bluuebunny/crossref_metadata_2025 huggingface dataset:
Transitioning from Texas Gyratory Compactor to Superpave Gyratory Compactor
Authors: Button Joe W. , Chowdhury Arif , Bhasin Amit
Published: May 2018

The Strategic Highway Research Program expended great effort in developing the Superpave® gyratory compactor (SGC) as a modern, technologically advanced tool for the design of hot-mix asphalt (HMA) paving mixtures and for preparation of realistic test specimens for laboratory evaluation. Since the widely accepted SGC was designed to produce specimens similar to actual pavement layers and since the current series of Texas Department of Transportation (TxDOT) HMA paving mixtures have demonstrated acceptable performance, TxDOT wished to replace the Texas gyratory compactor (TGC) with the SGC for the design of its current repertoire of dense-graded mixtures. In the first phase of this study, the authors developed a specification for the number of design gyrations with the SGC to achieve the same optimum asphalt content (OAC) as that obtained with the TGC. However, on the basis of past experience, review of the literature, and feedback from TxDOT, the design OAC was considered to be too low; mixtures that may be susceptible to fatigue cracking resulted. To mitigate this problem, the authors revised the specification for use of the SGC so that the resulting mixtures had an increased OAC. This revision was done by comparing the rutting resistance of HMA mixtures designed at different numbers of gyrations with the Hamburg wheel-tracking device and then selecting the lowest number of gyrations that did not compromise rutting resistance of the mixture. Results show that it is possible to select a considerably lower number of design gyrations with the SGC without a significant decrease in rutting performance of the mixtures.
Uniaxial Penetration Testing for Shear Resistance of Hot-Mix Asphalt Mixtures
Authors: Chen Xingwei , Huang Baoshan , Xu Zhihong
Published: May 2018

A laboratory study evaluated the uniaxial penetration test for its suitability to characterize the shear resistance of hot-mix asphalt mixtures at elevated temperatures. Four types of mixtures with three different binders and three different coarse aggregates were tested by the uniaxial penetration test at 40°C, 50°C, 60°C, and 70°C. In addition, triaxial compression tests were conducted for selected mixtures to compare the uniaxial shear resistance with the shear strength. The results of the current investigation indicated that the uniaxial penetration test was able to provide consistent results for the mixtures selected. Further studies were recommended for the uniaxial penetration test to be incorporated into mixture design as a simple performance test.
Evaluation of Testing Protocols for Dynamic Modulus of Hot-Mix Asphalt
Authors: Tran Nam H. , Hall Kevin D.
Published: May 2018

The dynamic modulus (| E*|) of hot-mix asphalt (HMA) is one of the fundamental inputs in the mechanistic–empirical (M-E) pavement design guide developed in NCHRP Project 1–37A. The M-E design guide provides three levels for | E*| input, which are related nominally to the reliability of pavement performance estimates generated by the guide. Level 1 | E*| inputs require laboratory-measured | E*|-values, and Level 2 and 3 | E*| inputs are estimated by using a predictive equation. To provide the laboratory-measured | E*| inputs for implementation of the M-E design guide, a comprehensive research effort was completed in Arkansas. The research included a study evaluating different | E*| testing protocols, derived by varying combinations of the number of test replicates and the number of measurement instruments affixed on each test specimen recommended in AASHTO TP 62-03. The testing protocols were evaluated in terms of the variability of the resulting | E*| test results. The total research effort included three replicate specimens from each of four aggregate types, three nominal maximum aggregate sizes, two performance grade binder grades, and two air void levels. The | E*| tests were conducted with five test temperatures and six loading frequencies. Even though all evaluated testing protocols produced standard errors of less than 15% (which is the requirement specified in AASHTO TP 62-03), a program utilizing four measurement instruments and two replicate specimens is recommended for future | E*| testing.
Permanent Deformation Analysis of Hot-Mix Asphalt Mixtures with Simple Performance Tests and 2002 Mechanistic–Empirical Pavement Design Software
Authors: Mohammad Louay N. , Wu Zhong , Obulareddy Sandeep , Cooper Sam , Abadie Chris
Published: May 2018

