All posts by mndotresearch

Preparing Roads for Connected and Autonomous Vehicles

Proprietary technologies, industry competition and federal regulatory concerns are slowing the advent of defined standards for connected and autonomous vehicles (CAVs). Researchers investigated the state of CAV implementation to help local agencies begin preparing for the infrastructure needs of these vehicles. CAV-friendly options are considered for eight infrastructure categories. Since truck platooning is the likely first application of this technology, and optical cameras appear imminent as an early iteration of sensing technology, researchers suggest that wider pavement striping and well-maintained, uniform and visible signage may effectively serve the needs of CAVs in the near future while enhancing infrastructure for today’s drivers. 

What Was the Need?

For transportation agencies, which manage infrastructure in time frames of decades, the potential of connected and autonomous vehicle (CAV) technology influences infrastructure upgrade plans. 

New pavements and overlays, traffic signal systems and signs may serve for decades, while pavement markings face shorter life cycles. Optimizing spending today requires anticipating future infrastructure needs, and the infrastructure requirements of CAVs may differ from standards currently in place.

It remains unknown how imminent the CAV future is, and competing technologies and designs for guidance systems, sensor formats and other facets of the developing vehicle technology keep outcomes unsettled. Enthusiasm in the technology and automotive sectors for this new model of road user tools nevertheless suggests that short-term preparations warrant consideration within the current limited-budget environment for infrastructure improvements. 

How local agencies can best brace their roadway systems for a CAV-driven shift in road usage remains unclear, and public transportation officials cannot predict what the technology will look like if and when autonomous vehicles roll onto streets in significant numbers. 

What Was Our Goal?

Researchers sought to create a toolbox for local road agencies to use in preparing for CAVs in the next five to 10 years. Recommendations would help agencies leverage ongoing infrastructure plans and expenditures to prepare for CAVs and the potential technologies for roadway navigation and travel the vehicles will deploy. 

What Did We Do?

Researchers began by studying the literature, attending conferences and consulting with industry experts to describe likely CAV technologies and potential implementation timelines. Based on this research and discussions with the project’s Technical Advisory Panel, investigators developed recommendations in eight categories of infrastructure needs. The research team also prepared seven case studies showing how road agencies have addressed different aspects of preparing for CAV fleets. 

What Did We Learn?

Industry competition and proprietary technologies make CAV outcomes difficult to project, and federal standards and regulations have yet to develop to meet potential forms of the technology. 

“Connected and autonomous vehicles are further away than we think. Full integration of driver assistance technologies—which is where the real power in CAVs is at this time—may be a slow process.”

—Shauna Hallmark, Professor, Iowa State University Department of Civil, Construction and Environmental Engineering 

Some consensus within the CAV industry suggests truck platooning, in which two or more CAV trucks follow one another at distances of 30 to 50 feet, seems the most promising initial implementation of CAV technology within the next five to 10 years. In addition, optical cameras will be a likely early iteration of sensing technology. Accommodating these technologies will impact two infrastructure categories—pavement markings and signage. Recommendations for these infrastructure needs follow: 

  • Pavement Markings. Consider California’s plans to install 6-inch-wide lane lines (the current Minnesota standard is 4 inches) on highways and Interstates during regular maintenance and new construction within three years.
  • Signing. Ensure that signs are standardized, easily visible, and not blocked, damaged or faded. 

The other six infrastructure categories impacted by CAVs entail less-specific recommendations: 

  • Traffic Signals. Create space at signal control cabinets for additional hardware related to CAV technologies.
  • Consistency and Standardization. Install and maintain striping, signing and signals consistent with CAV algorithms and technologies.
  • Pavement Maintenance. Continue to keep road surfaces well-maintained.
  • Data Capture and Information Sharing. Begin or continue collecting and organizing data for bridge heights, speed limits, load restrictions, crosswalks, roadway curvatures and other infrastructure characteristics. 
  • Communication Infrastructure. In new construction and information technology infrastructure built for agency use, ensure adequate conduits for power and fiber optic cables. 
  • High-Resolution Mapping. Consider developing high-resolution mapping capabilities.

What’s Next?

Case studies about developments in Los Angeles and in Iowa, Michigan, Ohio, Virginia and Wyoming explain how agencies are preparing for the needs of a CAV-friendly infrastructure.  

“Making sure that signing and striping are visible will be essential for accommodating autonomous cars. It’s also going to be good for all drivers, especially with an aging population.”

—Douglas Fischer, Highway Engineer, Anoka County 

A pilot project in Anoka County, Minnesota, informed decisions about signage to ensure visibility and consistent placement. Pavement markings were also addressed; currently the county continues to place 4-inch edge lines, lane lines and centerlines after resurfacing projects, and painting lines to 10-foot lengths at 40-foot gaps. Conversion to 6-inch markings could be accommodated on existing pavements; however, if a new standard is required for skip stripe spacing, it may only be economically feasible to do so on new surfaces.

This Technical Summary pertains to Report 2019-18, “Preparing Local Agencies for the Future of Connected and Autonomous Vehicles,” published May 2019. Visit the MnDOT research project page for more information.

U.S. DOT image shows current work zone warning signals that may be adopted in connected and autonomous vehicles.
Intelligent transportation system features like work zone warnings may be incorporated in CAVs.

