Category Archives: Traffic and Safety

Alternative designs identified for rural intersection warning signs

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.”

New performance measures identify truck delays and bottlenecks

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.

What Was Our Goal?

The aim of this project was to combine data from the U.S. DOT National Performance Management Research Data Set (NPMRDS) with information from other sources to build on the previous study’s analyses of mobility, reliability and delay along key TCMA freight corridors. New performance measures would more clearly identify the extent of system impediments for freight vehicles during peak periods in selected corridors, allowing researchers to identify causes and recommend mitigation strategies.

What Did We Do?

Researchers worked with stakeholders to prioritize a list of TCMA freight corridors with NPMRDS data coverage. The NPMRDS includes travel time data from probe vehicles at five-minute intervals for all National Highway System facilities. The travel times are reported based upon Traffic Message Channel (TMC) segments with link lengths varying from less than 1 mile to several miles. Researchers worked with 24 months of NPMRDS data from the selected corridors.

Because of varying TMC segment lengths, researchers used geographic information system (GIS)–based data to georeference the NPMRDS data to relevant maps. Combining these with average travel time data from passenger and freight vehicles, researchers used their data analysis framework to generate measures of truck mobility, reliability and delay at the corridor level.

A truck mobility analysis of all the selected corridors was performed using the truck-to- ar travel time ratio (TTR) for each TMC segment of each five-minute interval computed in AM (6-10 a.m.), midday (10 a.m.-4 p.m.) and PM (4-8 p.m.) peak periods using the 24- month NPMRDS data. A TTR of 1 describes a truck and a car traveling a distance in the same amount of time. On average, trucks are known to travel 10 percent slower than cars on freeways: a TTR of 1.1. A truck traveling 20 percent slower would have a TTR of 1.2.

Reliability measures evaluated the truck travel time reliability. Researchers computed truck delay during rush hour on the GIS network by fusing truck volumes, posted speed limit and NPMRDS data.

Researchers computed a truck congestion measure by comparing truck travel time with the target travel time in each TMC segment, which provided a measure of delay (in lost hours) at the segment and corridor level.

What Did We Learn?

The truck mobility analysis revealed that roadways with intersections have a higher TTR. Trucks on U.S. and Interstate highways take about 10 percent longer to travel the same distance as cars: TTR 1.1. On state highways, the TTR reaches 1.2 and 1.4 in the AM and PM peak periods, respectively. On county roads, trucks slow considerably: midday TTR is 1.5 and spikes to 1.7 and 1.9 in the AM and PM peak periods. Intersections in a TMC segment and delays at signalized intersections could have caused the TTR increases.

All reliability measures indicated that truck travel time in the PM peak period is less reliable than in the AM peak period. Similar to the TTR measure, roadways with signalized or unsignalized intersections were less reliable for truck traffic than freeways.

Truck congestion and delay measures revealed that the top five TCMA corridors with significant congestion had an average delay of over 3,000 hours in the AM and PM peak periods, with the PM delays notably greater. Also, in the AM peak period, eight additional interchanges had average delays of over 300 hours per mile. In the PM peak period, nine interchanges and eight segments showed significant congestion.

The top six TMC noninterchange segments exhibiting recurring PM peak period delays on average weekdays had delays ranging from 495 hours to 570 hours per mile.

Insufficient capacity, increasing demand, roadway geometry and density of weaving points (on-and off-ramps) were considered key causes of delay among these six bottlenecks.

What’s Next?

NCHRP Research Report 854, Guide for Identifying, Classifying, Evaluating and Mitigating Truck Freight Bottlenecks, provides guidelines for identifying, classifying, evaluating and mitigating truck bottlenecks. Follow-up research by MnDOT could potentially leverage this project’s effort with the NCHRP guidelines to develop mitigation strategies.

This post pertains to Report 2018-15, “Measure of Truck Delay and Reliability at the Corridor Level, published April 2018.

 

Prioritizing Pavement Markings on Low-Volume Roads

Researchers have developed a tool to help Minnesota local agencies make cost-effective pavement marking decisions in their counties. The spreadsheet-based tool was developed as part of a recently completed research study by the Minnesota Local Road Research Board.

What Was the Need?

Minnesota has many miles of low-volume roads, most marked with yellow centerline and white edge lines. Applying and maintaining these markings is a significant financial investment for local agencies, which typically work within very constrained budgets. These agencies needed more information about the value and the initial and ongoing costs of typical 4-inch and enhanced 6-inch pavement markings on low-volume roadways. They also needed clarification and guidance for prioritizing pavement marking installation and maintenance that could work within their limited budgets.

