Showing papers in "Journal of Transportation Engineering-asce in 2012"

Use of Recycled Construction and Demolition Waste Aggregate for Road Course Surfacing

Abstract: The need to manage construction and demolition waste (CDW) has led to environmentally-friendly actions that promote the reuse and recycling of this type of waste and other forms of waste valorization. The main priority is to foment sustainable construction work, which has the advantage of avoiding the deposit of large quantities of construction waste at landfills and greatly reducing the use of borrow material in construction projects. In this sense, the reuse of CDW materials significantly lessens the impact of construction work on the surrounding environment. The aim of this research study is to verify the technical viability of using construction waste as material for the base pavement layers of road surfaces. For this purpose, a field study was carried out, which included testing the performance of pavement composed of concrete, asphalt mix, and ceramic waste aggregate. This was done by analyzing the characteristics of the recycled material on a section of an actual road under real vehicle traffic conditions. It was observed that the load-bearing capacity of the recycled artificial CDW aggregate was satisfactory.

Effects of Fillers on Properties of Asphalt-Concrete Mixture

Abstract: The role of filler on the mechanical performance of asphalt-concrete mixture was investigated. Three wearing course (W3B) mixtures incorporating granite, hydrated lime, and kaolin as filler fractions were evaluated by the Marshall mix design method to determine their optimum asphalt content. The use of hydrated lime or kaolin as a filler requires more asphalt because of their relatively higher specific surface area. The highest stiffness performance was found for W3B-hydrated lime, followed by W3B-granite, and W3B-kaolin mixtures. W3B-hydrated lime and W3B-kaolin mixtures exhibited higher deformation resistance than that of W3B-granite mixture. The results showed that the presence of filler in an asphalt-concrete mixture affects the mixture’s performance in three ways: filler influences the amount of asphalt content, filler affects the workability during mixing and compaction, and the resultant properties of asphalt-filler mastic contribute to the mixture’s performance. The results show that the properties of the filler determine its interaction with asphalt and its contribution to the mixture’s performance.

Critical Assessment of Detecting Asphalt Pavement Cracks under Different Lighting and Low Intensity Contrast Conditions Using Emerging 3D Laser Technology

Abstract: After decades of research and development, a fully automated system for pavement crack detection with an intensity-based two-dimensional (2D) imaging data acquisition system under different lighting and low intensity contrast conditions still remains a challenge. With the advances of sensor technology, a three-dimensional (3D) laser technology that can collect high-resolution 3D continuous transverse pavement profiles for detecting cracks on the basis of their 3D elevation rather than 2D intensity has become available. This study, sponsored by the U.S. Department of Transportation (US DOT) Research Innovative Technology Administration (RITA) program, evaluates the feasibility of using emerging 3D laser technology to detect cracks under different lighting and poor intensity contrast conditions. For this purpose, 3D surface data from laboratory tests on cracks ranging from 1 to 5mm wide and tests on the actual pavement cracks of different widths and depths and under different lighting conditions wer...

Network-Scale Traffic Modeling and Forecasting with Graphical Lasso and Neural Networks

Abstract: Traffic flow forecasting, especially the short-term case, is an important topic in intelligent transportation systems (ITS). This paper researches network-scale modeling and forecasting of short-term traffic flows. First, the concepts of single-link and multilink models of traffic flow forecasting are proposed. Secondly, four prediction models are constructed by combining the two models with single-task learning (STL) and multitask learning (MTL). The combination of the multilink model and multitask learning not only improves the experimental efficiency but also improves the prediction accuracy. Moreover, a new multilink, single-task approach that combines graphical lasso (GL) with neural network (NN) is proposed. GL provides a general methodology for solving problems involving lots of variables. Using L1 regularization, GL builds a sparse graphical model, making use of the sparse inverse covariance matrix. Gaussian process regression (GPR) is a classic regression algorithm in Bayesian machine learning. Although there is wide research on GPR, there are few applications of GPR in traffic flow forecasting. In this paper, GPR is applied to traffic flow forecasting, and its potential is shown. Through sufficient experiments, all of the proposed approaches are compared, and an overall assessment is made.

