High-Tech Inspections to Keep Minnesota’s Timber Bridges Safe

Across Minnesota, hundreds of wooden bridges are reaching the end of their lifespan, but counties don’t know which ones to repair and which ones to replace.

In 2010, a timber bridge partially collapsed in Nobles County, heightening concerns about the state of inspections statewide.

“A lot of it right now is just visual and sounding the wood – striking it with a hammer and interpreting dull or hollow sounds,” said MnDOT State Aid Bridge Engineer David Conkel.

Timber bridges are at a critical point in Minnesota, not only because of the sheer number built in the 1950s and 1960s, but because it’s difficult to judge their structural soundness without advanced equipment.

While current inspection methods adequately identify areas of advanced decay, they do a poor job of detecting early decay or internal deterioration, especially in the timber substructure.

MnDOT and the Local Road Research Board have partnered to develop better inspection and repair methods on behalf of Minnesota counties. Training will be held in May and June for county inspectors. [Register here]

The most troublesome area of decay on a timber bridge are in the pilings, which usually have contact with the water. The drying and wetting of the water causes rot to form.
The most troublesome area of decay on a timber bridge are in the pilings, which usually have contact with the water. The drying and wetting of the water causes rot to form.

Identifying internal deterioration early is essential because once significant rot is noted, a timber bridge can slip into a severe condition within just two to three years.

Early bridge makers treated timber bridge elements with creosote to prevent decay from fungi and insect damage. However, because it was typically applied to the shell, a good external condition may hide severe internal deterioration.

“The timber bridge elements typically decay from the inside out due to the lack of preservative in the center of the timber,” explained Matt Hemmila, St. Louis County Bridge Engineer. “The outside will look okay, but the inside may be highly deteriorated.”

Better Inspection

Resistance microdrills and stress wave timers are two proven inspection tools that counties can use to see past the surface of a timber bridge and identify the actual amount and area of internal rot. But Minnesota counties have lacked this equipment and the training.

“These tools will enable us to identify the bad bridges before the decay shows up visually– but it will also tell us which bridges are still good so we can allocate the funds we have to replace the worst bridges,” Hemmila said.

A stress wave timer (video above) locates bad areas on a bridge by using probes to measure the time it takes for sound to travel through the material. A decayed piling will have a time that is more than double that of a sound piling.

A resistance microdrill (video below) can then be used to determine how much good wood is left in a piling or timber element by drilling a bit into the wood and measuring the resistance.

MnDOT and the LRRB are developing a customized inspection manual and standardized inspection protocols, which can be integrated into the state’s bridge data management software.

“Good inspections can catch potential problems early and possibly avoid emergency closures or load postings,” Conkel said. “It enhances safety while also helping stretch available funding for bridge repair and replacement.”

Baby Boomers

Minnesota has one of the highest concentrations of timber bridges in the country — 1,600 (down from 1,970 in 2001), more than half built before 1971.

These bridges typically start experiencing issues in their substructure when they reach 40 to 60 years old, with decay usually occurring where the piling meets the ground or water line – a perfect environment of air and moisture for rot to thrive and propagate.

Unfortunately, some bridges were unwisely built on the pilings of former bridges.

“Well-maintained, well-designed and well-treated bridges can last a long time, equivalent to other materials,” said Brian Brashaw, director of Wood Materials and Manufacturing Program at the University of Minnesota-Duluth.

Age of Minnesota's Timber BridgesBecause bridge engineers have been unable to fully assess the internal cross-sections of timber bridges, they have been very conservative when assessing timber bridges, Brashaw said, resulting in load limit reductions and bridge replacements.

“The use of advanced techniques will take the guess work out of the equation, allowing for better decision-making on which bridges need repair or replacement now,” Brashaw said.

With no formal national or state guidance, MnDOT and the Local Road Research Board undertook a research project to identify state-of-the-art inspection practices and marry those techniques with the needs of Minnesota county engineers.

“We don’t have enough money to just replace all the timber bridges, so we want to provide county engineers with more advanced inspection tools so they can determine how much decay there is in the piling, and other susceptible areas,” Conkel said.

