Researchers determined that natural soil amended with locally sourced materials performed well in bioslopes and bioswales. This practice will allow MnDOT to avoid hauling in costly commercial materials for stormwater management installations.Continue reading Using Regional Materials to Manage Stormwater Runoff
Researchers documented performance of an iron-enhanced ditch check filter to remove phosphorus from stormwater over three years. The filter was effective, but its performance decreased over time, and it will require relatively frequent maintenance. Several design changes may be considered.Continue reading Evaluating Iron-Enhanced Swale Ditch Checks for Phosphorus Removal
The Minnesota Local Road Research Board recently funded a project to survey and analyze the use of Geographic Information System (GIS)-based asset management tools for city and county public works departments.Continue reading New Project: GIS Tools and Apps – Integration with Asset Management
MnDOT has funded a study to evaluate the use of non-lethal ultrasonic acoustic devices to temporarily deter bats from bridges before and during construction projects.Continue reading New Project: Use of Innovative Technology to temporarily Deter Bat-Bridge Use Prior to and During Construction
Managing a fleet of trucks, heavy equipment, and other vehicles challenges road agencies large and small. While large agencies like MnDOT use software and specialized administrators to manage fleet management systems electronically, city and county agencies often do not. For some small agencies, fleet management may fall to a shop mechanic or two.
In a recent project from the Local Road Research Board’s Research Implementation Committee, researchers identified the fleet management needs of city and county agencies and reviewed various cost-effective tools that could help these agencies make fleet management decisions. They then developed a guidebook for local agencies that addresses the tools and methods needed to manage fleets effectively.
“The guidebook provides the benefits of fleet management, a comparison of various program features and attributes, and a contact for more information about each program,” says Guy Kohlnhofer, county engineer, Dodge County, and the project’s technical liaison.
The guidebook—Fleet Management Tools for Local Agencies (2017RIC01)—includes a matrix comparing the eight most widely used fleet management software tools among Minnesota agencies. Costs, equipment needs, tracking features, financial analysis applications, and other attributes are reviewed. Case studies of agencies that use spreadsheets, software, and specific fleet replacement strategies are also included.
Three approaches to fleet replacement planning are presented in the guide. “You may have a vehicle that has been driven 300,000 miles and needed little maintenance, while another vehicle has been driven 100,000 miles and has needed a lot of maintenance,” says Renae Kuehl, senior associate, SRF Consulting Group, Inc., one of the co-authors. “We provide three models to determine when you should replace each.”
One of the findings of the project is that spreadsheets are effective and widely available tools for managing fleets. They are easy to tailor to local needs and fleets, are well understood by most computer users, are part of most office software suites, and work well for small data sets. Disadvantages, however, include limitations in reporting features, easy corruptibility of data, and inconsistent data entry among users.
In contrast, fleet management software offers easy report generation; software linkage to fuel, financial, and other software systems or modules; secure and consistent data; and interagency shareability. However, these tools can be expensive. Software costs for managing fleets average almost $36 per vehicle, and annual support costs average about $18 per vehicle. Other disadvantages include the need for training and internet accessibility.
This article originally appeared in the September issue of the LTAP Technology Exchange.
Researchers evaluated the use of existing inductive loop installations in Minnesota for vehicle classification. Results showed that inductive loops may be effective at identifying and classifying individual vehicles as they pass, but the system will require further refining for Minnesota use.
What Was the Need?
MnDOT periodically counts vehicles on state highways and uses this data to plan for transportation infrastructure needs, apply for federal funding, anticipate traffic demand and potential congestion, and learn how drivers use the highway system.
Automatic traffic recorders (ATRs) and weigh-in-motion stations count and measure the size of commercial vehicles. Engineers also count total traffic, classifying vehicles by size or axle number according to the Federal Highway Administration’s (FHWA’s) system of 13 vehicle classes, which includes Class 2 for passenger cars; Class 3 for pickup trucks, some SUVs and minivans; Class 4 for buses; and Class 5 through 13 for commercial vehicles.
Vehicle classification counting usually entails manual counting or the use of pneumatic tubes stretched across vehicle lanes to record speed and the number of axles passing. Tube counts are conducted for 48 hours at each of 1,200 sites throughout the Minnesota highway system once every two years. This time-consuming, costly practice also places staff in danger. Video imagery can be used, but this also takes a considerable commitment of labor to view, analyze and record vehicles.
A 2013 U.S. DOT study in California evaluated the use of inductive loops in vehicle classification. This technology is commonly used on highways for monitoring congestion by counting vehicles and measuring speed. Inductive loops are embedded just below the pavement surface and linked to a data station nearby that records electronic signals from the metal chassis of each passing vehicle.