A complex laboratory study in characterization of permanent deformation resistance of hot-mix asphalt (HMA) mixtures is presented. Six plant-produced HMA mixtures were selected for this study. The main objective was to characterize the permanent deformation characteristics of HMA mixtures based on four laboratory tests, namely, the dynamic modulus | E*|, flow number, frequency sweep at constant height (FSCH), and Hamburg-type loaded wheel-tracking tests. The secondary objective was to evaluate the sensitivity of the dynamic modulus | E*|-test results in pavement rutting performance prediction with the 2002 mechanistic–empirical (M–E) pavement design software. Test results indicate that the | E*|-test was sensitive to the nominal maximum aggregate size in an HMA mixture. Larger aggregates combined with aged materials tend to have high | E*|-values at high temperatures. However, both the | E*|-and FSCH tests could not correctly rank the permanent deformation characteristics for the six HMA mixtures considered in this study. However, test results from the flow number and Hamburg tests correlated fairly well, and both tests were sensitive to the permanent deformation characteristics for the mixtures evaluated. The mixture ranking order obtained from the flow number tests was consistent with the use of those mixtures in the field. The predicted rut depths from the 2002 M-E pavement design software basically followed the same trend found in the | E*|-test results at high temperatures.
Determination of Asphalt Concrete Complex Modulus with Impact Resonance Test
Authors: Kweon Gichul , Kim Y. Richard
Published: May 2018

A methodology is presented to determine the dynamic modulus and phase angle of hot-mix asphalt (HMA) with much simpler, nondestructive impact resonance (IR) test. Thirty-five HMA mixtures with varying aggregate and binder characteristics were tested with the IR and conventional dynamic modulus tests. A comparison of the dynamic modulus and phase angle obtained from the IR tests and those measured from the conventional dynamic modulus tests demonstrates the reliability of the proposed procedure. However, it was found that the dynamic moduli from the IR tests at multiple temperatures constitute only the upper half of the master curve (i.e., the high frequencies). A combination of the IR test and the dynamic modulus test at 54.4°C or the IR test and Witczak's predictive equation at 54.4°C was found to provide accurate dynamic modulus master curves. The main advantage of these combinations of testing methods over conventional dynamic modulus testing is that they are much simpler and require less expensive testing equipment and setup.
Comparing Resilient Modulus and Dynamic Modulus of Hot-Mix Asphalt as Material Properties for Flexible Pavement Design
Authors: Loulizi Amara , Flintsch Gerardo W. , Al-Qadi Imad L. , Mokarem David
Published: May 2018

With the current trend toward developing mechanistic flexible pavement design and the need for more reliable design procedures, accurate characterization of hot-mix asphalt (HMA) properties is needed. Resilient and dynamic modulus tests were performed at five temperatures on two typical mixes used in the Commonwealth of Virginia to compare the test results. The dynamic modulus was measured at six frequencies at each of the testing temperatures, and the resilient modulus test was performed at one loading time. The study found that the size of the specimen statistically affected the measured resilient modulus value. Resilient modulus values obtained in the 100-mm-diameter specimens were higher than those obtained in the 150-mm-diameter specimens at all testing temperatures. No statistical differences were observed in the resilient modulus of the two mixes. However, statistical differences were found in the dynamic modulus of the two mixes. A strong relation between the dynamic modulus test performed at 5 Hz and the resilient modulus was found. Three different pavement structures were analyzed to estimate the variation of their bottom-up fatigue life when different moduli were used for the HMA layer. It was found that the measured dynamic moduli resulted in the highest fatigue life estimates for the three considered pavements. It is concluded that the dynamic modulus test provides a better characterization of HMA than the resilient modulus test because it provides full characterization of the mix over temperature and loading frequencies.
Observation of Crack Propagation in Asphalt Mixtures with Acoustic Emission
Authors: Li Xue , Marasteanu Mihai O. , Iverson Nathan , Labuz Joseph F.
Published: May 2018

Fracture in quasi-brittle materials is associated with the formation of microcracks, which release energy in the form of elastic waves called acoustic emissions. The use of acoustic emission (AE) in the characterization of the fracture behavior of asphalt mixtures at low temperatures is investigated, and a method that uses AE to locate the crack path is presented. An application of the method is detailed for fracture tests performed with the semicircular bend specimen on asphalt mixtures at low temperatures. A network of seven piezoelectric sensors was used to capture AE signals, and a nonlinear regression algorithm was employed to locate the AE events. The locations of microcracks were in good agreement with the crack path observed at the end of the test. When the load increased beyond 70% of the peak load, the rate of AE activity was significant, indicating the formation of microcracks, and the location of AE was concentrated in a distinct area called the process zone. Moreover, the location of AE in the postpeak load showed the movement of the process zone and identified the crack propagation in the macroscale.
Micromechanical Analyses for Measurement and Prediction of Hot-Mix Asphalt Fracture Energy
Authors: Birgisson Bjorn , Montepara Antonio , Napier John , Romeo Elena , Roncella Riccardo , Tebaldi Gabriele
Published: May 2018