Microsimulation Approach for Predicting Crashes at Unsignalized Intersections Using Traffic Conflicts

Abstract: A microsimulation approach is presented for assessing safety at unsignalized intersections using critical traffic conflicts computed in simulation models as a surrogate safety measure. The proposed approach was applied to a crash data set, collated over a 5-year monitoring period, corresponding to urban unsignalized intersections of the city of Salerno, Italy. Given that over 45% of accidents recorded at these intersections occurred more especially in six 1-h time periods during the day and that these hourly periods corresponded to the peak traffic volumes, it was considered worthwhile to investigate each of these 1-h concentrated time intervals. Traffic flows were computed by using video cameras placed at each intersection and expressed as peak-hour volumes in the analysis. A process of microsimulation model calibration and validation was carried out, and a good level of conformity between the traffic simulated in the peak hours and the corresponding one measured in the field was obtained. Subseq...

Freight Resilience Measures

Abstract: People, industries, and public agencies all face the possibility of sudden events that disrupt their normal activities. Disasters on the transportation network, whether attributable to nature, human error, or human intent, raise awareness of the need for plans of action to quickly restore mobility. Resilience of the transportation network is the capacity to absorb the effects of a disruption and to quickly return to normal operating levels. Resilience measures are useful to evaluate and predict disruptions and recovery and to guide infrastructure investments that protect against those disruptions or that accelerate recovery after a disruption. This paper presents a methodology for estimating two composite resilience measures—reduction and recovery. The method is illustrated by using resilience triangles derived from sampled truck speeds and counts along the Interstate 90/94 corridor from Hudson to Beloit, Wisconsin during two significant weather events in 2008. This paper presents a set of criteria, on the basis of observed effects on various sections of the highway corridor, to qualify the computed resilience measures. In this paper, the focus is on generalizing the characteristics of the resilience response rather than characteristics of the corridor sections that lead to patterns of the response for each section. The criteria and the measures together are a useful tool to evaluate resilience.

Mechanical Properties of Porous Asphalt Pavement Materials with Warm Mix Asphalt and RAP

Abstract: The objectives of this paper are (1) to characterize the mechanical properties of porous asphalt pavement mixtures containing reclaimed asphalt pavement (RAP) and a WMA additive (Advera® WMA) using Superpave™ gyratory compactor and dynamic modulus testing. Four types of porous asphalt mixtures were evaluated in this study. They are 1) control mixture, a conventional porous asphalt mixture; (2) porous asphalt mixture with WMA additive (Advera® WMA in this case); (3) porous asphalt mixture containing 15% reclaimed asphalt pavement (RAP); and (4) porous asphalt mixture containing 15% RAP and additional WMA additive. This study evaluated com- paction energy index (CEI), permeability, indirect tensile strength, and dynamic modulus (E � ) for all types of porous asphalt mixtures. All of the porous asphalt mixtures meet the typical minimum coefficient of permeability in this study. Compaction energy required for the WMA containing 0.25% Advera® WMAwas found to be lower compared with the control mixture (HMA). The results from the dynamic modulus test show that WMA made with 0.25% Advera® WMA had significantly lower values than the control HMA mixture. In addition, only a slight decrease in Ewas found when WMA additive was added to the porous asphalt mixture containing RAP. For indirect tensile strength testing, WMA containing RAP was found to have the highest tensile strength among all of the mixtures tested. DOI: 10.1061/(ASCE)TE .1943-5436.0000307. © 2012 American Society of Civil Engineers. CE Database subject headings: Porous media; Asphalts; Mixtures; Asphalt pavements; Mechanical properties. Author keywords: Porous asphalt mixture; Warm mix asphalt; Reclaimed asphalt pavement (RAP).