Bus–Highway Connections Make Transit More Competitive With Driving

Researchers developed a method for associating travel times and travel costs with transit mobility. In an evaluation of bus–highway system interactions, investigators found that park-and-ride lots and managed lanes put suburban and walk-up urban transit options on equal footing. Bus–highway system interactions improve access to job locations and have improved transit access to job sites by about 20 percent compared to automobile access. When wage-related costs are included, the benefit of automobile use over transit use diminishes significantly.

What Was the Need?

Bus service in the Twin Cities relies on MnDOT-built park-and-ride (PNR) lots and managed lanes—lanes for buses on streets and highways, including high-occupancy lanes—to help transit users travel from the suburbs and urban locations to job, retail, service and entertainment sites. 

One measure of how a transit system of PNR lots and bus service works for users is job accessibility—the number of jobs that can be reached by a mode of transportation within a certain travel time period.

The type of lanes a bus uses impacts travel times via bus, and the differences in these travel times in turn impact the transit user’s ability to reach locations using walk-up transit service. The transit alternative to walk-up service is drive-to-transit service via PNR lots. The Twin Cities transit system intersects with over 100 PNR lots where transit users park their vehicles and take express and limited-stop services to business districts and job locations. 

Understanding the impact of managed lanes and PNR lots on transit effectiveness in terms of job access requires diving into transit and travel data; developing ways to measure accessibility for walk-up, drive-to-transit and automobile-only travel modes; and adjusting methods so the cost of travel and the time of travel can be reasonably compared between modes. 

What Was Our Goal?

MnDOT sought to evaluate how the bus and highway systems interact in terms of job accessibility. The research would consider how managed lanes and PNR lots affect job accessibility for walk-up and drive-to-transit users, compare these findings to automobile-only usage, and profile how well the transit system of the Twin Cities serves users in terms of cost to use and travel time. 

What Did We Do?

In the first stage of work, the research team focused on the managed lane network to determine how it contributes to walk-up transit accessibility. Investigators developed a computer program to modify transit schedule data to reflect how buses operate in different managed lane configurations and calculate walk-up access to jobs systemwide. 

In the second stage, the team developed a method for calculating accessibility via PNR use, and PNR accessibility in terms comparable to access via walk-up transit and automobile use. 

In the third stage, researchers developed a mixed-mode accessibility profile of the system. 

“The researchers did more than just measure mobility; they quantified access to employment in terms of travel time and travel cost, as well. Results put park-and-rides and suburban transit on equal footing with walk-up transit in urban environments.”

—Jim Henricksen, Traffic Forecaster, MnDOT Metro Traffic Forecasting and Analysis 

The research team incorporated a monetary dimension to travel time accessibility measures, associating costs of automobile use, parking fees, transit fare and travel time with travel modes in a value of time unit to compare accessibility between automotive and transit usage. 

What Did We Learn?

Study results showed that PNR lots and managed lanes offer greater access to job sites. The longer the trip to a job site, the more competitive transit becomes with driving for commuting to work. Bus–highway interactions via managed lanes and PNR lots improve transit job accessibility relative to automobile use by 3.8 percent in a 30-minute commute and by 19.1 percent in a 60-minute commute. For the 60-minute scenarios, transit accessibility from the suburbs to the central business district improves by 319,322 jobs for the average worker. 

For managed lanes, the greatest benefit is for suburban regions near express routes. On the I-94 corridor, where the greatest improvement by transit to accessibility is felt, every mile of MnPASS lanes offers an increase of 98 jobs accessible to average riders. 

With express bus service, travel times from PNR lots to destinations decrease by an average of 10.7 minutes for the system. Compared to walk-up transit travel, drive-to-transit from suburban areas offers accessibility values roughly three times greater than travel by walk-up transit, in part because time spent driving in suburbs gets users to more transit facilities than the same time spent walking.  

“We developed tools and methodologies, and applied them metrowide to bring new insights to the role of highway operations and planning on access to jobs through transit.”

—Andrew Owen, Director, Accessibility Observatory, University of Minnesota

Researchers found pockets in the Twin Cities where transit and PNR are more competitive with automotive travel per dollar of travel. These areas highlight urban locations where the transit network is the most robust and suburban areas where automobile travel times are long compared to express transit. When researchers applied wage value to time spent traveling, the benefit of driving rather than using PNR lots and transit dropped 89.6 percent. The relative value of transit may increase further if measures account for productivity on transit. 

What’s Next?

This research helps MnDOT plan future PNR and managed lane facilities to maximize benefit to transit services. Value of time models and comparisons offer a way to measure the relative value of transit to automobile use in accessing jobs. 

Future analysis may include long-term fixed costs associated with vehicle ownership and show further improvement in the comparative value of transit services to automobile use. Methods from this study may also be applied to other mixed-mode transit options, like biking, scooters or ride-sharing to transit access points.

This Technical Summary pertains to Report 2019-17, “Accessibility and Behavior Impacts of Bus-Highway System Interactions,” published April 2019. Visit the MnDOT research project page for more information.

A MnPASS lane on Interstate 394 at the General Mills Boulevard exit. The express lane is closest to the highway median, indicated by a white diamond-shaped marker on the pavement and separated from three other traffic lanes by a solid white line. A highway sign above the lane indicates the fees for lane use.
MnPASS lanes are managed lanes that offer buses quicker access to downtown.

New project: Effectiveness of Teenage Driver Support System

The Minnesota Local Road Research Board (LRRB) has funded a follow-up study to determine whether a monitoring system it field tested for new drivers, called the Teen Driver Support System (TDSS), affected teenagers’ long-term driver behavior.