A second LRRB project, led by Iowa State University, is advancing the development of cost-effective repair techniques that counties can use to lengthen a bridge’s service life.

“We can’t build them fast enough, so we have to find a way to make them last longer so we can catch up,” Hemmila said.

Upcoming courses (see flyer) *

May 14: SE Minnesota – Register Here for Welch, MN

May 15: SW Minnesota – Register Here for Windom, MN

June 23: NE Minnesota – Register Here for Aitkin, MN

June 24: NW Minnesota – Register Here for Bemidji, MN

 

*All classes 9:00 a.m. to 3:30 p.m.

Bike to Work Day: progress in Minnesota, but miles to go

By Greg Lindsey

This blog post by University of Minnesota Professor Greg Lindsey was originally posted on the CTS Conversations blog.

April 9 is national Bike to Work Day, a day to celebrate those who choose bicycling as their principal mode of transportation for commuting, and a time to encourage more people to consider this healthy, efficient transportation option. Minnesota has much to celebrate in terms of bicycle commuting. Bike-Walk Twin Cities and Transit for Livable Communities are wrapping up the National Non-Motorized Pilot Program, a federally funded program to demonstrate the potential to increase biking and walking through focused investment in infrastructure and other interventions. Bicycle commuting rates in Minneapolis have climbed to 4.5%, and Minneapolis now ranks 20th in the nation in bicycle commute share. This is a noteworthy achievement, especially considering our notorious winter weather. These achievements, along with others such as the success of Nice Ride, our pioneering bike share program, have contributed to Minneapolis being named America’s most bike-friendly city by Bicycling Magazine. Celebration of these achievements – which represent hard work by hundreds of individuals and thousands of commuters – certainly is warranted.

But we only need look across municipal boundaries to know we had better put more energy into encouraging bicycling than into celebration. Bicycle commute rates in St. Paul remain below 2% less than half the Minneapolis rate, and rates in most suburban, exurban, and rural communities remain even lower. And the story remains essentially the same for all types of bicycle trips. Jessi Schoner, a doctoral candidate in the Department of Civil Engineering, is analyzing non-motorized mode shares for all trips recorded the Metropolitan Council’s recent Travel Behavior Inventory. Her analyses show that bicycling remains an urban phenomenon, with the share of all trips taken by bicycling highest in Minneapolis, followed by St. Paul, and then suburban and outlying communities. Why is this so? Better infrastructure no doubt is part of the reason, but there likely are other reasons, including housing patterns, access to employment, socio-demographic factors, and culture. Additional research is needed.

But this leads to additional reasons to be optimistic this Bike to Work Day: the commitments made by the Minnesota Department of Transportation (MnDOT) to foster multi-modal transportation systems and the agency’s investments in research to increase understanding of bicycle traffic patterns. In 2013, as part of the Minnesota Bicycle and Pedestrian Counting Initiative, MnDOT funded the installation of the state’s first two automated, continuous in-street bicycle counters. These counters, which monitor bicycle traffic around the clock, 365 days per year, will provide new insights into the bicycle traffic volumes and their daily and seasonal patterns. While bicycle traffic monitoring in Minnesota is only in its infancy, it represents progress towards establishing the evidence base we need to determine how to make bicycling safer and to invest in bicycle infrastructure.

And so celebrate this Bike to Work Day and thank your fellow Minnesotans for all they have accomplished. But also take time to reflect on the work that needs to be done to improve opportunities for cycling throughout the state, for we have miles to go.

Greg Lindsey is a professor at the University of Minnesota Humphrey School of Public Affairs. His areas of specialty include environmental planning, policy, and management. His current research involves studies of the relationship between the built environment and physical activity, specifically factors that affect the use of pedestrian and cycling infrastructure. Lindsey presented some of his bicycle and pedestrian data collection research at the 2014 Minnesota Transportation Conference held March 4-6.

MnDOT library director recognized for ROI work

One may not think of librarians as having a crucial role in the building of a road, bridge or trail, but in the state of Minnesota, they do.

