Over the last several years, MnDOT has been participating in a national pooled-fund study on using infrared cameras to spot subsurface damage on bridge decks. These damaged areas just below the deck surface are called “delaminations,” and they’re what causes potholes and cracks on the surface. Detecting them is a key part of what MnDOT bridge inspectors do, and it’s huge challenge.
Currently, one of the primary methods of locating delaminations is “chain-dragging” — literally, dragging chains across the surface of a bridge deck. Using this method, inspectors can listen for evidence of hollowed-out areas beneath the surface, which produce a different sound than solid areas. While it works, this practice forces bridge crews to close down lanes and work near moving traffic. These issues have led Minnesota and other states to look for alternatives, and infrared or “thermographic” imaging is one of the top contenders.
In the video above, MnDOT bridge inspector Eric Evens demonstrates how to inspect a bridge deck using an infrared camera (specifically, a FLIR T620 — the model selected for the study). The delaminated areas appear as white or “hot” spots in the image. Evens does a nice job of explaining some of the benefits and potential uses of the camera, including minimizing traffic delays. He also demonstrates the camera’s ability to simultaneously capture photos and infrared images, which could be useful for cataloging the conditions of bridge decks and programming schedules for repairs.
However, as Evens pointed out during the filming, there are both pros and cons to using infrared thermography. One downside is it’s really only effective as the bridge deck warms up in the morning. Another is that it takes some practice to be able to identify which of the “hot spots” are actual delaminations and which are merely dirt or debris on the deck surface, or some other kind of false positive.
MnDOT Research Services is excited to announce the launch of Accelerator, our new research newsletter.
The bimonthly publication will focus on bringing readers the latest news from MnDOT’s research program. Each issue will highlight recent transportation research results, along with photos, feature stories and a calendar of upcoming events.
Accelerator is geared specifically toward transportation practitioners. It features short summaries of research projects, with links and other resources to help professionals learn more about areas in which they have a particular interest. The ultimate goal is to help bridge the gap between research and implementation by transferring knowledge to those who can put it to work in the field.
Much like Catalyst, the excellent newsletter produced by CTS, Accelerator will be available both in print and online editions. The first issue is scheduled to be released Tuesday, Sept. 3. To subscribe or to learn more, visit our website.
A new research study is recommending ways to make it easier for developers and employers to select sites that encourage living-wage jobs and mixed-income housing near transit.
A key finding of the study, which was based on interviews with developers and business leaders, revealed a pent-up demand for transit access in the Twin Cities metropolitan region.
A team led by University of Minnesota researchers Yingling Fan and Andrew Guthrie found that providing a great work location is critical for employers in recruiting highly skilled young professionals who are likely to desire—or demand—urban living and access to transit.
They also found that multifamily residential developers, redevelopment specialists, and large corporate office tenants have a strong interest in transit-accessible sites, but regulatory barriers, cost issues, and uncertainty surrounding future development of transit often discourage both developers and businesses from selecting such sites.
A new study from researchers at the U of M’s Humphrey School of Public Affairs aims to help Minnesota practitioners get Complete Streets projects on the ground.
“The goal was to look at what it takes to move a community from Complete Streets concept to Complete Streets project,” says Carissa Schively Slotterback, one of the project’s lead investigators.
As part of the study, Slotterback teamed with her Humphrey School colleague Cindy Zerger to investigate what’s working well in a variety of Complete Streets implementation efforts across the country. The study was sponsored by MnDOT and the Minnesota Local Road Research Board.
Slotterback and Zerger investigated six best practices areas related to Complete Streets: framing and positioning, institutionalizing, analysis and evaluation, project delivery and construction, promotion and education, and funding. Project findings stressed the importance of project context, the need for institutional and cultural changes, and the benefits of engaging advocates and project champions.
Based on the findings, Slotterback and Zerger are creating 11 case studies and a guidebook to help practitioners apply best practices and lessons learned from other communities to their own projects. The materials are set for completion this fall.
