All posts by micaelaresh

Design Standards for Unobstructed Sight Lines at Left-Turn Lanes

Positive offset left-turn lanes are one solution to improving left-turning motorists’ visibility of opposing through and right-turning traffic.

MnDOT is revising its Road Design Manual and seeks to incorporate more information, policies and design guidance regarding positive offset left-turn lanes.

Researchers from the University of Wisconsin’s Traffic Operations and Safety Laboratory reviewed safety performance data from research that examined left-turn offsets. They also consulted 23 state DOT road design guides to understand the extent of available guidance.

Continue reading Design Standards for Unobstructed Sight Lines at Left-Turn Lanes

Evaluating the Performance of CIR Mixtures With Reduced Binder Content

Researchers examined the practice of reducing the binder content of cold in-place asphalt recycling mixtures in the field on especially hot days to improve workability. Laboratory testing of mixtures at various temperatures and binder levels found the practice keeps mixtures workable, improves compaction and does not significantly diminish performance.

Continue reading Evaluating the Performance of CIR Mixtures With Reduced Binder Content

High-Density Asphalt Pavement Mixtures Viable with local Aggregates

Researchers developed sophisticated models for high-density asphalt pavement mixtures. After calibrating the model to experimental data available from 5 percent air void asphalt mixtures, the research team conducted tests on three Minnesota mixtures to further refine the model. A Phase II study will develop multiple high-density mix designs for Minnesota applications.

Continue reading High-Density Asphalt Pavement Mixtures Viable with local Aggregates

Performance Testing of Regional Roadside Turfgrass

Keeping Minnesota’s roadsides green is about more than just aesthetics—healthy turfgrass can improve water quality, reduce erosion and road noise, and provide animal habitat. However, harsh conditions such as heat, drought, and salt use can make it difficult for roadside turfgrass to thrive.

Researchers tested a wide variety of turfgrass cultivars over several growing seasons—in both urban and rural environments across five states.

This multi-state research project aims to provide participating departments of transportation (DOTs) with unbiased, up-to-date information about the performance of turfgrass cultivars when used on roadsides in the northern United States.

What Was the Need?

Vibrant green grass along roadways is a significant feature of urban and rural Minnesota landscapes. Statewide, MnDOT maintains more than 24,000 acres of turfgrass planted along Interstate highway medians, roadway slopes, street terraces and other areas. Roadsides are challenging environments for establishing turfgrass, with many site-specific stressors.

Failed installations often result in the need to eliminate the existing vegetation and then reseed, which may cost between $150 and $530 per acre for seeds plus the cost of labor. Sod can cost nearly $20,000 per acre. Turfgrass installations fail for many reasons, but observation and previous research suggest that failures often occur when the wrong species is used at a given site. Using the correct turfgrass species for a specific area contributes strongly to successful turfgrass installation.

“The development of resilient turfgrass species and mixes is most effectively accomplished as a collaboration among cold climate states. Working across state lines, we can simultaneously test many species and mixes across a wide range of soil and weather conditions,” said Dwayne Stenlund, erosion control specialist, MnDOT Office of Erosion Control and Stormwater Management.

In previous studies, Minnesota has tested various turfgrass species at multiple sites. However, year-to-year weather variability does not allow for test sites in a single state to provide adequate information about grass tolerances to many roadside stressors. Further, new species cultivars with better heat, drought and salt tolerance are being released, but states have not updated their seed mixes to include them. Results of local testing could promote their use. MnDOT sought to test many turfgrass cultivars and some new, untested species in a wide range of soils and seasonal weather in roadside environments across selected northern states.

What Was Our Goal?

The primary objectives of the project were to assess the performance of potential roadside turfgrasses across multiple northern states and to collect resulting unbiased data for use by public agencies.  

What Did We Do?

The initial task was solicitation of cold climate states to participate in the project. Of the approximately 15 states contacted, five had the necessary university horticulture programs and departments of transportation (DOTs) to collaborate with researchers: Michigan, Minnesota, Nebraska, New Jersey and Wisconsin. Researchers in each of these states were to test 50 individual cultivars and 10 standard mixes—two from each state. The cultivars were chosen through breeder recommendations and public data that indicated potential use as a roadside turfgrass.

Researchers in each state seeded plots in two locations: an urban or suburban street with a curb and daily traffic volume of 10,000 to 15,000 vehicles; and a rural highway without a curb, a ditch sloped away from the road and daily traffic volume of at least 30,000 vehicles.

A researcher checks a turfgrass test site next to an asphalt roadway. A white-framed grid overlays the 5-by-3-foot plot, which shows very little growth.
A grid overlaid on a plot in New Jersey allows each grid intersection to be logged as originally seeded, a weed or bare soil.

A grid overlaid on a plot in New Jersey allows each grid intersection to be logged as originally seeded, a weed or bare soil.

Three replications of 5-by-3-foot test plots were planted in a randomized block design. Researchers used the same amount of seed and starter fertilizer, and identical germination blankets for all plots. Minnesota and Wisconsin applied early watering, while other states’ site plots relied on rain. Plots were mown as needed (rural areas less frequently than urban plots).

Soil samples were collected before seeding and each spring after thaw to determine residual winter salt. Researchers also tested for phosphorus and organic material, pH levels, electrical conductivity (indicating salt levels), sodium content and other factors. In addition, each state collected 24 core soil samples at the project’s start and end to determine physical soil characteristics.

Researchers assessed the sites using a grid intersection method. They counted the number and kinds of plants—grass or weed—at each intersection of a grid placed over the plot. Plots were assessed in October 2016, April and October 2017, and April 2018.

A website was created that incorporated all data from the test plots.

