<?xml version="1.0" encoding="utf-8"?><rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom"><channel><title>TRB Publications Index</title><link>http://pubsindex.trb.org/</link><atom:link href="http://pubsindex.trb.org/common/TRIS Suite/feeds/rss.aspx?tc=NN%3ARkmyy%2A" rel="self" type="application/rss+xml" /><description></description><language>en-us</language><copyright>Copyright © 2015. National Academy of Sciences. All rights reserved.</copyright><docs>http://blogs.law.harvard.edu/tech/rss</docs><managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor><webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster><image><title>TRB Publications Index</title><url>http://pubsindex.trb.org/Images/PageHeader-wTitle.png</url><link>http://pubsindex.trb.org/</link></image><item><title>Evaluating the Impact of Adaptive Cruise Control on Freeway Merging Performance Using VISSIM</title><link>http://pubsindex.trb.org/view/2701221</link><description><![CDATA[Adaptive cruise control (ACC) is an advanced driver assistance system (ADAS) designed to automatically adjust a vehicle’s speed to maintain a safe following distance, enhancing traffic flow and reducing driver workload. This study evaluates the impacts of ACC on traffic performance using microscopic traffic simulations in PTV VISSIM. A three-mile segment of southbound Interstate 5 (I-5) in California was modeled, incorporating real-world traffic volume and speed data for calibration and validation. The analysis examined five ACC penetration rates (0%, 25%, 50%, 75%, and 100%) under default and varied ACC parameter settings, focusing on key performance metrics such as flow, capacity, speed, and travel time. Additionally, time–space diagrams were generated to visualize vehicle trajectories and examine the microscopic effects of ACC on traffic stability and merging dynamics. The findings reveal that the adoption of ACC significantly enhances traffic flow. Average speeds increased notably with higher penetration rates, and travel times were reduced, particularly under varied ACC parameters, which demonstrated superior performance at lower penetration levels. Vehicle trajectories indicated smoother and more uniform spacing at higher penetration rates, reducing bottlenecks and enhancing merging efficiency. The results underscore the potential of ACC systems to mitigate congestion, increase capacity, and enhance flow stability.]]></description><pubDate>Mon, 11 May 2026 12:24:46 GMT</pubDate><guid>http://pubsindex.trb.org/view/2701221</guid></item><item><title>Exploring Relationships between Summary Resilient Modulus, California Bearing Ratio, and Light Weight Deflectometer Modulus for Unbound Coarse Materials in Idaho</title><link>http://pubsindex.trb.org/view/2570690</link><description><![CDATA[Mechanistic–empirical pavement design (using AASHTOWare Pavement ME Design software) incorporates inputs at three different levels (i.e., Level 1, Level 2, and Level 3). Level 1 input is preferred over Level 2 and Level 3 in AASHTOWare Pavement ME Design software. Level 1 inputs are project- or job-specific, and are obtained through direct measurements or laboratory testing. Level 1 input measurements, such as the resilient modulus (MR), might require additional resources to those required for Level 2 inputs. Many transportation agencies develop Level 2 inputs, which are more region-specific. For unbound materials, MR is considered one of the fundamental material properties. Measuring MR through laboratory testing requires advanced equipment and trained technicians, and the test is time-consuming. This study is an evaluation of the correlations between the resilient modulus of commonly used unbound materials in Idaho and the California bearing ratio (CBR) to develop Level 2 inputs. In addition, the recently introduced light weight deflectometer (LWD) modulus was correlated with the resilient modulus. The results of this study demonstrate a good and promising correlation between resilient modulus and LWD modulus, and a fair correlation between resilient modulus and CBR.]]></description><pubDate>Wed, 02 Jul 2025 13:49:08 GMT</pubDate><guid>http://pubsindex.trb.org/view/2570690</guid></item><item><title>Pilot Study to Incorporate Network-Level Structural Condition in Agency Pavement Management Practices</title><link>http://pubsindex.trb.org/view/2408321</link><description><![CDATA[The structural condition of roadway pavements is crucial in assessing the overall health of roadway networks and making informed decisions on maintenance and rehabilitation interventions. While current pavement management systems (PMSs) primarily rely on surface distress conditions, incorporating structural condition assessment at the network level can enhance decision-making processes. An approach is presented to incorporate network-level structural condition measurements obtained from the traffic speed deflectometer (TSD) in the Virginia Department of Transportation PMS. This involves determining a structural number, calculated using TSD