What Was Our Goal?

The goal of this research was to develop a prioritization approach and a decision-making tool for using pavement markings on low-volume roads based on the benefits and costs of these markings. Local agencies could then use these resources to make cost-effective decisions about installing and maintaining pavement markings.

Rural road with cyclist in bike lane
This segment of Minnesota Highway 38 has yellow centerlines and white edge lines that delineate a 4-foot bicycle lane

What Did We Do?

Researchers took a multistep approach to identifying critical pavement marking information and practices:

• Conducted a literature search of existing research on typical (4-inch) and enhanced (6-inch) pavement markings, focusing on the benefits (such as crash reduction and improved lane-keeping), costs and current maintenance practices.
• Surveyed Minnesota counties to learn about their current practices and management approaches for pavement markings.
• Reviewed existing County Road Safety Plan (CRSP) methodology to learn about research and data used to rank at-risk road segments and identify CRSP improvement strategies, specifically the range of pavement markings that CRSPs recommended.

Researchers were then able to develop a prioritization approach and a decision-making tool that incorporated both past research and local state of the practice. In addition to producing a final report describing task results, they developed a brochure explaining the approach, the tool and implementation steps.

“This innovative tool will help local agencies make pavement marking decisions under tight budget constraints, where the question is always how to best allot funds for competing needs. This tool clarifies the problems and helps prioritize the possible solutions,” said David Veneziano, LTAP Safety Circuit Rider, Iowa State University Institute for Transportation.

What Did We Learn?

The literature search revealed limited research addressing traditional pavement marking use and effectiveness on local roadways. Pavement markings produce safety benefits, including reduced crash rates, but showed no real effects on vehicle speed, indicating that pavement markings may not alter driver behavior. Only limited efforts were identified in the literature aimed at investigating the prioritization and management of pavement markings.

The survey of local Minnesota agencies revealed that most counties use centerline and/or edge lines, which may be the result of MnDOT State-Aid Operation Rules. Some counties mark all their roads; most use 4-inch latex paint or epoxy markings. Repainting schedules depend upon road age, marking condition and county budgets.

A review of Minnesota counties’ CRSPs showed they included pavement marking recommendations. The CRSPs recommended, on average, 109 miles of pavement markings in every county. Applying one linear foot of centerline costs about 5 cents; 100 miles of centerline cost $26,400. Because of the extent of these recommendations, researchers directly incorporated the methods and directives from the CRSPs into their prioritization approach and tool.

The spreadsheet tool produced through this project allows users to enter road site characteristics such as pavement condition, road width, the CRSP rating and traffic volume, as well as the age of extant markings, costs, durability and the potential for crash reduction. Pavement marking options include centerline and/or edge lines, high visibility markings and enhanced durability materials. The tool uses factor weights that assign a relative importance to each criterion for any potential marking approach compared to other alternatives. The result is a performance rating score for each marking alternative. Thus, the tool assists not only in identifying the physical aspects of a road segment, it also incorporates the agency’s preferences, priorities and budget through a priority-weighting feature that generates the cost or cost range for a marking project.

What’s Next?

Recommendations for further research include conducting a follow-up survey of users
of the new spreadsheet tool to facilitate future modifications, creating databases of roadway characteristics to simplify agencies’ use of the tool, and performing additional research on the safety and other effects of pavement markings. Researchers also encouraged agencies to keep in mind a proposed national retroreflectivity rule for the Manual on Uniform Traffic Control Devices that could affect pavement marking practices on low-volume roads. This rule has not yet been finalized or implemented.

This post pertains to LRRB-produced Report 2018-21, “Investigating the Necessity and Prioritizing Pavement Markings on Low-Volume Roads,” published June 2018. The Pavement Marking Prioritization Tool can also be found on the project webpage on the LRRB website.

Nontraditional Fog Seals Offer Value, Limitations Compared to Traditional Seals

MnDOT conducted field and lab analyses of nontraditional fog seals used by local agencies around the state. Results show that agriculture-based bioseals offer value that must be balanced against temporary reductions in retroreflectivity and pavement friction. Bioseals offer greater friction and visibility than traditional fog seals.

“There is some value to the bioseals. They seal the pavement, and they’re clear so they have a minimal effect on striping. These applications are appropriate in certain areas,” said Bruce Hasbargen, County Engineer, Beltrami County.

What Was the Need?

Maintenance crews often spray pavement surfaces with a “fog” of liquid sealant after pavement has been in service for a year or more. These fog seals extend the water resistance of asphalt and protect pavements from oxidation.