What Did We Learn?

The project highlighted the importance of multisite testing and difficulties in establishing turfgrass: Only six of the 10 sites resulted in first-year data due to weather and human interference.

“This project shows that state agencies should continue to investigate best management practices for turf establishment and maintenance to make sure the genetic potential of adapted cultivars is realized,” said Eric Watkins, professor, University of Minnesota Department of Horticultural Science.

Accumulated degree-days (the sum of the daily temperature above 40 degrees Fahrenheit) did not explain the differences in turf establishment, however. Successful fine fescue coverage appeared at sites with higher snowfall and, thus, higher salt amounts. In several cases, turfgrass establishments suggested that only genetics were at play.

Fine fescues are more tolerant of salt than other species and performed well at urban sites. Results also suggested that high salt usage sites would benefit from mixtures incorporating alkaligrass.

What’s Next?

This project is the first to provide participating DOTs with unbiased, up-to-date information about turfgrass cultivars and mixtures used on cold state roadways. Future studies would be most effective if they were coordinated with the same group of researchers or expanded to include more. One approach could be partnering with the National Turfgrass Evaluation Program to use its testing infrastructure.

This post pertains to Report 2019-38, Regional Roadside Turfgrass Testing Program, published August 2019.

New signs give highway drivers more reasons to stop at rest areas

According to recent survey results, new highway signs promoting rest area amenities are influencing motorists’ decisions to use them.

A sign posted on a rest area door invites readers to take a quick survey about the rest area. The sign includes a phone number to text or call, a QR code and a survey keyword.

Among the 947 respondents using an electronic customer feedback system, 33 percent said they had seen the signs and 29 percent were not sure if they had. Of these two groups, 27 percent indicated the signs influenced their decision to stop and 61 percent described the signs as helpful.

These visitors had the opportunity to take a quick survey via QR code displayed on door decals, stand signs and flyers at the rest areas.

“No other states have installed advance rest area signage that list amenities available at upcoming rest areas,” said Rob Williams, MnDOT’s Safety Rest Area program manager. “We believe this is a cost-effective way to entice people off the road for breaks.”

MnDOT began a two-year pilot project in 2015 to implement findings from its 2009 Rest Area Amenities Study, which suggested that more detailed signage about rest area amenities could encourage motorists to pull off and take a break – which could save lives. According to the National Highway Traffic Safety Administration, drowsy driving-related crashes resulted in 795 deaths in 2017. Williams applied for research implementation funds to install 36 signs advertising the amenities ahead of 21 rest areas along Interstate 35 and I-94, as well as at the Brainerd Lakes Area Welcome Center.

Safety rest areas are one tool to keep drivers safe by giving them a place to stop, rest and refresh. MnDOT operates 51 Class I rest areas throughout the state, but not all rest areas offer the same amenities. Depending on the traveler, it may be a family restroom, fenced dog park, or children’s play area that best serves their needs.

MnDOT’s Rest Area Program is continuously working to improve rest areas to better serve travelers and reduce driver fatigue accidents.

“Our rest areas provide an opportunity to directly interface with Minnesotans and visitors traveling through our state, and we want to provide them with the best possible experience,” Williams said.

Ongoing enhancements to our rest areas include improving safety, accessibility and sustainability by:

  • Increasing visibility in rest area lobbies and installing video recording systems to improve visitor safety
  • Improving accessibility and introducing family restrooms
  • Increasing sustainability by use of native vegetation, installing electric vehicle charging stations, using materials with lower life-cycle costs and, in some cases, developing green roofs

The safety rest area program will seek funds to install additional advance signage as rest areas are remodeled. To learn more about the safety rest area signage project, visit the Office of Research & Innovation.

Implementing CIM in Preliminary Design of Infrastructure

Using an existing county road project as context, researchers examined the digital technologies and processes associated with civil integrated management (CIM). A comparison of CIM with the traditional methods used in the proposed county project demonstrated the advantages of CIM.

Continue reading Implementing CIM in Preliminary Design of Infrastructure

Resources Help Local Agencies Plan for CAV Roadway Needs

In a recently completed project, funded by the Local Road Research Board, researchers developed a reference tool and compiled a literature review that local agencies could use to anticipate the infrastructure needs of connected and automated vehicles. Agencies can use these resources to plan for infrastructure upgrades and maintenance activities.

Continue reading Resources Help Local Agencies Plan for CAV Roadway Needs

Using Debonded Strands to Reduce End Stress in Bridge Beams

A new MnDOT-funded research study has found that most agencies in states with weather similar to Minnesota’s use debonded strands in prestressed concrete bridge beams. MnDOT may begin piloting debonding as an alternative to draping, which manufacturers claim is time-consuming, challenging to worker safety and expensive.

Continue reading Using Debonded Strands to Reduce End Stress in Bridge Beams

Collaboration with Minnesota Zoo aims to conserve wildlife

Turtles and other wildlife are at risk along Minnesota roadways.

MnDOT is collaborating with the Minnesota Zoo on a new research project installing small animal exclusion fencing. The fencing is intended to redirect turtles (and other small animals) to culverts and bridges where they can cross the road safely.

Continue reading Collaboration with Minnesota Zoo aims to conserve wildlife

Low-Temperature Cracking Test Produces Repeatable, Reliable Results

Researchers ran a sophisticated low-temperature asphalt cracking performance test at multiple labs to study the test, its variability and repeatability, and its additional promise in studying reflective cracking susceptibility of overlays. Results put MnDOT closer to implementing test specifications for low-temperature cracking test for pavement mixes.

Continue reading Low-Temperature Cracking Test Produces Repeatable, Reliable Results