood near Lake Owasso. The city thought pervious pavement could help meet community sustainability goals and federal clean water regulations by reducing pollutants in waterways and groundwater while keeping water safely off driving surfaces.
Traditionally, pervious concrete hadn’t been used for roadways because engineers didn’t consider it strong enough for traffic (this and other projects have now demonstrated its application for low-volume roads like neighborhood streets). The impact on ride quality, tire-pavement noise and filtration was also not well understood, particularly in cold climates with freeze-thaw cycles like those in Minnesota.
Pervious concrete also presented a maintenance challenge: Organic debris, sand and other grit can clog the pavement’s pores. Periodic vacuuming is required to maintain the intended flow of water through the pavement. Concerned about how best to maintain the pavement and interested in tire-pavement noise levels and filtering performance, Shoreview, MnDOT and the Local Road Research Board monitored the Woodbridge roadways for seven years.
Installation and Evaluation
Shoreview replaced 9,000-square -feet of asphalt roads with 7 inches of pervious concrete over 18 inches of coarse aggregate base; near the lake, highly drainable sand served as the base. About twice each year for five years, researchers tested sound absorption, water infiltration and ride quality one day after the pavement had been vacuumed. In 2015, they repeated these tests without vacuuming the day before.
The pervious pavement performed well in filtering stormwater. By 2012, at least 1.3 acre-feet of water had filtered through the pavement and ground, and by 2015, nearly 2 acre-feet of water had filtered through the surface—all of which would otherwise have run directly into Lake Owasso.
Water infiltration and sound absorption rates were higher than traditional concrete, although rates declined over time because organic material continued to clog pavement pores despite vacuuming twice a year.
Initial construction of the pervious concrete streets and stormwater filtration system was slightly more costly than construction of comparable asphalt pavement with culverts. Life-cycle costs, including projections of maintenance costs over 15 years, however, showed somewhat lower costs for pervious pavement. While the pervious concrete pavement may require diamond grinding after 10 years, monthly vacuuming could make this unnecessary. Asphalt pavement would typically require a mill-and-overlay at year 15, and culverts would require periodic cleaning.
Additional benefits of the pervious pavement system that were not included in cost calculations—but were clearly significant—included complying with the federal Clean Water Act, recharging groundwater and avoiding direct pollution of Lake Owasso. Shoreview’s investment in pervious concrete has paid off economically and environmentally.
For additional information about this line of research, see these resources:
In an effort to reduce dangerous right-angle crashes at rural intersections, the Minnesota Department of Transportation (MnDOT) has deployed dynamic warning signs at approximately 52 sites throughout the state. Using sensor technologies, these signs provide real-time traffic information to motorists at non-signalized intersections where cross traffic does not stop, warning drivers on the minor road when it is unsafe to enter the intersection. However, a number of sign-related complaints have been received from local road users.
To address this issue, a team of University of Minnesota human factors researchers studied the current dynamic warning sign to identify what features or layouts may be problematic and propose safe and efficient alternatives. “We directed special emphasis to the most vulnerable driver populations, such as older drivers and novice teenage drivers,” says Nichole Morris, director of the HumanFIRST Laboratory and the study’s principal investigator. The study was sponsored by MnDOT.
The research team first surveyed Minnesota county engineers regarding their experiences, perceptions, and complaints or comments from local road users. “In addition to the largely negative feedback from drivers, we learned that many county engineers incorrectly interpreted how the system functions—a number of them were not sure how the fail-safe/inoperable mode works,” Morris says.
Through iterative usability studies, researchers then examined alternative designs to produce three sets of sign options for a driving simulation study. The simulation study, with 120 participants, evaluated the safety effectiveness and efficiency of the sign options among teen drivers, middle-aged drivers, and older drivers.
The results indicate an overall safety benefit of sign deployment. “All the sign options except for one enhanced drivers’ gap-acceptance performance,” Morris says. “At intersections with inadequate sight distance, gap acceptance tended to be significantly better.”
The warning system’s benefits varied among the three age groups: middle-aged drivers demonstrated the most potential for safer gap acceptance; teenage drivers did not appear to be significantly assisted by the warning system, despite their self-reporting that the sign assisted them; older drivers tended to have a significantly reduced risk of accepting an unsafe gap but were also less efficient in using the system (they waited longer and rejected safe gaps more frequently).
The signs might simultaneously incur potential risks for drivers. “For example, the risk of stop-sign violations was found to be the greatest when the system was turned off due to a malfunction,” Morris says. Drivers also tended to check traffic much less often with the presence of the warning system.
After reviewing the study results, researchers identified an alternative sign design for future field tests that may demonstrate comparable safety benefits to the original sign with fewer potential risks. Specifically, certain design elements—an action word or icon—were recommended for consideration in follow-up field evaluations and future implementations.
“Intersection warning systems are an important tool for MnDOT as we push toward having zero deaths due to traffic crashes,” says Ray Starr, acting state traffic engineer with the Office of Traffic Engineering. “This study provides valuable information that is helping MnDOT consider any design changes for future versions of the warning system.”
The findings may also have a broader implication for the design, development, and implementation of effective intersection countermeasures on rural, urban, and suburban roadways, Morris adds.
Complete Streets is a transportation policy and design approach that requires streets to be planned, designed, operated, and maintained to enable safe, convenient and comfortable travel and access for users of all ages and abilities, regardless of their mode of transportation. A newly funded research project aims to demonstrate the economic and non-economic benefits of Complete Streets in the city of Richfield, which has been active in reconstructing several previously vehicle-oriented roads to allow for safe travel by those walking, cycling, driving automobiles, riding public transportation, or delivering goods.
By measuring the impacts of pedestrian- and bike-related improvements in Richfield, this Minnesota Local Road Research Board-funded study hopes to help guide future transportation investments for building sustainable and safe urban environments.
This analysis will include four closely related steps:
First, University of Minnesota researchers will select suitable improvement sites in Richfield to study and collect project information, including project maps, description of complete street features and GIS files at the parcel level before and after the project.
Identify economic and measurable non-economic benefits. The university will work with the City of Richfield to identify possible economic benefits (such as increased property value) and other measurable benefits (such as public health benefits associated with pedestrian or cycling activities) of the Complete Streets projects.
Estimate economic benefits, such as increased housing value or as additional business activities.
Lastly, researchers will quantify and monetize non-economic benefits, such as public health or environmental benefits related to pedestrian or cycling activities. Data about benefit indicators will be collected through survey or interview. These benefits will then be monetized using common value parameters identified from the literature.