A verification of fracture energy density is presented as a fundamental fracture threshold in hot-mix asphalt. Fracture energy density was evaluated with the semicircular bending (SCB) test. Experimental analyses were enhanced by a digital image correlation system capable of providing a dense and accurate displacement–strain field of composite materials at the microstructural level and suitable for describing the cracking behavior of materials at crack initiation. The resulting fracture behavior in the SCB was predicted with a displacement discontinuity method to explicitly model the microstructure of asphalt mixtures and to predict their fracture energy density. The input parameters for the displacement discontinuity micromechanical model of the SCB were obtained from the Superpave® indirect tensile test. The predicted crack initiation and crack propagation patterns are consistent with observed cracking behavior. The results also imply that fracture in mixtures can be modeled effectively with a micromechanical approach that allows for crack growth both along aggregate surfaces and through aggregates. Finally, the results presented lead to the promising statement that fracture energy density for mixtures is a fundamental fracture threshold and can be both consistently measured and predicted for different laboratory test configurations.
Computational Model to Predict Fatigue Damage Behavior of Asphalt Mixtures under Cyclic Loading
Authors: Kim Yong-Rak , Allen David H. , Little Dallas N.
Published: May 2018

Fatigue cracking and failure of inelastic heterogeneous asphalt concrete mixtures were modeled computationally with the finite element method. The model incorporates elastic behavior of the aggregate particles, viscoelastic behavior of the asphalt matrix, and time-dependent fracture both within the asphalt matrix and along boundaries between matrix and aggregate particles. Rate-dependent progressive cracking up to failure was implemented by incorporation of a cohesive zone fracture model. The resulting model was used to simulate comprehensive fatigue damage–associated mechanical behavior including microcracking, macrocracking, and eventual sample failure of several asphalt mixtures composed of different mixture constituents, which results in different damage evolution characteristics. Simulation results were compared with real fatigue testing data in both load-controlled and displacement-controlled modes and demonstrated good correlations to laboratory data with model calibrations. The approach proposed can be employed to predict complex fatigue behavior of asphalt mixtures by measurement of only fundamental material properties and fracture or damage properties of mixture constituents without recourse to expensive laboratory fatigue tests.
New Laboratory Equipment for Study of Reflective Cracking in Asphalt Overlays
Authors: Gallego Juan , Prieto Jorge N.
Published: May 2018

One of the current road maintenance problems continues to be the appearance of reflective cracks in asphalt overlays. It would be of real benefit if laboratory equipment were available during the design stage to allow the best solution to be selected for site laying. A new piece of laboratory equipment is reported on for the process known as the wheel reflective cracking (WRC) test based on the traditional wheel-tracking device. The WRC apparatus allows the chief failure mechanisms leading to the phenomenon of reflective cracks to be simulated in the laboratory. Initial results obtained with it on several overlay sections are consistent with the current Spanish experience in full-scale test sections. The WRC test can also be of help to researchers in this field since it enables test parameters to be varied for the purpose of carrying out sensitivity studies. In addition, it allows the loss of structural capacity and the shape of the cracks to be monitored beyond the mere comparison between different overlay sections.
Optimal Routing Design for Shuttle Bus Service
Authors: Jerby Shai , Ceder Avishai
Published: May 2018

A growing concern for public transit is its inability to encourage people to switch their mode of transportation from solo to shared driving. For example, most people arrive at rail stations via private cars; this creates traffic congestion and parking overloading in station areas. As a means of overcoming this problem, automated methods for designing circulated (shuttle, feeder) bus routes were developed. The problem input comprised an urban network with trip generation links and a single destination (main) node, average travel time between each link to the main node, and a constraint defining the maximal travel time along the route. The research components were threefold: ( a) a method for estimating potential passenger demand for a circulated (shuttle) bus route, ( b) an operations research model focusing on optimal route design, and ( c) a heuristic algorithm designed to account for road networks of all sizes. The optimal model and its heuristic alternative were compared in different scenarios on a small real-life road network. It was shown that the heuristic algorithm indeed provides good (optimal in the test case) results. The heuristic procedure was also implemented with medium and large networks, generated randomly, and found to provide good results within a reasonable running time.
Effects of Bus Stop Consolidation on Passenger Activity and Transit Operations
Authors: El-Geneidy Ahmed M. , Strathman James G. , Kimpel Thomas J. , Crout David T.
Published: May 2018

This research addressed changes in passenger activity and operating performance after implementation of a bus stop consolidation project at TriMet, the regional transit provider for the Portland, Oregon, metropolitan area. Extensive use was made of archived bus operations and passenger activity data from TriMet's automated Bus Dispatch System. Changes in passenger activity and operating performance in route segments where stop consolidation occurred were related to changes in adjacent route segments where stops were not consolidated. The findings indicated that bus stop consolidation had no significant effects on passenger activity, whereas bus running times improved by nearly 6%. Running time improvements may have been limited by insufficient schedule adjustments.
Empirical Analysis of Transit Network Evolution
Authors: Mohammed Amr , Shalaby Amer , Miller Eric J.
Published: May 2018

