Showing papers in "Journal of Transportation Engineering-asce in 2010"

Road Traffic Congestion and Crash Severity: Econometric Analysis Using Ordered Response Models

Abstract: There is an ongoing debate among transport planners and safety policy makers as to whether there is any association between the level of traffic congestion and road safety. One can expect that the increased level of traffic congestion aids road safety and this is because average traffic speed is relatively low in a congested condition relative to an uncongested condition, which may result in less severe crashes. The relationship between congestion and safety may not be so straightforward, however, as there are a number of other factors such as traffic flow, driver characteristics, road geometry, and vehicle design affecting crash severity. Previous studies have employed count data models (either Poisson or negative binomials and their extensions) while developing a relationship between the frequency of traffic crashes and traffic flow or density (as a proxy for traffic congestion). The use of aggregated crash counts at a road segment level or at an area level with the proxy for congestion may obscure the actual relationship. The objective of this study is to explore the relationship between the severity of road crashes and the level of traffic congestion using disaggregated crash records and a measure of traffic congestion while controlling for other contributory factors. Ordered response models such as ordered logit models, heterogeneous choice models, and generalized ordered logit (partially constrained) models suitable for both ordinal dependent variables and disaggregate crash data are used. Data on crashes, traffic characteristics (e.g., congestion, flow, and speed), and road geometry (e.g., curvature and gradient) were collected from the M25 London orbital motorway between 2003 and 2006. Our results suggest that the level of traffic congestion does not affect the severity of road crashes on the M25 motorway. The impact of traffic flow on the severity of crashes, however, shows an interesting result. All other factors included in the models also provide results consistent with existing studies.

Using GPS Data to Gain Insight into Public Transport Travel Time Variability

Abstract: Transit service reliability is an important determinant of service quality, which has been mainly studied from the perspective of passengers waiting at stops. Day-to-day variability of travel time also deteriorates service reliability, but is not a well-researched area in the literature partly due to the lack of comprehensive data sets on bus travel times. While this problem is now being addressed through the uptake of global positioning system (GPS)-based tracking systems, methodologies to analyze these data sets are limited. This paper addresses this issue by investigating day-to-day variability in public transport travel time using a GPS data set for a bus route in Melbourne, Australia. It explores the nature and shape of travel time distributions for different departure time windows at different times of the day. Factors causing travel time variability of public transport are also explored using a linear regression analysis. The results show that in narrower departure time windows, travel time distributions are best characterized by normal distributions. For wider departure time windows, peak-hour travel times follow normal distributions, while off-peak travel times follow lognormal distributions. The factors contributing to the variability of travel times are found to be land use, route length, number of traffic signals, number of bus stops, and departure delay relative to the scheduled departure time. Travel time variability is higher in the AM peak and lower in the off-peak. The impact of rainfall on travel time variability is only found significant in the AM peak. While the paper presents new methods for analyzing GPS-based data, there is much scope for expanding knowledge through wider applications to new data sets and using a wider range of explanatory variables.

Critical Assessment of Pavement Distress Segmentation Methods

Abstract: Image segmentation is the crucial step in automatic image distress detection and classification (e.g., types and severities) and has important applications for automatic crack sealing. Although many researchers have developed pavement distress detection and recognition algorithms, full automation has remained a challenge. This is the first paper that uses a scoring measure to quantitatively and objectively evaluate the performance of six different segmentation algorithms. Up-to-date research on pavement distress detection and segmentation is comprehensively reviewed to identify the research need. Six segmentation methods are then tested using a diverse set of actual pavement images taken on interstate highway I-75/I-85 near Atlanta and provided by the Georgia Department of Transportation with varying lighting conditions, shadows, and crack positions to differentiate their performance. The dynamic optimization-based method, which was previously used for segmenting low signal-to-noise ratio (SNR) digital radiography images, outperforms the other five methods based on our scoring measure. It is robust to image variations in our data set but the computation time required is high. By critically assessing the strengths and limitations of the existing algorithms, the paper provides valuable insight and guideline for future algorithm development that are important in automating image distress detection and classification.