Fog seals wear off after a few years, but can be inexpensively reapplied. The seals lengthen maintenance cycles, protecting asphalt between activities such as crack repair and surface treatment. Traditional fog seals, however, are dark, asphaltic mixtures that obscure pavement striping and reduce the reflectivity of materials. Fog seals also reduce friction, and so typically suit pavements with low-speed service conditions.

In recent years, city and county road agencies in Minnesota turned to bioseals—agriculture-based, clear liquids that manufacturers claim seal pavement against oxidation and water damage without concealing pavement markings. Bioseals are currently not less expensive than petroleum industry products, and little independent work had been performed to identify performance benefits.

What Was Our Goal?

To provide local agencies with more information about bioseal performance, the MnDOT Office of Materials and Road Research studied selected bioseal products in the lab and in the field (MnROAD test site pictured above), comparing them to traditional seals to determine product performance, durability and impact on friction and pavement marking visibility.

What Did We Do?

Following a literature review of fog seal treatments, investigators selected four seals for analysis: a traditional asphalt-emulsion sealer; a nontraditional, polymerized maltene emulsion longitudinal joint sealant (Jointbond); and two soy-based bioseals (RePlay and Biorestor). These seals were applied in 2014 to 8-foot shoulder sections built in 2013 on County Highway 75 in Wright County, north of Monticello. Seals were sprayed on shoulders outside painted markings, in shoulder space where investigators applied geotextile patches and strips of highly reflective striping tape commonly used on some roads. Untreated shoulder areas of 500 feet and 1,320 feet served as control sections.

Reflective marking tape on road shoulder
Researchers placed a swatch of geotextile and reflective pavement marking tape on shoulders before the shoulders were sprayed with nontraditional fog seals. Investigators then moved the textile and tape to MnROAD to study application rates and stripe performance.

After spraying, investigators removed the geotextiles to evaluate the quality of application work by bioseal distributors. They also removed some striping tape and reapplied it as shoulder striping to Cell 33 at the MnROAD test facility, where they could reliably monitor traffic passes over the biosealed markings and evaluate retroreflectivity over time. At the Wright County site, researchers examined pavement distress, friction properties and permeability on the shoulders for three years.

Lab studies included testing seal residue and stiffness in field-aged cores taken from the sealed test sections in year three. Finally, in year three researchers surveyed local agencies in Minnesota about their use of nontraditional fog seals.

What Did We Learn?

Geotextile coating levels showed that vendor application of bioseals is consistent and well-executed. Nontraditional seals do not obscure striping, but bioseals leave residue that temporarily reduces the retroreflectivity of sealed markings to below MnDOT-required levels. Acceptable levels of retroreflectivity returned to the Jointbond samples after 800 truck passes at MnROAD, and to Biorestor and RePlay samples after 1,600 truck passes.

Every tested seal reduced pavement friction. Recovery of friction for the three nontraditional products, which reduced friction by 11 to 17 percent, took about 200 days with no traffic. The traditional, asphaltic fog seal reduced friction by 67 percent and took longer to recover, remaining slippery for turning in wet conditions for over two years.

“Bioseals affect pavement friction, so agencies need to use some caution when using them. City streets are probably going to be very good for nontraditional seals,” said Eddie Johnson, Research Project Engineer, MnDOT Office of Materials and Road Research.

Each seal reduced pavement permeability for about two years; after two years, only the traditional seal continued to provide water protection. The permeability benefit of fog seals lasts significantly longer than the retroreflectivity reduction; when reflectivity recovers, the seals still provide water resistance. Field surveys also found that Biorestor and RePlay may help resist cracks.

Laboratory studies showed that high-temperature stiffness for every treatment was greater than control samples in the top layer than in the middle of cores, suggesting that seals may improve rut resistance of treated pavements in hot weather. Low-temperature stiffness was higher in the top sections for every treatment except the traditional fog seal.

Of the 57 agencies that responded to the survey, 32 have used nontraditional fog seals, preferring Biorestor and RePlay to others. Over half of these users recommend the use of such seals; responses suggest that bioseals offer sealing benefit for two years and, in some cases, up to six years.

What’s Next?

Nontraditional fog seals protect pavements from water and may help prevent cracking. Traditional seals offer longer-lasting water resistance, but also longer-lasting and greater friction reduction. Agencies must consider temporary reductions in retroreflectivity and friction for any seal, and may wish to continue using fog seals only in lower-speed environments.

