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.
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.
- Minnesota Department of Transportation Metro Barrier Extraction and LiDAR Project – Final Report #2014-22 (PDF, 1 MB, 13 pages)
- Using Mobile Mapping to Inventory Barriers – Technical Summary #2014-22TS (PDF, 1 MB, 2 pages)
This blog post was adapted from an article in our upcoming issue of Accelerator, MnDOT’s research and innovation newsletter.
One of St. Paul’s most iconic landmarks is helping the Minnesota Department of Transportation find the most cost-effective methods of maintaining concrete bridge decks.
For the last three years, the Smith Avenue High Bridge, which connects downtown St. Paul with the city’s west side, has served as a test bed for a variety of products used to seal cracks on bridge decks. Through MnDOT-funded research, various sealant products have been applied on different areas of the bridge deck, with their performance tracked over time.
“This project will help MnDOT make cost-effective maintenance decisions to preserve its current bridge infrastructure,” said Sarah Sondag, a senior engineer with MnDOT Bridge Operations Support.
The bridge was chosen in part because of its large deck area, which allowed for the application of 12 sealant products and three control sections.
Sealing deck cracks is a routine preventive maintenance task for bridge crews. Left untreated, cracks can allow moisture and chlorides to penetrate the bridge deck, which can lead to the corrosion of reinforcing steel, deck deterioration and the need for early deck replacement.
MnDOT maintains a list of approved bridge deck crack sealing products, but until now had little data on how well each one performs in the field. The recently published report also examined several products that are not currently on the Approved Products List.
Among the study’s findings: some of the products on MnDOT’s Approved Products List did not perform as well as other products that are not currently on the list. MnDOT is using the results of the study to update its qualification process for products to get on the approved list. Insights gained from studying application techniques will also be used to update MnDOT’s bridge maintenance manual.
*Note: This blog post was adapted from an article and technical summary that will be featured in the upcoming issue of the Accelerator newsletter.
- Concrete Bridge Deck Crack Sealant Evaluation and Implementation – Final Report (PDF, 40 MB, 164 pages)
- Developing a Preventive Maintenance Strategy for Bridge Deck Cracking – Technical Summary (PDF, 1 MB, 2 pages)
Stormwater can pick up chemicals and sediments that pollute rivers and streams. Roadside drainage ditches, also known as swales, lessen this effect by absorbing water. But until recently, MnDOT didn’t know how to quantify this effect and incorporate it into pollution control mitigation measures.
In a recently completed study, researchers evaluated five Minnesota swales, measuring how well water flows through soil at up to 20 locations within each swale.
“There’s a big push in Minnesota, and probably everywhere, to do more infiltration,” Barbara Loida, MS4 Coordinator Engineer, MnDOT Metro District, said. “We know that our ditches are doing some of that, but we wanted to look at how much infiltration these ditches are providing.”
A key finding: grassed swales are significantly better at absorbing water than expected, which may reduce the need for other, more expensive stormwater management practices, such as ponds or infiltration basins.
This could save MnDOT and counties significant right-of-way and construction costs currently expended on more expensive stormwater management techniques. While swales were recognized in the Minnesota Pollution Control Agency’s new Minimal Impact Design Standards, there was a need to quantify the amount of water a swale can absorb so it could receive the appropriate MIDS credits.
Researchers also tested the ability of carbon, iron chips, steel wool and other materials to remove pollutants as ditch check filters—material put into swales to enhance removal of pollutants.
A follow-up project, which the MPCA is participating in, will seek to clarify the impact of swale roughness on infiltration rates. The goal is a calculator for real-world infiltration rates that MnDOT and local agencies would be able to implement.
MPCA, MnDOT and the city of Roseville are also partnering on a project to install and test the effectiveness of ditch check filters in real-world locations.
Maintenance recommendations should help MnDOT and local agencies ensure that swales operate at maximum efficiency. These recommendations should continue to be revised as knowledge evolves.
- Assessing and Improving Pollution Prevention by Swales - Final Report (PDF, 3 MB, 134 pages)
- Pollution Control Benefits of Roadside Drainage Ditches – Technical Summary (PDF, 1 MB, 2 pages)
- Reducing Construction Pollution by Skimming Stormwater Ponds (August 2014)
- New Research Applies Drinking Water Solutions to Stormwater Runoff (September 2014)
New research from the Accessibility Observatory at the University of Minnesota ranks 46 of the 50 largest (by population) metropolitan areas in the United States for accessibility to jobs by transit.
The new rankings, part of the Access Across America study begun last year, focus on accessibility, a measure that examines both land use and transportation systems. Accessibility measures how many destinations, such as jobs, can be reached in a given time.
“This project provides the most detailed evaluation to date of access to jobs by transit,” says Andrew Owen, director of the Observatory. “We directly compare the transit accessibility performance of America’s largest metropolitan areas.”
The findings have a range of uses and implications. State departments of transportation, metropolitan planning organizations, and transit agencies can apply the evaluations to performance goals related to congestion, reliability, and sustainability. In addition, detailed accessibility evaluation can help in selecting between project alternatives and prioritizing investments.