What Was Our Goal?
MnDOT sought to evaluate the U.S. DOT approach in a Minnesota setting that would leverage existing technology. Researchers would use the method to record, identify and classify vehicles passing over inductive loops already installed throughout the Twin
Cities’ highway system.
What Did We Do?
Following a review of the 2013 U.S. DOT study and other research, the investigative team installed video systems and new loop signature circuit cards at five test sites: two at Interstate highways, one at a major highway and two at signalized intersections. Investigators gathered data at each location for three to four weeks.
Researchers then analyzed 10 to 14 days of loop and video data from each site. For ground truth, the team identified every individual vehicle from video, then analyzed loop data in two ways. First, they compared video and individual electronic signature readings for every vehicle. Then they analyzed loop signature data in 15-minute interval aggregations to evaluate how well the system works without verification on a vehicle-by-vehicle basis.
After evaluating vehicle classes using the FHWA classification system and a second classification system, researchers presented their findings and conclusions in a final report.
What Did We Learn?
The research team reviewed over 400 hours of video and counted over 807,000 vehicles. The match rate for all 13 FHWA classes averaged 75 percent with a standard deviation of 8 percent for individual vehicle matching. The overall matching rate was biased toward Class 2 and 3 vehicles, as sedans, pickups and SUVs share similar vehicle chassis configurations and loop signature patterns.
The 15-minute aggregated method showed a tendency to undercount Class 2 vehicles and overcount Class 3 vehicles by about 13 percent of total traffic. The secondary classification system results matched the FHWA system fairly well for consumer-level vehicles and tended to undercount some commercial vehicles.
Overall, Class 2 vehicles were matched by inductive loop signatures at a rate of 81 percent accuracy, with 17 percent of passenger vehicles misclassified as Class 3 vehicles. All other vehicle classes had matching rates of less than 50 percent. California results showed an average match rate across classes of about 92 percent.
These results were disappointing. Site conditions may have been a factor, particularly at one site where damaged hardware, broken sealants and other physical conditions were suboptimal. The library of vehicle signature signals in California was used as a basis for Minnesota analysis, but the data sets may not match precisely. Agricultural needs, for example, differ between states, and heavy agricultural vehicles feature different configurations, potentially generating different electronic signatures.
“We need a little more research, which will mostly be done by our office. If we get better accuracy, we’ll be able to get data continuously rather than just 48 hours every couple years,” said Gene Hicks, Director, Traffic Forecasting and Analysis, MnDOT Office of Transportation System Management.
The U.S. DOT study in California also used loops in circular patterns, and Minnesota’s loops are arranged in rectangular patterns. Data signal crossing, diminished signal quality and shadow data repeated on neighboring lanes may have corrupted findings.
Further research will be needed before loop signature data can be used reliably in traffic analytics. Researchers suggest that the investigation can be re-evaluated by installing four loop signature cards at two permanent ATR locations with loops, pneumatic tubes and video. Circuit cards can also be updated and classification algorithms better calibrated to vehicle signature profiles.
This post pertains to the LRRB-produced Report 2018-31, “Investigating Inductive Loop Signature Technology for Statewide Vehicle Classification Counts,” published October 2018. For more information, visit MnDOT’s Office of Research & Innovation.
A recently completed research study has identified turfgrass species and cultivars that perform best under the heat and salt on Minnesota roadsides.Continue reading Roadside Turf That Tolerates Salt, Heat and Ice
In a newly completed study, researchers found that stabilized full-depth reclamation has produced stronger roads for commercial loads in Minnesota, and the method shows promise for uses in rural agricultural areas. How much greater the strength gained with each stabilizing agent is better understood, though not conclusively.
What Was the Need?
With stabilized full-depth reclamation (SFDR), roadway builders pulverize and mix old (hot-mix or bituminous) pavement and on-site base aggregate with asphalt to create a new, thick layer of partially bound base over the remaining aggregate base of the former roadbed. The process eliminates the cost of hauling away old pavement and hauling in new, expensive aggregate, which is in limited supply.
Cracking and other damage in older pavements usually reflect through new asphalt and concrete overlays. SFDR roads, on the other hand, tend to avoid reflective cracking while meeting the increasing load demands of an aging roadway system in reduced funding environments.
To make a road stronger and more resistant to damage from heavy loads, most rehabilitation approaches require a thicker and wider roadway. SFDR may offer a way to build stronger roads without widening the road and without transporting old material from the road site and hauling new aggregate to the location.
