Tag Archives: minnesota department of transportation

Minnesota: Are You Ready to Mumble?

In the search for a quieter rumble strip, Minnesota may have found a winner in California.

California’s standard rumble strip design outperformed Minnesota’s and Pennsylvania’s in a comparison study along a rural highway near Crookston, Minnesota. (Read the recently published report.)

“California’s rumble strip still gave significant feedback to drivers, but it was significantly less noticeable outside the vehicle,” said engineering consultant Ed Terhaar, who performed a noise analysis with acoustical engineer David Braslau on behalf of the Minnesota Local Road Research Board.

A California-style sinusoidal rumble strip, installed along a Polk County Highway.
A California-style sinusoidal rumble strip, installed along a Polk County Highway.

Although they serve as an effective warning to drivers, rumble strips can cause unwanted noise when a vehicle drifts over a centerline or edgeline.

Both the LRRB and the Minnesota Department of Transportation, which is sponsoring a companion study, are interested in finding a new design that still captures the driver’s attention, but minimizes the sound heard by neighboring residents.

Polk County tests

Terhaar and Braslau’s research showed that Minnesota and California’s designs produce a similar level of interior noise. Although external decibel levels are not that different from each other either, Minnesota’s rumble strip has a considerably stronger tone that can be heard further away.

“California’s sound is less sharp, less intrusive and less noticeable,” Braslau said. “Minnesota’s has a really sharp peak. So while the absolute sound level of California’s isn’t all that much lower, its perception is less.”

Testing was performed using three different vehicles – a passenger car, pickup truck and semi-trailer truck – at three different speeds – 30, 45 and 60 miles per hour.

In general, Pennsylvania’s rumble strip had both a quieter interior and exterior sound than California’s and Minnesota’s.

Like Pennsylvania, California’s rumble strip has what is called a sinusoidal design – a continuous wave pattern that’s ground into the pavement (it’s the style commonly used in Europe and has been called a “mumble strip” because it’s quieter). The main difference between the two is that California’s wave length is 14 inches, while Pennsylvania’s is 24 inches.

Minnesota’s design is much different than the sinusoidal pattern used by the other two states.

“It’s not a continuous wave – it’s basically chunks of pavement taken out at certain intervals with flat pavement in between. It’s more of an abrupt design, whereas California and Pennsylvania’s are more continuous and smooth,” Terhaar explained.

The next step for researchers is to test variations of the California rumble strip design at MnDOT’s Road Research Facility (MnROAD).

The 8-inch rumble strip tested in Crookston is the typical edgeline design used by Polk County, but it was found to be too narrow for semi tires, so MnDOT will look at wider designs in its follow-up study. Researchers will also look at the impacts to motorcyclists and bicyclists, as well as the California rumble strip’s centerline striping capability.

The Minnesota rumble strip, left, and California rumble strip, right.
The Minnesota rumble strip, at left and also pictured in top photo, and California rumble strip, right.

Related Resources

Rumble Strip Noise Evaluation study

MnDOT looks for solution to noisy highway rumble strips – Crossroads article

MnDOT Tests Crowdsourcing to Improve Road Condition Reporting

The Minnesota Department of Transportation is testing a crowdsourcing application that will allow motorists to update winter weather road conditions on the state’s 511 system.

The Regional Transportation Management Center is planning a soft launch of Citizen Reporting in April, initially inviting MnDOT employees to post their experiences on routes they travel.  By next winter, the RTMC hopes to invite the public to do the same.

“We suspect that citizen reporters will be similar in ethic to the kinds of people who volunteer to be weather spotters,” said MnDOT Transportation Program Specialist Mary Meinert, who assists with day-to-day operations of 511.

511 Citizen Reporting
Iowa launched Citizen Reporting in November. Here is an example of a citizen report.

Currently,  MnDOT maintenance crews report road conditions, but Greater Minnesota lacks 24/7 coverage and its reports can become quickly outdated, especially on highways that aren’t plowed as frequently or lack traffic cameras, said 511 System Coordinator Kelly Kennedy Braunig.

