Virginia Tech Transportation Institute (VTTI)

Permanent URI for this community

https://hdl.handle.net/10919/5524

Browse

Now showing 1 - 20 of 34

Access Control Design on Highway Interchanges
Rakha, Hesham A.; Flintsch, Alejandra Medina; Arafeh, Mazen; Abdel-Salam, Abdel-Salam Gomaa; Dua, Dhruv; Abbas, Montasir M. (Virginia Center for Transportation Innovation and Research, 2008-01-01)
The adequate spacing and design of access to crossroads in the vicinity of freeway ramps are critical to the safety and traffic operations of both the freeway and the crossroad. The research presented in this report develops a methodology to evaluate the safety impact of different access road spacing standards. The results clearly demonstrate the shortcomings of the AASHTO standards and the benefits of enhancing them. The models developed as part of this research were used to compute the crash rate associated with alternative section spacing. The study demonstrates that the models satisfied the statistical requirements and provide reasonable crash estimates. The results demonstrate an eight-fold decrease in the crash rate when the access road spacing increases from 0 to 300 m. An increase in the minimum spacing from 90 m (300 ft) to 180 m (600 ft) results in a 50 percent reduction in the crash rate. The models were used to develop lookup tables that quantify the impact of access road spacing on the expected number of crashes per unit distance. The tables demonstrate a decrease in the crash rate as the access road spacing increases. An attempt was made to quantify the safety cost of alternative access road spacing using a weighted average crash cost. The weighted average crash cost was computed considering that 0.6, 34.8, and 64.6 percent of the crashes were fatal, injury, and property damage crashes, respectively. These proportions were generated from the field observed data. The cost of each of these crashes was provided by VDOT as $3,760,000, $48,200, and $6,500 for fatal, injury, and property damage crashes, respectively. This provided an average weighted crash cost of $43,533. This average cost was multiplied by the number of crashes per mile to compute the cost associated with different access spacing scenarios. These costs can assist policy makers in quantifying the trade-offs of different access management regulations.
Adaptive Traffic Signal Control: Game-Theoretic Decentralized vs. Centralized Perimeter Control
Elouni, Maha; Abdelghaffar, Hossam M.; Rakha, Hesham A. (MDPI, 2021-01-03)
This paper compares the operation of a decentralized Nash bargaining traffic signal controller (DNB) to the operation of state-of-the-art adaptive and gating traffic signal control. Perimeter control (gating), based on the network fundamental diagram (NFD), was applied on the borders of a protected urban network (PN) to prevent and/or disperse traffic congestion. The operation of gating control and local adaptive controllers was compared to the operation of the developed DNB traffic signal controller. The controllers were implemented and their performance assessed on a grid network in the INTEGRATION microscopic simulation software. The results show that the DNB controller, although not designed to solve perimeter control problems, successfully prevents congestion from building inside the PN and improves the performance of the entire network. Specifically, the DNB controller outperforms both gating and non-gating controllers, with reductions in the average travel time ranging between 21% and 41%, total delay ranging between 40% and 55%, and emission levels/fuel consumption ranging between 12% and 20%. The results demonstrate statistically significant benefits of using the developed DNB controller over other state-of-the-art centralized and decentralized gating/adaptive traffic signal controllers.
