Technical Reports (VTTI)

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Review and evaluation of models that produce trip tables from ground counts
Sivanandan, R.; Narayanan, Arvind; Lei, Peng (Virginia Center for Transportation Innovation and Research, 1996-02)
This research effort was motivated by the desires of planning agencies to seek alternative methods of deriving current or base year Origin-Destination (O-D) trip tables without adopting conventional O-D surveys that are expensive, time consuming and labor intensive. This study had two objectives: (t) to conduct a review of existing approaches and models that produce trip tables from ground counts, and to select a few models for testing and evaluation, and (2) to perform a detailed testing of selected models based on application to both hypothetical and real networks, and to conduct performance evaluation and sensitivity analyses of these models. Two models, namely, The Highway Emulator (THE), and the Linear Programming (LP) model developed at Virginia Tech, were chosen for comprehensive testing and evaluation. For test purposes, these two models were applied to the following three case studies: (1) Sample Network, (2) Purdue University Network, and (3) Pulaski Town Network. While the first network was a hypothetical one, the other two were real networks. Different cases of targetable information and combinations of percentage available target cells and link volume information were used in the tests. These tests enabled a comprehensive evaluation of the performance and sensitivity analyses of the models. The test results were judged by two criteria: (1) the closeness of the model output tables to the "correct" or "surveyed" tables, and (2) the replication of observed link volumes by the models. The test results led to the following key conclusions: In general, the LP model results have proven to be superior, both in terms of closeness of modeled trip tables to the "correct"/"surveyed" tables, and in terms of replicating observed link volumes, for all the case studies, The exception to this is the structural target case, when THE produced better results, in terms of closeness of output tables to the "correct "l" surveyed" tables. This is based on the assumption that the "correct"/"surveyed" trip tables used for the case studies were in fact "correct"/"true". 2. THE model performed superior to the LP model for the structural target case (almost all the cases), where the target contains 1/0 cell values, 1 for those cells which represent O-D Interchanges that are feasible, and 0 for those that are not. This has practical implications in that if a region does not have a prior table available as target, then a structural target could be used.A word of caution must be noted with regard to conclusion # 2 above. While one would be tempted to use THE with a structural target for applications where a prior table is not available, it must be noted that the modeled results of both THE and LP turned out to be poor when compared with the "correct"/"surveyed" tables for all the cases, even though THE results were better than those of LP. However, these conclusions are based on tests on specific and limited number of networks, and under the assumption that the data used in testing and evaluation were accurate enough. The adoptability of these models and the use of one model versus the other must be decided based on the above facts, and in the context of error rates reported in this study, However, this study has highlighted the value of using such theoretical models for trip table estimation without performing conventional surveys.
A Method to Enhance the Performance of Synthetic Origin-Destination (O-D) Trip Table Estimation Models
Sivanandan, R.; Nanda, Dhruv (Virginia Center for Transportation Innovation and Research, 1998-01)
The conventional methods of determining origin-destination (O-D) trip tables involve elaborate surveys, e.g., home interviews, that require considerable time, staff, and funds. To overcome this drawback, a number of theoretical models that synthesize O-D trip tables from link volume data have been developed. The focus of the research reported here was on two of these models The Highway Emulator (THE) and the Linear Programming (LP) model. These models use target/seed tables for guiding the development of output trip tables. In earlier research conducted by the Virginia Tech Center for Transportation Research for the Virginia Transportation Research Council, it was determined that the performance of these models could potentially be enhanced by using a superior target/seed table. The research in this report uses readily available socioeconomic data and link volume information to develop a methodology for obtaining an enhanced target/seed table through application of the trip generation and trip distribution steps of the four-step planning process. The enhanced table was then used as the target/seed to THE and LP models, and their performance evaluated. In addition to measuring the closeness of the output tables to surveyed tables and their capability to replicate observed volumes, their improvements over the case when a structural table is used as target was also studied. Tests showed that the use of the enhanced target/seed table significantly improved the performance of the LP model. However, mixed trends were obtained for THE.