Citizen reporting, especially on weekends, will help keep that information fresh.

“We try to explain on the website that we only update from 3–6 a.m., 3–6 p.m. Monday through Friday and as road conditions change, but we still get many emails requesting more frequent road condition information,” Braunig said.

Even a recent comment on MnDOT’s Facebook page pointed out the limitations in one area of the state: “Updates [only] come during government work hours.”

Growing Service

It’s actually a welcome sign that the public wants more from 511.

Seven years ago, when Braunig applied for her job, not many people used 511. In fact, at the time, she wasn’t even aware of the service, which provides information to travelers on weather-related road conditions, construction and congestion.

Today, 511’s online program and mobile app are accessed by more than 5,000 people per day during the winter (and about half as many during the summer). Data comes from MnDOT’s construction and maintenance offices, as well as state trooper data and incident response. This real-time information is available for all of Minnesota.

In the Twin Cities metro area, more than 700 traffic cameras allow MnDOT and State Patrol dispatchers to check the condition of 170 miles of highways and monitor traffic incidents at any time. Rochester, Duluth, Mankato and Owatonna also have cameras for incident management and traffic monitoring.

The 511 system’s greatest challenge is in Greater Minnesota, where road condition information is used daily by schools, ambulance personnel and truckers, as well as the traveling public, but information isn’t updated frequently outside of business hours.  Citizen reporting will be a beneficial resource.

Other states

Other northern states face similar challenges as Minnesota, but have been able to improve the timeliness of road condition data with assistance from truckers and other motorists.

In Wyoming, more than 400 citizen reporters (primarily truckers) call in road conditions to the Transportation Management Center. In Idaho, citizen reporters directly put the information into the 511 system. Minnesota will be the fifth state to adopt citizen reporting, following Iowa, which launched its service in November 2014.

Like Iowa, Minnesota’s citizen reporting will initially focus on winter roads.

To participate, people will need to take an online training module and then register their common routes, perhaps the highways they take to work or their way to the cabin on the weekends. These contributions will be marked as a citizen report on the website.

“Minnesota truck drivers are loyal users of the 511 system and we suspect they will also make some of our best reporters,” Meinert said.

Minnesota is part of a 13-state consortium that shares a 511 service technology provider. States with citizen reporting recently shared their experiences in a Peer Exchange sponsored by North/West Passage, a transportation pooled fund that is developing ways to share 511 data across state lines.

“With citizen reporting we hope to give people a voice and a chance to participate,” Braunig said.

Using History to Predict Bridge Deck Deterioration

Just how long will it be before a bridge deck needs to be rehabilitated?  Why not look to history to find out?

Researchers have put several decades of MnDOT bridge inspection records to good use by analyzing old bridge deck condition reports to calculate how quickly similar bridge decks will deteriorate.

MnDOT inspects bridges regularly, but had never used this historical data to help determine the rate of bridge deck deterioration and what factors influence it.

“We’re always trying to improve the timing of bridge deck repair projects and improve our understanding of what contributors affect the way our bridge decks deteriorate,” said Dustin Thomas, MnDOT’s South Region Bridge Construction Engineer.

Data-Crunching

From their analysis, researchers created deterioration tables that can be used to better predict the timing and costs of repairs and maintenance.

Researchers looked at the inspection history and construction details of 2,601 bridges to determine the impact of factors such as type of deck reinforcement, depth of reinforcement below the driving surface, traffic levels and bridge location.

Using the inspection data, researchers developed curves that show how long a bridge deck is likely to stay at a given condition before dropping to the next. They developed separate curves for each variable that had a significant impact on deck deterioration rates.