MnDOT Research Services recently released its 2013 request for proposals. If you have any kind of direct interest in transportation research in Minnesota, chances are you might have known that already. But those with more of a general curiosity might be interested to see the list of research need statements from the RFP, as they provide a nice preview of the next round of potential MnDOT research projects.
As you can see, some are of a highly technical nature. (It’s safe to say that a study on “PCC Pavement Thickness Variation Versus Observed Pavement Distress” would be of interest mainly to engineers.) Others, however, like “The Economic Impact of Bicycling in Minnesota,” might have a broader appeal. In any case, it’s a fascinating glimpse at the myriad of issues that MnDOT is attempting to address through research and innovation.
Here’s the list of research need statements from the 2013 RFP, broken down by category:
In 2010, MnDOT began a three-year long, $67 million repair and upgrade project on I-35 in Duluth. Dubbed the “Mega Project,” it created a serious disruption for Duluth-area commuters. To help mitigate the impact, the Duluth Transit Authority stepped up its bus services, offering free rides in newly established bus-only express lanes as well as access to new park-and-ride lots and various other enticements. Perhaps not surprisingly, many area residents took advantage of their new transit options to avoid construction-related travel delays. But what’s really interesting is what happened after the construction ended.
As described in a recently published MnDOT/University of Minnesota study, commuters who started taking the bus to avoid traffic caused by the construction ended up continuing to ride the bus even after the construction ended. Researchers surveyed riders during and after the 2010 and 2011 construction seasons and found that, even after bus fares went back to normal levels, only 15 percent of the new bus users switched back to driving. Researchers concluded that once riders developed a habit of using transit, the habit tended to stick.
The report author sums up the phenomenon quite nicely in her executive summary:
Human beings are creatures of habit. Most of us travel the same route every day to the same destination. Sometimes, however, something comes along to push us to examine our habits and possibly change them. A major highway construction project can be such an event. (…) This provides a very good opportunity to examine our travel patterns and possibly change our habitual modes.
Of course, this change didn’t just happen on its own. As the technical summary notes, the DTA marketed its services aggressively during this period. (The above photo is just one example.) The study also noted that the elimination of expanded bus services in the winter had a negative impact on ridership.
Geotextiles are synthetic polymer materials used to improve the performance of roadways. As discussed in this 2011 technical summary, geotextiles facilitate filtration and water drainage, improve the integrity and functioning of base materials, and provide a stable construction platform over soft or wet soils. These improvements can benefit both the cost-efficiency and longevity of pavements.
Geosynthetic materials have been used throughout Minnesota, and can be found in both reconstructed and new roadway projects. The use of geotextiles as a separator layer under concrete overlays, however, has had limited documentation in Minnesota and other cold weather climates. MnROAD‘s recent dedication of several test cells to this purpose will determine the performance of this application of geotextiles, with the goal of improving its applications on other Minnesota roadways.
The new test sections, designated as Cells 140 and 240, consist of a very thin, 3-inch concrete overlay over an existing 7-inch concrete pavement constructed 20 years ago. Some unique features of the design include the use of a fiber-reinforced concrete mix, two different thicknesses of the nonwoven geotextile, and the use of a special type of glue, rather than nails, to fasten it to the existing concrete before paving.
The fabric and fiber used in the concrete mix were supplied through a public-private partnership with Propex Geotextile Systems. The results of this study, along with other unbonded overlays constructed at MnROAD and around the country, will be incorporated into a new national pooled fund project — TPF 5-(269) — led by MnDOT. This project will develop an improved mechanistic design procedure for unbonded overlays.