Improvement of Conspicuity of Trailblazing Signs: Phase III-Evaluation of Fluorescent Colors
Neale, Vicki L.; Anders, Richard L.; Schreiner, Christopher S.; Brich, Stephen C. (Virginia Center for Transportation Innovation and Research, 2001-02)
This report represents a Phase III effort to design and evaluate a new sign design for incident route trailblazing. The colors evaluated were fluorescent coral, fluorescent purple, fluorescent yellow-green, and non-fluorescent purple. The results indicate no significant differences in driving performance with regard to the four experimental sign color combinations. Regarding the subjective preference questionnaires, significant questionnaire results along with trend information suggest that black on fluorescent yellow green was the most preferred by younger and older drivers during both day and night visibility conditions. Nonetheless, this sign color has been assigned by FHWA for pedestrian, school, and bicycle crossings, which eliminated the opportunity to use fluorescent yellow-green as a unique sign color for trailblazing in incident management situations. Preference for non-fluorescent yellow on purple consistently increased at night when the sign became more luminant; however, the overall preference for this sign color combination was lower than for the other sign color combinations tested in this study. With the elimination of these two signs, the remaining contenders for a unique sign color combination were black on fluorescent coral and fluorescent yellow on fluorescent purple. Black on fluorescent coral was ranked significantly higher than fluorescent yellow on fluorescent purple for visibility and for overall preference. Questionnaire trend information suggests that black on fluorescent coral was more preferred than fluorescent yellow on fluorescent purple during daytime viewing conditions and less preferred than fluorescent yellow on fluorescent purple during nighttime viewing conditions. The overlay film used for the fluorescent coral sign was a first generation material that can reasonably be expected to result in improved nighttime luminance when produced in a full production run. In addition to the study results, drivers commented that the arrow on the sign was too small to determine directional information from a comfortable distance. Based on such driver comments, the research conclusions, and the federal regulations enacted since the outset of this series of experiments, the following recommendations are made: (1) black on fluorescent coral should be used as a unique incident management sign color, and (2) the directional arrow on the sign should be larger.
Reducing fog-related crashes on the Afton and Fancy Gap Mountain sections of I-64 and I-77 in Virginia
Lynn, Cheryl; Schreiner, Christopher S.; Campbell, Ross (Virginia Center for Transportation Innovation and Research, 2002-10)
The Fancy Gap and Afton Mountain interstates have a long history of fog-related, multivehicle crashes. Because of its earlier involvement in the installation and evaluation of the original Afton Mountain in-pavement fog guide light system, and concerns about continuing fog crash problems, the Virginia Transportation Research Council (VTRC) created an expert panel made up of decision makers from the Virginia Department of Transportation (VDOT) and the Virginia Department of State Police (VSP). Personnel from the Virginia Tech Transportation Institute and VTRC staffed the panel. After detailed crash analyses, a review of the literature on fog and its effects, and an extensive survey of fog mitigation systems in the United States and abroad, the panel issued the following recommendations: (1) Install variable message signs (VMSs) immediately prior to the most fog-prone areas to warn drivers of detected incidents, fog-related vehicle stops, or slowdowns ahead. Use highway advisory radio within the fog zone to communicate with drivers. (2) Install video cameras on the Afton and Fancy Gap fog areas to allow police and VDOT officials to confirm the presence of high-density fog areas and to allow the public to better plan their travel routes. Explore the use of ultra-low temperature, infrared video cameras to penetrate fog. (3) Increase police visibility in the fog areas to improve compliance with posted speed limits and advisory limits, including increased patrols and possible staff assignments to I-77 at Fancy Gap and I-64 at Afton. (4) Seek authorization for experimental use of advisory and regulatory variable speed limits on I-77 as part of the new Fancy Gap fog mitigation system. (5) Conduct research to improve the legibility and visibility of VMSs in fog. Also, study the effectiveness of static signs augmented with strobes and lasers to warn drivers of detected incidents and slowdowns in the fog zone. Because the panel represented multiple levels of VDOT and VSP and had extensive experience with the fog problems under consideration, a wide variety of solutions were offered for consideration, and each was judged from a variety of perspectives. The result was that only practical, applicable, and highly effective solutions were chosen for implementation. Because the group had representatives with extensive technical expertise in intelligent transportation systems (ITS) to advise them, they had confidence that their recommendations would be both workable and effective. It may be that this method of building consensus and support can be used as a model to promote deployment of ITS technologies to serve site-specific safety problems.