Bidirectional Pedestrian Stream Model with Oblique Intersecting Angle

Abstract: In this paper, we develop a model of bidirectional pedestrian streams with an oblique intersecting angle that represents the crossing interaction of pedestrians moving in different directions on a walking facility. We formulate the model based on Drake's model in the traffic flow literature, and calibrate it using results from a set of controlled experiments in which two groups of pedestrians were asked to walk in different directions and cross on designated walkways with different levels of pedestrian flow and different intersecting angles. Their movements were video recorded, and macroscopic quantities such as speed, density, and flow were extracted to calibrate the model of bidirectional pedestrian streams. All of the parameters of the calibrated model are statistically significant at the 0.1% level. DOI: 10.1061/ASCETE.1943-5436.0000086 CE Database subject headings: Pedestrians; Two-dimensional flow; Traffic flow; Measurement; Experimentation. Author keywords: Pedestrians; Two-dimensional flow; Measurement; Experimentation.

Genetic Algorithm for Bus Frequency Optimization

Abstract: In this paper, a bilevel programming model for the bus frequency design is presented, which determines the optimal bus frequencies aiming to minimize the total travel time of passengers subject to the constraint on the overall fleet size of each company by accounting for the route choice behaviors of the users. The objective of the lower level is to assign transit trips to bus route network based on optimal strategy. In the upper level, bus frequencies of routes are optimized as a result of passenger assignment. An iterative approach, which consists of a genetic algorithm and a label-marking method, is used to solve the bilevel model. Finally, the model and the algorithms are illustrated with two test examples. The results show that the optimization can improve the local service level of one company, and the proper integration of several companies probably improves the efficiency of resources and the service level of the whole transit system.

Application of Shakedown Theory in Characterizing Traditional and Recycled Pavement Base Materials

Abstract: To facilitate the use of recycled materials in pavement construction, a mechanistic-based approach is required to better characterize pavement base materials. This paper demonstrates the application of the shakedown theory to characterize the behavior of traditional and recycled base materials based on laboratory repeated load triaxial RLT tests and full-scaled accelerated loading tests. A new approach that is based on dissipated energy is proposed to explain different shakedown responses of tested materials under repeated loading. The dissipated energy approach illustrated that there are two responses during RLT tests, namely, stable and unstable responses, which are dependent on the loading levels and type of tested material. It was also observed that the transition from the stable to unstable response represents gradual microstructural adjustments of tested materials to accommodate the applied loading. This gradual transition explains the difficulties in identifying some material responses within the shakedown theory based only on the permanent strain rate criteria. Based on the results of this study, a mechanistic-based design procedure to incorporate various recycled materials into pavement bases is recommended.

Road Roughness and Whole Body Vibration: Evaluation Tools and Comfort Limits

Abstract: An important element of achieving quality in a road network is the control of vehicle vibration due to pavement roughness and road irregularities. Scientific literature and international standards suggest that we evaluate these phenomena by measuring the whole body vibration (WBV) on the road user, but, for the practical aims of road engineering, this expression has to be related to road unevenness indexes, especially the most common one (the international roughness index, IRI). This index, in turn, is obtained from measured pavement geometric data using a conventional model of a mechanical system representing part of a vehicle. To better investigate the problem of user comfort, more complex models and analyses are needed. In this paper, a model of a real and common vehicle is presented and used, after a calibration process, to perform many dynamic simulations. The obtained results, in terms of weighted vertical acceleration ( aWZ , that is, the WBV index, according to ISO standard), show good correlation...