Each day, the MnDOT Library locates obscure-but-important information for engineers and transportation practitioners, such as the safety aspects of extra-tall concrete median barriers, the travel patterns of blind pedestrians and the environmental impact of treated lumber used on freeway noise walls.

“I like to say, ‘Google gets the easy stuff and we get the really difficult stuff,’ ” said Sheila Hatchell, MnDOT Library Director, who was recently recognized with an Innovation Award from the Special Libraries Association’s Transportation Division for helping transportation libraries demonstrate the value of this work.

Proving Your Library's Value: A Toolkit for Transportation Libraries
Proving Your Library’s Value: A Toolkit for Transportation Libraries

With few good examples to follow, Hatchell and two peers set out to develop a national guidebook for quantifying the benefits of a special library, in particular a transportation library.

“There is a wealth of studies demonstrating the value of public and academic libraries, but when it came to special libraries, there was almost nothing,” Hatchell said. “And what little there was, it didn’t pertain to state transportation libraries.”

Hatchell spent her weekends researching what other institutions have done and drafting much of the 52-page toolkit, “Proving Your Library’s Value,” which was published in early 2013 through the Transportation Library Connectivity and Development Pooled Fund Study.

Soon after, MnDOT put her work into practice, hiring a consultant through the department’s research program to perform a Return-On-Investment (ROI) study on the library.

2013 MnDOT Library Valuation/Return On Investment (ROI) Study Findings
2013 MnDOT Library Valuation/Return On Investment (ROI) Study Findings details the tangible and intangible savings realized from MnDOT’s library.

The study determined that for every $1 spent, the library produced nearly $2 worth of value — mostly due to the dollar value of research that might otherwise be provided by a paid consultant. The dollar figure doesn’t include the intangible value such information provides transportation projects.

In 2012, the MnDOT Library responded to more than 2,100 requests for information — many which took days or weeks to track down. They also loaned out nearly 3,800 items, routed 10,887 journal issues and distributed more than 560 journals and books borrowed from other libraries.

“A lot of people use the library and don’t even know it,” Hatchell said, since much of the data is shared with a wider audience.

Hatchell was asked to speak about her research this week at the Texas Library Association Annual Conference.

Helpful Resources

MnDOT Library ROI study

“Proving Your Library’s Value” national guidebook

 

MnDOT announces research implementation projects

Minnesota’s next round of research implementation projects will reduce the spread of noxious weeds along state highways, improve the quality of asphalt on Minnesota roads and enhance the inspection of state bridges.

MnDOT’s Transportation Research Innovation Group (TRIG) has announced 15 projects for funding in Fiscal Year 2015. (Project descriptions below.)

Each winter, MnDOT solicits proposals from staff who want to put local or national research into practice in their day-to-day work.

“Certain departments have problems they’ve been working on for a long time and they’ve spun their wheels or not had the staff resources to get something done,” said MnDOT Research Services & Library Project Advisor Bruce Holdhusen, who helps employees develop their proposal plans.

One implementation project: Further testing and demonstration of portable traffic control devices (auto flaggers) to increase their usage by highway maintenance crews.
One implementation project will complete testing and demonstration of portable traffic control devices (auto-flaggers) to increase their usage by highway maintenance crews.

MnDOT provides the funding needed for equipment, consultant services or researcher assistance. Supervisors also must sign off that they’ll make time for the staff member to implement the practice.

“Implementation means it’s changing the way some practitioner does their job,” Holdhusen said. “It’s not just trying something new; it’s got to stick.”

Highlights of this year’s projects:

  • Installation of GPS units on MnDOT mowers to alert highway maintenance crews to areas of noxious weeds. This is anticipated to cut herbicide usage in half.
  • Purchase of 3D sonar equipment for underwater bridge inspection, which is currently performed by engineer-divers.
  • Selection of an alternative, European-branded center-line rumble strip (Sinusoidal) that produces less stray highway noise.
  • Implementation of an innovative asphalt-quality test, developed by MnDOT’s Office of Materials and Road Research, to assess the cold temperature-cracking properties of asphalt mixes proposed by contractors.
  • Advertisement of state rest area amenities on highway notification signs. This pilot project will target 13 rest stops.