High-speed texture measurement of pavements
McGhee, Kevin K.; Flintsch, Gerardo W. (Virginia Center for Transportation Innovation and Research, 2003-02-01)
This study was conducted to validate high-speed texture measuring equipment for use in highway applications. The evaluation included two high-speed systems and a new static referencing device. Tests were conducted on 22 runway and taxiway test sections from the National Aeronautics and Space Administration's Wallops Flight Facility and 7 surfaces from Virginia's Smart Road. Texture estimates recorded with the high-speed (dynamic) equipment correlated extremely well with estimates made with static referencing methods. The system developed by International Cybernetics Corporation was very functional for most conventional highway surfaces. However, a better correlation may be achieved with the referencing methods by using a system (such as the MGPS surface system developed by the Federal Highway Administration) that produces the American Society for Testing and Materials' standard mean profile depth. Finally, an analysis conducted using the CTMeter (circular track meter, a laser-based but static system) demonstrated an important advantage of combining indices produced from high-definition surface profiles. By comparing the mean profile depth with the root mean square data for a particular surface, it is possible to characterize more fully the shapes that contribute to a pavement's macrotexture.
Using high-speed texture measurements to improve the uniformity of hot-mix asphalt
McGhee, Kevin K.; Flintsch, Gerardo W.; de León Izeppi, Edgar (Virginia Center for Transportation Innovation and Research, 2003-05-01)
This study introduces Virginia's efforts to apply high-speed texture measurement as a tool to improve the uniformity of hot-mix asphalt (HMA) pavements. Three approaches for detecting and quantifying HMA segregation through measuring pavement surface macrotexture were evaluated: (1) applying the methods proposed in NCHRP Report 441, which build on the ability to predict the expected "non-segregated" macrotexture; (2) using acceptance bands for texture similar to those used for HMA density; and (3) considering the standard deviation of the macrotexture as a measure of construction uniformity. Based on the findings from a series of field tests, the researchers concluded that macrotexture measurement holds great promise as a tool to detect and quantify segregation for quality assurance purposes. None of the available equations for predicting non-segregated macrotexture (the approach in NCHRP Report 441) was found to work for all the construction projects evaluated. Additional information is necessary to establish target macrotexture levels. The acceptance bands approach produced reasonable results in most of the field-verification experiments, but it was significantly influenced by the actual variability within the section. An approach that used target levels of standard deviations was selected for further testing and implementation on a pilot basis.
Modernizing bridge safety inspection with process improvement and digital assistance
Mills, Thomas H.; Wakefield, Ronald R. (Virginia Center for Transportation Innovation and Research, 2004-01)
This research effort was developed to record and analyze the Virginia Department of Transportation (VDOT) bridge/structure inspection processes as an aid to modernizing and automating these inspection processes through the use of mobile personal computer (PC) devices such as Palm/PPCs and other wearable computing devices. The research was conducted using an informal conversational interview process coupled with direct observations to match the perceived processes with actual processes. Once the interviews and observations were completed, workflows were mapped and analyzed for operational bottlenecks and process improvement opportunities. The results of the mappings and a comprehensive literature review were used to analyze the existing work processes. New process transformation maps were created and overlaid on current mappings to complete a transformation model. Redundancies were observed in the reporting function, and bottlenecks were identified within the inspection management and inspection functions. The research also indicates that the inspection process is readily transformable from one that relies on marking up paper reports in the field and then returning to the office for semi-manual reporting to one that is electronically assisted in areas of data capture, automated bridge inventory updates, and semi-automated report production. From this analysis a series of strategies and recommendations were made to assist VDOT in modernizing and transforming their current bridge inspection processes to more efficient digitally assisted processes.
Wet night visibility of pavement markings :executive summary
Gibbons, Ronald B.; Hankey, Jonathan M.; Pashaj, Irena (Virginia Center for Transportation Innovation and Research, 2004-10)
This executive summary describes an investigation into the performance of pavement markings in wet night conditions. The performance of a typical pavement marking will degrade when it gets wet. This is a result of the flooding of the marking optics, thereby reducing retroreflectivity. Several technologies are available to improve wet marking performance. In this project, six technologies were tested using both standard measurement methods and participant evaluations. The results show that two of the marking technologies, raised retroreflective markers and wet retroreflective tape, outperformed the group under all conditions. These markings were also highly accepted by the participants. The results also show that the standard paint and glass beads technology is the worst performing and the least desirable of those evaluated. A comparison of the ASTM retroreflectivity measurement methods and the measured luminance results also indicates that the methods are suitable for the conditions used in the evaluation; however, possible additions and corrections to the methods are outlined in this report. A follow-up study is underway to allow development of a performance-based specification for pavement markings for wet night visibility.
