Tag Archives: transportation

Bridges and Structures

Video: 3D Technology Enhances Underwater Bridge Inspection

Leave a comment

A new technology that uses 3D-imaging sonar will enable MnDOT engineers to visualize the substructure of a bridge in a way they never have before.

Until now, MnDOT has relied on human divers and depth finders to identify problems beneath the water.

Divers are limited by what they can see and feel in murky waters, however, and depth finders can only look down, not around.

“With this new technology, we will be able to provide high resolution three-dimensional images of underwater areas, structures and objects to show what is occurring, regardless of water clarity,” said MnDOT Bridge Waterway Engineer Petra DeWall, who has received funding from MnDOT’s Transportation Research Innovation Group to purchase the equipment.

Video imagery from a sonar inspection of Minneapolis’ Third Avenue bridge is above.

Currently, MnDOT hires engineer divers to physically inspect about 500 bridges every five years. They look for cracked concrete, exposed reinforcement and other detrimental conditions.

Although divers can spot issues, they can’t always thoroughly assess the scope of a problem, such as the amount of sediment being washed out around a bridge pier, a problem called bridge scour.

It can also be difficult — or dangerous — for divers to venture down for an inspection.

This was the situation last winter with the Third Avenue Bridge in downtown Minneapolis, where the streambed has degraded around a bridge pier, causing erosion to the pier.

“The Third Avenue inspection was not totally detailed. We knew there was a void under the bridge, but it was very hard to visualize,” DeWall said.

Early ice build-up halted further inspection in November, so MnDOT asked 3D sonar scanner manufacturer Teledyne BlueView to scan the area as a demonstration of its equipment.

A video of the inspection is below:

Multiple holes were cut in the ice sheet to deploy the sonar, which provided an image of the bridge scour by emitting sound-waves that created a point cloud.

“It gives you a large data set of where the sound reaches and comes back to the equipment,” DeWall explained.

The 3D image provides a level of detail that will enable repair and construction contractors to make more accurate bids, saving MnDOT money on projects.

Although dive inspectors are also beginning to invest in this new technology, MnDOT wants its own equipment to perform quick assessments of troublesome spots without going through the lengthy contracting process.

The Federal Highway Administration is conducting a pooled fund study to see if the technology eliminates the need for dive inspectors all-together.

MnDOT also plans to use its 3D scanning sonar to inspect repair projects and assess bridge construction.

One of DeWall’s first goals is to take a scan of the Hastings bridge after construction is complete, which will provide a baseline scan that can be compared against future inspections. The old bridge has had problems with the loss of rocks at its piers. It is unclear if the rock just sinks or is washed away downstream. Monitoring will let MnDOT see what is happening over time.

“Inspection is just one part of it,” DeWall said of the sonar equipment. “The big interest in this project is coming from our construction folks.”

Post-Construction

Imagine building a new house and not being able to complete the final walk-through.

This is the situation that transportation departments face when they build a new bridge, due to the limitations of underwater inspections.

“With 3D technology, you can go back afterward and check to make sure things were done the way they were supposed to,” DeWall said.

DeWall wishes the state had the scanner many years ago when a bridge was built that required expensive correction.

A bridge construction crew left construction material behind under the water, which wasn’t discovered until the redirected water flow caused significant erosion to the bridge pier.

Divers picked up that something was going on during a routine inspection, but engineers still had to bring in depth finders to get a better look. Due to the water current, they were limited in how close they could get to the bridge pier, and turbulence crashed their boat against the pier, damaging the transducer.

Not only would this 3D technology have provided a more thorough assessment than the depth finder, it also could have captured the imagery from a safe distance away.

Bridges and Structures, Environment, research

Culvert research aims to protect endangered small fish

Leave a comment
The Topeka shiner
The Topeka shiner, a small minnow that inhabits slow-moving prairie streams, was once widespread and abundant in portions of Iowa, Kansas, Minnesota, Missouri, Nebraska and South Dakota. It now inhabits less than 10 percent of its original geographic range.
(Photo courtesy of the Minnesota Department of Natural Resources)

In a new study funded by the Minnesota Department of Transportation, engineers are trying to ensure that new culverts do not degrade the habitat of an endangered fish in southern Minnesota.

