Kweon Y.-J.,Virginia Transportation Research Council |
Lee J.,University of Virginia
Accident Analysis and Prevention | Year: 2010
Beneficial effects of bicycle helmet use have been reported mostly based on medical or survey data collected from hospitals. This study was to examine the validity of the United States General Estimates System (GES) database familiar to many transportation professionals for a beneficial effect of helmet use in reducing the severity of injury to bicyclists and found potential risk of erroneous conclusions that can be drawn by a narrowly focused study when the GES database is used. Although the focus of the study was on bicycle helmet use, its findings regarding potential risk might be true for any type of traffic safety study using the GES data. A partial proportional odds model reflecting intrinsic ordering of injury severity was mainly used. About 16,000 bicycle-involved traffic crash records occurring in 2003 through 2008 in the United States were extracted from the GES database. Using the 2003-2008 GES data, a beneficial effect of helmet use was found in 2007, yet a detrimental effect in 2004 and no effect in 2003, 2005, 2006, and 2008, which are contrary to the past findings from medical or hospital survey data. It was speculated that these mixed results might be attributable to a possible lack of representation of the GES data for bicycle-involved traffic crashes, which may be supported by the findings, such as the average helmet use rates at the time of the crashes varying from 12% in 2004 to 38% in 2008. This suggests that the GES data may not be a reliable source for studying narrowly focused issues such as the effect of helmet use. A considerable fluctuation over years in basic statistical values (e.g., average) of variables of interest (e.g., helmet use) may be an indication of a possible lack of representation of the GES data. In such a case, caution should be exercised in interpreting and generalizing analysis results.
Fudala N.J.,University of Virginia |
Fontaine M.D.,Virginia Transportation Research Council
Transportation Research Record | Year: 2010
Variable speed limits (VSLs) have been shown to improve safety and operations on European freeways, but work zone applications of VSLs have been limited. In July 2008, a VSL system was installed on a congested portion of the Washington, D.C., Beltway (I-95-I-495) in a major work zone. A limited field evaluation of that system revealed some deficiencies related to the system's configuration, resulting in inconclusive operational effects. Those results raised questions about the relative importance of different VSL system parameters on the ultimate effectiveness of work zone VSLs. This paper describes an evaluation that used a calibrated simulation model to evaluate the influence of several parameters. The results showed that VSLs can delay the onset of congestion and help produce more rapid recovery from congestion, provided that demand volumes are not too far above the work zone capacity. When demand volumes are extremely high, VSLs offer no appreciable benefit over static speed limits. The simulation also showed that VSL sign location is extremely important, and signs must be positioned so that drivers will accelerate back to a reasonable speed once they pass through a bottleneck. Algorithm design also proved to play an important role in system effectiveness.
Edara P.,University of Missouri |
Sharma S.,University of Missouri |
McGhee C.,Virginia Transportation Research Council
Natural Hazards Review | Year: 2010
This paper focuses on traffic modeling of large-scale hurricane evacuation networks. Several research efforts to date have addressed the evacuation problem from a local perspective. The largest network found in the open literature on microscopic simulation of evacuation operations was of an area 45 miles long and 15 miles wide. The current study models 10 cities with a total length of approximately 2,000 miles of roadway including freeways, arterials, and local streets in two regions in Virginia-the Hampton Roads region and the city of Richmond. This research accomplished the following objectives: (1) estimate the traffic performance of evacuation routes and other major arterial streets; (2) locate the major bottlenecks, congestion, or other operational difficulties in the network; (3) estimate the total network evacuation time; and 4) recommend amendments to the traffic control plan to improve the traffic performance. The simulation results led to the following conclusions: (1) for a category 4 storm with high hotel occupancy, almost all vehicles (99%) were able to exit the network by the end of 27 h; (2) traffic demand on I-64 exceeded capacity for the section between I-64/Fort Eustis Blvd. and I-64/I-295 interchanges, significantly reducing the speed of evacuating vehicles; (3) the reversed lanes can carry more vehicles than their current assigned demand; and (4) for a category 3 storm, the throughput values for different evacuation routes are nearly the same with or without lane reversal. The modeling lessons learned from this research are also documented in the paper. For the network model development, geographic information system maps and a text processing scripting language (e.g., PERL) are shown to be useful tools. Parallel processing is recommended, especially for conducting statistical analysis of output data, given the enormously high run times (25-30 h in the current research) for the detailed simulations. The limitations of microscopic simulation in handling large-scale networks are identified and remedies are suggested. © 2010 ASCE.