measurements, selecting an appropriate structural condition measure (remaining structural service life) for use in the PMS, enhancing treatment selection decision trees, and conducting a cost analysis. The TSD-derived effective structural number, obtained following the American Association of State Highways and Transportation Officials (AASHTO) 1993 empirical design procedure, is utilized with traffic projections and other design information to estimate the remaining structural service life. In the treatment recommendation process, surface distress information is combined with the structural condition assessment, considering budget allocation and pavement useful life. For US Route 29 in Virginia, comparing treatment costs revealed a potential 33.2% cost saving for one maintenance cycle using the augmented decision process, which includes structural assessment, compared with surface distress assessment alone. This approach could provide a comprehensive framework for integrating structural condition assessment in PMSs, enabling more effective and cost-efficient decision-making for roadway networks. To further optimize resource allocation and improve accuracy, combining the augmented treatment selection process with deterioration predictions for a cost analysis over several maintenance cycles is recommended.]]></description><pubDate>Sat, 03 Aug 2024 16:24:50 GMT</pubDate><guid>http://pubsindex.trb.org/view/2408321</guid></item><item><title>Experimental Evaluation of Stiffness Properties of a Quicklime-Stabilized Clay Subgrade Using a Resistivity Plate Loading Testing Device</title><link>http://pubsindex.trb.org/view/2205306</link><description><![CDATA[Quicklime-mixing in soil stabilization applications for subgrade construction is crucial to its engineering performance and controlling quicklime and water content. Modern construction quality control devices and methods have improved construction quality control substantially. Certain devices, meanwhile, still need to be studied more thoroughly. This study used the resistivity plate loading device to assess the physical and stiffness properties of compacted quicklime-stabilized subgrade instantaneously and simultaneously for compaction quality control. The Taguchi L9 orthogonal array was used to design the experiment considering the dry density, test time, quicklime, and water content at various input factor levels. The pH, cation exchange capacity, conductivity, X-ray diffraction analysis (XRD), and scanning electron microscope (SEM) tests were further conducted. Analysis of the Taguchi experiment shows that the average soil electrical resistivity responses increased with dry density, test time, and quicklime content, and were highest at low water content. Whether the dry density, quicklime content, and test time are positively or negatively related to the average subgrade reaction modulus depends on the level of the water content. Regression equations are proposed to predict the average subgrade reaction modulus and soil electrical resistivity. The tested soils’ pH, conductivity, and cation ion exchange capacity properties were directly related to the test time, water, and quicklime content. The XRD showed nearly similar X-ray diffraction peaks. The SEM analysis confirmed marked changes in the microstructure of the samples that explained the changes in electrical resistivity and subgrade reaction modulus responses. The test results show that the resistivity plate loading device efficiently assesses compacted quicklime’s stiffness and physical properties at ease and instantaneously.]]></description><pubDate>Wed, 05 Jul 2023 19:01:21 GMT</pubDate><guid>http://pubsindex.trb.org/view/2205306</guid></item><item><title>Investigation of In Situ Strength of Various Construction and Widening Methods Utilized on Local Roads</title><link>http://pubsindex.trb.org/view/2120697</link><description><![CDATA[The project goal was to develop and verify a low-cost, repeatable, nondestructive methodology to characterize the load-carrying capacity of materials used in road widening and construction when established values are not available, and to establish a range of structural coefficients and moduli for these materials. Ninety-nine test sites were selected from 68 projects in eight counties across Ohio, grouped into five clusters. These sites included 19 different widening treatments. Each site was visited, tests conducted, and specimens gathered using the following techniques: falling weight deflectometer (FWD), portable seismic property analyzer, light weight deflectometer, dynamic cone penetrometer, and coring. The data and specimens collected were used to measure layer thicknesses, moduli, effective structural numbers, and layer coefficients applicable to each treatment. At least seven analysis methods were used to obtain the numbers from the data collected. The results were plotted in box plot and cumulative frequency formats for each material and analysis method. For each material, there was a wide variability of values both within and between sections. There were many sources of variability, however a range of numbers for moduli and layer coefficients were identified for most treatments, which could be utilized by local engineering personnel to design future projects. The procedure based on Section 2.3.5 of the 1993 AASHTO pavement design guide using FWD data provided the best estimate of published layer coefficients. However, using these values in other areas cannot guarantee accuracy; truly accurate layer coefficients result from careful monitoring of test sections under controlled loads.]]