Influence of Vertical Sensor Placement on Data Collection Efficiency from Bluetooth MAC Address Collection Devices

Abstract: The consumer electronics industry has made extensive use of the Bluetooth wireless protocol in many portable devices. A substantial number of these Bluetooth devices broadcast a unique identifier in the form of the media access control (MAC) addresses. These MAC addresses can be captured electronically and the same matching algorithms used in traditional license plate studies can be used to estimate segment travel time and origin-destination matrices. This paper briefly illustrates how these data can be used to estimate arterial link travel times and empirically illustrates the sensitivity of sample size to sensor placement. A controlled experiment with fixed lateral mounting and varying vertical mounting heights is then conducted to develop design recommendations for mounting Bluetooth monitoring devices. The paper concludes by recommending a Class I Bluetooth detector mounting height of at least 8 ft above the pavement grade. Based on a 24-h empirical data set on I-65 in Indianapolis, we found that 7.4%...

Effect of Surrounding Traffic Characteristics on Lane Changing Behavior

Abstract: Lane changing maneuvers could have a substantial influence on traffic flow characteristics as a result of their interfering effect on surrounding vehicles. The interference effect of lane changing is more pronounced when heavy vehicles change lanes compared to when passenger cars undertake the same maneuver. This is due to the physical effects that the heavy vehicles impose on surrounding traffic. This paper investigates and compares the traffic flow characteristics which influence the lane changing behavior of heavy vehicle and passenger car drivers on freeways under heavy traffic conditions. A trajectory data set comprising 28 heavy vehicle and 28 passenger car lane changing maneuvers is analyzed in this study. The results suggest a substantial difference exists between the traffic characteristics influencing the lane changing behavior of heavy vehicle and passenger car drivers. Heavy vehicles' speed changes little during a lane changing maneuver. Heavy vehicle drivers mainly move into the slower lanes to prevent obstructing the fast moving vehicles which approach from the rear. However, passenger car drivers increase their speed according to the speeds of the lead and lag vehicles in the target lane. They more commonly move into the faster lanes to gain speed advantages.

Comparative Analysis of Compact Multilane Roundabouts and Turbo-Roundabouts

Abstract: This paper presents a comparative analysis of the traffic performances of turbo-roundabouts and roundabouts in terms of capacity and delays. We chose to use a recent German procedure for roundabouts included in “Kreisel” software as our calculation procedure to determine the capacity of turbo-roundabouts. We found that the capacities of turbo-roundabout secondary entries were higher than roundabout capacities when the traffic flow in the inner lane of the circle is high and the traffic flow in the outer lane of the circle is in the low to lower-middle range. On the contrary, the capacities of the main entries to roundabouts are always higher than the capacities of the main entries to turbo-roundabouts. Taking into account the arithmetic or weighted mean behavior of the four entries, the total capacities of turbo-roundabouts, at both saturated and undersaturated conditions, are, in most cases, higher than the total capacities of roundabouts. In most of the important practical situations analyzed, delays we...

Differences in Off-Road Glances: Effects on Young Drivers’ Performance

Abstract: Young drivers display more risk-taking behavior than other age groups. Performing distracting tasks is one such risky behavior that is observed among young drivers. However, due to inexperience, young drivers may not be able to appropriately compensate for the effects of distractions. A driving simulator study with 53 young drivers (aged 18–21) was conducted to assess the level of engagement with an in-vehicle secondary task. A cluster analysis revealed three groups of drivers that differed based on eye glance behavior and driving performance: drivers with low-risk, moderate-risk, and high-risk behavior. A subset of these drivers was provided with feedback to help modulate their distracting activities with the riskiest group benefitting most from feedback as indicated by enhanced glance behavior and driving performance. The findings have implications for developing better crash countermeasures to mitigate the effects of distraction.

Microsimulation Study of Effect of Volume and Road Width on PCU of Vehicles under Heterogeneous Traffic

Abstract: The traffic volume and roadway capacity are the important basic inputs required for planning, analysis, and operation of roadway systems. Expressing traffic volume as number of vehicles passing a given section of road or traffic lane per unit time will be inappropriate when several types of vehicles with widely varying static and dynamic characteristics are comprised in the traffic. The problem of measuring volume of such heterogeneous traffic has been addressed by converting different types of vehicles into equivalent passenger cars and expressing the volume in terms of passenger car unit (PCU) per hour. The vehicles of highly heterogeneous traffic such as the one prevailing on Indian roads may occupy any convenient lateral position on the road, based on the availability of space, without any lane discipline. This study is concerned with the estimation of PCU values of vehicles in such traffic conditions, using microscopic simulation. The PCU values obtained for different types of vehicles, for a wide range of traffic volume and roadway conditions, indicate that the PCU value of a vehicle significantly changes with change in traffic volume and width of roadway.