In 2016, performance requirements of SFDR edged MnDOT and the Local Road Research Board (LRRB) closer to design standards for the technique by establishing testing, modeling and analytical methods for evaluating SFDR mixtures. Minnesota designers lack a method for giving SFDR designs structural design ratings to quantify how well the mixture will meet the needs of a new roadway. How much strength is gained by mixing in a stabilizer and laying the reclaimed road as a thick asphalt pavement base before adding the overlay remains unquantified.
What Was Our Goal?
Most replacement roadways need to be capable of bearing heavier commercial and agricultural loads than the original roads. Researchers sought to determine the structural value of SFDR in mixtures employing various stabilizing agents to help designers better accommodate rehabilitation and increased loading needs with SFDR.
“We’re really big on recycling, and we’ve been using SFDR and FDR for quite some time. We have increased confidence in SFDR. We just don’t know how high that confidence should be,” said Guy Kohlnhofer, County Engineer, Dodge County.
What Did We Do?
Researchers visited 19 Minnesota road sites to look at 24 pavement sections and surveyed pavement conditions, cracking and potholing for each segment. The team conducted stability testing with a dynamic cone penetrometer (DCP) at each section and removed three pavement cores from each for laboratory testing.
SFDR pavement can be difficult to properly core, and most specimens failed before laboratory testing. Researchers conducted tests of dynamic modulus in a way that simulated high and low vehicle speeds in the lab on the surviving 14 samples. The tests simulated the movement of wheels over pavement surface and examined the resiliency of the pavements in springing back from these rolling loads.
Based on these results, researchers plotted the laboratory test results in mathematical curves. They then analyzed their findings while referencing flexible pavement design procedures using the concept of granular equivalents (GEs) that is familiar to many avement designers in Minnesota. Finally, they estimated the structural difference between stabilized and unstabilized reclaimed materials and identified how the structural value varies with selected stabilization agents.
What Did We Learn?
Field surveys found roads performing well. Few of the pavement surfaces showed noticeable distress, and more recent surface coating treatments showed almost no distress over pavements in which distresses would quickly present themselves. DCP testing suggested that asphaltic stabilizers—asphalt, asphalt plus cement and modified asphalt—offered greater stiffness than fly ash and cement stabilization.
“We confirmed that what local engineers are doing has value, even if we weren’t able to generate more optimistic numbers,” said Charles Jahren, Professor, Iowa State University Department of Civil, Construction and Environmental Engineering.
Lab testing suggested that while SFDR mixtures offer less stiffness compared to regular hot-mix asphalt (HMA) layers, their stiffness diminishes less in comparison to HMA for slow-moving heavy loads like seasonal agricultural equipment. SFDR is worthy of additional consideration as a base layer, in such loading environments.
The most critical goal for this study was to quantify the granular equivalency of SFDR mixtures with various additives to standard aggregate bases. Foamed asphalt and engineered emulsion proved the most structurally beneficial stabilizers; SFDR mixtures with these materials offered GE values of 1.46 to 1.55, confirming the general MnDOT approach that SFDR can be used for a GE of 1.5. If road builders pulverize 4 inches of asphalt roadway with 4 inches of base aggregate and add foamed asphalt or emulsion stabilizer, the 8-inch asphalt base offers the strength of a 12-inch aggregate base. A pavement of HMA or portland cement concrete can follow to create a roadway section with greater strength than a roadway section with the same thickness of nonstabilized base.
SFDR performs well in the field and shows particular promise for use on rural roadways subject to seasonal, heavy agricultural loads. Researchers confirmed current GE inputs for SFDR and documented the performance of specific stabilizer options employed in Minnesota. Continued monitoring of SFDR road performance and additional testing and analysis would add more detail to design procedures and provide designers with greater confidence.
This post pertains to LRRB-produced Report 2018-33, “Field Investigation of Stabilized Full-Depth Reclamation (SFDR),” published November 2018. For more information, visit MnDOT’s Office of Research & Innovation project page.
The Minnesota Department of Transportation is working with other state agencies in a pooled fund study to improve methods for testing crack resistance of asphalt mixtures. To expand options further, MnDOT asked researchers to evaluate alternative tests with standard lab equipment. The new tests produced repeatable results. Methods include the semicircular bend (SCB) test in a nontypical configuration, a dynamic modulus test of smaller asphalt mixture samples, a bending beam rheometer (BBR) test of mixtures, and a BBR of asphalt material for binder selection.
What Was the Need?
A number of factors lead to cracking and other damage in asphalt. Cold temperatures cause pavements to contract, triggering internal tensions that lead to low-temperature cracking. Aging asphalt binder grows brittle and under loading pressure generates bottom-up, or fatigue, cracking. A variety of causes may contribute to top-down cracking, such as mixture properties, construction practices, tire design and loading.