This paper presents the results of the first phase of an ambitious research project aiming at modeling the changes over a 15-year period in the bus network of the city of Mississauga, Ontario, Canada, a fast-growing suburb in the greater Toronto area. Data for the Mississauga transit network, along with a host of demographic and socioeconomic variables, were analyzed. For each main route, a buffer zone representing its vicinity was constructed, and the relevant variables captured inside these zones were computed for inclusion in the proposed empirical models. Other global variables for the city were included as well to account for other effects. Results from multiple regression and simultaneous equation models attempting to relate transit supply to this group of demographic, socioeconomic, and route-specific variables are presented. Time and demand–supply interactions were taken into consideration in the simultaneous equation models. The models show that supply increases with demand and population density and decreases with number of schoolchildren in the vicinity.
OmniLink
Authors: Bruun Eric , Marx Eric
Published: May 2018

Potomac and Rappahannock Transportation Commission's OmniLink is an intelligent transportation system (ITS) assisted, hybrid public transportation service that permits flexible routing combined with the time points of conventional fixed-route services. OmniLink promotes mainstreaming of a significant portion of the disabled population eligible for paratransit under the Americans with Disabilities Act (ADA) while reducing the cost of accommodating these passengers. State-of-the-art ITS technology is used to accommodate passenger requests for off-route trips (route deviations). It gives an accept or reject decision to call-takers while the caller is on the phone; schedules all pickups and drop-offs; provides dispatcher oversight; conveys on-time performance and communicates all other relevant information between drivers and the control center; and incorporates passenger counting, navigation assistance to the operator, vehicle inspection documentation, and other utilities. The ITS package includes full post-processing capability to support service analysis and optimization. Initial service began in 1995, but full ITS functionality was achieved only in 2003 after the second procurement attempt. The identified monetary benefits exceed monetary costs by a wide margin. This success can be attributed to more mature technologies, a turnkey project contract model, and refined, firm specifications based on both practical and academic experience. ITS configurations similar to OmniLink's have the potential to solve several common bus transportation problems in lower-demand areas. Examples of benefits include forgoing or reducing ADA paratransit costs, substituting for large buses at night, serving pedestrian-unfriendly streets, and probing for demand in previously unserved areas.
Utility of Paratransit Modes in Cities of Assam, India
Authors: Ahmed M. Ali , Datta R. N.
Published: May 2018

This paper investigates paratransit modes available in cities of the Assam region of India, with the purpose of determining the utility of the modes. Three cities—Barpeta, Dibrugarh, and Guwahati—were examined in detail. Information was collected from both primary and secondary sources. The revealed modal split was obtained from a traffic survey. The stated modal choice was obtained from data collected through a home interview survey. The utility function of a particular paratransit mode was estimated with a logit model. The weighted least squares method and maximum likelihood method were used for estimates of the model. Eleven variables, five quantitative and six qualitative, were considered. After an estimation was made of the utility function for each mode in a city, a multinomial logit model was used to estimate the relative utility of each mode in that city. The logit models were estimated with the statistical tool SHAZAM. The predicted modal utility, stated modal choice, and revealed modal split were compared. The sensitivity of the utility of paratransit modes with respect to changes in the values of the variables also was studied.
Teenage Mobility in the United States
Authors: Cain Alasdair
Published: May 2018

This study was designed to investigate teenagers’ perceptions of public transit within the context of the wider issue of teenage mobility. Results showed a number of significant restrictions on teenage mobility in the United States, including driving age regulations, travel costs, parental safety concerns, and low-density development patterns that limit walking and cycling. As such, teenagers are an obvious market segment for transit agencies to target. Teenager–parent pairs were recruited to participate in a series of eight focus group sessions conducted in Tampa and Miami, Florida. Qualitative analyses of these sessions revealed a set of five mobility themes that play a major role in determining teenagers’ mode choice decisions: safety, cost, access–availability, reliability, and image. In many situations, teenagers viewed private vehicles as having distinct advantages over transit. However, some advantages associated with transit were identified, including independent mobility, travel cost, and travel safety. Different marketing messages that could be used to exploit these potential advantages were developed. A survey of transit agencies across the country was conducted to assess industry experience with promoting transit to teenagers. This survey showed that three different program types—educational programs, reduced fares, and transit passes—are used to promote transit to teenagers. Major marketing challenges included addressing the negative social image associated with transit, gaining the cooperation of school systems and parents, and retaining program budgets. The paper concludes with a series of recommendations for transit agencies interested in implementing, or improving, programs that target teenage riders.
Integrating Information about Complex Systems
Authors: Westlake Andrew , Wigan Marcus
Published: May 2018