Continued monitoring of applications would be helpful in determining long-term performance. The study observed that overlaying biosealed asphalt with a traditional fog seal should be effective in extending permeability.

This post pertains to the LRRB-produced Report 2018-18, “Nontraditional Fog Seals for Asphalt Pavement: Performance on Shoulder Sections in Minnesota,” published May 2018.  

Concrete Design Software Easier-to-Use, Capabilities Expand

MnDOT has upgraded its concrete pavement design software, MnPAVE-Rigid, to make it easier to use and allow more design inputs.

“In the original software, we only allowed one aggregate base thickness and one aggregate type. MnPAVE-Rigid 2.0 allows two base thicknesses and three base types,” said Tim Andersen, Pavement Design Engineer, MnDOT Office of Materials and Road Research.

MnDOT hired American Engineering Testing to update the design software as part of a research project advised by Andersen and funded by the state research program.

Background

MnDOT developed its own pavement design software, MnPAVE-Rigid, in 2014 that incorporated the methodology of the American Association of State Highway and Transportation Officials (AASHTO) Mechanistic–Empirical Pavement Design Guide (MEPDG). Minnesota’s pavement designers use MnPAVE to apply AASHTO’s most sophisticated design principles for both rigid and flexible pavement, focusing on mechanical properties of the pavement and prevention of early cracking and other distress.

2018-17-p2-image

AASHTO’s mechanistic–empirical (M–E) design methods entail hundreds of inputs, each a mechanical parameter, a measure of site-specific characteristics or a design goal. To simplify the input selection process, AASHTO’s M–E design software offers various input levels to reduce the data gathering and input burden. The most basic level uses default values for most of the inputs based on national averages, but still requires dozens of inputs for the number of pavement layers, traffic expectations, climate and other features.

MnPAVE-Rigid for concrete pavement design reduced that number of inputs to nine, operating like a module of AASHTO’s M–E software. MnPAVE-Rigid inputs work with a set of default values for jointed plain concrete selected by the MnDOT Office of Materials and Road Research in 2014, as described in the MnPAVE-Rigid 1.0 report.

“Many states ignored the challenge of adopting AASHTO M–E or they bought an AASHTO
software license. MnDOT used its accumulated knowledge of AASHTO M–E and Minnesota conditions to build MnPAVE-Rigid, and so can account for its M–E design results firsthand,” said Derek Tompkins, Principal Civil Engineer, American Engineering Testing, Inc.

Since implementing MnPAVE-Rigid 1.0, MnDOT has gathered feedback from users about their experience with the software. In the current project, MnDOT wanted to address this feedback, and expand and improve the original software by exploring additional options with some of the default parameters for concrete pavements.

What Was Our Goal?

The goal of this project was to update MnPAVE-Rigid 1.0 by expanding the range of inputs for traffic, subgrade type, base type and thickness, and to make the user interface more accessible.

What Did We Implement?

MnPAVE-Rigid 2.0 allows users to enter 11 inputs, including inputs related to specific traffic levels and aggregate base types; calculate the new design thickness; and print a project report that summarizes the inputs and the recommended thickness. The upgraded software is more user-friendly, and MnDOT can maintain or make future upgrades to the source code.

How Did We Do It?

Researchers met with the Technical Advisory Panel and reviewed the list of software improvements requested by pavement designers and the MnDOT Office of Materials and Road Research.

Because every change to an input affects a large number of default input variables, investigators ran over 21,000 simulations to analyze the impact of changes made to inputs for base type, base thickness, subgrade type and traffic level. The research team also modified the traffic input calculator to allow designers to enter traffic values from MnDOT’s weigh-in-motion and traffic counting data. The calculator runs input traffic data in software simulations and assigns the input an appropriate axle value for design.

MnPAVE-Rigid 1.0 ran designs based on Class 5 aggregate base over a subgrade like clay loam. Other aggregate types were added to simulations to determine how the software responds to these changes. Investigation also explored the addition of subgrade material options in design simulations.

The code developer modified elements of the advanced inputs tab and PDF report generation features to improve performance for software users, and rebuilt the software in JavaScript 2.0 code, including an installer for use with Windows software.

What Was the Impact?

MnPAVE-Rigid 2.0 is more user-friendly. Its tabs better match designer needs, and the software offers a design report PDF file for export. Instead of selecting from limited options for traffic volumes (default, normal and heavy), users can now input traffic data that the software will categorize. Designers can input Class 5 aggregate, Class 5Q (a higher quality aggregate with fewer fines) and open graded aggregate (no fines). Users can also choose 4-inch or 12-inch aggregate base thicknesses. An additional subgrade option was not included, as simulations indicated a sand subgrade input did not discernibly impact structural thickness outputs.