Asphalt Materials Characterization in Support of Implementation of the Proposed Mechanistic-Empirical Pavement Design Guide
Flintsch, Gerardo W.; Loulizi, Amara; Diefenderfer, Stacey D.; Galal, Khaled A.; Diefenderfer, Brian K. (Virginia Center for Transportation Innovation and Research, 2007-01-01)
The proposed Mechanistic-Empirical Pavement Design Guide (MEPDG) procedure is an improved methodology for pavement design and evaluation of paving materials. Since this new procedure depends heavily on the characterization of the fundamental engineering properties of paving materials, a thorough material characterization of mixes used in Virginia is needed to use the MEPDG to design new and rehabilitated flexible pavements. The primary objective of this project was to perform a full hot-mix asphalt (HMA) characterization in accordance with the procedure established by the proposed MEPDG to support its implementation in Virginia. This objective was achieved by testing a sample of surface, intermediate, and base mixes. The project examined the dynamic modulus, the main HMA material property required by the MEPDG, as well as creep compliance and tensile strength, which are needed to predict thermal cracking. In addition, resilient modulus tests, which are not required by the MEPDG, were also performed on the different mixes to investigate possible correlations between this test and the dynamic modulus. Loose samples for 11 mixes (4 base, 4 intermediate, and 3 surface mixes) were collected from different plants across Virginia. Representative samples underwent testing for maximum theoretical specific gravity, asphalt content using the ignition oven method, and gradation of the reclaimed aggregate. Specimens for the various tests were then prepared using the Superpave gyratory compactor with a target voids in total mix (VTM) of 7% - 1% (after coring and/or cutting). The investigation confirmed that the dynamic modulus test is an effective test for determining the mechanical behavior of HMA at different temperatures and loading frequencies. The test results showed that the dynamic modulus is sensitive to the mix constituents (aggregate type, asphalt content, percentage of recycled asphalt pavement, etc.) and that even mixes of the same type (SM-9.5A, IM-19.0A, and BM 25.0) had different measured dynamic modulus values because they had different constituents. The level 2 dynamic modulus prediction equation reasonably estimated the measured dynamic modulus; however, it did not capture some of the differences between the mixes captured by the measured data. Unfortunately, the indirect tension strength and creep tests needed for the low-temperature cracking model did not produce very repeatable results; this could be due to the type of extensometers used for the test. Based on the results of the investigation, it is recommended that the Virginia Department of Transportation use level 1 input data to characterize the dynamic modulus of the HMA for projects of significant impact. The dynamic modulus test is easy to perform and gives a full characterization of the asphalt mixture. Level 2 data (based on the default prediction equation) could be used for smaller projects pending further investigation of the revised prediction equation incorporated in the new MEPDG software/guide. In addition, a sensitivity analysis is recommended to quantify the effect of changing the dynamic modulus on the asphalt pavement design. Since low-temperature cracking is not a widespread problem in Virginia, use of level 2 or 3 indirect tensile creep and strength data is recommended at this stage.
Assessment of Vehicle-to-Vehicle Communication based Applications in an Urban Network
Kim, Taehyoung (Virginia Tech, 2015-06-23)
Connected Vehicle research has emerged as one of the highest priorities in the transportation systems because connected vehicle technology has the potential to improve safety, mobility, and environment for the current transportation systems. Various connected vehicle based applications have been identified and evaluated through various measurements to assess the performance of connected vehicle applications. However, most of these previous studies have used hypothetical study areas with simple networks for connected vehicle environment. This study represents connected vehicle environment in TRANSIMS to assess the performance of V2V communication applications in the realistic urban network. The communication duration rate and spatial-temporal dispersion of equipped vehicles are investigated to evaluate the capability of V2V communication based on the market penetration rate of equipped vehicles and wireless communication coverage in the whole study area. The area coverage level is used to assess the spatial-temporal dispersion of equipped vehicles for two study areas. The distance of incident information propagation and speed estimation error are used to measure the performance of event-driven and periodic applications based on different market penetration rates of equipped vehicles and wireless communication coverage in both morning peak and non-peak times. The wireless communication coverage is the major factor for event-driven application and the market penetration rate of equipped vehicles has more impact on the performance of periodic application. The required minimum levels of deployment for each application are determined for each scenario. These study findings will be useful for making decisions about investments on deployment of connected vehicle applications to improve the current transportation systems. Notably, event-driven applications can be reliably deployed in the initial stage of deployment despite the low level of market penetration of equipped vehicles.
Battery Electric Vehicle Eco-Cooperative Adaptive Cruise Control in the Vicinity of Signalized Intersections
Chen, Hao; Rakha, Hesham A. (MDPI, 2020-05-12)
This study develops a connected eco-driving controller for battery electric vehicles (BEVs), the BEV Eco-Cooperative Adaptive Cruise Control at Intersections (Eco-CACC-I). The developed controller can assist BEVs while traversing signalized intersections with minimal energy consumption. The calculation of the optimal vehicle trajectory is formulated as an optimization problem under the constraints of (1) vehicle acceleration/deceleration behavior, defined by a vehicle dynamics model; (2) vehicle energy consumption behavior, defined by a BEV energy consumption model; and (3) the relationship between vehicle speed, location, and signal timing, defined by vehicle characteristics and signal phase and timing (SPaT) data shared under a connected vehicle environment. The optimal speed trajectory is computed in real-time by the proposed BEV eco-CACC-I controller, so that a BEV can follow the optimal speed while negotiating a signalized intersection. The proposed BEV controller was tested in a case study to investigate its performance under various speed limits, roadway grades, and signal timings. In addition, a comparison of the optimal speed trajectories for BEVs and internal combustion engine vehicles (ICEVs) was conducted to investigate the impact of vehicle engine types on eco-driving solutions. Lastly, the proposed controller was implemented in microscopic traffic simulation software to test its networkwide performance. The test results from an arterial corridor with three signalized intersections demonstrate that the proposed controller can effectively reduce stop-and-go traffic in the vicinity of signalized intersections and that the BEV Eco-CACC-I controller produces average savings of 9.3% in energy consumption and 3.9% in vehicle delays.