></description><pubDate>Wed, 22 Feb 2023 17:15:31 GMT</pubDate><guid>http://pubsindex.trb.org/view/2120697</guid></item><item><title>Development of Toll Equivalency Factors for FASTag Lanes Under Mixed Traffic Conditions</title><link>http://pubsindex.trb.org/view/2078672</link><description><![CDATA[The traffic conditions in India consist of a high degree of heterogeneity in vehicle categories plying on the highways without any lane-following behavior. A similar behavior is observed at the toll plazas where a dedicated lane assigned to a vehicle class is encroached by the vehicles of other categories, causing a mixed nature of the traffic in the same lane. In the present study, service headway is taken as the measure of effectiveness for studying the effect of mixed traffic conditions on traffic operations at electronic toll collection system (ETC) lanes, which are called FASTag lanes in India. Service headway is composed of processing time and the clearance time of the vehicle. Videographic data were collected at three different toll plazas located on National Highways in India to capture the variability in traffic and human behavior. The results showed that the service headway for a vehicle varies between 1.56?s and 34.40?s. The service headway-based toll equivalency factors (HTEF) are developed for converting the mixed traffic flow into a homogeneous equivalent for FASTag lanes. The results showed that the HTEF varies from 1.01 to 2.61. The results are validated spatially with data taken from a different site, and no significant difference was found between both the converted and equivalent data. Field engineers can use the developed HTEFs to estimate the traffic flow in equivalent terms based on the traffic composition. Further, the present study results can also be used to study the capacity and level of service (LOS) of FASTag lanes.]]></description><pubDate>Thu, 08 Dec 2022 16:29:34 GMT</pubDate><guid>http://pubsindex.trb.org/view/2078672</guid></item><item><title>Sustainable Materials: A Review of Recycled Concrete Aggregate Utilization as Pavement Material</title><link>http://pubsindex.trb.org/view/1889032</link><description><![CDATA[In this paper, a comprehensive literature review was conducted on the utilization of recycled concrete aggregate (RCA), which is the dominant construction and demolition waste material, in base and subbase layers and its comparison with natural aggregate (NA). The effects of crushing on the particles as a result of the compaction on the resilient modulus, permanent deformation, and California Bearing Ratio are analyzed. The paper also contains the NA consumption and waste disposal policies of different countries, RCA standards, and the environmental-economic reasons for its use. This literature review mainly focuses on pavement layers as this is the main application of RCA in the use of recycled materials. Developing integrated construction and demolition waste management will help achieve the primary goal of preventing and reducing the generation of these wastes, both locally and globally. In this way, not only is the main purpose of preventing the increase in the production of construction and demolition waste achieved, but also the reuse and recycling of the waste materials produced are encouraged. Results show that RCA has equivalent or better performance than virgin aggregate for almost any application with proper care and process control, and can be used in unbound pavement layers or other applications requiring compaction. But it is always recommended that its mechanical properties and durability performance be evaluated with full-scale tests before use. The information provided will be useful for contractors and engineers to evaluate alternative solutions and to explore the rational use of such sustainable materials in applications.]]