What Is the Role of Multiple Secondary Incidents in Traffic Operations

Abstract: Traffic incidents are a major source of travel uncertainty, imposing substantial costs on the transportation system. Sometimes, an incident can result in one or more secondary incidents, which can be particularly problematic. To identify roadways where multiple secondary incidents are more likely to occur and analyze primary and secondary incidents, an innovative analysis method based on a detailed incident data set from Hampton Roads, Virginia was developed. Incidents occurring on major freeways are categorized on a three-point ordinal scale as (1) an independent incident, i.e., an incident not associated with any secondary incidents; (2) one primary-secondary pair; and (3) one primary with two or more secondary incidents in the same or opposite directions. This scale captures event adversity from a traffic management perspective, with the last category capturing multiple secondary events. To quantify associations with key factors that include incident characteristics, roadway geometry and traffic flow, ordinal regression models are estimated. The results indicate that longer duration crashes, shorter segments, and heavy traffic are associated with higher propensity for secondary incidents. Furthermore, multiple-vehicle involvement and lane blockage are associated with multiple secondary incidents. The findings provide engineers and planners with valuable information on targeting service patrols in areas that are more prone to multiple secondary incidents. Overall, this research contributes by characterizing and analyzing complex events involving secondary incidents using rigorous statistical methods.

Simulation-Based Assessment of Vehicle Safety Behavior under Hazardous Driving Conditions

Abstract: Future sustained economic growth of the nation very much depends on the reliability and efficiency of its highway infrastructure system. Some vehicles, such as trucks, emergency vehicles, and sport utility vehicles, often experience increasing risks of single-vehicle accidents under hazardous driving conditions, such as inclement weather and/or complicated topographical conditions. An advanced simulation-based single-vehicle accident assessment model is developed considering the coupling effects between vehicles and hazardous driving conditions, including wind gust, snow-covered or icy road surface, and/or curving. Compared to existing simulation models, the new model focuses on characterizing the transient process of accidents, introducing new critical variables on assessing the accident risks under more comprehensive hazardous driving conditions and establishing more realistic accident criteria. As a holistic deterministic model, it can be used to provide useful assessment and prevention information for traffic and emergency management. For example, it can be used to define appropriate safe driving speed limits for vulnerable vehicles under normal and extreme conditions and predict potential crash and injury risk of vulnerable drivers. Moreover, the new deterministic vehicle safety behavior simulation model lays a critical basis for future reliability-based studies of single-vehicle accident risks of vulnerable vehicles under hazardous conditions. After the model is introduced, numerical analyses on a typical truck under several representative hazardous scenarios will be conducted for demonstration purposes.

Interrater Reliability of Manual Pavement Distress Evaluations

Abstract: Many government agencies are faced with the challenge of pavement evaluation and maintenance as part of their pavement management systems. These agencies perform or contract manual or automated distress surveys over the pavement network to monitor the structure performance and obtain the necessary data to calculate pavement condition indexes. Although manual distress ratings are done according to well-defined criteria, a certain amount of subjectivity and the experience of the raters have an undoubted influence on the ratings. This study proposes a new approach to estimate the interrater or intercrew reliability for manual or semiautomated distress data collection. The proposed analysis acknowledges that a certain degree of variability in the visual distress ratings is likely to occur and, thus, minimum acceptable values of complete and partial agreements of the crews or raters are suggested. The statistical approach to validate the level of agreement between the ratings of two raters or crews is based on the use of the chi-square distribution to test hypotheses about multinomial experiments.