“It can help reveal how the costs and benefits of transportation investments are distributed,” Owen says.
Top 10 metro areas: job accessibility by transit (January 2014)
- New York
- San Francisco
- Los Angeles
- San Jose
The report—Access Across America: Transit 2014—presents detailed accessibility values for each of the 46 metropolitan areas, as well as detailed block-level color maps that illustrate the spatial patterns of accessibility within each area. In addition, time-lapse map videos for each area are forthcoming and new analysis of the data from the accessibility to jobs by transit rankings will be published periodically. Upcoming reports in the Access Across America series will explore more detailed aspects of transit accessibility to jobs, including accessibility to jobs of different wage levels and a comparison with accessibility by car.
In the study, rankings were determined by a weighted average of accessibility, giving a higher weight to closer jobs. Jobs reachable within 10 minutes were weighted most heavily; jobs were given decreasing weight as travel time increases up to 60 minutes. Travel times were calculated using full transit schedules for the 7:00 to 9:00 a.m. period. The calculations include all components of a transit journey, including “last mile” access and egress walking segments and transfers.
“Accessibility is the single most important measure in explaining the effectiveness of the urban transportation system,” says David Levinson, University of Minnesota civil engineering professor and principal investigator on the project.
According to Owen, accessibility can be measured for various transportation modes, to different types of destinations, and at different times of day. “There are a variety of ways to define accessibility,” Owen explains, “but the number of destinations reachable within a given travel time is the most directly comparable across cities.”
The research is sponsored by the Center for Transportation Studies at the University of Minnesota. Accessibility Observatory reports, including the analysis of job accessibility by auto published last year and interactive maps, are available on the Access Across America: Transit 2014 web page.
Before a national audience of 1,400 urban planners and transit enthusiasts, Hennepin County Commissioner Peter McLaughlin and others told the story of how the Twin Cities metropolitan area was transformed into a community that embraces “livability” and mass transit, including light rail.
“The growth was horizontal and there were lots of people who were saying it wouldn’t work in Minnesota,” said McLaughlin, during the opening plenary of the RailVolution conference in Minneapolis.
But the metro region bucked years of infighting and helped pass a transportation bill in 2008 that allows counties to tax for the expansion of transit in the metro area. Anoka, Ramsey, Hennepin, Dakota and Washington Counties decided to pool their resources from the quarter-cent transit sales tax, which is why the Southwest Light Rail Line is able to move forward.
“They had to believe their day would come,” McLaughlin said of the counties.
This was the first time the annual conference has been held in the Twin Cities, allowing Minnesota leaders to share their success stories.
Minnesota Department of Transportation Commissioner Charlie Zelle, who biked the Greenway trail to get to the conference, spoke of MnDOT’s commitment to multi-modal transportation and maximizing the health of Minnesota’s people and economy.
“MnDOT is more than a highway department,” he said. “We have a statewide bike plan and we will probably be the second state in the union to have a statewide pedestrian plan.”
Michael Langley of Greater MSP said a mix of transportation types is critical to attracting talented workers to the Twin Cities, especially millennials.
“Nearly every area of the world is facing a future workplace shortage,” he said. “It’s fueling a competition for talent like we’ve never seen.”
Federal Highway Administration Secretary Anthony Foxx on Tuesday addressed conference attendees about the need for a bipartisan compromise on funding. He proposed moving away from the Highway Trust Fund to a more inclusive transportation account (named the Surface Transportation Trust Fund) that also addresses rail needs, with $19 billion in proposed dedicated funding. He also discussed the recent announcement of $3.6 billion in resiliency funds for transit systems.
During his comments, he wore a red bicycle pin that the MnDOT commissioner frequently wears at multi-modal events.
During the five-day conference, attendees toured the recently completed Green Line and attended dozens of workshops on topics ranging from street walkability to bus-rapid transit to the use of mobile phones to enhance bus service. On Sunday, the Northstar commuter train traveled for the first time to St. Paul’s Union Depot and conference attendees took it back to Minneapolis.
The nation’s two largest pavement testing centers are planning to partner in order to better leverage research performed at their cold and hot-weather facilities.
MnROAD, located in Albertville, Minnesota, and its southern U.S. equivalent, the National Center for Asphalt Technology in Auburn, Alabama, are full-scale test tracks that evaluate different types of pavement material under real-life conditions using semi-trailer truck and live interstate traffic.
Each facility has a history of evaluating the performance of pavement preservation treatments, including chip sealing, micro-surfacing, crack sealing and thin overlays. To address needs in both northern and southern climates, similar test sections would be developed at each facility to address national issues.
“By working together we can maximize the potential for each track,” said MnROAD Operations Engineer Ben Worel. “A closer relationship between NCAT and MnROAD is a logical progression in developing and evaluating new sustainable technologies, pavement systems and construction methods that lead to safer, quieter, lower-cost and longer-lasting roads.”
The partnership idea was introduced to federal officials earlier this month at a national pavement performance conference in Minneapolis. Final details must still be worked out.