Critical Rut Depth for Pavement Maintenance Based on Vehicle Skidding and Hydroplaning Consideration

Abstract: Rutting is a major form of pavement distress in asphalt pavements. The main concern with rutting has been related to driving safety. Many highway agencies and researchers suggested that pavement rutting could lead to vehicle hydroplaning and loss of skid resistance in wet weather. However, to date no theoretical basis has been established for an analytical assessment of the severity of rutting for the purpose of pavement maintenance and rehabilitation. Most highway agencies classify rut severity on the basis of engineering judgment or field experience. This paper presents an analytical procedure to assess the severity of rutting based on vehicle skidding and hydroplaning analysis. It considers theworst-case scenariowhere a rut is filled with water and analyzes (1) if a car will hydroplane at a given speed; and (2) the length of braking distance required for the car traveling at the given speed. A finite-element simulation model is adopted to perform the analysis. For a given rut depth filled with water, the computer model computes the hydroplaning speed for a typical passenger car, and the required braking distance for the car traveling at a known speed. It was found that depending on the rut depth and the surface frictional property of a pavement, the severity classification of a rut may be governed by either hydroplaning risk or safety requirement of braking distance. The traditional method of using the same set of critical rut depths for all pavement sections in a road network is not ideal for effective handling of rutting maintenance. DOI: 10.1061/(ASCE)TE.1943-5436.0000336. © 2012 American Society of Civil Engineers. CE Database subject headings: Pavements; Maintenance; Skid resistance; Vehicles; Finite element method. Author keywords: Rut depth; Pavement maintenance; Skid resistance; Hydroplaning; Braking distance; Tire tread depth; Finite element method.

Multinomial Logistic Regression Model for Single-Vehicle and Multivehicle Collisions on Urban U.S. Highways in Arkansas

Abstract: Multivariate analysis can be used to identify the effects of several factors on the causes of a crash compared with univariate analysis. This paper uses a multivariate-analysis technique, the multinomial logistic regression (MLR) model, to examine the differences in crash-contributing factors for six collision types for both divided- and undivided-highway nonjunctions, given that a crash has occurred. Multinomial logistic regression was used to investigate (1) single-vehicle and (2) multivehicle collisions, which included (1) angular, (2) head-on, (3) rear-end, (4) sideswipe-same-direction, and (5) sideswipe-opposite-direction collisions. The risks associated with different collision types were found to be significantly influenced by various vehicle actions. The risk of sideswipe-same-direction collisions was higher while changing lanes and merging on undivided and divided highways. Similarly, while merging, drivers were prone to angular collisions, and when slowing down to rear-end collisions on ...

Integer Programming to Optimize Tamping in Railway Tracks as Preventive Maintenance

Abstract: In the area with railway engineering, scheduling preventive maintenance actions is an important issue for engineers and railway administrations because the optimization of maintenance actions at a preventive level allows maintenance costs to be reduced during the life cycle of the track, with the guarantee of its geometrical quality. This paper describes a model designed to optimize the tamping operations in ballasted tracks as preventive maintenance. The model, formulated as mixed 0–1 linear program, considers real technical aspects as constraints, which is a novel approach in the optimization of track maintenance over time. Global optimization is used to predict and to schedule tamping, taking into account four aspects: the evolution of the track degradation over time; the track layout; the dependency of the track quality recovery on the track quality at the moment of the maintenance operation; the track quality limits that depend on the maximum permissible train speed. Computational experience with two track stretches of the Portuguese Northern Railway Line is included to highlight the efficacy of the proposed methodology.

Application of Soft Computing for Prediction of Pavement Condition Index

Abstract: The pavement condition index (PCI) is a widely used numerical index for the evaluation of the structural integrity and operational condition of pavements. Estimation of the PCI is based on the results of a visual inspection in which the type, severity, and quantity of distresses are identified. The purpose of this study is to develop an alternative approach for forecasting the PCI using optimization techniques, including artificial neural networks (ANN) and genetic programming (GP). The proposed soft computing method can reliably estimate the PCI and can be used in a pavement management system (PMS) using simple and accessible spreadsheet softwares. A database composed of the PCI results of more than 1,250 km of highways in Iran was used to develop the models. The results showed that the ANN- and GP-based projected values are in good agreement with the field-measured data. In addition, the ANN-based model was more precise than the GP-based model. For more straightforward applications, a computer program was developed based on the results obtained.