Opus is a project funded by the European Union Statistical Agency (Eurostat). The project is developing a methodology for the coherent and consistent integration of information from multiple sources about complex systems (based on Bayesian statistical models) and a series demonstration of this approach. Most, but not all, of these are transport applications. Alongside the modeling frameworks being developed, the project has developed a framework for storing a complete audit trail, covering the specification and fitting of statistical models, and making use of a formal metadata specification to represent statistical models. This framework builds on ideas about metadata for processes that have been developed in other statistical projects. Practitioners are often skeptical about results derived from models. In practice, all analysis of survey or sample data involves some form of model, even if it is hidden in implicit assumptions. The approach to this skepticism is to open up the model to scrutiny and to present information about the reliability of results, under the title of provenance and reliability. All this comes from the metadata about the statistical model. The approach is generic, but the presentation needs to be domain specific and tailored to the level of expertise and understanding of the user of the results. This paper presents the motivation behind this approach and outlines the metadata structures and functionality being built to deliver this support to users of results from the Opus methodology.
Impact of Hourly Measured Speed on Accident Risk in the Netherlands
Authors: Brijs Tom , Wets Geert , Krimpenfort Robin , Offermans Col
Published: May 2018

Several scholars have defined the urgent need for more research to identify more fully the precise relationship between speed and crash involvement. This paper presents the first results of an exploratory study carried out in the Brabant Southeast police region in the Netherlands. Hourly speed measurement data over a period of 2 years were collected from loop detectors on the municipal and provincial road network and were related to crashes. Different aspects of traffic intensity, speed, and their impact on crashes, including absolute speed, speed variation, and the proportion of excessive speeders, for vehicles less than and more than 5.2 m long, were studied. The study also discusses a number of methodological aspects associated with this kind of analysis. The results show that although absolute speed plays a more important role on roads where speed limits are low, the variation in speed correlates more with crashes when speed limits are higher. Given the limited study area, the results of this work cannot be generalized without risk. However, they offer interesting insights that deserve further investigation in a nationwide cross-sectional study.
Intelligent Transportation System Spatial Data Modeling
Authors: Quiroga Cesar , Pina Robert , Hamad Khaled , Kraus Edgar
Published: May 2018

Transportation management centers (TMCs) generate and archive enormous amounts of multimodal transportation data. Archived intelligent transportation system (ITS) data applications today tend to focus on ITS data as a resource for transportation planning and research, mainly to generate aggregated system performance measures such as corridor travel times, speeds, and delays. As ITS data applications increase, interest is also growing in using archived ITS data to help optimize TMC operations. One area of considerable interest is incident management. This paper focuses on freeway ITS features and data. It describes a prototype geographically referenced framework for ITS data and summarizes spatial and temporal patterns in the distribution of incidents along instrumented freeways in San Antonio, Texas. The geodatabase uses architecture information and archived sensor and incident data from the San Antonio TMC (TransGuide). However, it is sufficiently generic for implementation at other TMCs with relatively minor variations. The paper focuses on data model and geodatabase development, although it includes a summary of application examples.
Heuristic Algorithm for Solving a Multimodal Location-Based Concierge Service Problem
Authors: Kang Seungmo , Oh Seung , Kim Tschangho John
Published: May 2018

As a location-based services problem, the concierge service problem is to find a minimum total cost for purchasing predetermined types and quantities of items with the shortest paths connecting the locations where the items are available. These locations are defined as points of interest (POIs). The total cost includes purchasing and stopping costs at POIs as well as the travel cost from origin to destination. To respond to a request for such a service, a search algorithm should be reasonably fast in computational time and high in accuracy. A heuristic search algorithm was developed by a Euclidean distance approach using a geographic information system. The algorithm was implemented with 1,248 POIs in the Seoul, South Korea, metropolitan area as a case study site. The road network is composed of 52,915 nodes and 77,339 links, and the existing subway network, and all existing bus routes were used for the implementation. Four scenarios were examined: a request for a service in peak and off-peak periods with and without turning restrictions. The results indicate that the computational time in each case is less than 4 s with the transit networks only and less than 30 s if the road network is used. The paper also evaluates the solutions generated from the algorithm.
Smoothing Methods to Minimize Impact of Global Positioning System Random Error on Travel Distance, Speed, and Acceleration Profile Estimates
Authors: Jun Jungwook , Guensler Randall , Ogle Jennifer H.
Published: May 2018