The complete list of projects, by category:

Environment
Maintenance Operations and Security
Materials and Construction
Multimodal
Bridge and Hydraulics
Traffic and Safety

Deicing treatments tested at Valleyfair, Canterbury Park

Excalibur and the High Roller may be closed for the season, but Valleyfair Amusement Park still has one attraction open for the season: a driving track for Minnesota snowplow drivers.

MnDOT-funded researchers are studying the effects of weather and vehicle traffic on different deicing treatments in the parking lots of Valleyfair and Canterbury Park in Shakopee, Minn.

It’s been a busy winter, but each week MnDOT Metro District snowplow drivers make one last stop before heading home, to apply different combinations of salt and anti-icing chemicals to nine 1,000-foot driving lanes. They also drive over each lane multiple times to test the effect of traffic.

“We’re running trucks up to 30 miles per hour with different speeds, wind conditions, traffic conditions and pre-wetting chemicals,” said Steve Druschel, a researcher with the Minnesota State University, Mankato. “Each lane is its own experimental unit.”

Professor Steve Druschel speaks with MnDOT snowplow driver John Hokkanen.
Professor Steve Druschel speaks with MnDOT snowplow driver John Hokkanen.

Professor Druschel’s students will review more than 17,000 photos from time-lapsed cameras to document how the snow melted in each experimental run.

“The influence of factors like pavement type and age, traffic volume, truck proportion, weather conditions and sun presence will be assessed to evaluate which techniques have special advantages for certain situations or roadways,” said Maintenance Research and Training Engineer Tom Peters.

In 2010, Druschel tested 25 anti-icing compounds in 1,500 different combinations in a laboratory to study the effectiveness of different deicers.

“Public work superintendents commented, ‘Great work. It looks good, except it’s all in the lab. Beakers aren’t what people drive on,’ ” Druschel said. “So we’re taking it from the two-inch ice cup to the real world in phase two of this study.”

With rock salt prices quadrupled, finding the most cost-effective methods of treatment is important.

This latest research will help determine the best times for applying anti-icing treatments and examine whether certain chemicals — such as a pre-storm liquid treatment that costs twice as much — melt enough snow to be worth the extra cost.

Test runs in Shakopee are strictly experimental, but in Mankato students are analyzing how real-world salting treatments are working on the North Star Bridge.

An article in the Mankato Free Press tells how Druschel’s team is collecting road melt runoff and documenting bridge traffic. (Big trucks, for instance, squeeze more water out of the snow.)

MnDOT snowplow driver John Hokkanen makes a test run at the research site at Canterbury Park.  (Photo by Nick Busse)
MnDOT snowplow driver John Hokkanen makes a test run at the research site at Canterbury Park. (Photo by Nick Busse)

Students plan to use time-lapsed photos, along with weather data and snowplow records, to determine what chemical treatments worked best – and when.

With the multi-pronged research project, Druschel hopes to put definitiveness to what some snowplow drivers have already tried in the field.

“The key to it is not so much that we’re so smart and we have a better idea or are inventing something new,” he said. “We’re just trying to enhance what they are already doing.”

Helpful resources

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) 

 

MnDOT leaders highlight TRB benefits at forum

As a graduate student 35 years ago, Bill Gardner attended his first Transportation Research Board Annual Meeting, and he still remembers the thrill.

“I felt like a kid in a candy shop,” recalled Gardner, who heads MnDOT’s Office of Freight and Commercial Vehicle Operations. “I was amazed at the diversity of topics… You could find people who have devoted their whole lives to the hazards of rural mailboxes.”

Gardner and other MnDOT leaders on Tuesday recounted their experiences from this year’s annual meeting — which drew more than 10,000 participants — and encouraged other MnDOT staff to get involved in the organization, which helps set national transportation guidelines, oversees collaborative research and facilitates the exchange of information.