Wet Night Visibility of Pavement Markings
Gibbons, Ronald B.; Hankey, Jonathan M.; Pashaj, Irena (Virginia Center for Transportation Innovation and Research, 2004-10)
This report describes an investigation into the performance of pavement markings in wet night conditions. The performance of a typical pavement marking will degrade when it gets wet. This is a result of the flooding of the marking optics, thereby reducing retroreflectivity. Several technologies are available to improve wet marking performance. In this project, six technologies were tested using both standard measurement methods and participant evaluations. The results show that two of the marking technologies, raised retroreflective markers and wet retroreflective tape, outperformed the group under all conditions. These markings were also highly accepted by the participants. The results also show that the standard paint and glass beads technology is the worst performing and the least desirable of those evaluated. A comparison of the ASTM retroreflectivity measurement methods and the measured luminance results also indicates that the methods are suitable for the conditions used in the evaluation; however, possible additions and corrections to the methods are outlined in this report. A follow-up study is underway to allow development of a performance-based specification for pavement markings for wet night visibility.
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.
Ground-Penetrating Radar Calibration at the Virginia Smart Road and Signal Analysis to Improve Prediction of Flexible Pavement Layer Thicknesses
Al-Qadi, Imad L.; Lahouar, Samer; Loulizi, Amara (Virginia Center for Transportation Innovation and Research, 2005-01-01)
A ground-penetrating radar (GPR) system was used to collect data over the different pavement sections of the Virginia Smart Road from June 1999 until December 2002. Three antennae at different frequencies were used for this research. The collected data were successfully used to evaluate the physical GPR detection limitations, to evaluate the GPR accuracy for pavement layer thickness determination, to control the installation of three different types of reinforcing meshes installed within the pavement, and to estimate the in-situ complex dielectric constant of several types of hot-mix asphalt (HMA). The data analysis results were verified by the well-documented structure and composition of each section of the road, in addition to the embedment of 35 copper plates (perfect electromagnetic reflectors) at the different layer interfaces during construction of the pavement. It was found that GPR is a feasible nondestructive tool to estimate the layer thicknesses of bound and unbound aggregate layers, HMA layers, and concrete slabs. However, interface detection can be altered if the layers have comparable dielectric constants. A technique was developed to estimate the frequency-dependent in-situ complex dielectric constant of HMA materials. Results have shown that the effect of the variations of the dielectric properties within the GPR bandwidth is insignificant vis-a-vis the accuracy of thickness estimation. The use of GPR as a quality control tool to verify the success of steel reinforcing mesh installation was also found to be feasible. Given the success of using GPR for the aforementioned applications in the Virginia Smart Road, it is recommended that the Virginia Department of Transportation use GPR more frequently as a quality control tool during new pavement construction projects and as an assessment tool prior to project rehabilitation and as part of Virginia's pavement management system.
Laboratory Tests for Hot-Mix Asphalt Characterization in Virginia
Flintsch, Gerardo W.; Al-Qadi, Imad L.; Loulizi, Amara; Mokarem, David W. (Virginia Center for Transportation Innovation and Research, 2005-06-01)
This project reviewed existing laboratory methods for accurately describing the constitutive behavior of the mixes used in the Commonwealth of Virginia. Indirect tensile (IDT) strength, resilient modulus, static creep in the IDT and uniaxial modes, flexural beam fatigue, and dynamic modulus tests were conducted on two typical mixes used in Virginia: SM-9.5A (surface mix) and BM-25.0 (base mix). The tests conducted produced a wealth of data on typical values for the properties of the two mixes studied over a wide range of temperatures and loading frequencies. The results suggest that the IDT strength test is an effective test to characterize the tensile strength of hot-mix asphalt (HMA), especially for thermal cracking evaluation. The resilient modulus test and the static creep test in the IDT setup are practical and simple to perform, but the analysis of the measurements is complicated, and the variability of the results is high. The compressive uniaxial dynamic modulus and the uniaxial static creep tests were found to be simple to conduct and to analyze because of the homogeneous state of stress in the specimen during testing. The flexural fatigue test was time consuming, but the test produces valuable information about the fatigue properties of hot-mix asphalt. The investigation also found good correlations among the IDT strength, resilient modulus, and dynamic modulus results. A variety of tests is recommended for characterizing the mechanistic-empirical pavement analysis and design. These tests would provide the properties needed to characterize the asphalt layers for the pavement analysis and design. The recommended tests are as follows: IDT strength for characterizing HMA susceptibility to thermal cracking, dynamic modulus for characterization of the constitutive behavior of the HMA, uniaxial creep for characterizing permanent deformation characteristics, and flexural fatigue tests to characterize fatigue properties. Materials characterization testing can be a valuable tool in pavement design. The use of mechanistic-empirical modeling can be used to predict the performance of a pavement. With this type of testing and modeling, the materials used in pavements will be of better quality and more resistant to environmental and structural deterioration. A more durable pavement will aid in reducing the frequency and costs associated with maintenance.
