The only way to test pavements is to destroy them — slowly and painstakingly, one moving vehicle at a time. At MnROAD, the state’s world-renowned pavement research facility, the bulk of this monotonous-but-necessary work is performed by live traffic passing through Albertville on I-94. But on the facility’s 2.5-mile low volume road test track, which simulates rural road conditions, more controlled methods are preferred.
Doug Lindenfelser is one of several MnROAD employees who take turns driving an 80,000-pound semi tractor trailer in laps around the closed-loop low-volume track. The truck is loaded to the maximum allowable weight limit on Minnesota roadways. As it passes over the facility’s 23 distinct low-volume test cells, an array of sensors capture data on the pavement’s performance, which researchers then use to design stronger, longer-lasting roads. The truck only drives on the inside lane; that way, the outside lane can be used as an “environmental lane” to compare damage caused by loading vs. damage caused by environmental factors.
He has other duties as well, but on a given day, Doug might drive the truck 60 or 70 times around the low-volume road test track. It might not sound very exciting, but as Doug explains, some days his job can be quite interesting. We interviewed him on camera during a recent visit to MnROAD. The resulting video is available above and on our YouTube channel.
For those who might be wondering, all this diligent destruction of pavement has paid off. It is estimated that MnROAD’s first phase of research (from 1994-2006) has resulted in cost savings of $33 million each year in Minnesota and $749 million nationally. Cost savings from its second phase (2007-2015) are being calculated, and the facility is scheduled to enter its third phase in 2016.
As public works employees come and go, past research efforts — and the valuable knowledge gained — often goes with them.
But a recently launched web application allows users to track innovative pavement projects for a lifetime.
“It’s something everyone has always said we need to have,” said MnDOT Research Operations Engineer Jerry Geib, who worked on the project for the Minnesota Local Road Research Board.
Using an online map, city and county engineers can enter road test sections that they want to observe for many years due to a particular construction method or material that was used. Too often, the knowledge about such projects is lost when a particular staff person leaves an agency.
Not only will the lessons learned be remembered within the organization, but the results can also be shared with others.
More than 1,400 projects (including some on state roads) previously identified by MnDOT have been entered into the system. Search fields allow users to look for a particular type of project anywhere in the state or they can zero the map in on a particular area of the state.
The website is still in beta form, but functional.
“It’s complete, we just want people to use it so we can improve it,” said MnDOT Research Project Engineer Melissa Cole, who began planning the site two years ago.
One featured project is a 1.8-mile section of dirt road in Wabasha County that had an Otta seal applied in 2007 (photo below). It is one of only a handful of lightly surfaced roads in the state (an improvement over a gravel road, but less expensive than asphalt ) so there is great interest in watching how it performs.
More to come
The LRRB initiated the project in 2009, but it was put on the back burner for a while due to funding constraints. MnDOT ‘s technology staff began development of the current site about 11 months ago.
Anyone can look at the website, but cities and counties require permission to post projects (contact ResearchTracking.DOT@state.mn.us for credentials). They can upload photos, plans and weblinks relating to a particular project.
“We want to track anything that is worthy of looking at a few years from now,” Geib said.
Because the website uses Google maps, users can also view archived satellite and ground-level 360-degree imagery of the roads and bridges.
The website is viewable on a tablet, but it still must be tested on smart phones. Developers hope that crews will be able to submit information right from the field.
“We’re pretty happy with it,” said MnDOT software developer John Jones. “We think we’re headed in the right direction.”
The website might eventually be expanded for other areas, such as geotechnical (foundation work), whose practitioners have already expressed an interest.
Using Dawn dish soap to grease the rails, MnDOT crews inched the new Larpenteur Avenue Bridge into place two weeks ago using an innovative construction method.
As the bridge reopens to traffic tonight over I-35E, MnDOT celebrates the success of its first slide-in place bridge construction.
“The slide-in worked very well,” said David Herzog, MnDOT’s project manager for the I-35E Corridor – MnPass Project. “I think the process has given us the confidence to possibly use it again in the future.”
The slide-in method has been used in the past for railroad bridges and large bridges with high traffic and limited construction options. Now, state agencies and the Federal Highway Administration are applying the method to smaller, more routine bridges to minimize impacts to the traveling public.
Whereas the typical phased construction of a bridge builds one-half of the structure at a time, slide-in bridge technology allows the entire superstructure to be built at once, requiring just a brief, temporary closure of the highway.
Crews constructed the 3.5-million-pound Larpenteur Bridge right next to the existing bridge and then slowly slid it into place during the course of two nights. This effectively sped up construction from 110 days to 47 and reduced traffic impacts to drivers. (Watch video of the slide.)