Carbon Fiber Reinforced Polymer Grids for Shear and End Zone Reinforcement in Bridge Beams
Ward, John; Magee, Mitch; Roberts-Wollmann, Carin L.; Cousins, Thomas E. (Virginia Transportation Research Council, 2018-01)
Corrosion of reinforcing steel reduces life spans of bridges throughout the United States; therefore, using non-corroding carbon fiber reinforced polymer (CFRP) reinforcement is seen as a way to increase service life. The use of CFRP as the flexural reinforcement in bridge girders has been extensively studied. However, CFRP transverse reinforcement has not been investigated as rigorously, and many of those studies have focused on carbon fiber composite cable (CFCC) stirrups. The use of C-Grid or NEFMAC grid as options for transverse reinforcing has not been previously investigated. This testing program first determined the mechanical properties of C-Grid and NEFMAC grid and their respective development lengths. Five 18-ft long, 19-in deep beams were fabricated to test the C-Grid and NEFMAC, as well as conventional steel and CFCC stirrups. The beams were loaded with a single point load closer to one end of the beam to create a larger shear load for a given moment. Overall beam displacement was measured, and beams were fitted with rosettes and instrumentation to capture initiation of shear cracking. Test results were compared to theoretical shear capacities calculated using four different methods. The design method which provided the best prediction of shear strength was the AASHTO modified compression field theory, using equations for β and θ. The manufacturer’s guaranteed tensile strength should be used for design, as long as that strength is the average strength, as determined by at least five tests, reduced by three standard deviations. Shear cracks were controlled to a similar width as in beams with steel stirrups when at least two layers of grid were in place. An additional study was undertaken to determine if CFRP grids, either alone or in combination with traditional steel stirrups, could be used to control cracking in the end zones of pretensioned I-beams. Unfortunately, it was determined that, due to its low modulus, the amount of CFRP grid required to control cracking in the end zones was not economically feasible. Nevertheless, this study concluded that C-Grid and NEFMAC grid are both viable shear reinforcement options outside of the end regions. This report presents the initial recommendations for design.
Composite Pavement Systems: Synthesis of Design and Construction Practices
Flintsch, Gerardo W.; Diefenderfer, Brian K.; Orlando Nunez (Virginia Center for Transportation Innovation and Research, 2008-11-01)
Composite pavement systems have shown the potential for becoming a cost-effective pavement alternative for highways with high and heavy traffic volumes, especially in Europe. This study investigated the design and performance of composite pavement structures composed of a flexible layer (top-most layer) over a rigid base. The report compiles (1) a literature review of composite pavement systems in the U.S. and worldwide; (2) an evaluation of the state-of-the-practice in the U.S. obtained using a survey; (3) an investigation of technical aspects of various alternative composite pavement systems designed using available methodologies and mechanistic-empirical pavement distress models (fatigue, rutting, and reflective cracking); and (4) a preliminary life cycle cost analysis (LCCA) to study the feasibility of the most promising composite pavement systems. Composite pavements, when compared to traditional flexible or rigid pavements, have the potential to become a cost-effective alternative because they may provide better levels of performance, both structurally and functionally, than the traditional flexible and rigid pavement designs. Therefore, they can be viable options for high volume traffic corridors. Countries, such as the U.K. and Spain, which have used composite pavement systems in their main road networks, have reported positive experiences in terms of functional and structural performance. Composite pavement structures can provide long-life pavements that offer good serviceability levels and rapid, cost-effective maintenance operations, which are highly desired, especially for high-volume, high-priority corridors. Composite pavements mitigate various structural and functional problems that typical flexible or rigid pavements tend to present, such as hot-mix asphalt (HMA) fatigue cracking, subgrade rutting, portland cement concrete (PCC) erosion, and PCC loss of friction, among others. At the same time, though, composite systems are potentially more prone to other distresses, such as reflective cracking and rutting within the HMA layer. Premium HMA surfaces and/or reflective cracking mitigation techniques may be required to mitigate these potential problems. At the economic level, the results of the deterministic agency-cost LCCA suggest that the use of a composite pavement with a cement-treated base (CTB) results in a cost-effective alternative for a typical interstate traffic scenario. Alternatively, a composite pavement with a continuously reinforced concrete pavement (CRCP) base may become more cost-effective for very high volumes of traffic. Further, in addition to savings in agency cost, road user cost savings could also be important, especially for the HMA over CRCP composite pavement option because it would not require any lengthy rehabilitation actions, as is the case for the typical flexible and rigid pavements.