“We’re heavily involved, but I think we could be more involved,” said Modal Planning and Program Management Director Tim Henkel, who has been part of the TRB for more than 20 years.

Henkel said TRB involvement benefits MnDOT in several ways, including access to national and international experts, the ability to keep tabs on hot-button issues and having a seat at the table in decision-making.

“It makes us a more enlightened and informed decision-making body,” Henkel said.

MnDOT has more than 60 staff serving on 114 TRB committees and contributes $125,000 annually to the TRB core program, gaining $127 in collaborative research for every $1 it contributes.

“It’s a very intense and very busy experience," said Chief MnDOT Engineer Deputy Commissioner and Chief Engineer Sue Mulvihill, who displayed the thick program book and other materials from this year’s Transportation Research Board Annual Meeting.
“It’s a very intense and very busy experience,” said MnDOT Deputy Commissioner and Chief Engineer Sue Mulvihill, who displayed the thick program book and other materials from this year’s Transportation Research Board Annual Meeting.

As part of a series of staff forums they will hold throughout the year, MnDOT leaders chose to highlight the TRB, which met in January. (MnDOT employees interested in attending next year or getting involved in the TRB should speak with their supervisor.)

State Bridge Engineer Nancy Daubenberger, who serves on a TRB subcommittee and gave a presentation at the recent conference, said it helps to hear about the challenges faced by agencies around the country.

Assistant Engineering Services Division Director Amr Jabr, who attended for the first time, said he used a smartphone app just to decide which of the approximately 3,500 sessions he wanted to attend.

“I thought it was an extremely good experience,” he said. “I picked up a lot of information and made a lot of new contacts.”

Smartphone app guides blind pedestrians through work zones (updated)

Each year, approximately 17 percent of road construction work zone fatalities nationwide are pedestrians.

At special risk are the visually impaired, who rely on walking and public transportation to get around.

A major challenge  for them is crossing the street — which is even more difficult if an intersection is torn up.

MnDOT has invested significant effort to accommodate pedestrians, particularly those with disabilities, in temporary traffic control situations. This includes requiring temporary curb ramps and alternative routes when a sidewalk is closed.

Researchers, funded by MnDOT, have now developed a cell phone application to guide blind pedestrians around a work-zone.

Illustration of Bluetooth beaconplacement at decision points around a work zone.
Illustration of Bluetooth beacon placement at decision points around a work zone.

Building on previous work to provide geometric and signal timing information to visually impaired pedestrians at signalized intersections, the smartphone-based navigation system alerts users to upcoming work zones and describes how to navigate such intersections safely.

The smartphone application uses GPS and Bluetooth technologies to determine a user’s location. Once a work zone is detected, the smartphone vibrates and announces a corresponding audible message. The user can tap the smartphone to repeat the message, if needed.

The federal government strongly encourages states to provide either audible warnings or tactile maps at work zones where visually impaired pedestrians are expected to be impacted.

“The smartphone application is a step in that direction,” said MnDOT technical liaison Ken Johnson. “It’s a way to see if this type of way-finding device would work.”

Since smartphone use is still limited, the state is also interested in special equipment that could relay the audible warnings at affected work zones.

“However, smartphone use is increasing in the general population, as well as with persons with disabilities, and there will likely be a day when it will be rare to not have a smartphone and this tool could meet road agency needs,” Johnson said.

Before developing the smartphone application, researchers surveyed 10 visually impaired people about their experiences at work zones and what types of information would be helpful in bypass or routing instructions.

The University of Minnesota research team, led by Chen-Fu Liao, tested the smartphone application by attaching four Bluetooth beacons to light posts near a construction site in St. Paul.

Additional research is now needed to conduct experiments with visually impaired users and evaluate system reliability and usefulness.

*Update 4/29/2014: Check out this story from KSTP on the app.

More information

Development of a Navigation System Using Smartphone and Bluetooth Technologies to Help the Visually Impaired Navigate Work Zones Safely — Final Report (PDF, 1 MB, 86 pages)

Flume research simulates Red River flooding to test road protections

Flooding in the Red River Valley is an almost annual occurrence, and the cost to roads, property and lives is huge.

