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3D Sensing Technologies Provide Reliable Data About Signs and Pavements

GEORGIARoad users rely on traffic signs for critical guidance about traffic regulations, road hazard warnings, and other geographic information. However, with time, their retroreflectivity—which makes them visible at night—deteriorates, and the signs must be replaced. Likewise, pavement surfaces become distressed over their life spans, requiring continual maintenance to keep them operational and safe. To avoid subjective, inaccurate, and time-consuming inspections of its traffic signs and pavements, the Georgia Department of Transportation (GDOT) turned to mobile light detection and ranging (LiDAR) and 3D digital imaging technologies.

Two objectives drove GDOT’s research into these technologies. First, the department wanted to develop a more accurate methodology to assess changes in sign retroreflectivity, and second, it wanted to analyze changes in pavement surface distress. To collect the traffic sign and pavement data simultaneously, the research team equipped a Georgia Tech Sensing Vehicle with both mobile LiDAR and 3D line laser imaging sub-systems. The technologies automatically collected data on retroreflectivity conditions (good, poor, and uncertain) for 338 signs along 63 miles of I-285, as well as 3D pavement surface data showing distresses and slab-level severity on Georgia interstate highways.

This research showed that the LiDAR and 3D imaging collection methods are consistent, reliable, and cost-effective. GDOT now has an enhanced approach for evaluating sign retroreflectivity conditions that could reduce its inspection efforts by 60 percent. Long-term change trends from this research will also help transportation agencies understand how sign retroreflectivity deteriorates over time and predict the optimal schedule for replacement. In addition, GDOT is using the extracted pavement distress data to inform its interstate long-term maintenance and rehabilitation planning, with annual pavement evaluations now including 3D laser technology. Final report.

R e s e a r c h 2 0 2 0Innovations from State DOTs

The eight maintenance, management, and preservation research projectshighlighted on these pages were selected by the Research Advisory Committee of the American Association of State Highway and Transportation Officials (AASHTO). They comprise high-value projects from each of the four AASHTO regions, funded primarily through the State Planning and Research (SPR) Program. As the nation’s cornerstone state research program, SPR provides Federal Highway Administration (FHWA) funding to the states to address top concerns and identify solutions at the state level. States further address areas of common concern through the Transportation Pooled Fund Program. This publication and its companion featuring high-value safety research complement Research Makes the Difference 2020, a compilation of award-winning transportation research across all fields. All of these publications may be found at research.transportation.org.

Find more high-value state DOT research projects at AASHTO’s research website,

research.transportation.org.

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Georgia Tech Sensing Vehicle integrating LiDAR and 3D line laser imaging (LCMS) sub-systems.

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Investigating Overhead Highway Sign Trusses to Determine Fatigue Life

KANSASThe Kansas Highway System has more than 450 overhead sign trusses, many of which are 30 to 40 years old. Most state highway agencies do not perform routine fatigue inspections on signs, increasing the potential for unseen fatigue cracking. These signs also experience cyclical loading due to wind gusts.

To help inspectors identify fatigue cracks that might otherwise go unnoticed, the Kansas Department of Transportation (KDOT) developed Fatigue Life Simulator Software (FLSS) that works with STAAD.Pro, a structural analysis design software, to estimate the remaining fatigue life for welded aluminum support structures on its sign trusses. Using FLSS and STAAD.Pro, KDOT evaluated member-specific stress ranges corresponding to wind speed data over a 45-year period. The researchers also incorporated these data into KDOT’s Sign Truss Interface to simulate wind pressure and generate structural models to determine stresses to the wind effect. Using Miner’s Rule, a ratio of consumed cycles to ultimate fatigue cycles close to zero, indicates a structure will likely have an infinite life, while a ratio close to one indicates it is at the end of its life.

The research showed that fatigue life for overhead sign structures varied by city. For example, structures in Garden City, Dodge City, and Goodland demonstrated nearly spent fatigue life within the 45-year period, while other cities with the same structures had less fatigue. Based on these results, KDOT modified the Sign Truss Interface’s output results to ensure wind stresses are calculated based on AASHTO wind load cases. Now, KDOT can feed data into the interface before simulating hundreds of structural models and incorporate the results in FLSS to calculate fatigue life, making FLSS the first software to analyze and estimate remaining life spans of aluminum structures throughout their service lives. Final report.

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STAAD.Pro simulated structure showing wind pressure perpendicular to the structure span, load number 4.

