Researcher with a hardhat working with research equipment

Policy and Planning, Research

Implementation of Research Strategic Plan Underway

Maintenance Operations, Traffic and Safety

New Project: Potassium Acetate As a Salt Alternative

Bicyclist in red jacket on a delineated bicycle path

Bicycling, Traffic and Safety

New Project: Guidance for Separated/Buffered Bike Lanes With Delineators

Materials and Construction, Policy and Planning

New Project: Development of Pavement Condition Forecasting for Web-based Asset Management for County Governments

Maintenance Operations

New Project: A Guide to Successfully Convert Severely Distressed Paved Roads to Unpaved Roads

Environment

New Project: Re-Using Water at Safety Rest Areas and Truck Stations

Maintenance Operations, Traffic and Safety

New system underway to determine road recovery time during snow events

November 5, 2018 mndotresearch 1 Comment

Researchers at the University of Minnesota Duluth (UMD) have developed a system that can use highway loop detector traffic flow and weather data to determine when road conditions have recovered from a snow event. Currently, the Minnesota Department of Transportation (MnDOT) relies on snowplow drivers to estimate when roads are back to normal. The new system aims to relieve drivers of that burden and increase overall fleet efficiency.

In two previous MnDOT-funded projects, UMD researchers looked at using data from loop detectors along with weather station data to develop an automated system that determines normal condition regain time (NCRT) based on changes in traffic flow patterns. The goal is to improve the accuracy of road condition estimates and give dispatchers a big-picture view of traffic flow.

2018-01-p1-image — A line drawing showing a rectangular closed wire loop approximately 6 feet long and 4 feet wide on a road lane beneath the pavement surface. The loop is attached by a length of wire to data collection equipment on the roadside.

“This is a shift to different criteria,” says John Bieniek, Metro District maintenance operations engineer at MnDOT. “The bare lane regain time is now based on judgments from plow operators on the highways and phone calls to dispatchers. We could use the new system to quickly direct trucks to harder-hit areas within and between stations as they are needed.”

The latest project, led by UMD civil engineering professor Eil Kwon, transformed a previously developed computer model into a user-friendly, integrated computer system. The system includes a data management module, a module for target detector station identification and speed recovery function, an NCRT estimation module, and a map- based user interface that allows dispatchers to generate the estimated NCRT for a specified area. Dispatchers and supervisors can also use the interface to assess traffic flow variations, assign plows, and generate reports for past snow events.

The team tested the new integrated system on data gathered from I-494 and I-694 during two snow events in 2015 and 2016. Results show the system was able to successfully generate NCRTs that met or exceeded the accuracy of estimates by maintenance personnel.

“The system developed in this research can provide consistent and objective estimates of the NCRT by utilizing the traffic flow data that are currently available from the existing detection systems in the metro area,” Kwon says.

Another goal of the project was determining a data-derived definition of normal traffic flow for snow-cleared roadways. As part of this effort, researchers found that traffic resumed free-flow conditions after roads were cleared, but always at a slightly slower speed than on normal, dry roads. Researchers then developed a process to determine the “wet-normal” free-flow speed at each detector station based on the traffic flow pattern during a given snow event.

So far, the system has only been used with data from past snow events and has not generated results in real time. Going forward, MnDOT plans to fund additional work that will incorporate big data tools to allow the system to operate in real time—as storms happen—to improve roadway snow operations.

This article originally appeared in CTSs Catalyst Newsletter, May 2018 and pertains to Technical Summary 2018-01TS. The full report, “Development of a Road Condition Recovery Time Estimation System for Winter Snow Events” 2018-01, published January 2018, can be accessed at mndot.gov/research/reports/2018/201801.pdf.

Bridges and Structures, Maintenance Operations, Policy and Planning

New measure allows comparison between bridge and pavement conditions

October 30, 2018 mndotresearch Leave a comment

Transportation planners lack a method to directly compare bridge and road conditions. In a new MnDOT-funded study, University of Minnesota researchers have proposed a Percent Remaining Service Interval (PRSI) measure that can uniformly assess the condition of bridges and pavements, enabling planners to make the most efficient use of preservation and improvement funding.

A nighttime view of workers and heavy equipment at a road construction site — Planners would like a condition measure similar to RSL that could be used to compare and prioritize needs for highway and bridge construction.

“Both the MnDOT Bridge Office and the Materials and Road Research Office have very good management systems in place,” says Mihai Marasteanu, a professor in the Department of Civil, Environmental, and Geo- Engineering (CEGE) and the study’s principal investigator. “There is a good potential to develop a new common metric that both offices could use.”

What Did We Do?

To begin developing this new measure, researchers conducted a literature review of current methods used in asset management and life-cycle cost analysis. The review of bridge research focused on performance measures and life expectancy assessment methods, while the study of pavement literature concentrated on performance measures as well as on the use of road service life measures.