Influence of Platform Walking on BRT Station Bus Dwell Time Estimation: Australian Analysis

Abstract: The common approach to estimate bus dwell time at a Bus Rapid Transit (BRT) station platform is to apply the traditional dwell-time methodology derived for suburban bus stops. Current dwell-time models are sensitive toward bus type and fare collection policy along with the number of boarding and alighting passengers. However, they fall short in accounting for the effects of passengers walking on a relatively longer BRT station platform. Analysis presented in this paper shows that the average walking time of a passenger at a BRT platform is 10 times more than that of a bus stop. The requirement of walking to the bus entry door at the BRT station platform may lead to the bus experiencing a higher dwell time. This paper presents a theory for a BRT network that explains the loss of station capacity during peak period operation. It also highlights shortcomings of present available bus dwell-time models suggested for the analysis of BRT operation.

Development of Railway Track Geometry Indexes Based on Statistical Distribution of Geometry Data

Abstract: In this paper, the statistical distribution of railway track geometry data is investigated using a significant volume of field data. Analyzing the results yields a general pattern for the statistical distribution of the track geometry data. This is used to develop new indexes for track geometry parameters including gauge, profile, alignment, and twist. An overall track geometry index is established by combining the new parameter's indexes. This combination is made by assigning a coefficient to each geometry parameter based on its role in the overall quality condition of the track. In comparison with the approaches previously used for the development of the track geometry indexes, this method has three distinguishing features. First, the mean values along with the SD of data are incorporated into the calculation of the new indexes. Second, the new indexes indicate not only the condition of the individual parameters but also the overall track geometry condition. Third, the track classification is considered, and an index is developed for each class of the tracks. A practical use of the new indexes is presented and discussed in the paper.

Multimodal Feeder Network Design Problem: Ant Colony Optimization Approach

Abstract: Significant service performance capabilities of high-capacity mass transit make it a remarkable part of any large metropolitan transportation system. Unfortunately it is not feasible to provide citywide direct access to high-capacity transit. Other modes of transit are used as feeders to collect and deliver passengers to high-capacity mass transit. By using feeder lines the possibility of use of high-capacity mass transit increases because the travel demand for a more extended area can be satisfied. In this research, multiple modes with various capacities and performances are used in the feeder network design based on the minimization of user, operator, and social costs. Other approaches have only used one mode (usually bus) for designing the feeder network.

Integration of GIS and Data Mining Technology to Enhance the Pavement Management Decision Making

Abstract: This paper presents a research effort undertaken to explore the applicability of data mining and knowledge discovery (DMKD) in combination with Geographic Information System (GIS) technology to pavement management to better decide maintenance strategies, set rehabilitation priorities, and make investment decisions. The main objective of the research is to utilize data mining techniques to find pertinent information hidden within the pavement database. Mining algorithm C5.0, including decision trees and association rules, has been used in this analysis. The selected rules have been used to predict the maintenance and rehabilitation strategy of road segments. A pavement database covering four counties within the state of North Carolina, which was provided by North Carolina DOT (NCDOT), has been used to test this method. A comparison was conducted in this paper for the decisions related to a rehabilitation strategy proposed by the NCDOT to the proposed methodology presented in this paper. From the experimental results, it was found that the rehabilitation strategy derived by this paper is different from that proposed by the NCDOT. After combining with the AIRA Data Mining method, seven final rules are defined. Using these final rules, the maps of several pavement rehabilitation strategies are created. When their numbers and locations are compared with ones made by engineers at the Institute for Transportation Research and Education (ITRE) at North Carolina State University, it has been found that error for the number and the location are various for the different rehabilitation strategies. With the pilot experiment in the project, it can be concluded: (1) use of the DMKD method for the decision of road maintenance and rehabilitation can greatly increase the speed of decision making, thus largely saving time and money, and shortening the project period; (2) the DMKD technology can make consistent decisions about road maintenance and rehabilitation if the road conditions are similar, i.e., interference from human factors is less significant; (3) integration of the DMKD and GIS technologies provides a pavement management system with the capabilities to graphically display treatment decisions against distresses; and (4) the decisions related to pavement rehabilitation made by the DMKD technology is not completely consistent with that made by ITRE, thereby, the postprocessing for verification and refinement is necessary.