Maximizing Infrastructure Investments with Real-Time Signal Performance Measurement

NEW JERSEY

The New Jersey Department of Transportation (NJDOT) uses a variety of signal configurations, equipment, and vehicle detection devices to evaluate traffic signal performance and identify deficiencies requiring maintenance. However, antiquated equipment and inefficient detection technologies make it difficult, if not impossible, for NJDOT to monitor signal performance in real time, preventing the department from getting the most benefits out of its infrastructure investments.

Looking for a solution, NJDOT decided to explore adaptive traffic signal performance measurement (ATSPM). ATSPM systems allow for consistent and dynamic monitoring of signal-controlled intersections, providing high-resolution data every 0.1 seconds. To develop a prototype system for NJDOT, researchers conducted a comprehensive literature review of existing public and commercial ATSPM platforms, as well as several stakeholder meetings to identify NJDOT’s challenges in measuring signal performance. They also inventoried NJDOT’s current detection, signaling, architecture, controller, video, and communication systems for arterial traffic signal management.

Based on these efforts, the research team developed performance metrics, system architectures, data management guidelines, and strategies for deploying a prototype ATSPM system using NJDOT’s existing and planned arterial infrastructure and technologies. One month of data have been pulled into the ATSPM prototype, and large-scale deployment is planned for phase 2 of this project. For NJDOT, the benefits are clear; in contrast to reactive operation and maintenance, ATSPM enables proactive, quicker problem-solving and provides a much more accurate picture of its signal system. Final report.

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ATSPM system operation data flow chart.

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Improving Bridge Inspection Accuracy with 3D Scanners

CONNECTICUTCurrent bridge evaluation methods are labor-intensive and depend on the subjective assessments of inspectors. Aware of the potential for inaccurate inspections to substantially—and perhaps detrimentally—impact bridge safety and the prioritization of repairs, the Connecticut

Department of Transportation (CTDOT) partnered with the University of Connecticut to explore an innovative alternative: 3D scanners. This commercially available technology provides high-accuracy, objective data for key inspection applications, such as section loss assessments for corroded steel beam ends.

After identifying a 3D scanner best suited to CTDOT’s bridge inspection needs, the research team conducted laboratory trials to develop a methodology for using the technology. These efforts were followed by five field trials on bridges throughout Connecticut, which proved that the 3D scanners can produce highly accurate 3D models representing current bridge conditions. The researchers are now finalizing 3D scanning training videos and manuals for CTDOT staff.

CTDOT has immediate plans to use the technology and methodology from this research to perform quality assurance checks on inspections and to measure section loss for load ratings and critical bridges that face closure or posting. Moreover, the improved inspection accuracy from 3D scanner measurements will also help CTDOT prioritize bridge rehabilitation projects and allocate retrofit funds. In the future, CTDOT plans to evaluate the use of 3D scanners to determine corrosion rates, map cracks, document bridge hits, and preserve/recreate historically significant details. Journal article.

Optimizing Snowplow Routes to Improve Maintenance Operations

IOWA

Iowa is no stranger to extreme winter weather conditions. The Iowa Department of Transportation (DOT) is responsible for providing winter road maintenance operations—such as removing snow and ice and spreading salt and sand to increase friction—to 24,000 lane miles of roadways. To further streamline these operations, Iowa DOT carried out a research project that focused on optimizing winter maintenance routes for District 3, which services nearly 4,000 lane miles from 20 depots.

Iowa DOT established two goals for this project: 1) design optimized winter maintenance routes for single depots under District 3’s current responsibility areas and fleet sizes, and 2) design optimized routes for multiple depots under modified responsibility areas and fleet sizes. During the project, the single-depot optimization scenario reduced the distance a truck travels while not performing maintenance services 13.2 percent compared to existing operations. Under the multiple-depot optimization scenario, the travel distance for all sectors was over 4,859 miles compared to 4,919 miles under the single-depot scenario, showing an insignificant difference between the two.

Using a memetic algorithm and taking into account truck capacity, the size and composition of each depot’s fleet, road-truck dependency, and road segment cycle time, Iowa DOT was able to achieve its goal of optimizing winter road maintenance routes. Thus, the department concluded that continuing with these modifications could result in significant cost savings, improved safety and mobility, and reduced environmental and societal impacts. Final report.

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Iowa DOT truck removes significant snow from a roadway.

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3D scanning of steel beams showing a) field use, b) transition from physical object to 3D point cloud and model, and c) measurement taken from model.