A second application being demonstrated at MnROAD is the use of a geosynthetic drainage system under several dowel bar baskets in new concrete pavement test section. Minnesota has historically used a dense-graded base layer under concrete pavements to provide a stable foundation and construction platform. However, this material drains very slowly, and traps moisture within the joints, leading eventually to significant distress (See Effect of Drainage on the Performance of Concrete Pavement Joints in Minnesota.) This application will compare the use of the geotextile drainage material placed under both sealed and unsealed joints, as well as a control joint without the drainage material.
Last week, MnDOT Research Services hosted a workshop on a forthcoming report, “Decision Tree for Identifying Alternative Trail Crossing Treatments.” It was broadcast as a webinar, the recording of which is now available online via Adobe Connect:
In 2010, the City of Minneapolis installed 55 energy-efficient streetlights from nine different manufacturers along 46th Street between 34th and 46th avenues. The project, part of Hennepin County’s Minnehaha-Hiawatha Community Works program, was designed to field test various models of light-emitting diode (LED) and induction lights. Over the course of two years, researchers observed, evaluated and compared the performance of various lighting products, detailing the results in a recently published report available on the MnDOT Research Services website.
In a broad sense, the results of the study would appear to confirm what has become common knowledge regarding energy-efficient technologies: while they cost more up front, in the long run they have the potential to save money in the form of reduced energy and maintenance costs. The study also demonstrates that energy-efficient streetlights are capable of producing adequate light output and are well-received by residents.
However, if the big question is whether energy-efficient streetlights can save local governments money, the answer is somewhat complicated. The study found that both the levels of light ouput and the amount of time it takes to recoup costs varies significantly by product. Page 16 of the report (page 25 of the PDF) features a table comparing various products’ light output and estimated payback time. With one notable exception, the results show that products with the highest light output (i.e. the highest performers and therefore the most desirable) tend to also have the longest payback time. The amount of time it takes to generate a cost savings from energy-efficient streetlights can be as short as 2.6 years or as long as 24 years, depending on the product.
Some other interesting tidbits from the study:
Researchers observed operational cost savings of 50-75 percent, depending on the product.
Eighty percent of the savings came from reduced maintenance costs, while only 20 percent came from reduced energy costs.
In a survey of area residents, 76 percent responded positively to the new, energy-efficient lights.
The study demonstrated that energy-efficient streetlighting is a feasible option for local governments, with the caveat that agencies need to research lighting products thoroughly before making a choice as to which one to use. Ultimately, considering the ever-decreasing cost of LEDs, the use of energy-efficient streetlighting technologies is likely to grow.
Following up on Nick’s post last week about transportation practitioners’ preferences for short research summaries, the Center for Transportation Studies recently published a two-page research brief highlighting results from a University of Minnesota study that explores the ridership and pedestrian impacts of the Hiawatha Line in the Minneapolis–St. Paul metropolitan region. The study compares the travel behavior of residents in the LRT corridor to those in similar corridors without LRT but with comparable bus service. It investigates the reasons why residents choose to live in the LRT corridor, the associations between transit use and residency in the LRT corridor, and the effects of LRT and the built environment on pedestrian travel.
The findings include:
Residents who lived in the Hiawatha Corridor when the light-rail transit (LRT) line opened increased their transit use substantially—a clear ridership bonus from LRT.
Residents who moved into the corridor after the LRT line opened use transit as often as new residents in similar urban neighborhoods without LRT.
When looking for a place to live, good transit service and job accessibility are important factors for both urban and suburban residents—ranked behind only housing affordability and neighborhood safety.
Residents choose to live near Hiawatha LRT stations because of their strong preference for transit access and quality.
To encourage transit use among station-area residents, the researchers recommend the following:
Consider development potential when planning LRT routes and design a vibrant place rather than a traffic node to ensure a mix of activities and users.
Create pedestrian-friendly connections between residential neighborhoods and rail stations.
The research was conducted by Assistant Professor Xinyu (Jason) Cao and research assistant Jessica Schoner of the Humphrey School of Public Affairs at the University of Minnesota and funded by the Transitway Impacts Research Program (TIRP).