What They Found

Several factors were found to have a notable impact on how quickly bridge decks deteriorate:

  • Decks without epoxy-coated bars built between 1975 and 1989 deteriorate more quickly than other bridge decks.
  • Bridges with less traffic showed slightly slower rates of deterioration than highly traveled bridges.
  • Metro area bridges drop to a condition code of 7 (good) more quickly than bridges in other parts of the state. This may be due to increased chemical deicer usage or because maintenance activities like crack-sealing are more likely to be delayed on larger metro bridges  because of the difficulty accessing middle lanes.
  • When a new deck is installed on an existing bridge, the deck performs like a brand-new bridge and so MnDOT should use the deterioration table for the re-decking year, rather than the year the bridge was originally constructed.

MnDOT plans to incorporate future bridge inspections into the dataset to enhance the predictive value of the deterioration tables.

Related Resources

The impact of overlays on bridge deck deterioration in Minnesota was not clear, but redecked bridges were found to perform similarly as brand-new decks.

New Tool Measures Impact of Heavy Trucks

A new tool developed by the Local Road Research Board helps cities and counties assess how much increased heavy vehicle traffic affects local roads.

Researchers created an analysis method and corresponding spreadsheet tool that city and county engineers can use to calculate the impact of heavy vehicles on asphalt roads beyond what was planned in the original pavement design.

The information will help agencies optimize services, such as garbage collection, for the least amount of damage. It will also help agencies better plan roads in new developments, as well as redesign existing roads that are nearing the end of their lives.

Lack of Data

Heavy trucks cause local roads to deteriorate more quickly than passenger vehicles, but it is challenging to quantify the impacts, especially for areas where traffic was not forecast at the time a road was designed.

Many local engineers in Minnesota have requested information about the impact of heavy vehicles in light of new construction, commercial distribution facilities and hauling routes. This information is needed to assist in local road planning and maintenance.

Two Methods

In a newly completed study, investigators developed two methods for calculating heavy vehicle impact:

  • Calculate the additional bituminous material (and associated costs) that would have been required to construct the pavement had the heavy truck traffic been predicted when the pavement was designed.
  • Calculate the portion of a pavement’s design life, measured in equivalent single-axle loads (ESALs), consumed by unanticipated vehicles.

“Before this project, there wasn’t an easy way for an engineer to determine how much a specific truck was going to decrease the life of a road,” said  Deb Heiser, Engineering Director, City of St. Louis Park.

Whereas previous research has calculated the impact of extremely heavy vehicles over the short-term (typically the course of a construction project), this project calculates the impact of long-term increases in traffic from vehicles that are heavy, but still mostly within normal legal weight limits.

The tool can be used for a single street segment or an entire road network. Users can also compare current situations with proposed ones to evaluate the impact of potential changes in heavy traffic levels.

Related Resources

Decoding the Deicers

The results of last season’s deicing study are in — just in time for our next snow.

Last winter, Minnesota State University researcher Steve Druschel set up experimental lanes at two Shakopee entertainment parks and a test site on a Mankato bridge to examine the life cycle of winter maintenance, from plowing and the application of chemicals to the drainage of chemical residue after the roadway has been treated.

What the Study Found

  • The majority of chloride appears to leave the roadway by plow ejection, vehicle carry-away or tire-spray spreading, rather than through storm drainage, even in warmer storms.
  • Pavements don’t hold chloride very long in a precipitation event, even after anti-icing/pre-treatment.
  • Deicer effectiveness. Warmer temperatures provide more melt from the deicer. Little melt was observed below
    10 degrees Fahrenheit unless sunlight provided warming, and prewetting produced no significant difference in deicer performance.
  • Dry pavements may be better candidates for pretreatment, with researchers noting that any wetness on the pavement ahead of a storm limited anti-icer effectiveness.
  • Truck traffic after deicer application was found to significantly improve deicer performance, resulting in both a wider and quicker melt.
  • Plow effectiveness. Even with different snow and temperature conditions, the evaluation of plow speed provided the same findings: snow rises higher in the curvature of the plow at higher speeds, creating a broader spray off the plow ends, and higher speeds decrease scrape quality.
Students pour water to form ice on a test lane in Shakopee.
Students pour water to form ice on a test lane in Shakopee.

What’s Next?