Determination of the In-Place Hot-Mix Asphalt Layer Modulus for Rehabilitation Projects Using a Mechanistic-Empirical Procedure
Loulizi, Amara; Flintsch, Gerardo W.; McGhee, Kevin K. (Virginia Center for Transportation Innovation and Research, 2006-07-01)
This project evaluated the procedures proposed by the Mechanistic-Empirical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. Thirty-three cores were extracted from nine sites in Virginia to measure their dynamic moduli in the lab. Falling-weight deflectometer (FWD) testing was performed at the sites because the backcalculated moduli are needed for the Level 1 procedure. The resilient modulus was also measured in the lab because it is needed for the Level 2 procedure. A visual pavement rating was performed based on pavement condition because it is needed for the Level 3 procedure. The selected cores were tested for their bulk densities (Gmb) using the AASHTO T166 procedure and then for their dynamic modulus in accordance with the AASHTO TP62-03 standard test method. Then the cores were broken down and tested for their maximum theoretical specific gravity (Gmm) using the AASHTO T-209 procedure. Finally an ignition test was performed to find the percentage of binder and to reclaim the aggregate for gradation analysis. Volumetric properties were then calculated and used as input for the Witczak dynamic modulus prediction equations to find what the MEPDG calls the undamaged master curve of the HMA layer. The FWD data, resilient modulus data, and pavement rating were used to find the damaged master curve of the HMA layer as suggested for input Levels 1, 2, and 3, respectively. It was found that the resilient modulus data needed for a Level 2 type of analysis do not represent the entire HMA layer thickness, and therefore it was recommended that this analysis should not be performed by VDOT when implementing the design guide. The use of Level 1 data is recommended because FWD testing appears to be the only procedure investigated that can measure the overall condition of the entire HMA layer.
Developing a Network-Level Structural Capacity Index for Structural Evaluation of Pavements
Bryce, James M.; Flintsch, Gerardo W.; Katicha, Samer W.; Diefenderfer, Brian K. (Virginia Center for Transportation Innovation and Research, 2013-03-01)
The objective of this project was to develop a structural index for use in network-level pavement evaluation to facilitate the inclusion of the pavement's structural condition in pavement management applications. The primary goal of network-level pavement management is to provide the best service to the users for the available, often limited, resources. Pavement condition can be described in terms of functional and structural condition. The current widespread practice of network-level pavement evaluation is to consider only the functional pavement condition. This practice results in suggested treatments that are often under-designed or over-designed when considered in more detail at the project level. The disagreement can be reduced by considering the structural capacity of the pavements as part of a network-level decision process. This study developed a flexible pavement structural index to use for network-level pavement applications. Available pavement condition data were used to conduct a sensitivity analysis of the index, and example applications were tested. The results indicated that including the structural index developed, named the Modified Structural Index (MSI), into the network-level decision process minimized the discrepancy between network-level predictions and project-level decisions when compared to the current network-level decision-making process. A pilot implementation of the MSI showed that it can be used to support various pavement management decision processes, such as network-level structural screening, deterioration modeling, and development of structural performance measures. The pilot test also indicated that the impact of the structural condition of the pavement on the performance of a maintenance treatment and its impact on life-cycle costs can be quantified.
Developing a Neural–Kalman Filtering Approach for Estimating Traffic Stream Density Using Probe Vehicle Data
Aljamal, Mohammad A.; Abdelghaffar, Hossam M.; Rakha, Hesham A. (MDPI, 2019-10-07)
This paper presents a novel model for estimating the number of vehicles along signalized approaches. The proposed estimation algorithm utilizes the adaptive Kalman filter (AKF) to produce reliable traffic vehicle count estimates, considering real-time estimates of the system noise characteristics. The AKF utilizes only real-time probe vehicle data. The AKF is demonstrated to outperform the traditional Kalman filter, reducing the prediction error by up to 29%. In addition, the paper introduces a novel approach that combines the AKF with a neural network (AKFNN) to enhance the vehicle count estimates, where the neural network is employed to estimate the probe vehicles’ market penetration rate. Results indicate that the accuracy of vehicle count estimates is significantly improved using the AKFNN approach (by up to 26%) over the AKF. Moreover, the paper investigates the sensitivity of the proposed AKF model to the initial conditions, such as the initial estimate of vehicle counts, initial mean estimate of the state system, and the initial covariance of the state estimate. The results demonstrate that the AKF is sensitive to the initial conditions. More accurate estimates could be achieved if the initial conditions are appropriately selected. In conclusion, the proposed AKF is more accurate than the traditional Kalman filter. Finally, the AKFNN approach is more accurate than the AKF and the traditional Kalman filter since the AKFNN uses more accurate values of the probe vehicle market penetration rate.