Evaluation of Effectiveness and Cost-Effectiveness of Asphalt Pavement Rehabilitations Utilizing LTPP Data

Abstract: This paper analyzed the effectiveness and cost-effectiveness of several asphalt pavement rehabilitations by investigating the long-term pavement performance (LTPP) database. The multiple regression method was employed to evaluate the influence of overlay thickness, pavement thickness, traffic volume, and preoverlay pavement conditions on the effectiveness and cost-effectiveness. The international roughness index (IRI) was selected as an indicator of pavement performance. The postrehabilitation IRI, IRI drop, roughness increase after rehabilitation, and the “benefit” were used as measures of treatment effectiveness. The results of the presented analyses indicated that thicker overlay and milling reduced the roughness after rehabilitation. Thin overlay, high traffic level, and poor prerehabilitation pavement condition increased the deterioration rate of new overlay. Using reclaimed asphalt material did not influence the treatment performance but was cost-effective in reducing the roughness of new ov...

Framework for Multiobjective Optimization of Physical Highway Assets Investments

Abstract: Optimization-based tools have been included in many engineering management systems for individual infrastructure asset classes such as pavement management systems (PMS) and bridge management systems (BMS). These tools typically include single-objective optimization analyses. However, real-world decisions concerning asset preservation and renewal often involve more than one objective reflecting the various goals of the agency and need to evaluate possible alternatives according to multiple criteria. Traditional single-objective optimization approaches for handling such situations optimize a selected most important objective while either neglecting the less important competing objectives or imposing them as known constraints in the optimization formulation. This approach often does not provide truly optimal solutions. Multiobjective optimization formulations have clear theoretical advantages but increase the complexity of the mathematical formulation. This paper presents a review of the application ...

Distribution Characteristics of Vehicle-Specific Power on Urban Restricted-Access Roadways

Abstract: The development of new fuel consumption and emission models creates the need to characterize traffic conditions by using vehicle-specific power (VSP) distribution. However, in existing transportation engineering, there has been a lack of knowledge of relationships between the VSP distribution and commonly used traffic parameters and a lack of models to develop the VSP distribution from traffic parameters. To examine how traffic conditions affect VSP distributions, this study uses large samples of floating car data collected from expressways in Beijing to associate VSP distributions with various average travel speeds. After a comprehensive analysis, regular patterns are found between the VSP distribution and the average travel speed. Specifically, when the average travel speed is more than 20 km/h, the VSP distribution comes close to a normal distribution. The mean of the VSP distribution is the VSP value when cruising at the average travel speed, and the standard deviation could be expressed as a power f...

Estimating Capacity and Motorcycle Equivalent Units on Urban Roads in Hanoi, Vietnam

Abstract: This paper presents an investigation of the accurate methodology of motorcycle equivalent units (MEUs) in mixed traffic flow by considering the characteristics of moving vehicles, such as velocity and effective space. In addition, the effective space of each kind of vehicle is computed with consideration of the influences of velocity, physical size of the subject vehicle, and the surrounding motorcycles in the proposed methodology. The field data were collected in Hanoi, Vietnam in the case study. The results indicated that the MEU values of cars, buses, minibuses, and bicycles are 3.4, 10.5, 8.3 and 1.4, respectively. On the other hand, the collection of the field data of vehicle flow and speed passing through road segments was conducted in three groups of divided roads with raised medians. The fundamental diagrams of vehicle speed-flow-density relationships, ranging from stable traffic flow to unstable conditions, were plotted in this paper. The values of capacity, maximum motorcycle flow, critical mean stream speed, and critical density of traffic flow were computed. Results indicated that the capacity values of urban roads with two, three, and four lanes per direction are 13,358, 21,725 and 24,335 (motorcycles per hour) respectively. The capacity, therefore, increases with the number of lanes of urban roads.

