Tag Archives: research

Research Pays Off Webinar Series: Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase

The National Road Research Alliance (NRRA) is hosting “Research Pays Off: Determining Pavement Design Criteria for Recycled Aggregate Base and Large Stone Subbase” on April 20 at 10 a.m. CST, presented by Bora Cetin, Ph.D., Michigan State University and Raul Velasquez, Ph.D., P.E., Minnesota Department of Transportation.

The NRRA’s monthly seminar highlights research topics that will make an impact on the work done here in the state of Minnesota and around the country.

Project Summary

Although recycled pavement materials have been used in roadway base layers for many years, a specific design method does not exist that describes how to build roadways with these materials. Many state Departments of Transportation (DOTs) assume recycled base materials behave similar to base layers built with conventional virgin aggregates (VA). There is a similar lack of an existing design methodology for pavement systems built with a large stone subbase (LSSB).

The proposed project has three main goals. The first goal of the project is to determine the field and laboratory performance of materials and test sections built with recycled aggregate bases (RAB) including recycled concrete aggregate (RCA), recycled asphalt pavement (RAP), and mixtures of these materials with VA. In addition, similar analyses will be conducted for the test sections built with 18 inches thick LSSB with different compaction methods (1-lift and 2-lift), and those 9 inches thick LSSB built with geogrids and geotextiles. To accomplish this goal, the research team will evaluate both the geomechanical and environmental properties of these pavement systems. It should be noted that the LSSB sections have only one type of aggregate base and the multiple recycled aggregate base sections do not have LSSB indicating that experiments for each different design methods are separate. The second goal of the project is to develop a method to estimate the stiffness and permeability of RAB and LSSB designs. This goal will be achieved by establishing correlations between common laboratory test data and both laboratory and field modulus and permeability values. The third goal is to prepare a pavement design and construction specification for roadways built with RAB and LSSB designs. This goal will be accomplished via a summary of the results of all tasks, taking into account the performance, cost benefits, and life cycle costs of these systems. The outcome of this research will optimize the use of recycled materials and LSSB designs, while maintaining pavement quality, resulting in cost savings and conservation of natural resources.

Visit the MnROAD website for webinar connection information.

Research Pays Off Webinar Series: FRC Jointless Roundabouts in Minnesota

The National Road Research Alliance (NRRA) is hosting “Research Pays Off: FRC Jointless Roundabouts in Minnesota” on March 16 at 10 a.m. CST, presented by Principal Investigator Peter Taylor, Ph.D., P.E., Iowa State and Technical Liaison Maria Masten, P.E., MnDOT.

The NRRA’s monthly seminar highlights research topics that will make an impact on the work done here in the state of Minnesota and around the country.

Project Summary

The use of roundabouts to improve safety and traffic flow in rural areas is growing rapidly in the U.S. Proper design details and construction methods are important to the long term performance of these facilities. Joint layout in roundabouts constructed with concrete pavement are especially challenging. To reduce the need for sophisticated joint layouts, some roundabouts are now be constructed without joints, utilizing structural fiber-reinforced concrete to bridge cracking that might occur. Fiber-reinforced concrete is also being used in thin concrete overlays to increase longevity and enhance joint load transfer capacity.

In 2018, Minnesota’s first jointless fiber-reinforced concrete (FRC) pavement roundabout was constructed near the city of Sleepy Eye. It is of interest to the NRRA Rigid Team members to understand the design, construction, and near-term performance of this roundabout. Also constructed in 2018 were two fiber-reinforced concrete whitetopping (bonded concrete overlay on asphalt) projects in southern Minnesota. These projects were unique in that early construction vehicle loading was applied to each project to encourage the deployment of transverse contraction joints. The NRRA Rigid Team members are interested in documenting the innovative steps performed during the early loading process.

The objectives of this study are twofold:

  1. Write a construction report and carryout a 3-year performance monitoring regime for the jointless FRC roundabout project
  2. Write a construction report for the two FRC whitetopping projects subjected to early loading.

Visit the MnROAD website for webinar connection information.

MnDOT Announces COVID-19 Research Funding

The COVID-19 crisis has affected every aspect of the transportation systems, with state DOTs and local agencies at the forefront of responding to changes, while continuing to meet core missions of providing safe, efficient, and effective transportation systems. To proactively respond and inform future decision-making related to COVID-19’s impact on the transportation sector, MnDOT is investing in research to answer questions specific to the impact of the COVID crisis on Minnesota’s transportation system.