Background

Motor vehicle crashes are the leading cause of teen fatalities. Because of inexperience and risk-seeking propensity, new teenage drivers are more prone to behaviors such as speeding and harsh maneuvers, especially during their first few months of licensure.

In an effort to reduce risky driving among new teenage drivers, in 2011, the LRRB funded a one-year field operational test of a prototype system developed by the University of Minnesota’s ITS Institute, which enabled parents to monitor their child’s driving behavior.

The software ran on a teen’s smart phone, which was mounted to the dashboard and provided instant feedback about risky behavior to the teen and communicated to parents if the behavior continued.

The system didn’t allow incoming or outgoing phone calls (except 911) or texting while driving. It provided visual and auditory warnings about speeding, excessive maneuvers (e.g., hard braking, cornering), and stop sign violations. It also monitored seat belt usage and detected the presence of passengers, two known factors that increase the risk of fatalities among teen drivers. The system could also be programmed to monitor if the teen was driving after the curfew set by parents or required by Minnesota’s graduated license requirements.

In January 2013, the University of Minnesota launched a 300-vehicle, 12-month field operational test in Minnesota to determine the effectiveness of the TDSS in terms of its in-vehicle information and feedback to parents.

Research results indicated an overall safety benefit of TDSS, demonstrating that in-vehicle monitoring and driver alerts, coupled with parental notifications, is a meaningful intervention to reduce the frequency of risky driving behaviors that are correlated with novice teen driver crashes. In particular, the system was shown to be an effective strategy for reducing excessive speeds when used with parental feedback and potentially even without parental involvement.

Project Scope

The TDSS study was cutting-edge at the time. Today, there are many systems in the marketplace which families may seek out to provide added support for their novice teen drivers. However, the long-term effectiveness of these systems is largely unknown. Furthermore, the extent to which the TDSS reduced crashes, injuries, and citations among those who participated in the study is unknown.

This new study will collect information on study participants’ self-reported driving behaviors and driving attitudes, as well collect traffic violation and crash history records from the Minnesota Department of Public Safety.

This study proposes to not only provide a follow-up to the TDSS study to further explore the benefit it may have had on participants, but also determine to what extent families, schools, and other organizations should continue to invest in in-vehicle coaching systems similar to the TDSS. Ultimately, the TDSS is a low-cost system, which, if found to have long-term efficacy beyond what was demonstrated in the original study, could help guide cost-effective implementations to reduce crashes among teen or other driver groups.

Watch for new developments on this project.  Other Minnesota research can be found at MnDOT.gov/research.

Concrete Grinding Residue Doesn’t Appear to Negatively Affect Roadside Vegetation and Soil

A new MnDOT research study determined that depositing concrete grinding residue (CGR) slurry at specific rates on roadside vegetation and soil may not cause lasting harm to plant growth and soil quality; however, follow-up research is recommended.

Study results showed that CGR did not appear to hinder vegetation growth or soil quality, but did change soil chemistry. At some roadside areas, the increase in soil pH enhanced plant growth. Results cannot be generalized for all soil types, plant communities, concrete residues or water sources in Minnesota. Access to real-time slurry disposal activity is needed for a thorough investigation.

Study background

Construction crews use diamond grinders to level newly cured concrete with adjacent slabs of older pavement and to smooth new pavement surfaces for improved friction and tire traction. Diamond grinders are fitted with hoses for rinsing grinding burrs with water to keep the burrs clean and prevent overheating. Vacuum lines then collect the residual dust and rinsing fluids, generating a slurry of concrete grinding residue (CGR) that is frequently discarded on roadside slopes and vegetation. 

When slurry dries, it leaves pale gray patches on roadside vegetation and other features, lightening the soil surface for a season or more. The effect of this slurry on vegetation, soil and drainage was unknown. Engineers and researchers presumed that the concrete dust temporarily coats roadside turf and plants, raises the soil pH, clogs soil pores and inhibits water drainage, invites invasive species to take root, and may infiltrate storm drains and waterways. 

What Was Our Goal?

MnDOT needed to study the impact of CGR on roadside vegetation and soil. Research would evaluate sites where residue has been deposited and determine its impact on vegetation and soils common to state roadsides. 

What Did We Do?

A literature review indicated that related research has been limited and that vegetation samples of only one or two species have been examined. Researchers developed two approaches for investigating the impact of CGR on plant density, plant growth and soil properties. 

First, researchers collected CGR slurry from a slurry tank at a Minnesota construction site to replicate residue application at the Kelly Farm, an Iowa State University research site near Ames, Iowa, that features prairie vegetation similar to that found along Minnesota roadsides. They applied slurry at application rates of zero, 10, 20 and 40 dry tons per acre. Plant cover, soil chemistry and soil structure properties, such as plant biomass, density, hydraulic conductivity, infiltration and pH, were measured before the slurry was applied and again at one-, six- and 12-month intervals after application. 

Second, researchers visited two roadside locations along Interstate 90 near Austin, Minnesota, where CGR had been applied. The research team evaluated vegetation content and cover, took soil samples and compared survey results to neighboring roadside environments that had not received CGR slurry.

The infiltrometer system setup at the Kelly Farm site in Ames, Iowa.
This water infiltrometer measured infiltration of water at the roadside environment test site.

What Did We Learn?