The AASHTO M–E software is expensive, and agencies that use it have to work closely with consultants to receive training and to explore or modify the code. MnDOT owns and manages the source code for MnPAVE-Rigid 2.0, can keep it secure, and can continue to change and upgrade it internally for Windows and Linux platforms.

What’s Next?

The updated MnPAVE-Rigid is now available online. Presentations about the software upgrades will be made at meetings for materials and soils engineers through the fall of 2018.

Still underway is an effort to further incorporate recycled material properties into MnPAVE Flexible, the design software for asphalt pavement.

This Implementation Summary pertains to Report 2018-17, “MnPAVE-Rigid 2.0,” published May 2018.

Reporting Driver Intrusions in Work Zones

Data from a new system for tracking work zone intrusions may be used to change work zone design and policies, reducing the risk of injury and death from intrusion crashes.

MnDOT and the Local Road Research Board engaged researchers to develop a user-friendly system that allows highway crews to quickly record instances of motorists’ intrusion into work zones, using a laptop, tablet or paper.

“This collaboration resulted in a fast, efficient and easy-to-use system because crews and supervisors let us know throughout the process exactly what they needed to consistently report work zone intrusions,” said Nichole Morris, Director, University of Minnesota HumanFIRST Laboratory.

What Was Our Goal?

The goal of this research project was to develop and test an efficient, comprehensive and user-friendly reporting system for intrusions into work zones. It was essential for the system to be accepted by highway workers. The information collected from the system, which was modeled after the existing MNCrash report, would then be used to examine risk factors to reduce intrusions and danger to workers. Safety data would be relayed back to workers and to MnDOT managers, providing an empirical basis for design changes to work zones, as well as future policy recommendations to the state government.

“To reduce work zone intrusions and make work zones safer, we need to track and analyze the intrusions. This reporting system will generate the data we need to make smart changes and possibly to influence legislative policy,” said Todd Haglin, Emergency Management and Safety Manager, MnDOT Office of Administration.

What Did We Do?

To design a usable system for reporting work zone intrusions, research designers had to:

  • Understand the characteristics of the typical system user (in this case, the work zone supervisors and crew).
  • Develop common or typical intrusion scenarios to realistically test the system.
  • Conduct iterative testing with typical users (supervisors and crew members) and incorporate revisions based on test results.

The research team interviewed work zone supervisors from rural and urban truck station locations across the state: in Baxter, St. Cloud and Duluth and at Cedar Avenue near Minneapolis-St. Paul. Researchers sought to learn what crews and supervisors considered an intrusion and what they thought should be reportable elements of the intrusion, such as the work zone layout, weather, location, time, visibility, road conditions and maneuvers of the intruding vehicle.

2018-09-p1-image
In a common type of close call, the dark car shown here fails to merge until it is too close to the work zone, forcing the silver car out of its lane.

Researchers used information gathered from the interviews to develop four typical intrusion scenarios—which were reviewed and revised by MnDOT supervisors—and used these scenarios to test the prototype reporting interface. Then they conducted usability tests with these scenarios and with actual intrusions that crews had experienced. Users suggested changes to the report format throughout the process.

Crews and supervisors collaborated with researchers during three rounds of testing, revising the reporting interface after each round. An online beta version had been supplemented with a paper version. Both versions were revised through this iterative design process.

What Did We Learn?

This design approach allowed the research team to produce a report interface incorporating the very specific needs of the work zone crews and supervisors:

  • The third major revision split the report decision flow into two options—a shorter report and a comprehensive report—based on whether the intrusion presented a risk to the crew. Without this revision, intrusions that workers considered minor were not likely to be reported.
  • Researchers surveyed users of the system with each revision. Supervisors liked the drop-down menus, the comprehensiveness of the system and its ease of use. They rated the final revision as good in terms of usability, ease of use and time to completion (five to six minutes on average).
  • The final design version was tested using a laptop, tablet and paper. Multiple reporting options made it more likely that workers and supervisors would quickly report data about a work zone intrusion before details were forgotten.

What’s Next?

Supervisors and workers involved in the design process gave high marks to the final version of the reporting system. The design is considered complete. Researchers had created the interface as a free-standing program, using the University of Minnesota’s digital resources to build and evaluate their design. For this reporting system to be made  vailable for use by MnDOT and other agency workers, MnDOT must engage MNIT, the state’s information technology professionals, to determine where the system will reside and to integrate it into the state’s existing computer platform.