The quality of the bridge also improves with this method, since it eliminates the deck construction joints and girder camber problems associated with phased construction, according to the FHWA. The pressure to use faster concrete cure times is also reduced.
With a quarter of the nation’s bridges in need of repair or replacement, the FHWA is pushing the slide-in method as a cost-effective technique that can cut construction time in half. It has previously been used in Oregon, Utah, Missouri, Michigan, Colorado and Massachusetts.
The concept has been around for more than a century, but slide-in technology is relatively new for small or medium-sized bridges, and it’s the first time MnDOT has attempted it on a state bridge.
Although MnDOT staff had flown out to Utah to view a slide-in, it was Burnsville-based Ames Construction that proposed reconstructing the Larpenteur Avenue bridge that way when it made its successful bid for the corridor project.
The slide-in method is about 15 percent more expensive, Herzog said, but it allowed the bridge to re-open in 47 days, versus 110 days.
Earlier this summer, Ames replaced the Wheelock Parkway and Arlington Avenue bridges in conventional fashion, although they were only closed for 65 days because they were constructed on a very accelerated timetable.
“Larpenteur is more of a major thoroughfare and we thought shortening the duration of its closure would be more valuable to MnDOT,” said Steve McPherson of Ames Construction, who was brought in from Utah to oversee the corridor project.
The fast reconstructions will allow the company to complete the bridge replacements and highway reconstruction in just 120 days. Next year it’ll finish the other half of the corridor.
All three bridges are being replaced to make room for the new MnPASS lane on I-35E.
One of the drawbacks to slide-in technology is that it requires ample room to build the bridge on-site. An alternative is to construct off-site.
The new Maryland Avenue/I-35E bridge was built off-site, as was the Hastings Hwy. 61 bridge. It was then loaded onto a barge, floated down the Mississippi River and lifted into place.
Aging roads and bridges, increased traffic and persistently constrained revenues put local road systems in peril, but the public is largely unaware of the pressures facing their communities, a Minnesota Local Road Research Board study has found.
The LRRB undertook the study to identify critical gaps in public knowledge about local road system challenges and to develop communication methods and tools to address these shortfalls.
Researchers found that even elected officials are unaware of the gap in funding needed to keep the road system going — in part because county engineers have been creative in a period of dwindling resources, and the cost of deferred maintenance has not been immediately visible.
In fact, only one Minnesota news outlet specifically covered the issue of local road system sustainability in a five-year period analyzed by researchers, with media coverage focused mainly on big events, like the collapse of the 35W bridge and the federal transportation funding bill.
There are multiple challenges to road system sustainability, including rising construction costs, declining tax revenues, heavier agricultural and industrial equipment and rising public expectations.
To help county engineers better educate the public, researchers looked at outreach strategies (such as open houses and focus groups) currently used in three Minnesota counties: Beltrami, Dakota and Jackson. The research team talked with county road managers to identify key issues and concerns and surveyed 91 residents who had participated in public engagement efforts.
The project revealed widespread confusion about local road system issues. For example, many participants erroneously believed that the gas tax covers (or was enacted to cover) the cost of maintaining local roads.
Researchers have produced a set of recommendations and tools for county engineers to use in designing effective public engagement processes that overcome confusion and a lack of information. A newly approved follow-up project will test the tools in three or four other Minnesota counties and cities.
Though no one can predict the future, thinking about how today’s changes may shape the future of transportation in our country is more important now than ever before.
“It’s critical that we understand the significance of things that are taking place and prepare for what may come,” said former Utah Department of Transportation CEO John Njord in the opening session of the 25th Annual CTS Transportation Research Conference. “For us to be relevant in the transportation business, at a minimum we have to be adaptable to change, and ideally we want to be leading change in the transportation industry.”
In his current position at Tom Warne and Associates, Njord has gained an in-depth understanding of the trends affecting the future of transportation in the United States while spearheading the Transportation Research Board’s “Foresight” project—part of the organization’s forward-looking NCHRP Report 750 Series. The project addresses a wide range of topics, including: What if the oil-fueled auto era ends and revenue from gas taxes dries up? What if engineering practices must be upgraded to ensure resiliency to natural disasters as global warming continues? What if technology such as self-driving cars eliminates or reduces the need for human drivers? What if tomorrow’s economy requires radically different freight patterns?
Perhaps most significantly, the project explores the possibility that Americans are losing their appetite for driving. Vehicle-miles traveled (VMT) per capita been dropping since 2004, without any signs of recovery. “It’s impossible to know whether that number will start growing again, stay flat, or continue to drop,” Njord said.