Statistical analyses established that at the Kelly Farm, CGR did not significantly impact soil physical properties and plant biomass, but did alter soil chemistry. Levels of soil pH, electrical conductivity, metals content and other properties rose significantly after CGR application. These effects increased with increases in application rate and decreased at increased soil depths. These changes did not reduce soil quality, and higher pH levels did not persist after one month. For certain warm-season grasses and legumes, increased pH improved plant growth. Some nutrients such as calcium and magnesium leached from CGR could benefit plant growth as well.

“Concrete grinding residue or slurry can, under certain conditions, be a benefit. It can act as a liming agent, changing soil pH in a positive manner.” —David Hanson, Integrated Roadside Vegetation Manager, MnDOT Roadside Vegetation Management

The two roadside environments yielded differing results. Slurries had been deposited in 2009 at the first site and in 2013 at the second. At the first site, soil bulk density and hydraulic conductivity in the slurried areas did not differ significantly from measures at the nonslurried areas; at the second site, the levels differed significantly. At both sites, electrical conductivity, calcium content and base saturation values were higher at the areas with CGR than the areas without CGR. 

Researchers concluded that at the Kelly Farm and at the roadside locations, slurry applications at a rate of up to 40 tons per acre did not reduce soil quality and vegetation growth for longer than three years. 

What’s Next?

Efforts to access grinding operations and CGR deposits in real time were not embraced by Minnesota’s concrete industry, and researchers were unable to properly assess residue composition and rates, and volumes of slurry deposition on roadway environments. A thorough investigation of residue impact will require such access and follow-up on site conditions after established periods of time. 

Researchers noted that findings cannot be easily generalized since CGR compositions may vary depending on source and water quality, influencing soil and vegetation differently, and soil and plant communities may differ in response to comparable CGR applications. Investigators recommended that MnDOT develop quick field measures of slurry pH, electrical conductivity and alkalinity to use in adjusting slurry spreading rates at grinding sites.

“This study was a great start to this topic. Follow-up research is recommended to evaluate live projects, field demonstrations and data collection.” —Halil Ceylan, Professor, Iowa State University Department of Civil, Construction and Environmental Engineering

This technical summary pertains to Report 2019-06, “Concrete Grinding Residue: Its Effect on Roadside Vegetation and Soil Properties,” published January 2019. Visit the MnDOT research project page for more information.

Rout-and-Seal Offers Slight Cost–Benefit Over Clean-and-Seal Repairs

In a recently completed study, Minnesota researchers compare the performance and cost-benefit of the clean-and-seal versus rout-and-seal techniques for repairing asphalt pavement cracks.

Survey results, construction data and field evaluation of new repairs and their performance over two years gave rout-and-seal repairs a slight cost–benefit edge over clean-and-seal repairs. At an average performance index level, rout-and-seal offered about four years of service before failure; clean-and-seal offered about three years. The study also recommends rout-and-seal for use over clay and silt subgrades in most conditions. Decision trees were developed to help planners and repair crews select an appropriate repair method.

Background

Preserving asphalt pavements so they maintain performance for decades requires a variety of repairs, including sealing cracks. Cracks allow water to seep into pavement structures, leading to damage from freeze-thaw expansion, stripping of the asphalt’s bond from the underlying structure, potholes and crack expansion.  

For most crack repairs, road crews clean the crack and apply an asphaltic filler or sealant. MnDOT uses two approaches to repair cracks and create a smooth ride for passing vehicles: clean-and-seal and rout-and-seal. Both treatments force traffic closures. 

Clean-and-seal asphalt crack repair begins by using compressed air to clean the crack before sealing it.

With clean-and-seal, compressed air is used to remove debris from the crack before a sealant is applied. With rout-and-seal, a saw or router is used to grind a shallow trench or reservoir over the crack. The routed seam is then filled with an asphaltic sealant. 

After routing a shallow channel over the pavement crack, repair workers fill the crack with asphaltic sealant.

Rout-and-seal requires more time and, in many cases, slightly more sealant, making it more expensive than clean-and-seal. Some agencies favor clean-and-seal because it is less expensive, reduces the time crews are on the road and frees more time to maintain other cracks. 

What Was Our Goal?

Researchers sought to determine which of the two repair methods offers the better value over time. If rout-and-seal delivers a longer-lasting repair, it may be more cost-effective than clean-and-seal in terms of life-cycle cost. The research team also needed to develop guidelines for selecting the most suitable repair method for the damaged pavement. 

What Did We Do?

Researchers conducted a literature search to see how agencies around the country approach asphalt crack repair. The research team then surveyed Minnesota road agencies to see which repair method agencies prefer and how long repairs typically last. 

To review performance of crack sealing, researchers evaluated the MnDOT construction logs of old repair sites and visited 11 new repair sites. These locations were revisited two, six, eight, 12 and 18 months following the repair. To calculate a performance index rating, researchers recorded data about site conditions that included sealant age, traffic level, subgrade soil type and crack sealing performance. Two sites were removed from the analysis when local crews applied chip seals to the pavements.

Investigators calculated performance index levels for each repair method at each site. They gathered cost data where available from bid-letting paperwork and determined life-cycle costs. Finally, the research team created decision trees that planners and maintenance crews can use to help select crack repair methods. 

What Did We Learn?

“This study provided very useful information. The rout-and-seal has a better cost–benefit over the life of the pavement than the clean-and-seal, however, they are relatively close. Agencies will need to decide if they have the manpower or resources to perform one over the other.”