This post pertains to Report 2018-09, “Work Zone Intrusion Report Interface Design,” published in February 2018. 

MnDOT is developing other initiatives to improve work zone safety,  including a personal warning sensor for construction workers. Search for “work zone” research projects here.

New Project: Real-Time Winter Weather Alerts Planned for Highway Message Signs

The longest winter in recent memory might have ended, but MnDOT’s traffic and maintenance staff are already planning how to make future winters easier on Minnesota drivers.

Recently, the Regional Transportation Management Center was awarded funding to deliver real-time winter weather warnings via its roadside and overhead highway message signs. The RTMC displayed blizzard warnings for the first time during six storms last winter, but the alerts had to be manually entered.

“This is similar information that you receive on your cell phone or the evening news,” said Brian Kary, RTMC Traffic Operations director. “But for somebody who’s traveling down I-90 and just passing through, they might not realize that they’re entering an area with a blizzard.”

Another initiative aims to expand the road condition data that’s available during winter storms by piloting the use of mobile sensors on maintenance supervisor trucks and above-ground sensors at select Road and Weather Information System sites.

Both projects are among eight research implementation projects recently selected for funding by the governing board for MnDOT’s transportation research program.

Multi-lane highway with real-time message boards

Weather Alerts

Minnesota has nearly 300 Dynamic Message Signs, which currently issue real-time warnings about traffic incidents, road work and congestion. Around 200 are in the Twin Cities metro; the rest are in Greater Minnesota.

Kary’s two-year project will develop a system that can automatically relay critical weather alerts, which change frequently, are labor-intensive and error-prone when physically entered. Only blizzard warnings from the National Weather Service are initially planned, but the system will be capable of broadcasting all types of weather alerts.

A number of other states already issue weather alerts via their Dynamic Message Signs, so MnDOT has case studies to look at.

It’s possible that the signs could also someday relay information from MnDOT’s Maintenance Decision Support System and roadside weather sensors. A current pilot project uses weather sensors and flashings on a rural stretch of highway near Dassel Cokato High School to warn motorists and notify maintenance staff of unexpected blow ice.

warning sign indicating ice on road when flashing

Improving Road Condition Information

Over the next two years, the Maintenance Office will test the use of mobile and above-ground sensors to expand the geographic coverage of RWIS sites, which feed valuable weather and road surface information to highway operations managers and advanced traveler information systems. This might lead to the elimination of in-road sensors, which require lane closures to maintain and must be replaced during road construction projects.

The mobile sensors will collect road condition information, such as temperature, humidity, due point, and friction, from five maintenance supervisor trucks. The other non-invasive sensors will be attached to an RWIS tower or a pole near the roadway and use laser technology to read road surface temperature and condition (water ice, slush and snow).

See this related news story from KSTP-TV.

County GIS Maps Help Road Departments Anticipate Slope Failure

In a recently completed pilot study, researchers developed maps for two Minnesota counties that rank the failure potential of every slope using a geographic information system (GIS)-based model.

“GIS mapping has been applied to very small watersheds. The two counties in this study are huge areas in comparison. We used a physics-based approach that shows engineers where slope failure is likely to occur,” said Omid Mohseni, Senior Water Resources Manager, Barr Engineering Company.

What Was Our Goal?

The goal of this study was to determine if slope failure models could be developed to help counties anticipate where failures may occur. Researchers used publicly available data, research findings and geotechnical theory to develop failure models that could then be mapped with GIS in two topographically dissimilar Minnesota counties. These maps would identify slopes susceptible to failure so that county highway departments could develop preventive strategies for protecting roadways from potential  lope failure or prepare appropriate failure response plans.

What Did We Do?

Researchers began with a literature review of studies about the causes of slope failure, predictive approaches and mapping. They were particularly interested in research related to potential failure mechanisms, algorithms used for predicting failures and slope-failure susceptibility mapping.

Then investigators collected data on known slope failures in Carlton County in eastern Minnesota and Sibley County in south central Minnesota to identify failure-risk factors not found in the literature. Researchers reviewed various statewide data sets, identifying topographic, hydrologic and soils information that could be used in GIS-based modeling. Next, they developed a GIS-based slope-failure model by incorporating the available data with geotechnical theory and probability factors from hydrologic data, and writing computer code to allow the data to be input into mapping software.

Researchers tested the software on known failure sites to refine soil parameter selection and failure models. The refined models and software were then used to identify and map slope failure risks in Carlton and Sibley counties.