Laboratory Investigation of Open-Graded Friction-Course Mixtures Containing Polymers and Cellulose Fibers

Abstract: Open-graded friction course (OGFC), which consists of an open gradation mostly of coarse size aggregate with little fines, is a special purpose mixture that is increasingly used in pavement surfacing around the world. The typical benefits of an OGFC mixture are increased surface permeability, noise reduction, and enhanced surface friction, especially in wet conditions. This paper presents results of a study focusing on the use and properties of OGFC mixtures containing reclaimed polyethylene modified binder (RPEB), crumb rubber modified binder (CRMB), and neat 60=70-grade binder with cellulose fibers. The relative performance of mixtures and an aspect relating to the design of such mixtures, based on the laboratory study, have been presented in detail. Several laboratory tests were carried out in this study to evaluate open-graded friction course mixture properties by adopting two different types of Marshall compaction. A draindown test, a Cantabro stone loss test, a permeability test, an indirect tensile strength test, a resilient modulus test, a rutting test, and a skid resistance test were used to evaluate the performance of OGFC mixtures. The addition of fiber stabilizers and polymerized asphalt significantly reduced the potential for draindown in OGFC mixtures. Mixtures compacted by 50 blows on one face by a Marshall hammer were found to give improved results with respect to abrasion and other related mixture properties of the OGFC mixtures. The test results indicated that polymer modi- fication of the binder enhances the relevant engineering properties of the OGFC mixtures. Tensile strength ratio (TSR) values were found to be less for mixtures with modified binders than the mixtures with unmodified binders and fibers. DOI: 10.1061/(ASCE)TE.1943-5436 .0000304. © 2012 American Society of Civil Engineers.

Regime-Based Short-Term Multivariate Traffic Condition Forecasting Algorithm

Abstract: Predictions of fundamental traffic variables in the short-term or near-term future are vital for any successful dynamic traffic management application. Univariate short-term traffic flow prediction algorithms are popular in literature. However, to facilitate the operationalities of advanced adaptive traffic management systems, there is a necessity of developing multivariate traffic condition prediction algorithms. A new multivariate short-term traffic flow and speed prediction methodology is proposed in this paper where the traffic flow and speed observations from uncongested (or linear) and congested (or nonlinear) regimes are regime-adjusted to ensure consistent system dynamics. The prediction methodology is developed by using artificial neural networks (ANN) algorithms in conjunction with adaptive learning rules. These learning rules demonstrate significantly improved accuracy and simultaneous reduction in computation times. Additionally, the paper attempts to identify the most suitable adaptiv...

Anisotropic Viscoelastic Properties of Undamaged Asphalt Mixtures

Abstract: A test protocol and a data analysis method are developed in this paper on the basis of linear viscoelastic theory to characterize the anisotropic viscoelastic properties of undamaged asphalt mixtures. The test protocol includes three nondestructive tests: (1) uniaxial com- pressive creep test, (2) indirect tensile creep test, and (3) the uniaxial tensile creep test. All three tests are conducted on asphalt mixture specimens at three temperatures (10, 20, and 30°C) to determine the tensile and compressive properties at each temperature and then to construct the master curve of each property. The determined properties include magnitude and phase angle of the compressive complex modulus in the vertical direction, magnitude and phase angle of the tensile complex modulus, and the magnitude and phase angle of the compressive complex modulus in the horizontal plane. The test results indicate that all tested asphalt mixtures have significantly different tensile properties from compressive properties. The peak value of the master curve of the tensile complex modulus phase angle is within a range from 65 to 85°, whereas the peak value of the compressive moduli phase angle in both directions ranges from 35 to 55°. In addition, the undamaged asphalt mixtures exhibit distinctively anisotropic properties in compression. The magnitude of the compressive modulus in the vertical direction is approximately 1.2 to ∼2 times of the magnitude of the compressive modulus in the horizontal plane. Dynamic modulus tests are performed to verify the results of the proposed test protocol. The test results from the proposed test protocol match well with those from the dynamic tests. DOI: 10.1061/(ASCE)TE.1943-5436.0000302. © 2012 American Society of Civil Engineers. CE Database subject headings: Asphalts; Mixtures; Anisotropy; Poisson ratio; Viscoelasticity; Material properties. Author keywords: Asphalt mixtures; Anisotropy; Viscoelasticity; Complex modulus; Poisson's ratio; Master curve.