></description><pubDate>Tue, 02 Nov 2021 12:46:06 GMT</pubDate><guid>http://pubsindex.trb.org/view/1889032</guid></item><item><title>Generalized Methodology to Develop Mechanistically Informed Asphalt Mixture Layer Coefficients for AASHTO 1993 Pavement Design Approach</title><link>http://pubsindex.trb.org/view/1880160</link><description><![CDATA[This paper presents a generalized framework for determining mechanistically informed layer coefficients (a-values) for asphalt mixtures in the AASHTO empirical pavement design approach. The layer coefficients influence the layer thicknesses and consequently the structural capacity of pavements. Therefore, it is critical to determine reliable mechanistically informed a-values. A set of 18 commonly used asphalt mixtures in New Hampshire was selected for investigation including different types of hot mix and cold central plant recycled mixtures that are used as wearing, binder, and base course layers. Laboratory characterization was conducted using the complex modulus, semi-circular bend, and direct tension cyclic fatigue testing methods. The mixtures were evaluated using three performance index parameters: complex modulus rutting index parameter, rate-dependent cracking index parameter, and a new continuum damage parameter (NfatCNfS=100). The measured field performance of wearing course mixtures in terms of International Roughness Index was used to back-calculate the in situ performance-based layer coefficients (aIRI-values). Using a normal distribution function, the results from performance testing were incorporated with the aIRI-values to develop mechanistically informed mix-specific layer coefficients. In addition, a typical layer coefficient at specific reliability levels for each mix category including hot mix wearing course, hot mix binder and base course as well as cold central plant recycled mix course are proposed for New Hampshire. The recommended a-values are 0.48 for hot mix wearing, 0.41 for hot mixed binder and base, and 0.28 for cold recycled base mixtures; these are approximately 25% higher than the currently used a-values in New Hampshire.]]></description><pubDate>Mon, 27 Sep 2021 18:21:57 GMT</pubDate><guid>http://pubsindex.trb.org/view/1880160</guid></item><item><title>Developing Mixed Traffic Equivalency Factors to Estimate Saturation Flow at Urban Signalized Intersections</title><link>http://pubsindex.trb.org/view/1866650</link><description><![CDATA[This study proposes a time occupancy approach to estimate passenger car units (PCUs) at urban signalized intersections with different interaction levels between vehicles under saturated green time conditions. The study shows a variation in PCUs with varied traffic and geometric conditions. Traffic data have been collected through videography techniques at signalized intersections in three metropolitan cities in India. Traffic flow discharge and clearance time of different vehicular categories have been extracted from the video during the saturated green time. The observed ranges of dynamic PCU values for two-wheelers, three-wheelers, big cars, light commercial vehicles, and heavy vehicles are 0.12 to 0.32, 0.45 to 0.80, 1.40 to 1.80, 1.60 to 2.20, and 3.50 to 6.50, respectively. Regression-based PCU models have been developed for each vehicle category to address the variation of individual vehicle PCUs with traffic compositions and flow rates. The model analysis shows that traffic compositions and flow rates are significantly affecting the PCU values. The PCU is a complex parameter requiring several field attributes. Therefore, to overcome the complexity of estimating PCUs, a concept of flow equivalency factor (FEF) has been proposed based on the estimated PCUs. The FEF can directly convert the mixed motorized vehicular flow into an equivalent standard passenger car flow without actually making use of different vehicles’ PCU factors. All the developed models have been validated for field conditions and results are found promising with field data. The developed approach can be used effectively for developing countries with a mixed traffic stream.]]></description><pubDate>Wed, 21 Jul 2021 16:51:35 GMT</pubDate><guid>http://pubsindex.trb.org/view/1866650</guid></item><item><title>Determining an Acceptable California Bearing Ratio (CBR) Value for Kansas Subgrades Based on Pavement Rutting Data</title><link>http://pubsindex.trb.org/view/1760009</link><description><![CDATA[This study investigates how to find a minimum allowable subgrade strength (CBR) value required to limit rutting in pavements. Weak subgrade condition can significantly contribute to excessive rutting, which is a major type of distress in flexible pavements. Hence, a minimum subgrade strength needs to be maintained to prevent unacceptable rutting. Nevertheless, there is a lack of established relationship that would quantify the effect of subgrade strength on rut development. Currently available studies provide complex rut prediction models that consider multiple contributing factors. The main goal of this study is to establish a direct correlation between subgrade strength and development of pavement rutting. The study investigates the existence of a statistical correlation between rutting development and subgrade strength (DCP/CBR), based on which the criterion for selecting a minimum acceptable subgrade strength is proposed. It is based on the data selected from pavements located in seven counties in Kansas. Dynamic Cone Penetrometer (DCP) tests were performed in the subgrade of these pavements in excessive rut condition. Corresponding CBR values were obtained based on DCP data by using the empirical equation. DCP test data and correlated CBR data are independent variables in the statistical model. The average yearly rut development starting from the year of zero rut condition is the dependent variable. Statistically significant correlation with 0.001 significance level is observed between the DCP test data and rutting development in pavement. Finally, a criterion for selecting the minimum acceptable CBR value of subgrade is proposed to avoid excessive increase in pavement rutting.]]