Development of a Framework for Evaluating Yellow Timing at Signalized Intersections
Rakha, Hesham A.; El-Shawarby, Ihab; Amer, Ahmed (Virginia Center for Transportation Innovation and Research, 2011-02-01)
Studies show that the proper design of clearance intervals has significant implications for intersection safety. For example, in 2001, approximately 218,000 red-light-running crashes occurred at signalized intersections in the United States. These crashes resulted in nearly 181,000 injuries and 880 fatalities and an economic loss of $14 billion. Driver behavior while the driver is approaching high-speed signalized intersections at the onset of a yellow indication varies as a function of many parameters. Some of these parameters are related to the driver's attributes, e.g., age, gender, perception-reaction time, and acceptable deceleration levels. Other parameters that relate to the intersection geometry include the approach speed, distance, and time to the intersection at the onset of the yellow indication. This study developed a novice approach for computing the clearance interval duration that explicitly accounts for the reliability of the design (probability that drivers are not caught in a dilemma zone). Lookup tables based on the limited data available from this study are provided to illustrate how the framework could be used in the design of yellow timings. The approach was developed using data gathered along Virginia's Smart Road test facility for dry and clear weather conditions for two approach speeds: 72.4 km/h (45 mph) and 88.5 km/h (55 mph). Each dataset includes a complete tracking of the vehicle every deci-second within 150 m (500 ft) before and after the intersection. A total of 3,454 stop-run records were gathered. These include 1,727 records (687 running records and 1,040 stopping records) for an approach speed of 45 mph and 1,727 records (625 running records and 1,102 stopping records) for an approach speed of 55 mph. Using these data, models that characterize driver perception-reaction times and deceleration levels were developed. The application of the proposed approach demonstrates that the current design procedures are consistent with a reliability level of 98%.
Environmental Impact of Freight Signal Priority with Connected Trucks
Park, Sangjun; Ahn, Kyoungho; Rakha, Hesham A. (MDPI, 2019-12-01)
Traffic signal priority is an operational technique employed for the smooth progression of a specific type of vehicle at signalized intersections. Transit signal priority is the most common type of traffic signal priority, and it has been researched extensively. Conversely, the impacts of freight signal priority (FSP) has not been widely investigated. Hence, this study aims to evaluate the energy and environmental impacts of FSP under connected vehicle environment by utilizing a simulation testbed developed for the multi-modal intelligent transportation signal system. The simulation platform consists of VISSIM microscopic traffic simulation software, a signal request messages distributor program, an RSE module, and an Econolite ASC/3 traffic controller emulator. The MOVES model was employed to estimate the vehicle fuel consumption and emissions. The simulation study revealed that the implementation of FSP significantly reduced the fuel consumption and emissions of connected trucks and general passenger cars; the network-wide fuel consumption was reduced by 11.8%, and the CO₂, HC, CO, and NO_X emissions by 11.8%, 28.3%, 24.8%, and 25.9%, respectively. However, the fuel consumption and emissions of the side-street vehicles increased substantially due to the reduced green signal times on the side streets, especially in the high truck composition scenario.
Estimation of Traffic Stream Density Using Connected Vehicle Data: Linear and Nonlinear Filtering Approaches
Aljamal, Mohammad A.; Abdelghaffar, Hossam M.; Rakha, Hesham A. (MDPI, 2020-07-22)
The paper presents a nonlinear filtering approach to estimate the traffic stream density on signalized approaches based solely on connected vehicle (CV) data. Specifically, a particle filter (PF) is developed to produce reliable traffic density estimates using CV travel-time measurements. Traffic flow continuity is used to derive the state equation, whereas the measurement equation is derived from the hydrodynamic traffic flow relationship. Subsequently, the PF filtering approach is compared to linear estimation approaches; namely, a Kalman filter (KF) and an adaptive KF (AKF). Simulated data are used to evaluate the performance of the three estimation techniques on a signalized approach experiencing oversaturated conditions. Results demonstrate that the three techniques produce accurate estimates—with the KF, surprisingly, being the most accurate of the three techniques. A sensitivity of the estimation techniques to various factors including the CV level of market penetration, the initial conditions, and the number of particles in the PF is also presented. As expected, the study demonstrates that the accuracy of the PF estimation increases as the number of particles increases. Furthermore, the accuracy of the density estimate increases as the level of CV market penetration increases. The results indicate that the KF is least sensitive to the initial vehicle count estimate, while the PF is most sensitive to the initial condition. In conclusion, the study demonstrates that a simple linear estimation approach is best suited for the proposed application.