—Dan Knapek, Assistant County Engineer, Sherburne County Public Works

Limited research was identified that compared clean-and-seal and rout-and-seal treatments. Most studies of asphalt crack sealing compared unsealed and sealed pavement performance and have established that sealing does extend pavement life. None compared cost–benefits of the two methods.

Of 47 survey respondents, 68 percent use rout-and-seal and 32 percent use clean-and-seal. Responses identified no clear trends in life expectancies for the two methods, with predictions for service until failure falling predominantly in two to 10 years for clean-and-seal and two to 15 years for rout-and-seal. The most common criteria for choosing a method were crack or pavement condition (46 percent of respondents) and predetermined maintenance schedules (24 percent). 

Analysis of MnDOT construction data found no statistically significant difference in life expectancies for the two methods, with service lives of 6.4 years for rout-and-seal and 6 years for clean-and-seal. A similarly slight advantage for service lives of both treatments was identified for low-volume roads over higher-volume roads. 

After one year of service, the new seal sites delivered strong performance index figures. Short-term performance on rural roads was identical for the two methods. After the severe 2018-2019 winter, however, performance dropped significantly; spalling damage was frequently observed at rout-and-seal sites. 

Analysis of old and new seal projects showed that at an average performance index level, rout-and-seal repairs last about four years and clean-and-seal about three. Life-cycle cost analysis found rout-and-seal slightly more effective. Because the difference is slight, factors such as treatment cost, life expectancy, ease of operation, traffic level and crew manager opinion may guide selection of sealing strategies. 

What’s Next?

Researchers developed two decision trees for selecting a repair method: one for pavement management and another for maintenance crews. Rout-and-seal is recommended for pavements over clay and silt subgrades. 

Research that extends monitoring of the new crack seal sites for up to five years would provide useful data on performance and comparison of the effectiveness of the two methods.

“To help select an appropriate crack repair method, we developed two decision trees: a detailed one and a simple one with only three variables—crack size, traffic level and the number of times a crack has been sealed.” 

—Manik Barman, Assistant Professor, University of Minnesota Duluth Department of Civil Engineering

This Technical Summary pertains to Report 2019-26, “Cost/Benefit Analysis of the Effectiveness of Crack Sealing Techniques,” published June 2019. Visit the MnDOT research project page for more information.

MnDOT’s Smart Bridge Sensors Are Leveraged to Measure Vertical Displacement

A Minnesota Department of Transportation research study has developed a new method for estimating vertical displacements on bridges using accelerometers installed on the Interstate 35W St. Anthony Falls Bridge in Minneapolis. The dual-model approach shows potential for using these sensors to measure vertical displacement on steel, cable-stayed and other less-stiff bridges where traffic generates higher vibration frequencies. The method expands the industry’s knowledge of how to use smart sensors in new ways.

What Was the Need?

Since September 2008, the I-35W St. Anthony Falls Bridge has carried traffic over the Mississippi River in Minneapolis and funneled sensor data to researchers and MnDOT bridge engineers. This smart bridge features over 500 sensors that monitor strain, load distribution, temperature, bridge movement, and other forces and functions.

Sensors help designers and bridge managers learn more about how bridges shift and flex over time. Concrete expands and contracts, and bearings shift; sensor systems continuously gather data about these minute changes, offering an alternative to time-consuming inspection.

Sensors attached to a steel beam to study vibrations in a laboratory.
Sensors attached to a steel beam to study vibrations in a laboratory.

Researchers continue to identify potential uses for sensor data and new ways to use such information to analyze bridge properties and performance. In a 2017 study about monitoring bridge health, researchers learned to distinguish and associate specific vibration frequencies with structural damage, weather conditions and other factors. These frequencies were gathered by accelerometers, which measure structural vibrations triggered by traffic and environmental conditions.

Decks, piers and other structural elements displace vertically under loads and environmental conditions. Researchers and bridge managers wanted to know if accelerometers could be used to measure vertical displacements and help monitor bridge health.

What Was Our Goal?

MnDOT needed a procedure for measuring and monitoring vertical displacement on bridges under traffic and environmental forces. Investigators would use the sensor systems on the I-35W St. Anthony Falls Bridge to design and analyze this procedure.

“We need to learn more about sensors because we don’t have a lot of experience with them. This study gave us valuable information about accelerometers and the information they provide,” said Benjamin Jilk, Complex Analysis and Modeling Design Leader, MnDOT Bridge Office.

What Did We Do?

Indirect analysis and measurement of vertical displacements rely on estimations obtained through modeling. Investigators evaluated the most well-developed approach for measuring vibration frequencies like those tracked by accelerometers and refined the method. The team developed a dual-model approach: One model estimates loads and the other estimates displacements.

In a laboratory, investigators evaluated the impact of loading on displacement and vibration frequencies on a girder with contact sensors and accelerometers under moving and stationary loads. Researchers applied the dual-model analysis to laboratory displacement readings to compare the effectiveness of the model with contact sensor responses to loading.

Using laboratory data, investigators tuned the dual-model approach to accelerometer data available from the I-35W St. Anthony Falls Bridge. The research team then applied its identified tuning approach to the data from the bridge’s 26 accelerometers to determine the procedure’s suitability for estimating vertical displacement from vibration response on this bridge and its potential for other structures in the MnDOT bridge system.