Apeagyei A.K.,Virginia Transportation Research Council
Journal of Materials in Civil Engineering | Year: 2011
This study was conducted to investigate rutting resistance of asphalt concrete (AC) mixtures as a function of dynamic modulus and gradation. The flow number (FN) test, the recommended procedure (NCHRP 9-19) for evaluating rutting resistance of AC mixtures, was used to simulate rutting in the laboratory. The FN test involves applying a repeated creep load to AC specimens for 10,000 cycles or until an accumulated strain of 5%. FN tests were conducted at 54.4°C and accumulated strain was monitored for each load cycle. The results were used to determine the onset of tertiary flow (or FN) for 16 AC mixtures (eight surface mixes, five base mixes, and three stone matrix asphalt) produced in Virginia. First-order multiple regression models were developed to describe the relationship among FN, dynamic modulus, and gradation. The results showed FN was strongly correlated to dynamic modulus values at 38°C, and gradation (percent passing various sieve sizes) for the 16 AC mixtures. By using previously published data, the veracity of the relationship of FN as a function of dynamic modulus and gradation was verified for 12 mixtures. The results suggest dynamic modulus and gradation could be considered as potential rutting specification parameters for QC/QA purposes in the field. The results may also be useful for optimizing the laboratory mix design process. © 2011 American Society of Civil Engineers.
Apeagyei A.K.,Virginia Transportation Research Council
Construction and Building Materials | Year: 2011
A laboratory study was carried to investigate whether certain antioxidants could be used to reduce age-hardening in asphalt binders. Several additives including: Vitamin E, Irganox 1010, Irgafos P-EPQ, carbon black, hydrated lime, and DLTDP/furfural, were evaluated. The modified asphalt binders were subjected to two accelerated oxidative aging regimes in the laboratory. Short-term oxidative aging of the binders was simulated using a rolling thin film oven while long-term aging was performed using a pressure aging vessel. The effects of aging on the binders were evaluated based on changes in rheological properties of asphalt binders undergoing oxidative aging. Binders modified with a combination of furfural and DLTDP was found to posses the lowest aging index. The antioxidant-treated binders exhibited improved performance at both high and low pavement temperatures. © 2010 Elsevier Ltd. All rights reserved.
Ozyildirim C.,Virginia Transportation Research Council
Transportation Research Record | Year: 2010
A study described the development of the Virginia Department of Transportation's (VDOT) end-result specifications (ERSs) for hydraulic cement concrete. The work had two phases. In Phase 1, a special provision was developed and applied to two pilot projects. In Phase 2, the special provision was applied to more pilot projects from districts across Virginia. Pay adjustments were not applied for the pilot projects; VDOT's current specifications were applied for acceptance and rejection. The ERSs have three parts. The first part introduces process control measures. The contractor is responsible for the concrete design and is required to provide a quality control plan. The plan addresses all elements that affect quality, including mixture designs, aggregate sources, ingredients, tests and testing frequency, fresh and hardened concrete properties, and control charts. The second part covers the mixture design approval by VDOT. The third part covers project acceptance, which includes pay adjustments depending on test results. The pilot projects are continuing. However, some of the features of the ERS are already included in the supplemental specifications, such as using combined cementitious material and using curing boxes with continuously recording thermometers. Or they are permitted if requested by the contractor and approved by the project engineer, such as using combined aggregates, mixing gravel and crushed stone, combining retarding admixtures and water-reducing admixtures, and exceeding the 300 revolution limit or the time limit of 1.5 h from the addition of water.
Apeagyei A.K.,Virginia Transportation Research Council
Proceedings of the Institution of Civil Engineers: Transport | Year: 2011
The correlation between dynamic modulus of asphalt concrete and rutting was investigated in the laboratory. Five asphalt concrete mixtures of different stiffnesses produced according to Virginia specifications were tested using dynamic modulus and flow number tests. The dynamic modulus (E*) tests were conducted at a single temperature. (38°C) and six loading frequencies (25, 10, 5, 1, 0 5, 0.1 Hz) and flow number (FN) tests, designed to evaluate rutting, were conducted at a temperature of 54°C. An asphalt mixture performance tester was used to perform both the dynamic modulus and flow number tests. The results were used to develop correlations between E* and FN at each of the testing frequencies used. Very good correlation (R2= 94) was found between E* at 0.1 Hz loading frequency and FN at 54°C. Additionally, the correlation between FN and the slope of the graph of E* plotted against frequency. was also found to be equally good (R2 = 95). The results suggest rutting susceptibility could be evaluated using E* testing performed at 38°C. The results of this study may be useful to agencies with field or district laboratories looking for an epigrammatic test to valuate rutting susceptibility during mix designs and field quality control and quality assurance (QC/QA).