></description><pubDate>Thu, 04 Feb 2021 11:00:51 GMT</pubDate><guid>http://pubsindex.trb.org/view/1760009</guid></item><item><title>Structural Assessment of Cold in Place Recycling Sections Used for Pavement Preservation</title><link>http://pubsindex.trb.org/view/1759239</link><description><![CDATA[Cold recycling of asphalt pavements is a widely practiced technique used to prolong pavement life as a low-cost preservation method. Research in recycled materials has become necessary to further evaluate the material properties and performance of this sustainable technology. The National Center for Asphalt Technology (NCAT) has constructed several test sections as part of its Pavement Preservation Group (PG) Study along Highway US-280 near Opelika, Alabama. The preservation sections were built in the summer of 2015, and part of the experiment included two different sections using cold in-place recycling (CIR) with asphalt emulsion and foamed asphalt as recycling agents. A one-inch thin dense-graded asphalt overlay was placed as the wearing surface. Field data collection has been in progress since September 2015. The data collected included roughness, rutting, cracking, and deflections. Field performance measurements showed that the use of cold recycled materials influenced rut depths, falling into the fair threshold of the MAP-21 rating system during the first four and a half years of service. Cracking levels have been low, with under 1.5 percent of the total area. Roughness in the CIR-foamed section was steady over time, while the CIR emulsion section had a mild increasing trend. The backcalculated pavement modulus showed the cold recycled sections have temperature-dependent behavior, with more temperature susceptibility in the CIR-emulsion section. The obtained results were used to calculate the structural contribution of the recycling technologies from a pavement design perspective. The structural layer coefficients of the recycled materials ranged between 0.31 and 0.35.]]></description><pubDate>Thu, 04 Feb 2021 10:57:25 GMT</pubDate><guid>http://pubsindex.trb.org/view/1759239</guid></item><item><title>Effect of Temperature Difference on the Thickness Design of Pervious Concrete Pavements</title><link>http://pubsindex.trb.org/view/1733947</link><description><![CDATA[Pervious concrete pavement (PCP) is a porous paving material that facilitates the rapid infiltration of runoff. The significance of temperature difference (?T) between the top and bottom of traditional concrete pavements for stresses and structural design is well known. However, with their low thermal conductivity, the question exists whether PCPs develop large ?Ts that vary during the day and between seasons. If so, the extent of the effect of such ?Ts on stresses in the slab and the thickness design of PCP needs to be investigated. In this study, temperature data collected from three PCP sections (in two different climate regions) instrumented with thermocouples were used to analyze ?T for multi-year periods. Frequency distribution of ?Ts showed bimodal trends with peaks ranging between –6°C and 17°C occurring during the day and night of spring and summer seasons. In winter, ?T distribution was unimodal, with peaks ranging from 0°C to 3°C. Finite element analysis was conducted to quantify the stresses in PCP sections with different flexural strength (MR) and modulus of subgrade reaction under combinations of critical ?Ts and axle loading. The resulted stresses were used in a PCP fatigue model to estimate fatigue life and slab thickness for PCPs. Based on the expected load repetitions in a 20-year design life, a database of recommended thicknesses for PCPs with various material properties and under four traffic categories was developed. Increasing MR from 2.4 to 3.1?MPa resulted in reducing PCP design thicknesses by 20–55?mm under the same loads. Moreover, incorporating ?T in the thickness design of PCP resulted in a higher minimum required thicknesses by up to 100?mm compared with PCP with no ?T under the same traffic loads.]]