Dynamic Incident Progression Curve for Classifying Secondary Traffic Crashes

Abstract: The classification of secondary crashes is a useful performance measure of incident management systems. Previous classification methodologies used a static threshold for classifying secondary crashes. Such a threshold represents the spatial and temporal influence of a primary incident, such as 3.2 km upstream (2 mi) and 2 h after the incident. The dynamic methodology described herein improves upon existing static methodology by marking the end of the varying queue throughout the entire incident using incident progression curves. The four steps in the development of incident progression curves are: (1) processing of intranet incident reports; (2) filling in of incomplete incident reports; (3) nonlinear regression of incident progression curves; and (4) merging of individual incident progression curves into a master curve. The result from a 640 sample validation set shows that the dynamic methodology reduces Type I error by 24.38% and Type II by 3.13%. The application to a 5,514 freeway crash data set shows the results from using dynamic versus static methodology can differ by more than 30%.

Investigating the Impacts of Green Signal Countdown Devices: Empirical Approach and Case Study in China

Abstract: This paper presents an extensive investigation regarding the impacts of green signal countdown devices (GSCD) on the intersection safety and efficiency, based on field observation of critical driver and vehicle related parameters at two similar intersections (one with GSCD and the other without GSCD) in Shanghai. Statistical analysis results have revealed that the installation of GSCD can (1) encourage drivers to pass the stop-line during the amber time with higher speeds and thus result in better utilization of the amber time and increased capacity of the intersection approach; (2) smooth the driver's response to the phase transition and effectively prevent the sudden change of speeds; (3) effectively eliminate the intersection dilemma zones by allowing the drivers to envision the phase transition and make decisions in advance; and (4) significantly reduce the number of red-light violations. Despite its effectiveness in facilitating the driver decision-making process, the installation of GSCD may adversely increase the possibility of collisions with unexpected crossing vehicles or pedestrians due to the significantly increased speeds of vehicles approaching the amber time. The analysis results from this study will offer the basis for traffic practitioners, researchers, and authorities in China to assess the impact of GSCD with respect to its operational and safety performance, and propose guidelines for its proper field installation.

How Lane Arrangements on Freeway Mainlines and Ramps Affect Safety of Freeways with Closely Spaced Entrance and Exit Ramps

Abstract: The number and arrangement of lanes on freeways are important considerations in freeway geometric design. The objective of this study is to evaluate the safety impacts of lane arrangements on freeway segments with closely spaced entrance and exit ramps. Three different types of lane arrangements were considered. They were designated as Type A, Type B, and Type C arrangements. The research team compared crash frequency, crash rate, crash severity, and collision types for freeway segments with different types of lane arrangements. Crash prediction models were developed to relate crash counts to various explanatory variables such as traffic conditions and geometric characteristics. The crash data analysis results show that the Type C arrangement reported the lowest average crash frequency and crash rate. The Type C arrangement uses a continuous auxiliary lane to connect the entrance and exit ramps; and the auxiliary is dropped in a one-lane exit. Freeway segments with the Type B arrangement reported the highest average crash frequency, crash rate, and percentage of fatal plus severe injury crashes. Based on the crash prediction models, if other factors remain constant, a Type B arrangement results in 113% more total crashes and 102% more severe crashes than does a Type C arrangement. Crash data analysis results suggest that the Type B arrangement should be used cautiously when entrance and exit ramps are closely spaced.