One of the workshops at the event discussed the proposed partnership between MnROAD and NCAT. Further talks are expected at the end of October.
“NCAT is thrilled about the opportunity for a partnership with MnROAD to address pavement research needs at a national level,” said NCAT Director Randy West. “Bringing NCAT and MnROAD results together will expand the climate base, loading distribution and other important pavement factors.”
Pavement engineers from around the nation gathered Sept. 2 to 5 for the Midwestern Pavement Preservation Partnership forum and the SHRP2 R26 Workshop for the Preservation of High-Traffic-Volume Roadways, which featured tours of MnROAD, Minnesota’s cold weather pavement testing facility.
Conference participants also reviewed the latest preservation techniques being developed for high volume roads. MnROAD’s chip sealing study, which demonstrated that highways with an average daily traffic (ADT) of 58,000 can be successfully chip sealed, was especially attention-grabbing for agencies who don’t chip seal on roads with more than 2,000 ADT.
A national panel of speakers included Michael Trentacoste, director of the federal Turner-Fairbank Highway Research Center (pictured in top photo), who discussed Federal Highway Administration’s support of pavement preservation research and implementation.
With about 160 people in attendance over four days, MnDOT Materials Engineer Jerry Geib said the conference was successful in sharing the benefits of pavement preservation techniques with other state DOTs and federal highway officials who want adopt new practices to help alleviate budget constraints.
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.”
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.
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.
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.
- Leveraging the Advantages of Indefinite Delivery/Indefinite Quantity Contracts – Technical Summary (1 MB, 2 pages); Final Report (expected Fall 2014)
There’s nothing like colored concrete to make a crosswalk, sidewalk or breezeway look snazzy.
But the extra touch that many cities are putting into their downtown streetscapes may not be so pretty in just a few short years.
Early cracking has prompted the city of Vadnais Heights to tear up its colored concrete, and the city of Centerville — which installed colored concrete only six years ago — plans to follow suit, said MnDOT’s Senior Road Research Engineer Tom Burnham.
Both cities participated in a recent study, sponsored by the Local Road Research Board and conducted by MnDOT, to determine what is causing the early deterioration.
Across Minnesota, many of the estimated 45 colored concrete projects have experienced early deterioration, particularly microcracking near contraction joints. While this type of distress also occurs with regular concrete, it appears to be accelerated in the colored concrete projects, within five years in some instances.
Although the newly released study identifies likely causes for the failing colored concrete, further research is needed to evaluate proposed solutions.
Researchers determined that the colored concrete mixtures have likely been too porous for Minnesota winters, allowing deicing chemicals to leach in and wreak havoc. Although not quite as problematic for sidewalks and medians — which aren’t salted as heavily — it is especially bad for colored crosswalks.
A denser concrete mixture (one formed with less water) is recommended; however, constructing the concrete panels this way will require extra steps.
“There are chemicals that can be added to the mixture to artificially lower that water-to-concrete ratio,” Burnham said. “This will allow a denser mixture to be more easily placed.”
Color in vogue
Although there was a spate of colored concrete construction in Ramsey County in the late 1990s, it has only come into fashion in the rest of the state within the last five to six years, according to Burnham.
“You go to almost any community and they’re installing it — on their sidewalk and medians and also crosswalks,” said Burnham, who coordinated the research study.
Because of the added expense, cities may be very disappointed in the results.
The city of Stillwater, which installed a colored concrete panel crosswalk on its main street just two years ago (see top photo), is already experiencing cracking and deterioration in several panels.
Although reducing the porosity of the colored concrete mixture should help, it won’t solve everything.
Another issue is the curing. The typical white curing product can’t be applied like it is with standard concrete, so curing the colored panels is more challenging, Burnham explained.
There are possible remedies, however, to assist with the curing, such as wet burlap or curing blankets.
Adding complexity to the issue are the new deicing chemicals on the market, which are also impacting regular road materials.
Several test samples showed evidence of chemical attack of the cement paste and fine aggregates, as well as an alkali-silica reaction, which can cause cracking or spalling and isn’t normally seen in regular concrete.
“Is there anything unique with the coloring that would accelerate the observed chemical reactions? We didn’t feel we had enough samples and knowledge at this point to conclusively say,” Burnham said.
Different construction techniques could go a long way toward increasing the livelihood of colored concrete; however, it could take several years of observation to determine if other methods work.
MnROAD is considering adding colored concrete panels to its facility for testing.
Until more questions are answered, MnDOT researchers are recommending repair techniques and alternative streetscaping ideas to cities, such concrete stains, pavers or colored high friction surface treatments.
In addition to sharing the findings with cities and counties, Burnham wants to educate contractors.
“We hope this research is a wake-up call for the colored concrete industry too because we don’t want the industry to die in Minnesota,” he said. “If it can work, we want cities and counties to be able to use it.”
*Editor’s Note: This story was updated 09/04/2014 to specify that this research project was funded entirely by the Local Road Research Board, and that MnDOT conducted the research.
- Investigation and Assessment of Colored Concrete Pavement — Final Report (PDF, 20 MB, 368 pages); Technical Summary (forthcoming)