The research team has proposed a third phase of this project to continue their work in the field, which is expected to include further examination of the impact of truck traffic on deicer effectiveness, variations in plow setup and expanded testing under varying weather conditions and snow structure.

Related Resources

Field Effects on Deicing and Anti-Icing Performance – Technical Summary (PDF, 1 MB, 2 pages); Final Report (coming soon)

Salt Brine Blending to Optimize Deicing and Anti-Icing Performance –Technical Summary (PDF, 1 MB, 2 pages) and Final Report (PDF, 11 MB, 151 pages) (previous study) 

Continuous Scour Monitoring Improves Bridge Safety

A leading cause of bridge failure is bridge scour, which occurs when rapidly moving water erodes riverbed soil around abutments or piers.

Monitoring bridge scour with traditional inspection methods can be dangerous and difficult, so MnDOT has been working with researchers from the University of Minnesota’s St. Anthony Falls Laboratory to develop a continuous monitoring system to test certain bridges more safely and efficiently.

MnDOT currently monitors 45 scour-critical bridges — and local Minnesota agencies monitor 360 more — using visual inspections or water data websites during flooding events. Once a predetermined threshold is exceeded, portable scour monitoring equipment is deployed to measure scour depth.  If scour has undermined the foundations of a bridge, inspectors close it for repair.

But portable scour monitoring systems can be difficult and dangerous to deploy from the bridge deck or boat in fast-moving water. It can also be difficult to get inspectors to sites quickly enough in areas subject to flash flooding.

A better alternative for such situations are fixed scour monitoring devices that continuously monitor scour and send data wirelessly to bridge personnel, alerting them when scour reaches a dangerous level.

The Highway 43 Bridge in Winona was affixed with continuous bridge scour monitoring equipment.
The Highway 43 Bridge in Winona was affixed with continuous bridge scour monitoring equipment.
New technology

MnDOT has not historically made use of fixed scour monitoring equipment, but as advances in technology have made these devices more affordable and reliable, the agency  became interested in exploring the use of fixed monitoring equipment at locations where the use of portable equipment is problematic. ( A major concern for fixed scour monitoring is damage from debris and ice.)

Researchers have installed fixed remote monitoring stations on four such bridges.

Stations on the first two bridges (Highway 14 over the Minnesota River in Mankato and Highway 43 at the Mississippi River in Winona, pictured at top) ran successfully for three years, with outages due to primarily to power and communication issues.

Researchers learned valuable lessons from these bridges and have now installed monitoring equipment on two more: The Old Hastings Bridge (Highway 61 over the Mississippi River), on which float-outs were installed; and the Dresbach Bridge (Interstate-90 over the Mississippi River), which had a tilt meter and underwater sonar device installed.

“The less familiar personnel are with technical equipment, the less they tend to use it,” said Andrea Hendrickson, State Hydraulics Engineer, MnDOT Office of Bridges and Structures. “This research project gave us the familiarity and technical information we need to be comfortable using fixed scour monitoring equipment on bridges that warrant it.”

Related Resources

*Editor’s note: This article was adapted from an article in the latest issue of our newsletter, Accelerator. Read it online, or sign up to receive it by mail. 

Video: Load Testing for the Winona bridge

New video, below, shows how explosions are used to test the bedrock for the new Highway 43 bridge in Winona.

Bridge engineers use “pile load testing”  to find out how much weight and resistance the ground will bear. It not only saves time and money, but helps design a bridge that will sit securely on the bedrock, below the river.

The statnamic test used in the video is one part of this process.

Winona Bridge Statnamic Test

 

How load testing works: 

It begins with digging and pounding.

Two different kinds of piles are put into the ground:

  • A hollowed shaft, which is filled with rebar and concrete. It goes 30 to 50 feet below the bedrock to create a solid pillar that can assess how much weight and sway the ground will bear.
  • A steel pipe that is hammered into the ground. Since the bedrock is about 100 to 150 feet below the river, these pipes are welded together end-to-end to reach that length.

Once the piles are in, they’re tested two different ways.