Continue reading MnDOT Announces COVID-19 Research Funding

New Office, Director to Foster ‘Culture of Innovation’

Katie Walker, Director of the Office of Research & Innovation

Katie Walker, formerly of Hennepin County, was recently named director of MnDOT’s new Office of Research & Innovation (formerly the Research Services & Library section), a role in which Walker will lean on her experience leading organizational change at Hennepin County.

Continue reading New Office, Director to Foster ‘Culture of Innovation’

New video traces progress of accessibility research

CTS has been celebrating its 30th anniversary this year with a look back at significant milestones. One of our goals for the anniversary was to show how research progresses over time to lead to new knowledge.

In February we shared videos that trace the path of progress in two of our key research areas: traffic operations and pavement design. Today, at our 28th Annual Transportation Research Conference, we debuted a video about another important research topic: accessibility metrics.

In the new video, Andrew Owen, the director of the U’s Accessibility Observatory, explains how accessibility looks at the end-to-end purpose of transportation: fulfilling people’s need to reach destinations. “The Observatory is pushing the envelope and staying ahead of research into what new types of metrics are possible,” he says.

The Observatory builds on tools and expertise developed in two previous University research studies: the Transportation and Regional Growth Study (1998–2003) and the Access to Destinations study (2004–2012).

Register for the annual CTS Research Conference

Join us at the 28th Annual CTS Research Conference to hear about new learning, emerging ideas, and the latest innovations in transportation. This year’s event is scheduled for November 2 at The Commons Hotel in Minneapolis.

Attendees will learn about research findings, implementation efforts, and engagement activities related to a variety of transportation topics. This year’s keynote presentations feature:

  • Joung Lee, policy director at AASHTO, on how we pay for transportation infrastructure
  • Joshua Schank, chief innovation officer at LA Metro, on policy innovation at his agency

To browse the full program or register for attend, visit the CTS website.

Reducing Driver Errors at Two-Lane Roundabouts

Researchers studied driving behavior at four multilane roundabouts to better understand the relationship between traffic control designs and driver errors. Data collected showed that certain traffic control changes decreased turn violations but failed to eliminate yield violations. Researchers were unable to identify long-term solutions for improving roundabout design and signage, and recommended further research to improve the overall safety and mobility of multilane roundabouts.

“Even though the study did not provide a silver bullet on how to prevent crashes at multilane roundabouts, it did create an efficient tool to analyze and quantify driving behavior data,” said Joe Gustafson, Traffic Engineer, Washington County Public Works.

“This study has advanced our knowledge in multilane roundabout safety and is one step closer to providing much needed improvements to roundabout design guidance,” said John Hourdos, Director, Minnesota Traffic Observatory, University of Minnesota.

What Was the Need?

Roundabouts have been shown to improve overall in-tersection safety compared to traditional traffic signals. However, noninjury crashes are sometimes more frequent on multilane roundabouts than on single-lane roundabouts due in part to driver confusion. Common driver errors such as failing to yield and turning violations on multilane roundabouts have contributed to an increase in noninjury crashes.

Given the benefits of improved mobility, traffic throughput and injury reduction of multilane roundabouts, reducing the noninjury crash rate at multilane roundabouts is important to facilitating their use by Minnesota cities and counties. Identifying solutions to reduce common driving violations would be more sustainable than the current practice of converting multilane roundabouts back to single-lane roundabouts.

In a previous study on a two-lane roundabout in Richfield, Minnesota, researchers demonstrated that traffic control  changes could reduce some of these driver errors. However, more data was needed to support study results. Understanding driver behavior and improving traffic control devices are key factors in designing safer multilane roundabouts.

What Was Our Goal?

With limited research on modern multilane roundabouts, the Minnesota Traffic Observatory sought to collect more data to evaluate the correlation between traffic control design features and collisions. Instead of conducting manual observations, researchers used an innovative video analysis tool to collect and process recorded videos of driving behaviors at test sites. Based on the analysis, they attempted to identify driver behaviors and error rates to help reduce noninjury crashes at multilane roundabouts.

What Did We Do?