New Project: Extreme Flood Risks to Minnesota Bridges and Culverts

Extreme flooding is a threat to Minnesota’s transportation infrastructure and the safety and economic vitality of its communities. A spate of recent flooding events around the state has demonstrated this and heightened the level of concern. Furthermore, climate change — a factor not traditionally accounted for in the design of the state’s infrastructure — is projected to enhance precipitation and the threat of flooding in coming decades.

Given this, MnDOT is undertaking an effort to better predict the threat flooding poses to its bridges, large culverts and pipes, which may be increasingly called upon to convey higher, more frequent flood flows than they were designed for.

The state transportation research program recently launched a two-year extreme flood vulnerability analysis study, which will develop a methodology for characterizing the vulnerability of the state’s bridges, large culverts, and pipes to flooding.

The effort builds upon the previously completed Flash Flood Vulnerability and Adaptation Assessment Pilot Project (2014), which scored bridges, large culverts, and pipes in MnDOT Districts 1 and 6 for flood vulnerability, allowing detailed assessments of adaptation options for each of their facilities to be prioritized.

This new study, which will be conducted by WSP, aims to develop and test ways to enhance the vulnerability scoring techniques used in the previous study and ensure their applicability throughout the state. Researchers will not actually undertake the statewide assessment, but specify an approach that could be used for it. They will also explore how the outputs of the analysis can be incorporated into MnDOT’s asset management systems. The results of this work will be a clear path forward for MnDOT to use for prioritizing adaptation actions — a key step towards enhancing agency resilience and maintaining good fiscal stewardship.

Project scope

The primary intent of this study is to develop a methodology for characterizing the flood vulnerability of bridges, large culverts, and pipes statewide. As part of the development process, the methodology will be tested on a limited, but diverse, set of assets across the state. Following a successful proof of concept, recommendations will be made on how the outputs (i.e., the vulnerability scores) can be incorporated into the state’s asset management systems.

By determining which facilities are most vulnerable to flooding through the techniques developed on this project, MnDOT can prioritize where adaptation measures will make the biggest impact, ultimately decreasing asset life-cycle and road user costs. Without the development of assessment techniques, adaptation measures run the risk of being implemented in a more reactive and/or ad-hoc fashion, with less regard to where the biggest “bang for the buck” can be realized.

This project will produce several technical memorandums, and is expected to be completed in early 2021.

Culvert Design Manual Provides Guidance for Accommodating Fish Passage

Several years of research have culminated in the publication of a culvert design manual that promotes the safe passage of fish and other aquatic organisms, as well as stream connectivity, throughout the state.

“Engineers designing culverts for Minnesota’s diverse ecological regions will benefit from this document, which offers sound guidance from many practicing experts about how to design culverts that allow aquatic organism passage and preserve stream integrity,” said Petra DeWall, former Bridge Waterway Engineer, Minnesota Department of Transportation (MnDOT).

What Was the Need?

Minnesota’s 140,000 miles of roads and approximately 92,000 miles of streams and rivers meet at tens of thousands of places. Culverts are a cost-effective solution to allow traffic to cross over smaller waterways. Historically, culverts have been designed with the safe passage of vehicles in mind. Recently, a state and national appeal for the safe passage of fish and other aquatic organisms, as well as for waterway integrity and connectivity, has influenced culvert design.

A pair of Topeka shiner fish
The Topeka shiner, once found throughout the state, is one species of federally endangered fish in Minnesota that must traverse culverts to survive.

MnDOT has supported many research projects examining fish and aquatic organism passage (AOP) through culverts, and nationally, a number of published resources exist on appropriate design. Because of the variety of ecological regions in the state, the range of culvert geometries and many other factors, no single solution can accommodate AOP through culverts statewide. A comprehensive culvert design guide was needed to inform designers about solutions that can effectively facilitate the movement of fish and other aquatic organisms in Minnesota while maintaining healthy streams.

What Was Our Goal?

The objective of this project was to produce a comprehensive and accessible culvert design guide that could be used by Minnesota practitioners to design culverts for AOP and stream connectivity. The guide would provide the following benefits:

• More efficient culvert design and permitting process for AOP.
• A central definition of typical designs, which would improve contractors’ familiarity with designs and lower construction costs.
• Avoidance of designs that could be detrimental to the natural environment.
• Avoidance of designs likely to lead to roadway damage and need for repairs.
• Fishery improvement through increased stream connectivity.

What Did We Do?

To determine the scope of the guide, researchers worked with experts from the Minnesota Department of Natural Resources (DNR), the U.S. Forest Service and others with knowledge of civil engineering, AOP and stream geomorphology.

They then sought information for the guide from a wide range of authoritative resources. A literature search examined current and past research by the research team and others; guidance documents from federal agencies; guidance from other states; permit requirements from the DNR and other agencies; and databases of fish populations, stream attributes and culvert data. The literature search also sought to reveal gaps in knowledge where further research specific to Minnesota was needed.

Additionally, researchers surveyed a cross section of highway design engineers and managers from MnDOT, county and city agencies, resource agencies and engineering consultants to identify current design practices for AOP and stream connectivity, and the degree of their effectiveness.

What Did We Learn?

The project resulted in the Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts, a thorough guide for culvert designers, hydraulic engineers and others involved in culvert design and construction in Minnesota. Topics addressed in the guide include:

• The need for culvert designs that include AOP and stream connectivity, as well as the current regulatory context.
• An overview of culvert design, categories of design methods that incorporate AOP and waterway connectivity, and a list of best practices.
• Site characteristics, analysis and tools related to energy dissipation, hydraulic analysis for AOP and sediment transport.
• A design method selection chart, information on certain designs and references for further information.
• Further guidance about design issues such as multiple barrel and floodplain culverts, grade control, retrofits and other cost considerations.