Evaluation of the Cargill Safelane Surface Overlay
Sprinkel, Michael M.; Roosevelt, Daniel S.; Flintsch, Gerardo W.; de León Izeppi, Edgar; Mokarem, David W. (Virginia Center for Transportation Innovation and Research, 2009-02-01)
A recent development in polymer concrete overlays is the Cargill SafeLane surface overlay (SafeLane overlay). The 3/8-in-thick overlay is constructed with epoxy and broadcast aggregates, as are typical multiple-layer epoxy overlays that are used to provide a skid-resistant wearing surface for bridge decks that protects the decks again intrusion by chloride ions. Reportedly, the SafeLane overlay is unique in that Cargill indicates that the limestone aggregate used in the overlay can absorb and store liquid deicing chemicals that are applied to the surface of the roadway. The purpose of this research was to compare the SafeLane overlay and the Virginia Department of Transportation (VDOT) modified EP-5 epoxy concrete overlay (hereinafter called the VDOT modified EP-5 overlay) based on an evaluation of their construction, initial condition, and effectiveness in preventing frost, ice, and snow formation on the surface of the roadway. The comparison was limited to overlays placed on four bridges on I-81 in 2004 and 2005 (two SafeLane and two VDOT modified EP-5 overlays) and on four sections of continuously reinforced concrete pavement on the Virginia Smart Road in 2006. The evaluation with respect to the initial condition of the overlays on I-81 was based on a comparison of the as-constructed properties, including aggregate properties, bond strength, permeability, skid resistance, and chloride content. The evaluation with respect to the initial condition of the overlays on the Smart Road was limited to skid resistance. The evaluation of the overlays with respect to their effectiveness in preventing frost, ice, and snow formation was based on visual observations and skid measurements of overlay surfaces under typical interstate winter conditions at the I-81 sites and under artificial snow and ice conditions at the Smart Road. In addition, the effectiveness of the overlays at the Smart Road in preventing frost, ice, and snow formation was compared with that of a bare-tined concrete surface. The evaluation indicated that the SafeLane overlay can provide a skid-resistant wearing and protective surface for bridge decks. The study was not able to determine the performance of the overlay with respect to providing a surface with less accumulation of ice and snow. Further, there has not been sufficient time to evaluate chloride penetration into the decks overlaid with SafeLane overlays in Virginia.
Evaluation of Traffic Responsive Control on the Reston Parkway Arterial Network
Abbas, Montasir M.; Abdelaziz, Sherif (Virginia Center for Transportation Innovation and Research, 2009-02-01)
Traffic responsive plan selection (TRPS) control is considered an effective operational mode in traffic signal systems. Its efficiency stems from the fact that it can capture variations in traffic patterns and switch timing plans based on existing traffic conditions. Most of the research performed to date has focused on either small traffic networks-with up to five intersections-or theoretical networks. Past research has also focused on the threshold mechanism implemented in the National Electrical Manufacturers Association (NEMA) traffic controllers. There is very limited research on the pattern-matching mechanism implemented in the 170 controllers. This report documents a new approach to generating traffic scenarios for large networks, addressing issues such as the unequal traffic distribution and the large combination of traffic movements from multiple intersections. This approach is based on the selection of significant critical movements controlling the network using statistical correlation analysis of actual detector data and the use of synthetic origin-destination analysis of the entire network. The proposed approach was applied in the design of the traffic responsive control mode for the Reston Parkway arterial network, which has 14 intersections. Detector data were used to validate the results of the proposed approach. The validation process showed that the traffic system was correctly modeled and sufficiently represented by the proposed approach. Multi-objective optimization was used to generate the final timing plans and the TRPS pattern-matching parameters. Simulation analysis revealed that implementation of the traffic responsive control mode in the Reston Parkway network can achieve an average delay reduction of 27 percent and an average stops reduction of 14 percent on weekends and an average delay reduction of 18 percent and an average stops reduction of 21 percent on regular week days. The methodology documented in this report should be followed to implement TRPS control on large arterials in an optimal and stable manner. Optimal and stable operation of TRPS could significantly reduce congestion while capitalizing on existing traffic control infrastructure with a 46:1 benefit-cost ratio.