The research team selected four multilane roundabouts in Minnesota — two in Mankato, one in Lakeville and one in St. Cloud — to observe undesirable driving maneuvers. At each roundabout site, researchers mounted video cameras at key locations to record one to two weeks of driving behavior. Only one roundabout could be observed at a time because only one set of specialized video equipment was available.

The raw videos were processed to produce a data set for analysis. Researchers used TrafficIntelligence, an open-source computer vision program, to automate extraction of vehicle trajectories from the raw footages. They used the same software to correct any errors to improve data reliability. The resulting clean data from the recorded videos were supplemented with historical crash frequency data reports obtained from the Minnesota Department of Public Safety. Collectively, data from both sources allowed researchers to thoroughly investigate the frequency and crash types from the four roundabouts. A statistical analysis of the data revealed that turn violations and yield violations were among the most common driving errors.

Researchers also looked at how violation rates vary with the roundabout’s location and relevant design features. Based on these findings, researchers proposed signage and striping changes to reduce driver errors at the two Mankato test sites. After the changes were implemented, they collected additional video data.

What Did We Learn?

This study provided one of the most comprehensive analyses to date of driving behavior at multilane roundabouts. Researchers were successful in finding solutions for reducing turn violations, but they were unable to identify solutions for yield violations despite the vast amount of data.

Minor differences in the design at each roundabout presented specific challenges. The analysis focused on how each varying design feature impacted driving behavior. Proposed traffic control changes such as extending solid lines between entrance lanes, adjusting the position of yield signs and adding one-way signs successfully decreased turn violations. However, data from before and after traffic control changes showed an insignificant impact on decreasing yield violations. Importantly, the study produced a list of ineffective traffic control methods that can be eliminated from future studies, saving engineers time and money.

The TrafficIntelligence tool was crucial in efficiently processing and cleaning large amounts of raw video. With improvements made to the software program, the tool should be an asset to future research on roundabouts and to other studies requiring observations of driving behavior.

What’s Next?

The traffic control changes that were successful at reducing crashes at two-lane roundabouts should be implemented by traffic engineers. In particular, large overhead directional signs or extended solid lines between entrance lanes should be installed to help reduce turning violations. The analysis method used in this study could also be used for a robust before-and-after evaluation of future modifications to traffic control devices.

Additional research could further scrutinize the data already collected, and researchers recommend that more data be collected to examine additional traffic control methods and other intersection design elements to improve the overall safety and mobility of two-lane roundabouts. This research could also serve as an impetus for the study of numerous roundabouts in a pooled fund effort involving several states.


This post pertains to the LRRB-produced Report 2017-30, “Evaluation of Safety and Mobility of Two-Lane Roundabouts,” published July 2017. A webinar recording of the report is also available.

MnDOT Chooses EasyMile for Autonomous Shuttle Bus Project

ST. PAUL, Minn. – The Minnesota Department of Transportation chose EasyMile, a France-based company specializing in driverless technology, to lead its autonomous shuttle bus pilot project. MnDOT announced in June it will begin testing the use of an autonomous shuttle bus in a cold weather climate.

“We’re excited to partner with EasyMile to help MnDOT test autonomous technology,” said Jay Hietpas, MnDOT state traffic engineer and project manager. “Their expertise will help us learn how these vehicles operate in a winter weather environment so we can advance this technology and position MnDOT and Minnesota as a leader.”

EasyMile, which has a location in Colorado, has conducted driverless technology cold weather tests in Finland and Norway. Minnesota will be their first cold weather test site in the U.S. EasyMile will use its EZ10 electric shuttle bus that has already transported 160,000 people more than 60,000 miles in 14 countries. The shuttle was tested in various environments and traffic conditions. During these tests, the shuttle operated crash-free.

The shuttle operates autonomously at low speeds on pre-mapped routes. It can transport between six and 12 people.

Initially, it will be tested at MnROAD, which is MnDOT’s pavement test facility. Testing will include how the shuttle operates in snow and ice conditions, at low temperatures and on roads where salt is used.

Testing is scheduled to start in November and go through February 2018. The shuttle will also be showcased during the week of the 2018 Super Bowl.

Hietpas said 3M will also be a partner in the project so the company can research various connected vehicle concepts including sensor enhancement and advanced roadway safety materials. When optimized, these materials would aid in safe human and machine road navigation.


Read more about the autonomous shuttle bus pilot project:


Related MnDOT research: