All posts by mndotresearch

Applying LiDAR to county transportation systems

A handful of county highway department employees in the Rochester area gathered recently at the Olmsted County Public Works Service Center for a presentation and live demonstration by University of Minnesota Research Fellow Brian Davis about his team’s work involving light detection and ranging – or LiDAR.

“LiDAR is like radar, but with light,” Davis said. “It gives you information about what’s around the sensor.”

Event attendees gather around a sedan outfitted with a spinning LiDAR sensor. (Photo by Micheal Foley, MnDOT)
Event attendees gather around a sedan outfitted with a spinning LiDAR sensor. (Photo by Micheal Foley, MnDOT)

Davis and his fellow researchers have outfitted a sedan with special LiDAR equipment and other technology that is capable of capturing a 360-degree, 3-D view of a scene in real time.

“We use the car as a test bed,” Davis said. “We have a lot of different types of sensors on the car that we use for the different projects that we’re working on. Right now we have a LiDAR sensor on top. Sometimes we have a high-accuracy GPS receiver in there. We have a cellular modem. We have a handful of inertial sensors. So it’s a lot of different stuff that we use to cater to the application.”

For his presentation, Davis showed the attendees some of the data his team had already collected.

Davis presents data that shows the LiDAR-equipped sedan moving along a roadway. (Photo by Micheal Foley, MnDOT)
Davis presents data that shows the LiDAR-equipped sedan moving along a roadway. (Photo by Micheal Foley, MnDOT)

“We showed a handful of pre-collected data at a handful of intersections around Rochester and Minneapolis,” Davis said. “What it shows is the point cloud collected by the sensor – just the raw point cloud with no post-processing done. In that information you can see people moving through it, cars moving through it, buses and light rail trains.”

Event attendees move around the sedan to see how the LiDAR sensor views them. (Photo by Micheal Foley, MnDOT)
Event attendees move around the sedan to see how the LiDAR sensor views them. (Photo by Micheal Foley, MnDOT)

After the presentation, Davis led the group to the parking lot for a close-up look at the technology and how it collects data and displays that data in real time. Le Sueur County GIS manager Justin Lutterman was among those who could envision possible applications for LiDAR.

“It’ll be interesting to see where this can go,” Lutterman said. “I’m sure the private industry will take off with this and emergency management, or the sheriffs and ambulances, would appreciate this kind of technology on their vehicles for a situation they might have to recreate. Roads and traffic designers  would be able to monitor their resources, pavements, traffic counts and things like that.”

Over the coming months, researchers will gather more data to develop a workshop for county personnel interested in learning more about LiDAR and how it can be applied in their transportation systems.

“The next steps for this project are to collect some data with the car at intersections. Then we can use that information to fine tune our algorithms,” Davis said. “What the algorithms are going to do is take that raw data and give us useful information, like the number of cars, or the time a car passes through an intersection. That all feeds into the workshop we’re developing. The workshop is going to be for county GIS workers, traffic engineers and county engineers who are interested in learning about these technologies.”

Riprap grout protects bridge abutments

Bridges over Minnesota waterways need to be protected from currents by a field of interlocking angular rocks called riprap. Without these rocks along the abutment, moving water could wear away the soil that supports a bridge’s foundation. The faster the water, the larger the riprap must be to provide adequate protection.

While some parts of Minnesota have quarries rich with angular rock, other parts don’t – particularly the northwest and western regions. Bridge projects in those areas sometimes resort to the expensive practice of trucking in stones. Other times field stones are used, but they are less effective and must be replaced more often.

There soon could be a better option thanks to research coordinated by the Minnesota Department of Transportation and funded by the Minnesota Local Road Research Board.

At a few test sites around the state, researchers have used a grout mixture to cement smaller, rounded rocks together at a bridge abutment. Once applied to the rocks, the mixture forms what is called “matrix riprap.” The concept is in use in Europe for many bridge piers, but MnDOT was more interested in learning how it could be used on bridge abutments.

Matrix riprap is currently in use in Minnesota at the following bridges:

  • Highway 23 over the Rum River in Milaca
  • Highway 8 over Lake Lindstrom channel in Lindstrom
  • Prairie Road over Coon Creek in Andover
A MnDOT crew applies grout to rounded rocks at a bridge abutment in Milaca in May 2012. The grout cements the rocks together to form matrix riprap, which has shown to be significantly stronger than conventional riprap.
A MnDOT crew applies grout to rounded rocks at a bridge abutment in Milaca in May 2012. The grout cements the rocks together to form matrix riprap, which has shown to be significantly stronger than conventional riprap.

In May 2012, matrix riprap was placed at the Milaca bridge, which sits alongside a high school. Researchers hoped the use of matrix riprap would prevent vandals from removing the riprap rock and throwing it into the river. According to Nicki Bartelt, a MnDOT assistant waterway engineer, the matrix riprap has proven to be extremely strong and effective.

“Not only is matrix riprap significantly stronger than regular riprap, but it helps prevent vandalism as well,” Bartelt said. “The Milaca installation has been in place for three years now. It looks pretty good and it’s weathering well.”

In the lab, matrix riprap held up extremely well on mechanical pull tests and hydraulic flume tests. In fact, researchers were unable to determine the matrix riprap fail point on many tests, even after applying 10 times the shear stress that regular riprap can withstand. Matrix riprap was tested with both angular and round rock with no change in performance.

A new matrix riprap installation recently went in on the Highway 95 bridge over the Rum River in Cambridge. Later this summer, plans call for an installation on the Highway 60 bridge over the north fork of the Zumbro River in Mazeppa.

“The Highway 60 bridge is being replaced, and the river there has extremely high velocities, so we’re using the matrix riprap instead of regular riprap just because of the size of rocks that would be needed,” Bartelt said.

At least two more installations are planned for 2016. In the future, researchers plan to determine the fail point for matrix riprap. They also hope to study potential environmental effects the grout may have underwater.

MnDOT has also worked with local governments that have tried matrix riprap for themselves. One municipality is trying it as a heavy duty erosion control measure. The concept is catching on outside Minnesota as well.

“We have gotten a lot of inquiries from other states, and we have lent out the spec a lot,” Bartelt said. “Iowa, New Hampshire, Maine, Indiana, Wisconsin and Illinois are among the states to express interest. We have talked to a lot of people about it, so they tend to use our research.”

Read the research