Feasibility Study for Using Piezoelectric-Based Weigh-In-Motion (WIM) System on Public Roadway
Xiong, Haocheng; Zhang, Yinning (MDPI, 2019-07-31)
Weigh-in-Motion system has been the primary selection of U.S. government agencies as the weighing enforcement for decades to protect the road pavement. In recent years, the number of trucks has increased by about 40% and in 2017, they travel 25% more annually than in 2016. The lack of the budget has slowed down the expansion of weighing enforcement to catch up with the growing workload of vehicle weighing. Unsupervised pavement section suffers more pavement damage and increased repairing cost. In this work, a piezoelectric material based WIM system (P-WIM) is developed. Such a system consists of several piezoelectric material disks that are capable of generating characteristic voltage output from passing vehicles. The axle loading of the vehicle can be determined by analyzing the voltage generated from the P-WIM. Compared to traditional WIM system, P-WIM requires nearly zero maintenance and costs 80% less on capital investment and less labor and effort to integrate. To evaluate the feasibility of this technology to serve as weighing enforcement on public roadways, prototype P-WIMs are fabricated and installed at a weigh station. The vehicle loading information provided by the weigh station is used to determine the force transmission percentage of the installed P-WIMs, which is an important parameter to determine the vehicles’ axle loading by generated voltage.
Field Investigation of High Performance Pavements in Virginia
Flintsch, Gerardo W.; Al-Qadi, Imad L.; Loulizi, Amara; Lahouar, Samer; McGhee, Kevin K.; Trenton Clark (Virginia Center for Transportation Innovation and Research, 2005-01-01)
This study evaluated 18 pavement sections located in high-traffic highways in Virginia to find a premium pavement design with a life span of 40 years or more using current and past field experience. The selected pavement sections were thought to perform well. Eight flexible pavements, six composite pavements, two continuously reinforced concrete pavements, and two jointed plain concrete pavements were investigated. Field testing consisted of (1) falling weight deflectometer (FWD) testing to assess the structural capacity of the different pavements and to backcalculate the pavement layer materials' moduli, (2) ground-penetrating radar (GPR) scanning to determine layer thicknesses and to locate any abnormalities inside the pavements, (3) digital imaging to determine condition indices, (4) longitudinal profile measurements to calculate International Roughness Index, and (5) coring and boring to perform material characterization of pavement layers. Hot mix asphalt tests included resilient modulus and creep compliance. Concrete was tested for compressive strength. The analysis of the collected data suggests that premium pavement designs can be obtained. The field investigations suggest that all the tested sites are performing satisfactorily and show very low structural distress. Limited material-related problems were found at some sites, which induced non-load related distresses. It was also confirmed that FWD, GPR, and digital imaging are very useful tools to assess the condition of existing pavements. Since the three categories of pavements (flexible, composite, and rigid) were found to perform well, the study recommends that evaluation of other pavement sections, which are thought to perform in a less than optimal state, be conducted to define the causes of the less than desired performance. The selection of the most appropriate premium pavement design should be based on a detailed life-cycle cost analysis; hence, such analysis should be performed. Mechanistic empirical modeling of the best performing section within each category would allow the prediction of future pavement performance for use in the life-cycle cost analysis.
Field Performance of High Friction Surfaces
de León Izeppi, Edgar; Flintsch, Gerardo W.; McGhee, Kevin K. (Virginia Center for Transportation Innovation and Research, 2010-06-01)
This report describes an evaluation of high friction surface (HFS) systems. The goal of this evaluation was to develop guidance for agencies when considering whether an HFS was an appropriate solution when addressing specific instances of low skid resistance and/or especially high friction demand. HFS systems are specially designed thin surface treatments that provide significant additional skid resistance of pavements and bridge decks without significantly affecting other qualities of the surface such as noise, ride quality, or durability. This report documents the location and climatic conditions where some of these systems are placed, recounts the experiences reported by the agencies that were responsible for their placement, and summarizes key HFS service-level indicators (friction and texture). The agency experiences include a sample benefit-cost analysis from an installation in Wisconsin that justified an HFS application through crash reductions that resulted following the measured increase in skid resistance. Analysis of the service-level indicators included development of the coefficients necessary to obtain the International Friction Index (IFI) values for each of the tested systems. Review of the IFI values suggested that more experiments with different types of wearing surfaces, to include HFS systems as well as more conventional surface treatments, are necessary in order to demonstrate the validity of the speed gradient and friction coefficients recommended by the ASTM standard for the IFI.