MnDOT, in partnership with the National Center for Asphalt Technology, and four other state transportation agencies are part of a pooled fund study to develop mixture performance testing focused on cracking. This group, termed the Cracking Group, installed eight different pavement cells at MnROAD in the summer of 2016 to examine pavement performance and testing approaches for low-temperature, top-down and fatigue cracking.
The group’s approach does not embrace every potential test, including some examinations other agencies and research organizations have found potentially valuable in predicting cracking behavior of asphalt pavement materials.
What Was Our Goal?
MnDOT sought to investigate the viability of testing methods not included in Cracking Group studies. These tests would be conducted on asphalt mixtures sampled during construction of the test sections at MnROAD to help in material selection, quality control and forensic investigation of paving materials.
“This was a knowledge-building, data-gathering study that will help fill out our materials library database to correlate test results of asphalt materials to field performance.”
—David Van Deusen, Research Operations Engineer, MnDOT Office of Materials and Road Research
What Did We Do?
Preliminary testing focused on the eight MnROAD cells, pulling cores from the existing pavement before reconstructing new sections. Researchers tested these cores to refine methods for proposed tests. The team then gathered details on the binders and mixtures used in the 2016 reconstruction to use in its planned tests.
Researchers ran three tests on the eight asphalt mixtures and one test on the five asphalt binders used in the pavement mixtures at MnROAD. The asphalt mixture tests were:
- Bending beam rheometer (BBR) test of mixtures to obtain creep stiffness and strength of asphalt mixtures. This approach uses small beam specimens useful in forensic investigations.
- Low-temperature semicircular bend (SCB) test to measure fracture energy in mixtures. Currently there is no national standard test for fracture energy, but based on previous pooled fund work, MnDOT implemented the disk-shaped compact tension (DCT) test. The SCB results will be used to tie in the previous work and compare to the DCT.
- Dynamic modulus test of mixture resilience that uses smaller cylindrical specimens, a benefit in forensic studies.
To obtain asphalt binder strength, researchers used a variation of the BBR test for mixtures.
What Did We Learn?
The four tests proved to be viable options for materials selection testing, quality control and forensic examination of samples from existing asphalt pavements. The SCB and dynamic modulus can be run with research equipment. These tests yielded repeatable results and identified differences in the eight mixtures that are expected to impact performance. In particular, the BBR test of mixture has potential for being a practical field screening test.
The BBR test of mixtures measures strength and creep of ½-inch-thick asphalt mixture specimens compared to an indirect tensile test of strength on 2-inch asphalt pucks, and the test produces similar results. The dynamic modulus test uses the same configuration as the indirect tensile test, but instead of applying vertical compression to a 6-inch asphalt core, it applies pressure on a 1.5-inch puck diametrically, yielding similar results on an asphalt mixture’s resistance to loading.
The SCB test, an alternative to the DCT test, provides similar results in measuring the fracture energy of asphalt pavement mixtures. Either of these two newer tests is viable for MnDOT use. The binder BBR strength test represents a viable alternative to the direct tension test that, due to complex sample preparation and expensive equipment, is not frequently used.
“These test methods produce repeatable, consistent results, are simple to perform and differentiate between mixtures. They could provide critical information on the evolution of pavement performance since they can be used for forensic analyses.”
—Mihai Marasteanu, Professor, University of Minnesota Department of Civil, Environmental and Geo-Engineering
All tests found sample performance highly dependent on temperature. Fracture resistance does not correlate directly with other tested values; two mixtures that share similar creep stiffness, for example, may not have similar fracture resistance. Results indicate the eight mixtures tested may perform similarly, although one with high recycled asphalt content and another with a highly modified asphalt binder may be outliers. Based on the laboratory test results, mixtures with performance-graded binders do not differ markedly when one is mixed with recycled asphalt materials. As is the case with all pavement field studies, time is required for the mixes to begin to distinguish themselves from one another in terms of field performance.
MnDOT will share test results from this study with the Cracking Group team and include them in the overall examination of the MnROAD test cells. Researchers recommend comparing results to observed distresses and core tests periodically from these pavement cells to correlate field conditions and tested mixture performance over time. MnDOT will consider some of these testing methods and findings in its continuing effort to develop a performance-based balanced mix design approach for asphalt pavement.
This post pertains to Report 2019-03, “Investigation of Cracking Resistance of Asphalt Mixtures and Binders,” published January 2019. For more information, visit MnDOT’s Office of Research & Innovation project page.