Prediction Model of Bus Arrival Time at Signalized Intersection Using GPS Data

Abstract: Accurate prediction of bus arrival time at the stop line is a vital element to the bus signal priority system, but most previous approaches focused on predicting bus arrival times at next bus stops only. This paper develops a travel time prediction model to predict bus arrival time on the basis of global positioning system (GPS) data. Bus travel time from the detected location to stop line is divided into three parts: travel time from present point to the end of anterior queue, waiting time for the green light, and time for discharging anterior queue vehicles. Case studies were conducted in real-life signalized intersections to evaluate the performance of the model. Results showed that the presented model provided acceptable prediction accuracy. In addition, by considering the log interval of GPS data and prediction error, a determination method of the optimal decision-making zone when using sequential GPS data was developed.

Bus-Arrival-Time Prediction Models: Link-Based and Section-Based

Abstract: Bus-arrival-time information service is a key component of an advanced transit information system. Instantaneous and accurate prediction of bus arrival time can help improve the quality of service, and attracts additional ridership. On the bases of analyses of bus running processes, bus arrival time was divided into interzone link travel time and section travel time. A self-adaptive exponential smoothing-based algorithm was proposed for interzone link travel time prediction, whereas link-based and section-based algorithms were proposed for section travel time prediction. With the automatic vehicle location data collected from an actual bus route, an experiment was conducted to measure the performance (accuracy and precision in prediction) of link-based and section-based models with respect to three dominant factors: day of week, time of day, and length of segment. The research results show that: (1) the overall performance of section-based models is superior to that of link-based models on all weekdays bu...

Classification and Regression Tree Approach for Predicting Drivers’ Merging Behavior in Short-Term Work Zone Merging Areas

Abstract: This study aims to use the classification and regression tree (CART) approach, one of the most powerful data mining techniques, to predict drivers’ merging behavior in a work zone merging area. On the basis of the eight factors affecting drivers’ merging behavior, a binary CART is built using the merging traffic data collected from a short-term work zone site in Singapore. The CART comprises 7 levels and 15 leaf nodes to predict drivers’ merging behavior in the work zone merging area. The results show that the CART provides much higher prediction accuracy than the conventional binary logit model. Traffic engineers can easily understand how drivers make merging/nonmerging decisions. This demonstrates that the CART approach is a good alternative for investigating drivers’ merging behavior in work zone merging areas.

Trade-Off Analysis for Multiobjective Optimization in Transportation Asset Management by Generating Pareto Frontiers Using Extreme Points Nondominated Sorting Genetic Algorithm II

Abstract: Investment decision making in transportation asset management is typically characterized by a wide diversity of asset types for purposes of optimization at overall system level. To enhance investment analysis and decision making for these multiobjective problem types, the analysis of trade-offs associated with different performance measures can be illuminating and informative. This paper provides techniques for efficient trade-off analysis as part of multiobjective-optimization for transportation asset management. The multiobjective-optimization problem is first formulated by establishing the objectives expressed in terms of network-level performance measures underlying the analysis of trade-offs. Then, the Extreme Points Nondominated Sorting Genetic Algorithm II (NSGA II) technique, an improvement over traditional NSGA II, is applied to generate Pareto frontiers that illustrate the trade-offs. Using candidate projects from a varied range of asset types as a case study, the paper successfully conducts the trade-offs between performance objectives and cost, and then among the performance objectives. The paper also shows that Extreme Points NSGA II has a faster convergence speed and yields a distribution that is superior to the traditional NSGA II.