Fatigue Life Characterization of Superpave Mixtures at the Virginia Smart Road
Al-Qadi, Imad L.; Diefenderfer, Stacey D.; Loulizi, Amara (Virginia Center for Transportation Innovation and Research, 2005-08)
Laboratory fatigue testing was performed on six Superpave HMA mixtures in use at the Virginia Smart Road. Evaluation of the applied strain and resulting fatigue life was performed to fit regressions to predict the fatigue performance of each mixture. Differences in fatigue performance due to field and laboratory production and compaction methods were investigated. Also, in-situ mixtures were compared to mixtures produced accurately from the job mix formula to determine if changes occurring between the laboratory and batch plant significantly affected fatigue life. Results from the fatigue evaluation allowed verification of several hypotheses related to mixture production and compaction and fatigue performance. It was determined that location within the pavement surface, such as inner or outer wheelpath or center-of-lane, did not significantly affect laboratory fatigue test results, although the location will have significant effects on in-situ fatigue life. Also the orientation of samples cut from an in-situ pavement (parallel or perpendicular to the direction of traffic) had only a minor effect on the laboratory fatigue life, because the variability inherent in the pavement due to material variability is greater than the variability induced by compaction. Fatigue life of laboratory-compacted samples was found to be greater than fatigue life of field-compacted samples; additionally, the variability of the laboratory compacted mixture was found to be less than that of the field-compacted samples. However, it was also found that batch-plant production significantly reduces specimen variability as compared to small-batch laboratory production when the same laboratory compaction is used on both specimen sets. Finally, for Smart Road mixtures produced according to the job mix formula, the use of polymer-modified binder or stone matrix asphalt was shown to increase the expected fatigue life. However, results for all mixes indicated that fatigue resistance rankings might change depending on the applied strain level. This study contributes to the understanding of the factors involved in fatigue performance of asphalt mixtures. Considering that approximately 95% of Virginia's interstate and primary roadways incorporate asphalt surface mixtures, and that fatigue is a leading cause of deterioration, gains in the understanding of fatigue processes and prevention have great potential payoff by improving both the mixture and pavement design practices.
Transit Signal Priority Project Phase II Field and Simulation Evaluation Results
Rakha, Hesham A.; Ahn, Kyoungho (Virginia Center for Transportation Innovation and Research, 2006-03-01)
Transit Signal Priority (TSP) is recognized as an emerging technology that is capable of enhancing traditional transit services. Basic green-extension TSP was implemented on U.S. Route 1 in the Northern Virginia Area (or Washington, DC metropolitan area). This study quantifies the impact of TSP technology on transit-vehicle performance using field-collected Global Positioning System (GPS) data and evaluates the system-wide benefits of TSP operations using computer simulations to expand on the field evaluation study. The field study demonstrated that overall travel-time improvements in the order of 3% to 6% were observed for TSP-operated buses. However, the results also demonstrated that green-extension TSP can increase transit-vehicle travel times by approximately 2.5% during congested morning peak periods. In addition, the study demonstrated that TSP strategies reduce transit-vehicle intersection delay by as much as 23%. The field study demonstrated that the benefits associated with TSP were highly dependent on the roadway level of congestion and were maximized under moderate to low levels of congestion. However, the simulation results indicated that TSP did not result in statistically significant changes in auto or system-wide travel times (differences less than 1%). Furthermore, a paired t-test concluded that basic green-extension TSP did not increase side-street queue lengths. An increase in the traffic demand along Route 1 resulted in increased system-wide detriments; however, these detriments were minimal (less than 1.37%). The study demonstrated that an increase in side-street demand did not result in any statistically significant system-wide detriments. Increasing the frequency of transit vehicles resulted in additional benefits to transit vehicles (savings in transit vehicle travel times by up to 3.42%), but no system-wide benefits were observed. Finally, TSP operations at near-side bus stops (within the detection zone) resulted in increased delays in the range of 2.85%, while TSP operations at mid-block and far-side bus stops resulted in network-wide savings in delay in the range of 1.62%. Consequently, we recommend not implementing TSP in the vicinity of near-side stops that are located within the TSP detection zone. The simulation results indicated that a TSP system generally benefits transit vehicles, but does not guarantee system-wide benefits. In this study, a maximum transit vehicle travel-time savings of 3% to 6% was observed with the provision of green-extension TSP from both the field and simulation evaluation studies. However, the green-extension TSP operation did not benefit nor damage the non-transit vehicles in most cases. Also, it should be noted that the results of the study may be specific to Route 1 corridor because of the unique characteristics of the study corridor, the specific traffic demand, and TSP logic implemented. Finally, the study recommends the calibration of current TSP settings to improve the effectiveness of TSP operation. Also, different transit priority strategies or a combination of other TSP strategies should be investigated to increase the benefits of TSP operations. A conditional TSP system that only provides priority to transit vehicles behind schedule and an intelligent transit monitoring system are also recommended to improve the TSP system on the Route 1 corridor.