Next, the research team, which included civil engineering bridge professor Arturo Schultz, surveyed both bridge management staff and pavement management staff from state transportation agencies. Team members then analyzed the asset management practices of MnDOT’s Office of Bridges and Structures and Office of Materials and Road Research to identify methods for assessing service lives and rehabilitation needs and to highlight the similarities and differences in approaches.

Based on the findings from the survey and analysis, researchers suggested the new method of PRSI that would serve both pavement and bridge needs and offered guidelines for the next steps in developing and implementing a unified PRSI procedure.

“Ultimately, funds for guardrail repairs are drawn from the same purse that pays to fill a pothole or repair a deck joint,” Marasteanu says. “With PRSI, planners could target average values across systems to optimize life-cycle costs and pursue an even distribution of PRSI values to make planning consistent from year to year.”

What’s Next?

In the next phase of the project, researchers will work with the pavement office to identify relevant data for calculating PRSI for pavements. “In addition, we plan to identify the time and costs required to reach the evenly distributed configuration of PRSIs necessary for planning consistency, assess how preservation activities impact funding efficiency, and calculate recommended metrics for asset sustainability,” Marasteanu says.

This article originally appeared in the Center for Transportation Studies’ Catalyst Newsletter, October 2018. The full report, published July 2018, can be accessed at “Remaining Service Life Asset Measure, Phase I,” .

Bridges and Structures, Maintenance Operations, Traffic and Safety

Answers Loose Anchor Bolts on Overhead Signs and Light Poles

October 26, 2018 mndotresearch Leave a comment

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.

Base of an overhead sign that shows large bolts — Researchers attached strain gages to the bolts and the mast of a new overhead sign. Installers followed new procedures and specifications to tighten the bolts so that investigators could evaluate the effectiveness of the new standards.

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.

What’s Next?

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
Overhead Signs

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 post pertains to Report 2018-27, “Re-Tightening the Large Anchor Bolts of Support Structures for Signs and Luminaires,” published August 2018.

Environment, Materials and Construction

Pervious Concrete Pavement Reduces Runoff into Shoreview Lake

August 22, 2018 mndotresearch Leave a comment

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.

Conclusions

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:

Seven-year study final report
Technical summary of preliminary study of pervious concrete
Related ongoing study: Permeable Pavement for Road Salt Reduction

Traffic and Safety

Alternative designs identified for rural intersection warning signs

August 20, 2018 mndotresearch Leave a comment

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.

intersections2 — Compared to the original sign (left column), the proposed alternative (right column) might offer comparable safety benefits but fewer potential risks. The sign consists of three different sign states: “Don’t cross/turn” state (top row); “Sign is on/operating and no traffic is detected” state (middle row); and “Sign is off/inoperable” state (bottom row).

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.

This article originally appeared in the Center for Transportation Studies’ Catalyst Newsletter, August 2018. The full report, published May 2018, can be accessed at “Rural Intersection Conflict Warning System Evaluation and Design Investigation.”

Multimodal, Policy and Planning

New Project-Quantifying the Impacts of Complete Streets: The Case of Richfield

August 17, 2018 mndotresearch Leave a comment

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.

Policy and Planning, Traffic and Safety

New performance measures identify truck delays and bottlenecks

August 16, 2018 mndotresearch Leave a comment

A new freight transportation study takes the next step in lessening traffic bottlenecks by pinpointing location and time of recurrent delays.

Freight transportation provides significant contribution to our nation’s economy. Reliable and accessible freight network enables business in the Twin Cities to be more competitive in the Upper Midwest region. Accurate and reliable freight data on freight activity is essential for freight planning, forecasting and decision making on infrastructure investment.

Researchers used detailed and specific data sets as tools to investigate freight truck mobility, reliability and extent of congestion delays on Twin Cities metropolitan area corridors. Precise locations and times of recurrent delays will help to mitigate future traffic bottlenecks.

“This research provided tools and metrics with new levels of precision concerning truck congestion. The results will allow us to take the next steps toward future investment in addressing freight bottlenecks,” said Andrew Andrusko, Principal Transportation Planner, MnDOT Office of Freight and Commercial Vehicle Operations.

What Was the Need?

The corridors of the Twin Cities metropolitan area (TCMA) provide a freight transportation network that allows regional businesses to be competitive in the Upper Midwest. However, traffic volumes on many of these roadways are facing overcapacity during peak travel periods. Heavy truck traffic is only expected to increase, and delays will continue to disrupt freight schedules.

A 2013 study by MnDOT and the Metropolitan Council suggested the need to identify when and where truck congestion and bottlenecks developed in the TCMA. Previous research funded by MnDOT examined heavy truck movement along 38 Twin Cities freight corridors. Researchers created freight mobility and reliability measures, and worked to identify significant bottlenecks. Further research was needed to extract more precise data to better understand TCMA freight traffic congestion.

2018-15-p2-image — The top five congested AM and PM peak corridors in the TCMA are listed above with the delay hours for each period. The large delay hours arise from heavy truck volume and speeds far below base free-flow speeds.