Combinatorial Optimization of Exclusive Bus Lanes and Bus Frequencies in Multi-Modal Transportation Network

Abstract: Bus priority strategy has widely been recognized as an effective countermeasure in the practical field of urban traffic congestion mitigation. This study proposes a bi-level programming model to comprehensively analyze the combinational optimization problem of exclusive bus lanes (EBLs) with variable bus frequencies (BFs) in multi-modal transportation networks. The objective function is to minimize the sum of the road users’ travel costs and the transit operating costs. The upper level model is an optimal decision-making program for setting up EBLs and BFs, and the lower level is a multi-modal transportation network equilibrium model. An efficient genetic algorithm is designed to solve the problem. The results of the numerical analysis show that the combinatorial optimization scheme of EBLs and BFs performs well with regard to the objective function in the model. The outperformance of combinatorial optimization scheme becomes greater with increased traffic demand, whereas oversetting of EBLs can result in reduced operating efficiency of the transportation system.

Understanding the Dynamics of Heavy Vehicle Interactions in Car-Following

Abstract: Heavy vehicles and passenger cars differ in their maneuverability and acceleration capabilities. Heavy vehicles thus influence other traffic in a different manner than passenger vehicles, causing different levels of traffic instability. Increasing number and proportion of heavy vehicles in the traffic stream may result in quite different traffic flow characteristics. Over the last five decades many studies have investigated passenger car drivers’ car-following behavior. However, the existence of heavy vehicles in the traffic stream has not received the same attention. This paper investigates the different car-following behavior of drivers in congested heterogeneous traffic conditions. It specifically focuses on the existence of heavy vehicles in general traffic and their interaction with other vehicles. Four different combinations of passenger car and heavy vehicle were considered. These combinations include passenger car-following a passenger car, passenger car-following a heavy vehicle, heavy vehicle following a passenger car, and heavy vehicle following another heavy vehicle. A data set from a freeway in the United States was used to show the different car-following behavior of drivers for each combination. This study analyzes space and time headways, drivers’ reaction times, and vehicle accelerations. It also introduces different car-following thresholds for each car-following combination. It was found that the presence of heavy vehicles causes larger space and time headways, longer reaction time, and more robust car-following behavior. It also shows that the car-following thresholds are of the four combinations studies. The findings of this paper indicate that further research is required to develop a generalized car-following model that can be used when different vehicle types are in the traffic stream.

Differentiating between Left-Turn Gap and Lag Acceptance at Unsignalized Intersections as a Function of the Site Characteristics

Abstract: Left-turn gap acceptance at an unsignalized intersection is dependent on many factors. The Highway Capacity Manual (HCM) uses a single value of critical gap for all types of intersections; however, this may be oversimplistic and lead to inaccurate estimates of left-turn delay and capacity. Most existing studies also do not differentiate between gap and lag when evaluating gap acceptance. In this paper, binary logit models were developed to estimate the probability of accepting or rejecting a given gap or lag for a left-turning vehicle from a major road at an unsignalized intersection considering a number of potential influencing factors. Gap acceptance behavior was found to be influenced by the type of gap presented to the driver (gap or lag). Gap duration, total wait time, time to turn, distance to next signal downstream, and median type were found to be significant factors in predicting the probability of accepting or rejecting a gap. In the model for lag acceptance lag duration, time to turn, crossing width, speed limit, and distance to next signal downstream were found to be significant. Equations for estimating the critical gap and lag were developed. Critical gap and lag were found to be varying over a wide range of values depending on the type of intersection. The range was smaller for critical gaps than lags. The findings from this study can improve operational analysis of left turns at unsignalized intersections by using different critical gaps for different traffic and geometric conditions. Language: en