Intersection Decision Support: Evaluation of a Violation Warning System to Mitigate Straight Crossing Path Collisions
Neale, Vicki L.; Perez, Miguel A.; Doerzaph, Zachary R.; Lee, Suzanne E.; Stone, Scott R.; Dingus, Thomas A. (Virginia Center for Transportation Innovation and Research, 2006-04)
This project entailed the design, development, testing, and evaluation of intersection decision support (IDS) systems to address straight crossing path (SCP) intersection crashes. This type of intersection crash is responsible for more than 100,000 crashes and thousands of fatalities each year. In developing these IDS systems for both signalized and stop-controlled intersections, a top-down systems approach was used that determined the necessary system functions and evaluated the capability of different technologies to perform those functions. Human factors tests were also conducted that evaluated the effectiveness of warning algorithms and infrastructure-based driver-infrastructure interfaces in eliciting a stopping response from drivers about to be involved in an SCP intersection crash. Results indicated that further technological development is needed for the sensing and intersection state IDS functions. Furthermore, infrastructure-based warning interfaces tested were greatly outperformed by previously-tested in-vehicle warnings. Thus, future research on IDS systems should focus on their infrastructure-cooperative configuration, where the system supports an in-vehicle warning.
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.
Pavement Marking Visibility Requirements During Wet Night Conditions
Gibbons, Ronald B. (Virginia Center for Transportation Innovation and Research, 2006-11)
This study investigated the performance of pavement markings in wet night conditions. Typically, performance will decrease in wet conditions. The degradation is a result of flooding of the marking optics and a change in the optical media, thereby reducing retroreflectivity and the visibility distance. Several technologies are available to improve the visibility of markings under wet conditions. This study used four technologies and evaluated them in a dynamic situation. In the experiment, vehicles were driven by older participants and visibility was measured based on the detection distances of the beginning or ending of a continuous edge marking. The results indicate that a specifically designed wet retroreflective tape performed better than the currently used paint and glass bead technology. Paint with large glass beads and profiled thermoplastics also showed an improvement over the standard paint and glass bead technology. A relationship between retroreflectivity and the detection distance was found, which was used to postulate a minimum required value for visibility during wet night conditions. A value of 200 mcd/m2/lx appears to provide a reasonable detection distance for a minimum performance requirement.
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.
Live Stop-Controlled Intersection Data Collection
Doerzaph, Zachary R.; Neale, Vicki L.; Bowman, Jodi; Wiegand, Kendra (Virginia Center for Transportation Innovation and Research, 2007-12)
This report describes an experimental investigation performed at live intersections to gather infrastructure-based naturalistic driver approach behavior data. This data was collected and analyzed with the goal of understanding how drivers approach intersections under various speeds and environmental conditions. Six stop-controlled intersection approaches across five intersections in the New River Valley, Virginia area were selected for data collection. The sites were selected based on the intersection characteristics and crash statistics. Data was collected from each site for at least two months resulting in over sixteen total months of data. A data acquisition system was devised and implemented to obtain the first intersection data set with fidelity sufficient for developing intersection collision avoidance threat assessment algorithms. An explorative analysis of driver stopping behavior and vehicle trajectories was also performed. Results indicate that an intersection collision system for stop-controlled intersections is feasible. Avenues for future research and potential uses of this new database are highlighted.
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.

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