></description><pubDate>Sun, 06 Sep 2020 16:56:01 GMT</pubDate><guid>http://pubsindex.trb.org/view/1733947</guid></item><item><title>Structural Characterization of Fractured Portland Cement Concrete Pavements in Pennsylvania from Falling Weight Deflectometer Data</title><link>http://pubsindex.trb.org/view/1726024</link><description><![CDATA[Hot mix asphalt (HMA) overlays on fractured Portland cement concrete (PCC) is a common rehabilitation alternative used for PCC pavements in Pennsylvania. Several fracture techniques including rubblization, crack and seat (C&amp;S), and break and seat (B&amp;S) have been used for decades to minimize reflective cracking by reducing the effective slab length and, with it, expansion/contraction movement. The design of this type of overlay requires knowledge of the structural capacity of the fractured PCC layer. The AASHTO 93 and Pavement ME design methods are used by the Pennsylvania Department of Transportation (DOT). These methods and the Pennsylvania DOT documentation recommend certain values to characterize the structural capacity of the fractured PCC. However, the guidance envisaged the selection of these values provided by these design methods and the Pennsylvania DOT documentation is limited. The objective of this study is to determine realistic Pennsylvania-specific elastic modulus (EPCC) values and layer coefficients (LC) to characterize the in situ behavior of fractured PCC layer for jointed reinforced concrete pavements (JRCP) and jointed plain concrete pavements (JPCP). To obtain these structural properties, 11 different rehabilitation projects located in Pennsylvania were analyzed using falling weight deflectometer (FWD) data, backcalculation programs, and statistical methods. Based on this analysis, the recommended values of EPCC and LC for C&amp;S overlay design are 360?ksi (kips per square inch) and 0.32, respectively. In the case of B&amp;S overlay design, these values correspond to 400?ksi and 0.34, respectively. The variability of the slab fracturing process and the reduction of the structural capacity caused by fracturing were also analyzed in this investigation.]]></description><pubDate>Mon, 10 Aug 2020 10:37:26 GMT</pubDate><guid>http://pubsindex.trb.org/view/1726024</guid></item><item><title>Novel Framework for the Quantification of Pavement Damages in the Overload Corridors</title><link>http://pubsindex.trb.org/view/1716659</link><description><![CDATA[Recent traffic trends and permit issuance show significant mobility demands in the energy sectors across the nation. The increase in the axle loads and frequency of operations of over-weight (OW) trucks resulted in severe damage to transportation infrastructures. Traditionally, the damage imparted by OW vehicles has been quantified by means of the equivalent axle load factors (EALFs) concept. However, because of the nature of assumptions in the development of damage equivalency factors, the field distresses substantially deviate from the prediction models. Therefore, this study aimed to bridge this gap by developing a mechanistic framework to determine damage equivalency factors tailored toward the specific characteristics of OW vehicles operating in the OW corridors, while considering the environmental conditions and the unique features of transportation facilities in the network. To achieve this objective, initially, the authors devised a plan to collect traffic information using portable weigh-in-motion devices at two intervals for 10 representative sites in the energy corridors of Eagle Ford Shale region. Subsequently, a series of nondestructive tests were conducted in the field to determine the material properties of the pavement layers for further numerical simulations. This information was further incorporated into a 3D finite element system to calculate critical input parameters in the modified damage factor models. The proposed mechanistic approach confirmed that the modified damage factors were substantially higher compared with traditional industry-standard values. Further investigation of environmental factors and pavement profiles in this study underscored the significance of these components for accurate assessment of the damage equivalency factors.]]></description><pubDate>Mon, 06 Jul 2020 16:55:09 GMT</pubDate><guid>http://pubsindex.trb.org/view/1716659</guid></item><item><title>Methodology for Determination of the Structural Layer Coefficient of Unbound Base Materials in Florida</title><link>http://pubsindex.trb.org/view/1716580</link><description><![CDATA[The main goal of this study was to assess methodologies for the determination of base structural layer coefficients (SLCs) in Florida base materials. The aim was to streamline the traditional empirical and observationally based technique for determining layer coefficients either by an accelerated loading process or by the computer simulation of pavement performance. The paper describes a methodology in which the structural numbers (SN) of two paired test sections are used to backcalculate the unknown SLC. The SNs are determined from the AASHTO performance equation using a prediction of pavement performance from the University of Florida top-down cracking (TDC) model. The paper presents a positive application of the methodology for two test sections in Louisiana and two sections in Florida.]]></description><pubDate>Fri, 26 Jun 2020 17:18:04 GMT</pubDate><guid>http://pubsindex.trb.org/view/1716580</guid></item></channel></rss>