Modeling Travel Time under the Influence of On-Street Parking

Abstract: On-street parking is an important component of the parking system. Because of its occupancy of roadway resources, it can significantly impact traffic performance and safety. The aim of this paper is to give a quantitative analysis of the influence of on-street parking on travel time. The travel time data of the motor vehicles moving in the road sections with on-street parking are gathered by observers. A proportional hazard-based duration model is proposed to analyze the influential factors related to on-street parking, including effective lane width, the number of parking maneuvers, and occupancy. The results show that on-street parking has a significant impact on the travel time of vehicles. In addition, various factors can modify travel time in different degrees, and the model can be used to estimate the travel time under assumed conditions. It is hoped that this paper will help to improve the planning and management of on-street parking.

Evaluation of Continuous Deflection Testing Using the Rolling Wheel Deflectometer in Louisiana

Abstract: The Rolling Wheel Deflectometer (RWD) offers the benefit to measure pavement deflection without causing any traffic interruption or compromising safety along the tested road segments. This paper presents a detailed field evaluation of the RWD system in Louisiana, in which 16 sites representing a wide array of pavement conditions were tested. Measurements were used to assess the repeatability of RWD measurements, the effect of truck speeds, and the relationship between RWD and (FWD) deflection measurements and pavement conditions. On the basis of the results of the experimental program, it was determined that the repeatability of RWD measurements was acceptable, with an average coefficient of variation at all test speeds of 15%. In addition, the influence of the testing speed on the measured deflections was minimal. The scattering and uniformity of the FWD and RWD data appear to follow closely the conditions of the roadway. Both test methods appear to properly reflect pavement conditions and structural integrity of the road network by providing for a greater average deflection and scattering for sites in poor conditions. The RWD deflection measurements were in general agreement with the FWD deflections measurements; however, the mean center deflections from RWD and FWD were statistically different for 15 of the 16 sites. DOI: 10.1061/(ASCE)TE.1943-5436.0000349. © 2012 American Society of Civil Engineers. CE Database subject headings: Pavements; Structural analysis; Deflection; Tests; Traffic safety; Louisiana. Author keywords: Pavement structural evaluation; Falling Weight Deflectometer; Rolling Wheel Deflectometer; Deflection profiles; Pavement management system.

Development of a VISSIM Simulation Model for U-Turns at Unsignalized Intersections

Abstract: The simulation of U-turns is currently of great interest to many transportation professionals due to the widespread use of indirect driveway left-turn treatments. In this study, a procedure...

Conventional, Flexible, and Variable-Type Bus Services

Abstract: To provide efficient public transportation services in areas with high demand variability over time, it may be desirable to switch vehicles between conventional services (with fixed routes and schedules) during peak periods and flexible route services during low-demand periods. This option is called variable-type services. Conventional, flexible, and variable-type service alternatives optimized for various conditions are compared to explore when variable-type bus services might be preferable to purely conventional or flexible service. The optimization models used for purely conventional or flexible service are adapted from previous studies. These models are integrated into a new model for optimizing variable-type bus service. The results of sensitivity analyses show how demand variability over time and other factors affect the relative effectiveness of conventional, flexible, and variable-type bus services.

Investigating Benefits of IntelliDrive in Freeway Operations: Lane Changing Advisory Case Study

Abstract: IntelliDrive, the integration of vehicles and the infrastructure through wireless communication, has generated great interest in the transportation community. It is widely expected that IntelliDrive will support significantly improved transportation operations. However, there have been few studies investigating (1) how IntelliDrive will be used to improve operations, and (2) how to estimate expected benefits of IntelliDrive operations applications. In this study, the research team investigated the application of IntelliDrive to address merging conflicts created by freeway on-ramps. Although merging conflicts contribute significantly to freeway congestion, transportation engineers have limited options with existing traffic surveillance and management tools. IntelliDrive offers the potential for more active management of the surface transportation system, providing capabilities that may be of significant benefit in ramp management. In this research, a lane changing advisory algorithm was developed ...