Highway 1 gets torn up year after year, only to be rebuilt in time for next year’s flood, joke residents in the little town of Oslo, which becomes an island whenever the roads close.

While not much can be done to prevent swollen farm fields from overflowing, what if a road embankment itself could be bolstered to prevent physical damage to the underlying structure of the road?

“We can’t just raise the road because it would create backwater upstream,” explained JT Anderson, Assistant District 2 Engineer. “Our best bet is to let the water over-top the road and try to protect the road when it does.”

Researchers have built a flume inside the University of Minnesota’s St. Anthony Falls Laboratory to test six methods of embankment protection specific to the needs of towns like Oslo.

“It is not uncommon for one over-topping site to have a half-mile long stretch of road being damaged,” said university research engineer Craig Taylor. “One road being protected should cover the cost of the study and the cost of deploying the erosion control product for that road.”

Nationally, research of this kind has mostly been restricted to high-intensity flooding.

“Those really high-depth, short duration events, you can only protect an embankment with concrete and boulders,” Taylor said. “With longer duration, low-depth floods, we may be able to protect roads with soft armoring, like reinforced vegetation.”

The damage in northern Minnesota has been the worst on east-west roads, where the river flow runs perpendicular to the center of the road, causing the road to act like a dam and the water to jump at the edges.

“It eventually eats through that road embankment and makes the road collapse,” Anderson explained.

Researchers will examine how a cross-section of a road holds up under various erosion control methods at different levels and speeds of water-flow.

The damage from flooding was less in 2010 after engineers added rocks and vegetation to the side of Highway 9, near Ada.
The damage from flooding was less in 2010 after engineers added rocks to the side of Highway 9, near Ada, Minn.

One test will be to slow the flow of water by covering the road shoulder with a rubberized membrane and temporary water-filled tubes.

Permanent schemes — such as turf reinforcement mats and rocks — will also be tested.

“These methods have been deployed in the field, but you never really know under which conditions they survived or failed,” Taylor said.

In the Red River Valley, MnDOT engineers have tried a combination of vegetation and boulders, as well as concrete blocks covered with topsoil, to protect highways. Flattening a slope is another option.

“I expect that a single erosion protection technique will not cover every situation our road embankments may be exposed to at any given location,” Anderson said.  “Rather, I expect we would look at using several different techniques in concert to develop an effective erosion protection system for the expected velocities.”

Funding highway projects with value capture could speed project completion

There’s broad agreement that the U.S. transportation system cannot continue to be funded with existing financing and revenue-generation methods. What’s unclear, however, is how to pay for highway projects in the future. The current transportation funding system emphasizes user fees, but there is growing interest in alternative funding strategies. One promising strategy is value capture, which aims to recover the value of benefits received by property owners and developers as a result of infrastructure improvements.

In recent years, University of Minnesota researchers have helped lead the way in value capture research with a series of reports identifying value capture strategies. In a newly published study, the research team applied their previous work to a real-world scenario, with impressive results.

The new research, sponsored by the Minnesota Department of Transportation, focused on the planned development of Trunk Highway 610 (TH 610) in Maple Grove, Minnesota—a stretch of planned state highway delayed for years by state transportation funding shortages. Researchers set out to discover how the value of the enhanced accessibility provided by the planned improvements could be predicted and captured to help fund the project’s completion.

To accomplish their goal, researchers first defined a study area of about 10 square miles surrounding the unfinished highway segment. Then, they modeled property values based on five factors using parcel-level data. This model was designed to isolate the so-called “highway premium” by controlling for other factors that affect land value including water views, open space, railroads, transit stops, and existing highway exits. Using this model, researchers found significant evidence that the completion of the highway could lead to an over $17 million increase in property value.

Researchers expect these findings to have significant benefits for the TH 610 project and beyond.

Read the full article in the March issue of Catalyst.

Photo courtesy of SRF Consulting Group, Inc.

Minnesota's transportation research blog