Video and statistical analyses showed that arterial bus rapid transit (ABRT) along Snelling Avenue in Minneapolis-St. Paul had no significant impact on traffic volume and wait times at intersections. Survey results demonstrated that users prefer the A Line over local bus service and consider it roughly equivalent to express bus, light rail and commuter rail service. Though ABRT has not converted automobile drivers to transit riders, users enjoy its easy payment format, cleanliness, route service and convenience. This study also provided recommendations for future ABRT line design considerations.
“Arterial bus rapid transit is perceived positively by users. It’s much like light rail and commuter rail—people think of it as equally useful as light rail.” —Alireza Khani, Assistant Professor, University of Minnesota Department of Civil, Environmental and Geo-Engineering
What Was the Need?
Bus rapid transit (BRT) entails dedicated lanes for buses and off-board payment for users who purchase fares before boarding the bus. In recent years, arterial BRT (ABRT) has developed as an alternative for metropolitan areas that lack roadway width for dedicated lanes. ABRT uses off-board payment but not dedicated lanes; instead, it uses existing roadway arterials and limited stops, offering a fast and efficient commute for users.
In 2016, the A Line opened on the Snelling Avenue corridor in Minneapolis-St. Paul, the area’s first ABRT line. It quickly gained popularity among transit customers as an alternative to local bus service, complementing the Twin Cities’ light rail system and commuter rail service from the suburbs.
Because the A Line operates within existing lanes of traffic and does not feature pullouts at its stops, it could slow corridor traffic when buses stop to load and unload. A preimplementation study of the corridor and A Line service suggested that traffic impacts would be minimal. The A Line’s actual impact on traffic, however, had not been determined, and user perceptions had not been assessed.
What Was Our Goal?
MnDOT sought to examine the traffic impacts of the A Line in its first year of deployment, and to identify and quantify the A Line’s appeal to riders, including the service’s strengths and weaknesses, and how the transit experience of the A Line compares to local service. In addition, MnDOT needed to assess the characteristics of the service that could be used in new ABRT lines in the Twin Cities.
What Did We Do?
Researchers employed two strategies to evaluate A Line performance. First, the team conducted a traffic and transit capacity study. Investigators analyzed bus system data for ABRT and regular bus service capacity. In August 2017, researchers deployed four cameras each at two intersections: Snelling and University north of Interstate 94 (I-94), and Snelling and Dayton, south of the Interstate. Cameras collected video data for weeks before the 12-day Minnesota State Fair, which is held at the fairgrounds on Snelling Avenue, and additional video during the fair through its conclusion in September. Researchers analyzed recordings of four signal cycles before and after bus arrival at the intersections for traffic queues and volume.
Next, investigators studied the results of a 2016 Metro Transit survey of passengers on the A Line and four parallel standard bus lines. The study compared transit usage data from 2016 and 2017, before and after the A Line opened. The research team surveyed A Line passengers, station area residents, business workers and owners, automobile users, bicyclists and pedestrians. Team members also reviewed a recent study of Minneapolis-area real estate developers on transit facilities and options.
What Did We Learn?
Video and data analyses revealed that the A Line increased overall transit capacity, and the time its buses spent not moving while passengers were loading and unloading during a green traffic signal had no significant impact on intersection queue length or traffic flow at the two intersections—during and outside State Fair dates. The A Line carries more riders than the local bus along the same route, and the greatest rider turnover occurs at the Snelling and University station, which connects with light rail service.
Surveys identified the five attributes most important to satisfactory transit service: easy fare payment format, hours of operation, complaint resolution, personal safety while riding and courteous transit drivers. A Line users were more satisfied with ABRT than with local bus service, and showed no significant difference in satisfaction with the A Line compared to express buses, light rail and commuter rail. For most individual service attributes such as payment procedures, travel time, shelter cleanliness, and route and bus signage, the A Line performed better than local buses, the same as light rail but not as well as commuter rail. Nonuser surveys indicated a positive perception of the ABRT, but mixed impact on pedestrian and bicycling activities and little impact on reducing preferences for using automobiles instead of transit.
To improve A Line service, transit managers should focus on operating hours, the on-board safety of riders, reliability and total travel time. Researchers noted that rider satisfaction does not consider costs associated with improved service and recommended that future ABRT plans weigh improvements in the five key attributes of transit service against costs in planning new lines. The study findings and recommendations will be used in planning future ABRT lines.
“We will use this study to show MnDOT staff that arterial bus rapid transit should have minimal to no impact on existing traffic and signal operations.” —Carl Jensen, Transit Advantages Engineer, MnDOT Metro District
This Technical Summary pertains to Report 2018-35, “After Study of The Bus Rapid Transit A Line Impacts,” published December 2018. For more information, visit MnDOT’s Office of Research & Innovation project page.