The state has already researched how to better accommodate fish passage at river and stream crossings. Now it is looking at design guidelines for culverts that specifically impact the Topeka shiner, a small endangered fish found in five Midwestern states.

In Minnesota, the Topeka shiner is known to live in at least 57 streams, totaling 605 miles, within the Big Sioux and Rock River watersheds.

“The Topeka shiner is reported to have been erased from about 50 percent of its historic range in Iowa and much of its range in Minnesota, which is why Minnesota is so intent on doing what it can to help this fish thrive here,” said Alan Rindels, MnDOT’s project coordinator for the research.

The Topeka shiner is endangered due to the degradation of stream habitat, stream channelization, non-native predatory fishes and construction within waterways.

Culverts might impede the passage of this small minnow for a number of reasons, including that they might be too long, lack sufficient depth or carry water too fast.

Culverts allow water to pass under roads.
Culverts (also called small bridges) allow water to pass under roads. Occasionally, they can harm a stream’s fish habitat by inadvertently acting as a barrier to fish passage or migration. On the West Coast, large-scale efforts are under way to protect migratory salmon, and in Minnesota, culvert designers are concerned about fresh water species.

In addition, long culverts block sunlight, which possibly discourages fish from swimming through. Typically, older culverts are replaced with longer culverts to improve road safety and minimize maintenance costs. To eliminate or minimize impacts to the Topeka shiner, the state is trying to determine if light mitigation strategies are necessary.

Researchers from the University of Minnesota’s St. Anthony Falls Research Laboratory will monitor a newly installed culvert (110 feet in length) and a few other culverts in critical Topeka shiner habitat streams during spawning and fall movement.

Additionally, a laboratory-based light manipulation experiment will examine the behavior of the warm-water fish when presented with a dark culvert.

Guidelines for culvert design in Topeka shiner habitat will be developed based on these results, as well as examples from neighboring states. The state is also collaborating with the U.S. Fish and Wildlife Service and affected Minnesota counties.

Maintenance Operations

New videos show how frost heave ravages roads

Leave a comment

Regardless of whether you’re familiar with the term “frost heave,” if you live in Minnesota and drive on the roads, you’re already familiar with its destructive capacity. Many of the dips, bumps, potholes and cracks that appear on our roads every spring are a direct result of frost heave, which occurs when water accumulates in the soil beneath the pavement and begins freezing and then thawing along with the changing seasons. The resulting expansion and contraction weakens the road base and leaves it susceptible to damage from traffic loading.

These new videos produced by the Local Road Research Board explain how frost heave works, and describe some of the strategies public works departments use to combat it. The top video is is the shortened, executive-summary version, while the bottom video is the full, 13-minute version meant for transportation professionals.

Traffic and Safety

New LRRB videos focus on work zone safety

Leave a comment

The Minnesota Local Road Research Board is a major source of funding for transportation research in the state. Occasionally, it also produces educational videos designed to raise public awareness of important transportation topics.

Two new video offerings from the LRRB (embedded above and below) are focused on save driving in work zones. While not directly research-related, they might prove a useful resource to transportation professionals. More importantly, they serve to remind us all of the very real and dramatic consequences of work zone crashes, of which there are approximately 2,000 per year in Minnesota.

You might want to also check out some of their other recent YouTube offerings, including explanations of why we need stop signs and speed limits, as well as a fascinating look at how potholes are patched.

research

Previewing MnDOT’s next round of research projects

1 Comment

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:

Environment

Maintenance

Materials and Construction

Multimodal

Policy and Planning

Traffic and Safety

Policy and Planning, Public Transit

What happens when you incentivize transit use during construction projects

Leave a comment

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.

Read more:

Traffic and Safety

Best practices for trail crossings – webinar and draft report

Leave a comment

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:

http://mndot.adobeconnect.com/p8hlfripuwe/

The final report is coming soon, but in the meantime you can see the draft version on our website (link), along with case studies and other related documents.