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Agro-Based Anti-Icers Are Eco-Friendly and Cost-Effective

WASHINGTONOne turn too fast or too slow in snowy and icy road conditions can cause a vehicle to lose control, a risk that the Washington Department of Transportation (WSDOT) knows all too well. Rather than relying on chloride-based anti-icing salts, which are expensive and significantly harm the environment, WSDOT sought to develop a “green,” cost-effective anti-icing formulation consisting of agro-based materials. Produced by fermenting and processing beet juice, molasses, corn, and other agricultural products, agro-based chemicals are a non-corrosive, inexpensive, water-soluble, renewable, and readily available alternative to traditional anti-icers.

In this project, researchers tested 21 eco-friendly, agro-based materials mixed with salt brine and commercial additives that pose minimal toxicity to the environment. WSDOT’s main criterion for choosing the best performing anti-icer was its ice-melting capacity—though ice-penetration rate, ability to protect asphalt binder and concrete, effect on the friction coefficient of deiced and anti-iced asphalt pavement, and anti-corrosion performance were also important considerations.

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Extending Life Expectancy of Signs Saves Costs While Ensuring Safety

SOUTH CAROLINAAlthough far less travel happens at night, nighttime crashes are much more prevalent than daytime crashes. This led the FHWA to adopt new standards in 2007 for traffic sign retroreflectivity, which makes signs brighter and easier to see in the dark. To meet the standards, the South Carolina Department of Transportation (SCDOT) adopted a strategy to replace its traffic signs every 10 years. But SCDOT needed to make sure this replacement interval was both safe and cost-effective, so it initiated a project to predict when the retroreflectivity of its traffic signs would actually fall below FHWA’s minimum standard.

Over the course of 9 months, SCDOT collected and analyzed data from 1,600 signs across South Carolina. Researchers developed linear and non-linear regression models for four sign colors (red, yellow, white, and green) to determine what variables—such as age and direction—influence sign retroreflectivity. They also analyzed degree of shade, a previously unstudied variable that was found to significantly degrade retroreflectivity. The regression models showed that age and degree of shade were statistically significant for all sign colors, while a northwest-facing direction was significant for red signs.

Based on the regression model results, as well as historical replacement data and measurements taken from older signs, SCDOT determined that it could safely extend its sign replacement interval to 12 years. Not only does this extension comply with FHWA standards, but it will also lead to a reduction of approximately 1,250 sign replacements per year and annual savings of around $93,000. In addition, SCDOT found that simply washing signs can improve their retroreflectivity by 22.5 percent, lengthening life spans by about 2 years for yellow, white, and green signs and 5 years for red signs. Final report.

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Rating system to determine degree of shade.

Full Shade Example Mostly Shade Example Partial Shade Example No Shade Example

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Researchers collect soil samples to determine secondary compression rate.

Agro-Based Anti-Icers Are Eco-Friendly and Cost-Effective(continued...)

After ranking the anti-icer solutions using a decision matrix, the researchers found that the best performer was a mixture of concord grape extract, glycerol, sodium formate, and sodium metasilicate. This mixture considerably decreased the snow–pavement bond shear strength. Laboratory friction tests also showed that the effect of deicing and anti-icing on the friction coefficient highly depends on pavement type. Ultimately, WSDOT expects these innovative, agro-based snow- and ice-control chemicals to significantly reduce the costs of winter maintenance operations. Final report.

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Automated trafficking machine used for simulating vehicle traffic to test anti-icing solutions in the laboratory.

Reducing Long-Term Consolidation Settlement from New Embankments

UTAHThe addition of new bridge-approach embankments or building loads brings the threat of post-construction, secondary compression of underlying soils. Secondary compression can cause long-term settlement damage—that often goes unnoticed for years—to bridges, their foundations and approach embankments, overlying pavements, and other nearby infrastructure. To address this threat in the state of Utah, the Utah Department of Transportation (UDOT) decided to design and implement an improved surcharging strategy, a process that reduces the magnitude of secondary compression by adding temporary fill to earthen embankments and their underlying compressible soils.

A research team from the University of Utah worked with UDOT to collect and analyze soil consolidation data from past project sites, and they performed 22 laboratory consolidation tests and 88 time-rate tests on fine-grained, cohesive soil samples from sites along the Wasatch Front to predict the rate and amount of secondary compression. Through their analysis, the researchers found that higher amounts of secondary settlement will occur in Utah’s soils than previously predicted.

UDOT used the study results to develop a recommended design method for surcharge fill that considers secondary compression, and it included the method in its Geotechnical Manual of Instruction. Ride quality at one of the first bridges to implement the research results has been promising thus far, and UDOT anticipates that widespread implementation will lead to improved ride quality at bridge approaches on new projects thanks to better-designed embankment surcharges that reduce long-term settlement. Final report.