The Georgia Institute of Technology is evaluating the feasibility and effectiveness of mileage-based pricing programs as transportation control measures. Incentives were provided to study participants who change driving behavior in response to cent per mile pricing (fixed pricing and pricing as a function of congestion level). In-vehicle Global Positioning System (GPS) devices were used to estimate distance traveled and driver behavior (e.g., speed and acceleration profiles). The accuracy of estimated mileage accrual speeds by road classification, and acceleration rates used in pricing algorithms, is paramount. Various data-smoothing techniques were applied to the instrumented vehicle GPS speed data, and performance of the algorithms was evaluated in minimizing the impact of GPS random error on speed, acceleration, and distance estimates. The conventional discrete Kalman filter algorithm was modified to enhance its ability to control GPS random errors. Each smoothing method produces different second-by-second speed and acceleration profiles ( t-test and χ2 tests) except for the Kalman filters. The techniques provided different travel distance estimates, but the modified Kalman filter was the most accurate compared with distance estimates from the onboard vehicle speed sensor monitor. The modified Kalman filter is the recommended technique for smoothing GPS data for use in pricing studies. Additional smoothing methods will be evaluated as they are identified.
Proportion-Based Format System for Conventional Road Guide Signs
Authors: Meeker Donald T. , Pietrucha Martin T. , Garvey Philip M.
Published: May 2018

The Manual on Uniform Traffic Control Devices and the Standard Highway Signs Book have been developed around the use of the FHWA Standard Alphabets in an all-uppercase format for use on conventional road guide signs. These publications include a complex series of dimensions and tables based on specific legend sizes for various standard signs; however, the standards do not include guidance for the myriad different layouts that are developed to address unique local conditions. The mathematical relationship of the legend to the border, border size, and line spacing and the mathematical relationship of the graphics to the panel are not based on any standard criteria; as a result, sign layouts are not consistent for signs of similar types. In this paper, a recommendation is made to simplify the formatting of conventional road guide signs. Although these signs are used for many purposes, a similarity in their general design principles provides a basis for a common system of sign layout that relates all of the various dimensions (e.g., border width, word and graphic spacing, and line spacing) to a single common element, the height of the letters used on the sign (for mixed-cased applications, the height of the initial capital letter). To accommodate the use of mixed-case words, a series of proportion-based grid formats has been developed. This series of layout grids is based on the value X, where X is the size of the initial capital letter of the primary legend. The proposed formatting is called the proportional grid system.
Effectiveness of Animal Advisory Messages on Dynamic Message Signs as a Speed Reduction Tool
Authors: Hardy Amanda , Lee Scott , Al-Kaisy Ahmed F.
Published: May 2018

Animal–vehicle collisions (AVCs) are a growing concern as the number of vehicle miles traveled and human encroachment into wildlife habitat increase throughout the United States. Measures to prevent AVCs, such as fencing and wildlife passages, can impose significant investments for transportation agencies. An alternative and potentially less expensive approach is the use of signs to modify driver behavior to reduce these collisions. This study investigated the effectiveness of seasonal animal movement advisories as a speed reduction tool on Interstate highways. Two permanent and one portable dynamic message signs (DMSs) were used to post messages advising motorists to watch for wildlife moving across Interstate 90 in the Bozeman Pass region of southwestern Montana. One control and three treatment messages were displayed on the DMSs, and driver reactions to these messages were recorded through speed observations. The control message comprised a blank message; and the treatment messages included a general transportation message, one general wildlife advisory message, and another, similar wildlife advisory with an updated tally of the actual number of animals observed to have been hit on Bozeman Pass for the year. The results suggest that wildlife advisory messages posted on permanent and portable DMSs are generally effective in reducing average motorist speeds. The results also suggest that the advisory messages are more effective at reducing speeds during dark conditions. Furthermore, the messages on the portable DMS were found to have a more significant impact on average speed than the messages on the permanent DMSs.
Variable Time Headway Criteria to Improve Reliability of Speed Control System Evaluations
Authors: Pesti Geza , Brewer Marcus A.
Published: May 2018

The effectiveness of a particular speed control system depends on how it influences the behavior of those drivers whose speed selection is unaffected by other vehicles around them. A common rule of thumb that can be used to separate these so-called unconstrained or free-flowing vehicles from a traffic stream is to set a time headway threshold (e.g., 5 s) and consider only those vehicles that have headways greater than or equal to the preset threshold. Although this time headway criterion has been widely accepted, there are some problems with its use. In certain cases, motorists keeping longer headways may still be affected, whereas others keeping shorter headways may be unaffected by the vehicle in front of them. This paper identifies potential problems associated with the use of constant headway thresholds and recommends an alternative approach. A methodology that uses variable headway thresholds is presented, and its application is illustrated with speed and headway data collected in a freeway work zone in Texas. The advantage of the proposed variable headway thresholds is that they can account for a number of site-specific variables, such as roadway geometry and traffic and driver characteristics. They are determined from the actual raw data collected at each site and therefore provide a headway threshold more realistic than the constant headway criteria used to separate free-flowing and constrained vehicles in evaluations of speed control measures. Therefore, in many cases, they are expected to improve the reliability of evaluations of speed control systems.
Method of Processing Closed-Circuit Television Digital Images for Poor Visibility Identification
Authors: Hagiwara Toru , Ota Yuji , Kaneda Yasuhiro , Nagata Yasuhiro , Araki Keiji
Published: May 2018