Car-Following Interaction and the Definition of Free-Moving Vehicles on Two-Lane Rural Highways

Abstract: This paper presents an investigation into car-following interactions on two-lane rural highways. Empirical data from several study sites on two-lane and four-lane rural highways in the state of Montana were used in this investigation. Three separate yet relevant analyses are presented in this paper. The first analysis involves a preliminary characterization of time headways and their distributions and shows how they are affected by passing restrictions on two-lane highways. The second analysis presented in this paper involves an investigation of speed-headway relationship to establish a headway threshold that could be used in defining free-moving vehicles on two-lane highways. The third and last analysis investigates the "following by choice" phenomenon on two-lane highways using data from two-lane as well as four-lane study sites. The study found that the car-following interaction generally ceases when headways exceed a value of approximately six seconds. Also, a significant proportion of drivers choose to maintain relatively short headways while following other vehicles on two-lane highways regardless of passing restrictions.

Roughness Model Accounting for Heterogeneity Based on In-Service Pavement Performance Data

Abstract: Deterioration modeling is a key component in a transportation infrastructure management system. It serves to capture and predict the performance of a facility. A sound deterioration model should incorporate: 1 relevant variables that affect deterioration process; 2 physical principle that reflects deterioration mechanism; and 3 rigorous statistical approach to estimating the model. This paper addresses these critical aspects with particular focus on highway pavements. Data collected from in-service pavement sections as part of the Minnesota Road Test project are used to capture the real-world pavement deterioration process. A number of variables involved in the system are thoroughly investigated, which include pavement design, materials, traffic, environment, and maintenance factors. Performance uncertainty due to unobserved heterogeneity is incorporated in the proposed model. The unobserved heterogeneity stems primarily from variability in the materials and the construction process. The model is estimated through maximum simulated likelihood estimation. It is demonstrated that the results are consistent with observations and engineering judgment in the context of pavement design and performance. In addition to population-level parameters representing the general deterioration mechanism, section-specific or individual-level parameters are obtained through Bayesian approach. The two levels of parameters can be used to accommodate network- and project-level analysis in pavement management. DOI: 10.1061/ASCE0733-947X2010136:3205 CE Database subject headings: Surface roughness; Pavements; Deterioration; Heterogeneity. Author keywords: Pavement management; Deterioration; Roughness; Statistics.

Assessing the Agreement among Pavement Condition Indexes

Abstract: Pavement condition indexes are numerical indicators of the structural and material integrity of a pavement. Because these indexes appear to be similar (essentially a 0–100 scale, with 100 indicating ideal condition), it can be tempting to use different indexes for comparing the performance of pavement networks in different states or jurisdictions within a state. To ascertain the level of agreement among these condition indexes, six pavement condition indexes from five DOTs in the United States are discussed and compared using distress and ride quality data obtained from the Pavement Management Information System of the Texas Department of Transportation. The computed scores were compared visually (using scatter plots) and statistically (using paired t -test). The results provide empirical evidence that there are significant differences among seemingly similar pavement condition indexes.

Factors Affecting Driver Speed Choice along Two-Lane Rural Highway Transition Zones

Abstract: Two-lane rural highways attract trips between traffic generators such as residential villages or small commercial areas and are generally uninterrupted flow facilities that provide a high level of mobility with high posted speeds limits. When passing through developed areas, the posted speed limit may be lowered to encourage reduced vehicle operating speeds. No published guidelines currently exist for the design of transition zones that connect high- to low-speed operating environments on two-lane rural highways. The objective of this research was to collect operating speed and roadway characteristic data along two-lane rural highway transition zones in Pennsylvania to explore the roadway, roadside, and traffic control factors that are associated with driver speed differentials. Single- and multilevel models were estimated and compared. The posted speed limit reduction as well as a change in the paved shoulder width, total number of driveways, various advance warning signs, the transition zone length, and the presence of horizontal curves were shown to increase the expected speed reduction in transition zones in the models. Additionally, drivers entering transition zones at higher speeds were found to have greater speed reductions than drivers entering the transition zone at lower speeds.