What’s Next?

The culvert design guide will be made available to users online. Future considerations for this project include an associated webinar and efforts to coordinate information presented in the guide with expectations and permitting requirements of MnDOT departments charged with culvert creation and implementation. Additional research is underway to assess culverts and fish passage with respect to storm vulnerability and future hydrologic scenarios.

This post pertains to the MnDOT and LRRB-produced Report 2019-02, “Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts,” published January 2019.

Affordable GPS-Based System Warns Drivers About Lane Departures, Approaching Curves

Researchers have developed an affordable camera-free curve and lane departure warning system that relies on consumer-level GPS, rather than sophisticated, expensive digital maps.

The technology uses cumulative driving trajectory data from GPS points detected every 100 milliseconds to predict driving path trajectories and compare these to mapped curves and lanes. With further development, the system can be used as an inexpensive smartphone app or retail device to warn drivers of lane drift and approaching curves.

“The goal of the project is to reduce lane departure crashes. We viewed this as a seed project and demonstrated that the system can be successful,” said Victor Lund, Traffic Engineer, St. Louis County.

What Was Our Goal?

The Minnesota Local Road Research Board sought research to develop a camera-free curve and lane departure warning system that uses consumer-level GPS capability without reliance on sophisticated, expensive digital maps.

What Was the Need?

Lane departures and run-off-road crashes cause more fatalities and serious injuries in Minnesota than any other accident type.

Many current warning technologies rely on cameras that identify lane position based on pavement markings. In inclement weather, stripes and pavement markings can be difficult or impossible to identify; markings also wear off over time, reducing visibility even in clear conditions. Camera-based lane departure warning systems are also expensive and generally restricted to newer luxury vehicles, making them inaccessible to the general driving public.

Though in-vehicle technology for the public usually falls outside the research interests of the Minnesota Department of Transportation and the Minnesota Local Road Research Board, the agencies have been funding development of lane departure warning technologies to improve driver safety. GPS technologies offer an intriguing path to consumer-level lane departure warning systems.

High-level GPS can be accurate to the centimeter level, but access is restricted and use is expensive. These systems also rely on accurate, lane-level roadway mapping, an elusive data set with high access costs.

What Did We Do?

Researchers began with a literature search of the uses of standard GPS receivers in lane departure and navigation. The research team then developed an algorithm for travel direction that uses standard GPS in a straight road lane departure system to determine driving trajectories at accuracy levels suited to safe driving needs.

Investigators adapted a publicly available digital mapping platform to the same algorithm to identify navigational points along curves and develop the curve lane departure warning system. The team enhanced standard safe distance methods to consider driver reaction time in determining when approach warnings should be issued.

Researchers then brought the two developmental stages of the system together with a warning system that identifies vehicle speed, curvature characteristics and safe speed limits, and calculates distance for driver response times to issue an audible warning to drivers on lane drift and a text warning of when and how much to reduce speed as the vehicle approaches a curve.

Two figures, each with a photo of a road segment an a graph that plots roadway curve distances with warning times.
The advanced curve warning system issued audible lane departure warnings when cumulative trajectories showed lateral drift within a curve.

For project testing and demonstration, investigators programmed the algorithm into a device with a built-in GPS receiver, connected it to a laptop for messaging and conducted driving tests on Rice Lake Road and on Interstate 35 near Duluth.

“From a technical point of view, this approach works. We developed a warning system with standard GPS that everyone has in a phone or vehicle. This is a lifesaving technology in a sense,” said Imran Hayee, Professor, University of Minnesota Duluth Department of Electrical Engineering.

What Did We Learn?

Finding no research on development of consumer-grade GPS for lane departure purposes, the research team adapted previous work on the relative accuracy of GPS readings from a MnDOT study on wearable GPS for work zone safety.

Researchers adapted a consumer-level GPS device to acquire data at 10-hertz frequency, which yields a GPS position point of 2.7 meters if a vehicle is driven at 60 mph.

The system calculates lane trajectory from cumulative readings and detects turns or drift. The curve warning system plots trajectories and compares these with open-source digital maps with road-level (rather than lane-level) accuracy to anticipate curves.

Illustrations show how the warning system uses shape points from maps with driving path averages to determine lane departures.

In road testing, the system issued audio warnings for every one of the approximately 200 lane changes, including curves. For curve warnings, the system scanned for curves at least half a mile ahead and calculated the vehicle’s speed and the distance to a curve to issue a timely text warning of the curve ahead and an advisory speed limit. Additional messages were issued when the vehicle was on the curve and when the curve had ended.

False alarms—warnings issued when the vehicle was not departing its lane—occurred in 10 percent of the tests, usually on sharp curves. Further adjustment of the algorithm and additional testing reduced false alarms significantly as the system accumulated data over multiple uses of the same roadway.

What’s Next?

Investigators filed a patent for the technology and will continue to develop the system. Further refinement of reference road direction information will improve accuracy and safety; the research team has developed a new project to employ vehicle-to-vehicle dedicated short-range communication technology to expand road direction reference data. The system will then need to be adapted for a consumer-level device or a smartphone app for use in any vehicle.