This study proposes a method for identifying poor visibility under adverse weather conditions by processing closed-circuit television (CCTV) digital images. The weighted intensity of the power spectrum (WIPS) was examined to determine its applicability as a value for the identification of poor visibility. The magnitude of WIPS represents the difference in spatial frequencies within the image on the basis of the human contrast sensitivity function. WIPS was calculated by the following image-processing procedure: the spatial frequency of the cutout image was calculated with a two-dimensional Fourier transform, and the power spectrum of the cutout image was calculated; WIPS was totaled at spatial frequencies that ranged from 1.5 to 18 cycles per degree. Two kinds of experiments were performed to determine whether WIPS represented the subjective visibility assessment values (SVAVs) given by the test subjects. Clear linear relationships between WIPS and SVAVs were found in both experiments. In addition, the two correlation lines overlapped within the whole range of WIPS. These results suggest that WIPS may be appropriate for identifying poor visibility by the use of digital images.
Influence of Vertical Illuminance on Pedestrian Visibility in Crosswalks
Authors: Gibbons Ronald B. , Hankey Jonathan M.
Published: May 2018

This project investigated the lighting levels required for crosswalk illumination. The current European methods for lighting suggest a crosswalk lighting level of 40 vertical lux for ensured safety. Two major questions were studied: the required vertical illuminance level for adequate pedestrian visibility and the selection of an object that could act as a surrogate for the pedestrian. The vertical illuminance was determined from an experiment that measured the visibility of pedestrians at lighting levels of 5, 20, 40, and 60 vertical lux. During the experiment, a crosswalk scene was presented to the participants and the time taken for identification of an object was measured. In addition to the lighting level, the conditions used in the experiment were lamp type (metal halide versus high-pressure sodium), the presence of glare, the use of overhead lighting, and the type of pedestrian clothing (white, black, and denim). The study found that a lighting design level of 20 vertical lux is likely adequate for proper pedestrian visibility. Except in selected cases, the lamp type was not significant. The impact of glare was not influenced by the lighting design. Three surrogate objects were developed for the experiment and were tested in the same manner as the pedestrians. The surrogates used were an extruded octagon, a cylinder, and a cylinder with a ball on top. These surrogates were selected to allow easy lighting design calculations while best representing a pedestrian. The experiment found that all surrogates performed equally well and that the surrogate can be chosen on the basis of the ease of calculation. It is recommended that a cylinder be used as a pedestrian surrogate.
Color Performance of Yellow Pavement Markings at Night in the Field
Authors: Schnell Thomas , Aktan Fuat , Miller Cameron
Published: May 2018

A field experiment was conducted to determine the perceptual color correlates of yellow pavement markings at night under tungsten–halogen and high-intensity–gas-discharge headlamps. Participants viewed a battery of yellow pavement markings laid out in a skip line pattern on a straight and level roadway. Four different thermoplastic pavement markings with organic yellow pigments and a waterborne latex paint-type pavement marking were used. Three of the four thermoplastic pavement markings were custom tailored for the experiment and differed by the recipes of the titanium dioxide (which is white) content to vary the yellow saturation while trading off retroreflectivity. The participants were asked to identify each pavement marking color at different distances as either yellow or white when the markings were presented in a set of six markings in a random design. Pavement marking type and viewing distance affected the participants’ responses. Headlamp type did not have a statistically significant effect. A first-order interaction between pavement marking type and viewing distance was also significant, suggesting that some pavement markings preserved their yellow appearance better at far distances. A second-order interaction between pavement marking type, viewing distance, and headlamp type was also statistically significant. This interaction indicates that some materials preserved their yellowness at far distances only under a specific headlamp type. Materials with less retroreflectivity appear to be less capable of rendering saturated yellow colors at long distances. The reason for this is that the cones in the retina require a certain level of luminance for color perception to take place.
Development of a Model to Calculate Roadway Luminance Induced by Fixed Roadway Lighting
Authors: Aktan Fuat , Schnell Thomas , Aktan Mehmet
Published: May 2018