2018-05-p2-image
A detailed GIS map of a length of County Highway 210, color-coded to show slope failure susceptibility along the roadway.

What Did We Learn?

After analyzing the literature and the failure and geotechnical data, researchers identified the following key causal factors in slope failure: slope angle, soil type and geology, vegetation, land use and drainage characteristics, soil moisture, and rainfall intensity and duration.

Researchers then developed mapping models for the two counties using three key data sets. The first was data from 3-meter resolution, high-quality lidar, which measures distances with laser range finders and reflected light, available through Minnesota’s Department of Natural Resources website. The team augmented this data with U.S. Department of Agriculture soils survey data, and with National Oceanic and Atmospheric Administration and National Weather Service hydrologic data for precipitation and storm duration information.

Based on research in geotechnical theory, researchers developed algorithms for anticipating failure and built these into the lidar-based topographic mapping model. They also developed input parameters based on the failure factors and established output parameters representing five levels of failure susceptibility: very low, low, moderate, high and very high.

After testing the GIS-based model against a slope along County Highway 210 in Carlton County, researchers confirmed that failure potential correlated well with documented or observed slope failure. The team further validated the model by applying it to several small areas in the adjacent Carver and Sibley counties, finding similarly effective correlation with identifiable failure sites.

Independent geotechnical experts examined the modeling software and further refined geotechnical, soil and hydrologic elements. Finally, the team developed maps of Carlton and Sibley counties that assigned failure susceptibility levels to slopes in the two counties. Viewing maps through the software remains the most useful way to examine slopes, although large-format maps are available.

“If county engineers have higher slopes adjacent to roadways, they can use this basic tool to predict slope failures and then hire a geotechnical consultant to investigate the site.” – Tim Becker, Public Works Director, Sibley County

What’s Next?

With additional funding, mapping could be extended to every county in Minnesota to further refine failure modeling. Maps may also be useful in identifying structures such as roadways, ecological features, transmission lines and pipelines, bridges and culverts that may be threatened by slope failure susceptibility. Potential risks could be used to prioritize slope treatment plans.

This research effort is part of a slope failure risk mitigation strategy that includes the recently released Slope Stabilization Guide for Minnesota Local Government Engineers. Another project, underway at MnDOT, is identifying, mapping and ranking slopes vulnerable to slides that could affect the state highway network. The project

This post pertains to the Local Road Research Board-produced Report 2018-05, “Storm-Induced Slope Failure Susceptibility Mapping,” published January 2018. More information is available on the project page.

Taking on potholes with new prevention and repair strategies

Potholes are one of the biggest and most costly ongoing maintenance challenges faced by highway agencies. Despite considerable progress in pavement materials and mechanics, pothole repair has remained an area in which little progress has been made.

To make headway in this area, Minnesota transportation researchers studied critical factors in pothole formation and repair in order to identify solutions that would reduce the occurrence of potholes and increase the durability of repairs. They also investigated the potential of newer materials, such as taconite and graphite nanoplatelets (GNP), in repair mixes. Researchers looked at how to make winter patches more durable and also different shapes of patches.

“Our goal was to provide a scientific assessment of pothole repair materials and practices,” said University of Minnesota professor Mihai Marasteanu, the lead researcher. Project sponsors were the Minnesota Department of Transportation (MnDOT) and the Minnesota Local Road Research Board.

What Did We Do?

Researchers began by reviewing national and international literature about pothole causes and repair activities. They also surveyed MnDOT maintenance superintendents and local engineers on current repair practices.

Next, the research team conducted simulations of square, diamond, and round pothole repair shapes to determine if some shapes were more conducive to reducing stress in repair materials. This stress analysis included the use of different common pothole filling mixes and their interface with existing pavement materials.

In the next stage of research, the team evaluated six asphalt mixes for relevant mechanical properties: four winter mixes, a polymer-modified hot-mastic asphalt mix suitable for winter and summer use, and a summer mix in two forms modified with GNP. Mixes were evaluated for compaction and bonding, tensile strength, and water penetration.

Laboratory test of pothole repair sample
Pothole repair samples performed poorly in water penetration tests, which suggested that most mixes will perform poorly under seasonal freeze-thaw stresses.

Finally, researchers studied national and international pavement preservation and pothole prevention practices and the cost-effectiveness of pothole repair.

What Did We Learn?

Through this work, researchers learned that pothole prevention requires repairing pavement cracks as they develop—and sometimes, even timely repairs only slow pothole development.