  • Pile Dynamic Analysis, with gauges affixed to the top of the pile to read the pressure put on it when hit with a pile driver.
  •  A Statnamic test (shown in videos), which involves accelerating a heavy weight by setting off a controlled combustion reaction. This shows how much resistance the pile can take.

Once the data is collected for the bridge design, the piles are cut off two feet below the river bed.

Mobile imagery, LiDAR help MnDOT maintain its assets

How do you quickly and cost-effectively get an accurate inventory of transportation assets spread out along more than 1,100 miles of roadway?

That was the problem facing the Minnesota Department of Transportation’s Metro District, which needed an inventory of its plate beam guardrail and concrete barriers.

To accomplish this, engineers in the district launched an innovative research implementation project using a pair of mobile mapping technologies — Light Detection and Ranging (LiDAR) and mobile imaging — that can collect vast amounts of geospatial data on highway infrastructure in a safe and efficient manner.

Mobile imaging uses a camera mounted on a vehicle driving at highway speeds to take high-resolution photos at regular intervals. It’s accurate to within 1 foot, which makes it suitable for use in preliminary (30 percent) design plans without additional field surveys. In this project, researchers collected mobile images of roadway barriers and extracted data from them along Metro District roadways, including all ramps, overpasses, interchanges, weigh stations, rest areas and historical sites.

A MnDOT worker replaces a section of broken guardrail.
A MnDOT worker replaces a section of broken guardrail on I-94 near the Lowry Tunnel in Minneapolis. (Photo by Dave Gonzalez, MnDOT)

Researchers also collected LiDAR data at three Metro District sites. LiDAR uses a laser range finder and reflected laser light to measure distances. It provides survey-grade data accurate to within 0.1 foot, but it is significantly more expensive to collect than mobile imaging.

“Mobile imagery and mobile LiDAR are relatively new technologies, but this research shows that they are options that we can use. Collecting this information manually would have taken a lot more time and money,” said MnDOT Asset Management Engineer Trisha Stefanski.

MnDOT’s barrier inventory will provide invaluable information for design, planning and maintenance. The data will be published on MnDOT’s Georilla map server, where it will be beneficial to a variety of projects and recurring tasks. For example, if a vehicle hits a barrier, maintenance staff will be able to check the database to see the type of barrier and end treatment to ensure they bring the right equipment to make repairs. Although the project focused on barriers, the imagery contains data on other assets as well. MnDOT has already used the imagery to extract noise wall and sign data.

This blog post was adapted from an article in our upcoming issue of Accelerator, MnDOT’s research and innovation newsletter.

3D-vertical
Thousands of data points can be extracted from this image of a Highway 61 roadway segment created with LiDAR Technology.

Drinking water solutions may help construction site runoff

The same chemicals used to treat drinking water might now be able to treat stormwater runoff to reduce the amount of pollutants entering Minnesota lakes and rivers from road construction sites.

A research project headed by Mankato State University and funded by the Minnesota Department of Transportation has identified three chemical flocculants that are effective at removing a broad range of Minnesota soils from water.

“Water is leaving construction sites carrying too much sediment,” said Minnesota State University-Mankato Environmental Engineering Professor Steve Druschel. “Chemical treatment has been used to treat drinking water for 70 to 80 years, and our thought was to try it in construction as well.”

Adding flocculant to a sample of water from the Minnesota River causes sediment to clump and sink.
Adding flocculant to a sample of water from the Minnesota River causes sediment to clump and sink.

Recent MnDOT research has investigated monitoring the amount of sediment in stormwater runoff and using temporary ponds to let sediment settle out of stormwater before it runs off the construction site. MnDOT also wanted to examine the possibility of treating  construction runoff with flocculants, which are chemicals that cause suspended sediment to form clumps that quickly settle out of the solution.

Researchers tested 21 chemicals to see how well they could remove 57 types of soil from water. While no chemical was effective for the entire range of Minnesota’s soils, three chemicals were broadly effective on a range of samples.