Flexible Pavements and Climate Change: A Comprehensive Review and Implications
Qiao, Yaning; Dawson, Andrew R.; Parry, Tony; Flintsch, Gerardo W.; Wang, Wenshun (MDPI, 2020-02-02)
Flexible pavements and climate are interactive. Pavements are climate sensitive infrastructure, where climate can impact their deterioration rate, subsequent maintenance, and life-cycle costs. Meanwhile, climate mitigation measures are urgently needed to reduce the environmental impacts of pavements and related transportation on the macroclimate and microclimate. Current pavement design and life cycle management practices may need to be modified to adapt to changing climates and to reduce environmental impacts. This paper reports an extensive literature search on qualitative and quantitative pavement research related to climate change in recent years. The topics cover climate stressors, sensitivity of pavement performance to climatic factors, impacts of climate change on pavement systems, and, most importantly, discussions of climate change adaptation, mitigation, and their interactions. This paper is useful for those who aim to understand or research the climate resilience of flexible pavements.
Full-Scale Laboratory Evaluation of Hybrid Composite Beams for Implementation in a Virginia Bridge
Moen, Cristopher D.; Roberts-Wollmann, Carin L.; Cousins, Thomas E. (Virginia Transportation Research Council, 2018-08)
This research project studied a steel-reinforced concrete and fiber-reinforced polymer (FRP) structural element called the Hybrid-Composite Beam (HCB). The beam was used in a skewed simple span superstructure replacement project over the Tides Mill Stream in Colonial Beach, Virginia. For typical HCB construction, each beam is transported to site as a lightweight FRP beam shell. Self-consolidating concrete is pumped into the shell interior arch form, and when the concrete hardens, it stiffens and strengthens the beam so that it can act as falsework to carry the weight of a cast-in-place concrete bridge deck. Unstressed prestressing strands are embedded in the FRP shell bottom flange during the resin placement, and these strands equilibrate thrust in the arch and stiffen the beam to meet service deflection criteria. After the deck is placed, the HCB system performs as a longitudinal flexural member, with the bridge deck resisting compression and prestressing strands and the FRP bottom flange resisting tension. The primary research goal was to document the HCB as a structural component and as a bridge system, with the outcome being validation of key assumptions that can be applied to future designs such as, for example, strain compatibility between the FRP shell and steel strands. The research was conducted in five phases. In Phase 1, the HCB flexural rigidity and through-depth strain distributions were quantified considering just the FRP shell with unstressed strands. These tests confirmed flexural rigidity estimated by hand calculations and strain compatibility under uniform loads. Phase 2 evaluated flexural behavior of the HCB FRP shell and poured concrete arch. Phase 3 testing was performed after three HCBs were made integral with cast-in-place concrete end diaphragms and a reinforced concrete bridge deck. Point loads, to simulate an HL-93 design truck as specified in American Association of State Highway and Transportation Officials (AASHTO) LFRD Bridge Design Specifications, were applied to the bridge deck to maximize shear, flexure, and torsion in the skewed bridge. Live load distribution between the three girders was approximately equal and the assumption of strain compatibility between the bridge deck, FRP shell, and steel strand was confirmed. Stresses in bottom flange FRP strands and the top of deck concrete were less than 30% of material limits under service level live loads. The concrete arch fell below the composite neutral axis, placing it in tension along the span. After the live load system tests, a more detailed investigation was performed in Phase 4 to explore transverse deck behavior. Transverse flexural demands were approximately 20% of the design capacity and standard truss bars, as specified by the Virginia Department of Transportation, are not necessary because of the small clear span of the slab between beams. In Phase 5, the bridge system was saw-cut longitudinally to separate it into three individual HCB composite beams. Two beams were load tested to failure at the Structures Laboratory at Virginia Tech. For one of the two beams tested at Virginia Tech, 14 out of a total 22 strands were cut at mid-span to simulate strand deterioration and for comparison the other beam remained undamaged prior to testing. The observed beam failure modes were mid-span concrete crushing for the undamaged beam and mid-span strand-FRP bond failure for the damaged beam. In support of Phase 5, a three-dimensional (3D) finite element model was developed to explore flexural and shear force distributions along the span, which led to a shear design procedure in which shear force is distributed based on the relative moments of inertia of the FRP shell and arch. Shear resistance is provided by the FRP shell webs and the concrete arch and fin.

Browse

Browsing Virginia Tech Transportation Institute (VTTI) by Department "Civil and Environmental Engineering"

Results Per Page

Sort Options