Laboratory analysis showed that cold mixes compact and bond poorly. To be more effective, these materials require significant curing not possible in the field unless heating is provided. The polymer-modified mastic patching material that was heated was stronger than the winter mixes even at very cold temperatures. Most mastics are used in warm weather, but this material may be effective for winter uses.

Durable winter repairs require expensive patching materials and on-site heating technologies such as truck-mounted microwaves. “To make winter repairs last longer, you need to provide an external source of heat to cure winter patching materials,” Marasteanu says.

Taconite-based materials activated chemically or by heating potholes before and after filling offer promise for more durable repairs. GNP modifiers improved compaction, tensile strength, fracture energy, and fracture resistance in the summer mix.

Pothole repair samples performed poorly in water penetration tests, which suggests that most mixes will perform poorly under seasonal freeze-thaw stresses.

Also of note, the study’s exploration of pothole repair shapes found that circular repairs offer the best filling and compacting performance; repair materials cannot fill corners, even with significant compaction.

 

“We had been squaring off potholes, making sure patches were all at right angles. But in this study, we found that square patches increase stresses at the boundaries. The ideal is a circular patch,” said Todd Howard, Assistant County Engineer, Dakota County.

What’s Next?

The most common pothole repair in Minnesota is throw-and-roll with HMA (using a truck’s tires to compact shoveled-in asphalt). Newer, more durable repairs include taconite-based materials activated chemically or by heating potholes with a truck-
mounted microwave unit before and after filling. While promising and, in the case of the microwave method, potentially effective in extreme cold, these approaches require further research before becoming widely used in winter and spring repairs.

GNP-modified mixes also warrant further study, especially in winter mixes. If MnDOT can encourage cost tracking, analysis of the cost-effectiveness of various pothole repair methods, including the mastic tested in this research, may become possible.

This research is part of a larger effort by MnDOT to improve pothole repair approaches and develop pothole repair guidance for crews throughout the state, including a recently released asphalt patching best practices guide with decision trees.

This post pertains to the Report 2018-14, “Pothole Prevention and Innovative Repair,” published April 2018. Part of this story was adapted from a June 2018 article by the Center for Transportation Studies. Further information is available on the project page and technical summary.

More Saint Paul drivers stopping for pedestrians, thanks to pilot study

A two-year research project underway in the City of St. Paul is already improving pedestrian safety and driver behavior by applying lessons learned from a national award-winning pedestrian traffic study. The city began using the practices last fall with the “Stop for Me” campaign, and driver yield rates have already gone up by 9 percent.

Background

Each year, dozens of Saint Paul pedestrians legally crossing the street are struck by vehicles driven by motorists who fail to stop. In 2015, 40 pedestrians died in Minnesota after being hit by a motor vehicle; 900 were injured. In 2017, there were 192 vehicle-pedestrian crashes in Saint Paul, three of which proved deadly.

Pedestrian fatalities and injuries represent a growing percentage of traffic fatalities and injuries nationwide. For example, pedestrian fatalities comprised 10.9% of all traffic deaths nationwide in 2004, but 14.5% in 2013.

A recent study supported by the National Highway Traffic Safety Administration demonstrated that driver behavior can be changed on a city-wide basis. The introduction of highly-visible pedestrian right-of-way enforcement in Gainesville, Florida increased driver yield rates for pedestrians by 22% to 30%.

Objective

University of Minnesota researchers are charged with reviewing the City of St. Paul’s efforts to improve pedestrian safety and investigate whether a program similar to the one in Gainesville can change driver yielding for pedestrians and speed compliance. The activities in St. Paul are being planned together with city traffic engineers and enforcement officers and will include various educational, engineering and enforcement countermeasures and media campaigns.

Last fall, St. Paul began the “Stop for Me” campaign, which enforces pedestrian laws, increases driver and pedestrian education and works towards enhanced signage and other changes to crosswalks around the city.

A group of people holding signs with traffic safety messages
Stop For Me is a campaign to improve safety for people who use St. Paul’s sidewalks and cross its  streets.

On June 25, the St. Paul Police Department began the second phase of the campaign by ticketing drivers who fail to stop for pedestrians at crosswalks.

Additionally, police officers are ticketing drivers for “endangerment” if they pass a vehicle that is stopped for a pedestrian at a crosswalk. This citation leads to a mandatory court appearance for the driver.

Weekly stopping percentages can be viewed at eight intersections across the city from now until the end of fall.

Watch for new developments on this project (expected end date of August 2019) here.  Another MnDOT study is looking at pedestrian traffic safety in rural and tribal communities. Other Minnesota research on pedestrian travel can be found at MnDOT.gov/research.