Other trends make the future outlook equally complex. In 50 years the United States will likely be home to 100 million more people, so even if VMT per person stays flat or declines, it’s likely total VMT will be larger than it is today. The population is also aging: by 2030, 20 percent of the population will be over 65 and will likely drive less. In addition, Millenials are staying home longer and waiting until later in life to get married and have children—all of which affects their travel behavior.
To help transportation planners consider all possible futures, the Foresight project encourages the use of multiple-scenario planning. “We need to begin considering all the possible scenarios and generating plans that are independent and distinct from one another,” Njord advised. “The act of thinking about these things is fundamentally important, because the shift that is now taking place means we’re going to have to do things much differently in the next 50 years than what we’ve done in the past 50 years.”
Following Njord’s presentation, a panel of experts discussed how the the Foresight project could relate to what’s happening in the Twin Cities region. An article summarizing their comments is available in the July issue of Catalyst.
The Minnesota Department of Transportation has launched a new website called “Get Connected” to answer Minnesotans’ most basic questions about how the state invests its transportation dollars.
The one-stop site answers these topics through interviews with MnDOT leaders, links to long-term transportation plans and graphics showing where the money goes (such as this eye-opening snow-and ice removal cost chart).
“Minnesotans have a right to know how their tax dollars are being invested and to be confident that MnDOT is spending public money effectively on transportation,” said Tracy Hatch, MnDOT deputy commissioner, chief financial officer and chief operating officer.
It’s old news already, but any blog about transportation research and innovation in Minnesota would be remiss if it didn’t mention this amazing video of MnDOT workers sliding the new Larpenteur Avenue Bridge into place late last week.
The slide-in method is an accelerated bridge construction technique that allowed MnDOT to speed up the project and cut the the amount of time the bridge will be closed by more than half. It’s also cheaper and safer. This project marks the first time the slide-in method has been used in the state.
I-35W’s MnPASS lane, where vehicles can frequently enter and exit the high-occupancy toll lane, is just as safe as the MnPASS lane on I-394, where motorists only have a few shots to enter the system, a new study finds.
“The federal government has very strong arguments against the open system. They’re saying it’s going to be dangerous – cause more disruption and more congestion,” said John Hourdos, director of the Minnesota Traffic Observatory. “We found that both roadways are working very well today because they were designed appropriately for their location.”
The definition of an open system is one that has more opportunity for access than restriction. On 35W, a dotted white lane means vehicles can enter the toll lane at will, and a solid line bars access.
Vehicles must have two occupants on-board or an electronic pay card to use the express lanes during rush hour.
The reason I-35W allows vehicles to enter MnPASS more frequently than I-394 is because there are more ramps where new vehicles are entering the freeway and might want to get on MnPASS.
Researchers studied whether accidents are more likely to occur by studying the number of accident-inducing vehicle movements along the 35W corridor. They found that areas where accidents are mostly likely to occur are also where the lane would have to allow access anyway under a closed system like 394.
The study also looked at mobility, determining that MnPASS users have just as good free-flowing traffic under the open system.
Researchers also created design tools that engineers can use to determine where access points should be on MnPASS lanes.
Until now, engineers have relied on rule of thumb. For example, the general guidance for allowing access on a closed system was 500 feet for every lane between the entrance ramp and the HOT.
The tools can be used to automatically determine how fluctuations in the MnPASS fee will affect congestion within the lane.
The fee to use MnPASS depends on the time of day.
As the express lane become more congested, the fee to use it increases. This slows the number of cars entering the lane, increasing the speed of the vehicles already in the lane.
“We ran the tool on three locations on 35W and found that, for example, on Cliff Road, you can increase the traffic by 75 percent and still be okay,” Hourdos said. “You have more leeway there than north of the crossroads of Highway 62 and 35W, for instance.”
Two years ago, MnDOT installed a series of electronic speed limit advisory signs over Interstate 94 between Minneapolis and St. Paul. The Variable Speed Limit (VSL) system is designed to reduce congestion and help prevent crashes by recommending lower speed limits to motorists during periods of high traffic.
The new technology has worked in other places, including China and Germany. In Minnesota, a similar VSL system on I-35W reportedly had moderate benefits in reducing the total amount of congestion during the morning commute south of Minneapolis.
Although the verdict on I-94 congestion is still pending, a newly released study has found that the new system has not made a measurable impact so far on crashes in an accident-prone stretch of freeway in downtown Minneapolis. Why not?