Concrete Slab Installed with Carbon Fiber Heating Wire for Bridge Deck Deicing

Abstract: A method of deicing with carbon fiber heating wire (CFHW) buried inside concrete slab is presented in this paper, which avoids the negative effects on structure function and environment caused by traditional deicing salt. The rational interval range of CFHW buried inside concrete slab is determined by the temperature field of four heating CFHW and the minimum input powers for deicing under the conditions of different air temperatures and ice thicknesses are summarized by the laboratory experiments. Snow melts more quickly than the ice with same weight under the same input power condition by comparison the deicing processes in refrigerator. The field experiments of concrete slab performed satisfactorily: the snow on slab with the thickness of 10, 40, and 70 mm was melted in 0.75, 2.5, and 3.5 h, respectively, under an appropriate input power. It demonstrated that the electrothermal method of CFHW for bridge deck deicing is practicable.

Speed prediction models for multilane highways: Simultaneous equations approach

Abstract: Past speed-related research has focused on the operational effects of roadway geometrics along rural two-lane highways using ordinary least-squares regression models. More recent research has focused on the association of traffic flow characteristics on vehicle operating speeds along multilane, limited access highways using a simultaneous equations approach. Few research studies, however, have been conducted to determine the combined association between various geometric design features and traffic flow on operating speeds along multilane highways. This research considers both geometric design and traffic flow parameters, in a simultaneous equations framework, to model the mean operating speed and speed deviation on four-lane highways (two lanes in each direction). Models for both left- and right-lane mean speeds and speed deviations were estimated. The three-stage least-squares estimator was used to investigate the possible endogeneity of mean speed and speed deviation in the system of equations and to account for the contemporaneous correlation between the disturbances across the equations. The results indicate that different geometric design features are associated with mean speed and speed deviation in the left- and right-lane models. As such, it is recommended that future multilane highway speed models consider using a simultaneous equations framework.

Data Analysis Techniques for GPR Used for Assessing Railroad Ballast in High Radio-Frequency Environment

Abstract: Railroad ballast supports heavy rail loading, prevents track deformation, and provides drainage of water from the track structure. However, over time, ballast is fouled by the breakdown of ballast aggregate and/or the infiltration of fines, which undermine the ballast functions and affect the railroad track structural capacity. Ground penetrating radar (GPR) provides a rapid, effective, and continuous way to assess railroad track substructure condition; especially ballast. However, the GPR system faces some challenges during field surveys including high radio-frequency interference from railroad communication and automation, and strong reflections from rails. In this study, appropriate techniques were used to remove the interference and reduce the strong clutter from rails to obtain clear GPR data of railroad substructure. A time-frequency method, short-time Fourier transform, was then applied to extract ballast fouling condition over depth. A field survey using multiple sets of 2-GHz air-horn antennae was conducted during summer 2007 at the Transportation Technology Center, Inc. in Pueblo, Colo. Compared to ground-truth excavation and ballast gradation analysis results, GPR was found to be an effective technique to assess railroad track ballast substructure condition.

Evolution and Development of Multiairport Systems: Worldwide Perspective

Abstract: This paper presents an analysis of the dynamics of evolution of multiairport systems worldwide that can help to guide their effective development in the future. Given the capacity constraints on existing major airports, the development of multiairport systems is going to be a key mechanism by which air transportation systems around the world will be able to meet future demand. In order to better understand how these systems will evolve, a systematic case study analysis of 59 airport systems worldwide was performed. The analysis showed significant differences in the evolution of multiairport systems across world regions. In the United States and in Europe, the recent development of multiairport systems primarily involved the emergence of secondary airports. This dynamic was driven by the entry of low-cost carriers seizing the opportunity of using existing airport infrastructure but also by the barriers and opposition to the construction of green field airports. In Asia, multiairport systems have generally evolved through the construction of new high capacity airports, due to a much weaker set of available airports, high-perceived benefits of strong growth of traffic and weaker opposition to the construction of airports. This study suggests that, in the United States and in Europe, protecting existing underused airports will be key to meeting future demand. In Asia, where the existing underused airport infrastructure is weak and where projections of high volume of demand are high, there is the need to apply a dynamic approach to develop multiairport systems by reserving land area that can later be developed into airports.