The research will contribute to improved treatment of stormwater runoff from construction sites and reduce the amount of sediment pollution entering the state’s rivers and lakes.

Although flocculants have been used to treat drinking water for seven decades, there has been only limited testing of their use in treating construction runoff. Research was needed to evaluate the effectiveness of this approach.

Adding flocculant to stormwater runoff can be as simple as drilling a hole in a bucket of the chemical and mounting it above the water (as shown here), although thorough mixing must be ensured. MnDOT hopes to develop a system that will automatically dispense a precise dose based on the amount of sediment in the water.
Adding flocculant to stormwater runoff can be as simple as drilling a hole in a bucket of the
chemical and mounting it above the water (as shown here), although thorough mixing must be ensured. MnDOT hopes to develop a system that will automatically dispense a precise dose based on the amount of sediment in the water.

Since it is not feasible for workers to constantly monitor sediment concentration in stormwater runoff, MnDOT hopes to leverage the knowledge gained from this project to develop an automated system that measures the amount of sediment in runoff and automatically adds the appropriate dose of flocculant to treat the water.

“We’re trying to develop a portable water treatment plant that can be applied to construction projects to deliver clean runoff water after a storm,” said MnDOT Environmental Specialist Dwayne Stenlund.

Any chemicals recommended for field usage will need to be approved by the Minnesota Pollution Control Agency, and methods for disposing of used chemicals will need to be identified as the environmental impacts of residual chemicals are unknown.

*Editor’s note: This article was adapted from the September-October 2014 issue of our Accelerator newsletter. Read it online or sign up for your free subscription.

Related Resources

MnDOT saves time, money with new contracting method

Thanks to a flexible new contracting method, the cost and time of delivering small highway projects in Minnesota should go down.

The Minnesota Department of Transportation is now able to put road construction contractors on standby for certain types of projects, rather than bid each project individually, due to the adoption of Indefinite Delivery/Indefinite Quantity (IDIQ) contracts.

“IDIQ contracts give MnDOT more flexibility and the ability to get to the field quicker for work that we need repeated routinely, such as culvert repairs, overlays and seal coats,” said Kevin Kosobud, project development engineer with MnDOT’s Office of Construction and Innovative Contracting.

IDIQs also provide flexibility when needs are uncertain.  Contracts are often used for multiple small projects that are similar in scope, but difficult to quantify in cost and timing.

For instance, the state of Florida awards IDIQs for hurricane debris removal, activating and paying contractors only when a hurricane necessitates the service.

Although IDIQs showed great promise, MnDOT had to develop a framework to implement them.

The federal government has used IDIQ contracts since the 1980s, but only a small number of state DOTS have used them to procure construction services. No standard procedures existed for their use by state DOTs, and federal procedures are not always applicable at the state level.

MnDOT hired Iowa State University researchers to examine IDIQ usage across the country and develop implementation procedures for Minnesota. (Read a summary of their research here.)

Researchers examined contracting practices at 14 different transportation agencies to  recommend guidelines for Minnesota to follow, which allowed MnDOT to begin awarding IDIQ contracts in April 2013.

Case study analyses show clear benefits where IDIQ has been used: acceleration of the project delivery period, reduced construction costs and flexible delivery scheduling.

“IDIQs can help DOTs get better prices for routine services via an economy of scale, for instance, by awarding a contract for a larger number of culvert repairs rather than awarding a single contract for each repair,” explained Doug Gransberg, professor of construction engineering at the Iowa State University Institute of Transportation.

Agencies can award IDIQ contracts individually or collectively.

With a single-award contract, a single contractor is awarded task orders based on the pricing furnished in the initial bid package; multiple-award contracts determine a pool of qualified contractors who may subsequently bid on task orders.

*Editor’s note: This article was adapted from the September-October 2014 issue of our Accelerator newsletter. Read it online or sign up for your free subscription.

Related Resources
  • Leveraging the Advantages of Indefinite Delivery/Indefinite Quantity Contracts – Technical Summary (1 MB, 2 pages); Final Report (expected Fall 2014)