Kweon Y.-J.,Virginia Transportation Research Council
Journal of Advanced Transportation | Year: 2012
This study was to evaluate traffic safety of four-legged signalized intersections and to develop a spreadsheet tool for identifying high-risk intersections taking into consideration vehicle movements, left-turn signal phase types, and times of day. The study used data from Virginia and employed count data models and the empirical Bayes (EB) method for safety evaluation of such intersections. It was found that crash pattern defined by vehicle movements involved in a crash and time of day are important factors for intersection crash analysis. Especially for a safety performance function (SPF), a model specification (Poisson or NB), inclusion of left-turn signal types, type of traffic flow variables, variable functional forms, and/or magnitudes of coefficients turned out to be different across times of day and crash patterns. The spreadsheet application tool was developed incorporating the developed SPFs and the EB method. As long as Synchro files for signal plans and crash database are maintained, no additional field data collection efforts are required. Adjusting the developed SPFs and the spreadsheet for recent traffic and safety conditions can be done by applying the calibration methods employed in the SafetyAnalyst software and the Highway Safety Manual. Implementing the developed tool equipped with streamlining data entry would greatly improve accuracy and efficiency of safety evaluation of four-legged signalized intersections in localities and highway agencies that cannot operate the Safety-Analyst. © 2010 John Wiley & Sons, Ltd.
Dougald L.E.,Virginia Transportation Research Council
Transportation Research Record | Year: 2016
On April 8, 2013, the Virginia Department of Transportation installed a rectangular rapid-flashing beacon (RRFB) system at Belmont Ridge Road in Loudoun County, Virginia; two units at the Washington and Old Dominion Trail crossing were included in addition to advance warning units for the northbound and southbound travel directions. The purpose of the present study was to evaluate the utility, effectiveness, and safety of the RRFB system during a 1-year period. Of particular interest were (a) the percentage of trail users who pressed the push button to activate the RRFBs and whether that action varied by mode (pedestrians versus bicyclists), (b) motorist behavior when the RRFB system was activated and not activated, and (c) trail user impressions of the system relating to perceptions of safety. The results of the study indicated that the RRFB systems had a positive effect on motorist awareness. This finding was evidenced by the increased yield rates when the system was activated rather than not activated, speed reductions when the system was activated, and trail user perspectives on increased opportunities to cross and increased safety at the crossing location. In addition, the RRFB system was perceived by trail users as an enhancement to safety at the Belmont Ridge Road crossing, trail user perceptions of RRFB system benefits grew over time, and there was a correlation between trail user activations and the presence of traffic.
Diefenderfer S.D.,Virginia Transportation Research Council
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2011
The Virginia Department of Transportation (VDOT) is expecting to transition to using the methodology described in the Guide for the MechanisticEmpirical Design of New & Rehabilitated Pavement Structures (MEPDG) in the near future, and decisions must be made regarding the hierarchical level of desired asphalt material inputs and the extent to which asphalt mixture characterization must be performed. Thus a study was undertaken to investigate the effects of these variables using input values measured from 11 typical plant mixtures (i.e., three surface, four intermediate, and four base mixtures). The predicted fatigue and rutting distresses were used to evaluate the response of the MEPDG to differences in the mixture properties and to assess the future needs for implementation. Two example pavement sections were modeled: a primary and an interstate roadway section. Pavement distress data were compiled for an interstate and primary route corresponding to the modeled sections and were compared to the MEPDG-predicted distresses. Predicted distress quantities for fatigue cracking and rutting were compared to the calculated distress model predictive errors to determine if the material property input levels were statistically different. There were differences between all rutting and fatigue predictions using level 1, 2, and 3 asphalt material inputs, but they were not statistically significant. Various combinations of level 3 inputs showed expected trends in rutting predictions when increased binder grades were used, but the differences were not statistically significant when the calibration model error was considered. Fatigue distress predictions were approximately comparable to the pavement distress data, but the model predictive errors were greater than the distress predictions. Although this study was limited, it indicated several steps VDOT should take prior to implementing the MEPDG. Additional work to identify the source of predictive insensitivity to changes in both asphalt mixture properties and the level of input values is necessary. The comparisons of predicted fatigue and rutting distresses to pavement distress data for the primary and interstate pavement indicate the need to consider local calibration and verification of the predictive models.