This post pertains to the LRRB-produced Report 2018-34, “Development and Demonstration of a Cost-Effective In-Vehicle Lane Departure and Advanced Curve Speed Warning System,” published December 2018.

 

New Resource for Using Cone Penetration Testing in Geotechnical Design

Designing foundations for bridges and pavements requires understanding the soil conditions and properties at the site. One of the best methods for calculating site conditions is the cone penetration test (CPT), in which a rod with a cone-shaped tip outfitted with sensors is driven into the soil. Engineers attach more rods to the first as the device is gradually driven to depths of 30 to 150 feet.

Researchers have developed a new manual to show geotechnical engineers how to conduct the CPT and use the data it gathers. The guide walks engineers through the process of CPT-based foundation design for sand and clay soils in deep and shallow foundations, helping engineers put the best technology to use.

A supplement to the Minnesota Department of Transportation’s Geotechnical Engineering Manual, this resource will provide improved methods for using CPT data in geotechnical design.

What Was the Need?

Designs for new bridges and structures require geotechnical investigation of a site’s soil conditions to evaluate the strength, settlement and drainage of a proposed foundation. Common design procedures rely on boring samples from the site and on standard penetration tests (SPT), which entail driving a weighted steel rod into the soil and recording the number of blows it takes to drive the rod a specified distance. Using lab analysis of samples and on-site tests, engineers determine foundation properties for the new design.

The cone penetration test (CPT) has become an attractive alternative to the SPT. CPT employs a probe with a cone-shaped tip outfitted internally with various sensors. Equipment in a CPT truck pushes the probe into the soil at the site; engineers attach rod sections behind the probe to continue pushing it in the soil to the desired investigation depth, which is usually 30 to 150 feet for transportation projects. Standard sensors allow the CPT to directly measure tip stress, pore water pressure and soil resistance; other parameters can be measured with additional sensors.

“One of the biggest impediments to deploying cone penetration testing more widely has been the lack of a practical document that integrates the latest findings and best approaches, and puts that information to use,” said Derrick Dasenbrock,
Geomechanics/LRFD Engineer, MnDOT Office of Materials and Road Research.

The CPT safely and efficiently produces accurate data and repeatable results, yet relatively few engineers in the United States know how to employ these tests and use the data for geotechnical design inputs. Users can search geotechnical engineering resources to learn how CPT results can be applied, but no standard procedure or manual is widely available for transportation projects.

cone penetration vehicle along roadway
Cone penetration testing can be conducted safely from inside a truck container alongside a highway.

What Was Our Goal?

Investigators sought to develop a new CPT design guide based on the most current CPT in situ testing research and development. The guide is intended for use in evaluating the performance of proposed bridges and structures, embankments and roadway features.

What Did We Implement?

The research team produced the 2018 CPT Design Guide for State Geotechnical Engineers, with step-by-step instructions for using the CPT to evaluate soil properties at sites and to design shallow footings and deep foundations. The document provides an overview of the CPT, its use in analyzing and characterizing soils, background on computing engineering parameters derived from CPT measurements, and detailed procedures for using those parameters to design and analyze shallow and deep foundations. Also included are derivation background, case studies and examples to help guide the user through the design process.

How Did We Do It?

Investigators began by reviewing guidelines for geotechnical engineering design based on CPT methods. The research team identified the key soil properties measurable by the CPT that are required for designing shallow and deep foundations. Then team members evaluated numerous CPT-based methods used for shallow foundations and over 40 use for deep foundations. Using the results of this evaluation, investigators identified methods with sufficiently robust and reliable performance that could be easily implemented by design engineers.

The team used CPT data from MnDOT geotechnical site investigations and developed short design case studies applying the recommended CPT design methods. After reviewing the CPT procedures with the Technical Advisory Panel, investigators organized design modules for soil characterization, shallow foundations and deep foundations, and documented the process in the design guide.

What Was the Impact?

The new guide is based on the current best practices for the CPT and was developed to establish MnDOT’s geotechnical design process while accommodating ongoing research. The guide presents recommended design methods and offers step-by-step instruction on how to calculate engineering parameters from CPT measurements and apply those design inputs to efficiently design foundation systems. Examples of problems and solutions are provided in the context of Minnesota cases, although the techniques are broadly applicable.

“Engineers can start using this design guide immediately in Minnesota—and elsewhere. The format is adaptable; California could add another module about earthquakes, for instance,” said David Saftner, Associate Professor, University of Minnesota Duluth Department of Civil Engineering.

The guide begins with a focus on characterizing soil properties from CPT measurements, providing an example for both sand and clay soils. The shallow foundation design module describes how to determine strength and soil settlement characteristics from CPT sensor readings using a method based on 166 full-scale field load tests. The deep foundation design module explains how to use the CPT to determine the required axial compression capacity of piling from a method based on 330 pile load tests.

What’s Next?

The guide is a much-needed resource for geotechnical engineers both within MnDOT and outside of the agency. The improved methods for using CPT data will encourage more frequent and widespread use of the method, improving the quality and reducing the time and cost of site investigations.

Available on MnDOT’s Geotechnical Engineering website as a supplement to the 2019 revision to the Geotechnical Engineering Manual, the guide will also be shared with a Federal Highway Administration CPT users group. Future considerations for the guide include a module on characterizing peat in organic soils and on seismic soil analysis.

This post pertains to Report 2018-32, “Cone Penetration Test Design Guide for State Geotechnical Engineers,” published November 2018.