University of Minnesota researcher John Hourdos has a few theories.
One is a simple time lag in the congestion reporting system. Another is a requirement that all lanes display the same speed limit, which he said causes confusion when only one lane is actually congested. The complexity of the I-94 commons also appears to be beyond what the VSL system was designed to do. And according to Hourdos, one of the most significant problems is the driving public simply doesn’t understand what the signs are telling them.
“People do not know what the system really does,” Hourdos said. “There hasn’t been much education on it other than a couple of news articles over the years. And when they try to decipher it on their own they get even more confused.”
The advisory speed limits are posted in response to varying traffic conditions. As vehicles approach the commons area, the system measures speeds at the bottlenecks. If the traffic slows, the system transmits a reduced advisory speed to drivers approximately 1.5 miles upstream from the location of the slow-down.
Hourdos said many motorists mistakenly believe the speed displayed on the signs is either a reflection of the speed on the current stretch of highway or an indication of the speeds on the highway ahead, rather than a suggested speed for them to follow.
The requirement to display the same speed limit on all signs also compounds the problem, Hourdos said, because when drivers see that the slowdown is only occurring in certain lanes they tend to ignore the signs altogether.
“In the lane that is congested, the real speeds drop much faster than what the VSL system can respond to, reducing the functionality of the system to the eyes of the drivers,” Hourdos said, “while on the fast-moving lanes, it seems the system has no purpose at all.”
So is the I-94 VSL system useless? Not necessarily. For one, the new study didn’t measure the system’s impact on congestion — only its ability to reduce crashes on a small portion of I-94. Moreover, the area in question, the I-94 Commons, is fairly unique, having two major bottlenecks, the highest crash rate in the state (nearly one every other day), and five hours of congestion during the afternoon rush hour alone.
“The VSL system was designed for implementation on any freeway and may not have been well-suited for the I-94 Commons area, which is a very complex corridor with high volume weaves and significant shockwave activity,” said MnDOT Freeway Operations Engineer Brian Kary.
Generally speaking, the VSL system was designed to identify slow traffic ahead of where free-flowing traffic is approaching slow or stopped traffic.
“The crash problems within the commons are caused by speed differentials between lanes and shockwave activity within the congestion,” Hourdos said. “The current VSL system was not developed to handle these types of conditions.”
MnDOT and the researchers aren’t giving up, either. A new project is starting later this year to develop and deploy a queue warning system specifically for this high-crash rate location.
Minnesota farm equipment is getting larger and heavier, causing strain on rural bridges. However, there are no nationally recognized specifications for what size and weight of tractors can safely travel over them.
Currently, bridge load limits are based off semi-trucks, not farm machinery, which have much different axle configurations and wheel dimensions.
“Their geometry is atypical; their length, widths are different; they have different suspension characteristics,” explains Brent Phares, director of the Bridge Engineering Center at Iowa State University.
A new pooled fund study led by the state of Iowa is attempting to determine how much stress heavy farm vehicles put on bridges. This data will be used by local agencies to develop weight restrictions specifically for farm equipment.
“It will help limit the confusion of current load posting signs for farmers,” said MnDOT bridge load rating engineer Moises Dimaculangan.
Wisconsin, Minnesota, Nebraska, Oklahoma, Illinois, Kansas and the United States Department of Agriculture are also participating in the study, which is examining three types of local bridge superstructures: those with steel girders and concrete decks; bridges with steel girders and timber decks; and timber bridges with timber decks.
Through physical testing and modeling, the study will determine how different types of farm machinery distribute their loads on the bridge superstructure.
About a half-dozen farm vehicles were tested on 20 different bridges which were representative of those tending to be the most problematic for farm equipment traffic on secondary road systems, Phares said.
Instrumentation measured the response of the structures to the vehicles. This data was then used as a baseline to calibrate analytical models, which could be applied to 250 different bridges and 121 different farm vehicles.
Researchers will develop a generic tractor profile, which represents the worst-case scenario, for use in determining load limits. With the information developed, signs might be able to be added to the bridges, which show a tractor and the weight limit.
“I get a number of pictures emailed to me of bridges that have failed with a tractor implement of husbandry on top,” Phares said. “That’s the problem that people are looking to avoid; the goal isn’t to restrict the size of farm vehicles, but to develop better tools for engineers to make sound and solid analyses for the bridges, so they can provide that information to the people who need to have it.”
Phares said a couple previous studies have also looked at farm machinery weight restrictions. One study, from around 2004, took a high level look at the impact of farm vehicles on bridges. A more recent pooled fund study analyzed the impact of machinery on pavements.