Overhead luminaires often provide illumination on pavement, pavement markings, and nearby objects for nighttime drivers. Earlier studies have characterized the bidirectional reflectivity distribution functions of typical roadway surfaces. The luminaire spatial photometric beam distributions and relative spectral distributions have been investigated in part by the Illumination Engineering Society (IES). Mathematical models for luminance calculations are also established by the Commission Internationale de l'Eclairage (CIE; the International Commission on Illumination) and IES. Yet no computer models integrate such data to determine roadway luminance induced by overhead luminaires in conjunction with headlamp illumination for any given roadway geometry for the nighttime driver. Furthermore, existing models are limited to photopic vision, whereas nonphotopic (i.e., mesopic) vision prevails at night. With the Tarvip model being a suitable platform, work was undertaken under the sponsorship of FHWA to develop a computer model that would combine the available data and assess the performance characteristics of different overhead luminaires under different configurations and roadway characteristics for the nighttime driver. The model accommodates horizontal and vertical curves; custom luminaire configurations; and the CIE standard photopic, mesopic, and scotopic observers. With such a model, it is possible to analyze the visual benefits of existing or fictitious overhead luminaires under different configurations (i.e., different heights and gaps) on various roadway surfaces and geometries while oncoming vehicle glare is factored in without the need for field studies. The fixed overhead lighting module that was developed has been verified and validated in the field.
Accident Frequency Model Using Zero Probability Process
Authors: Nam Doohee , Lee Jinsun
Published: May 2018

Statistics show that the South Korean railroad system ran about 114 million vehicle miles in 2004 and operated through almost 3,600 highway–rail grade crossings nationwide. Highway–rail grade crossing accidents result in severe crashes with trains and other vehicles every year and account for approximately 95% of all grade crossing fatalities. Despite the number of highway–rail grade crossing accidents, quantification of the effect of possible countermeasures has been surprisingly limited because of the absence of data needed to analyze rigorously those factors that affect the frequency of highway–rail grade crossing accidents. This study provides some initial insight into this important problem, including detailed data from a database of roadway geometric and grade crossing elements that were used to analyze highway–rail grade crossing accidents on 100 individual grade crossings in South Korea. Zero-inflated models of accident frequency were developed, and the findings isolated a wide range of factors that significantly influence highway–rail grade crossing accident frequency. The marginal effects of these factors were computed to provide an indication of the effectiveness of potential countermeasures. The findings show promise for the methodological approach undertaken and provide important directions for future railroad research.
Modeling Signalized Intersections near Highway–Railroad Grade Crossings
Authors: Cho Hanseon , Rilett Laurence R.
Published: May 2018

Many roadway intersections throughout North America are located near highway–railroad grade crossings (IHRGCs). Numerous safety, operational, and legal challenges are associated with IHRGCs; and these become significantly more complex when traffic signals are present. Because of the complexity of traffic operations at IHRGCs, existing macroscopic analysis approaches are not suitable for in-depth analyses. Consequently, a more detailed methodology for the analysis of intersections with traffic signals located near IHRGCs was developed. The approach is microsimulation based and relies on hardware-in-the-loop architecture to model the traffic signal controller. To demonstrate the methodology, sensitivity analyses of key design parameters were undertaken, and their impacts on safety and delay were analyzed. Specifically, ( a) the maximum train speed and the corresponding length of the detector, ( b) the effect of the pedestrian volume, and ( c) the effect of the addition of an additional upstream train detector were examined in terms of safety and delay at the IHRGC. The methodology was tested with empirical data from a test bed in College Station, Texas. It was found that the manner in which the maximum train speed was calculated could have a statistically significant effect on delay and a detrimental effect on safety. It was also shown that the addition of an additional upstream detector could reduce delay and increase safety.
Development of a Tool to Assess the Quality of Collected Pavement Management Data
Authors: Wolters Angela S. , McGovern Ginger , Hoerner Todd
Published: May 2018

Over the past 4 years, the Oklahoma Department of Transportation (ODOT) has implemented a pavement management system (PMS) to provide the agency with accurate, current, and relevant pavement condition information for use in prioritizing candidate pavement projects based on economic and engineering analyses. Now that the implementation process has been completed, ODOT routinely uses its PMS to enhance network- and project-level decision making. Currently, ODOT contracts with a vendor to collect network-level sensor, geometric, and distress data using automated data collection techniques. The data are then processed with a combination of automated and semiautomated techniques. The agency recognized that the value of the recommendations made by its PMS is greatly dependent on the quality of the collected information included in the PMS. Therefore, ODOT has emphasized the importance of checking the quality of data before they are used for important management decisions. As one way of assessing the data quality, ODOT developed checks of the data collected and submitted by the vendor. ODOT realized the value of creating an automated procedure for checking the final delivered pavement condition database to provide a rapid, repeatable, and accurate assessment of the data quality. To address this need, ODOT developed a visual basic application tool based on Microsoft Access to provide a user-friendly interface to the systematic procedure of conducting the many required data quality checks. In addition to the control and verification site testing procedures and distress ratings checks, this tool will be used by the agency as part of a comprehensive approach to assessing pavement condition data accuracy and completeness. Details regarding the creation and function of the quality assurance tool are provided in this paper.