bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity to Uncertainty: Need for a Paradigm Shift
Authors: Avineri Erel , Prashker Joseph N.
Published: April 2007

Existing common route choice models are based on random utility theory, which follows the maximum utility assumption. Recent intelligent transportation system applications have highlighted the need for better models of the behavioral processes involved in route choice decisions. Therefore, prediction of travelers' responses to uncertainty was analyzed. Route choice experiments were conducted to evaluate the effect of the feedback mechanism on decision making under uncertainty. The experimental results were compared with those from a model based on cumulative prospect theory and models based on learning approaches. It is shown that a traveler's sensitivity to travel time differences is lower when variances in travel times are higher. This better understanding of route choice behavior predicted by learning models may improve traffic predictions, as well as the design of traffic control mechanisms.
Empirical Investigation of Household Vehicle Type Choice Decisions
Authors: Mohammadian Abolfazl , Miller Eric J.
Published: April 2007

Automobile ownership models are an integral part of comprehensive transportation modeling systems. Recent work and ongoing advances in the area of activity-based travel demand modeling have recognized the need for increased experimentation with automobile choice models. On the other hand, while automobiles are very important in people's everyday lives, they also have a serious impact on the environment. This impact occurs at the micro level (pollution) as well as the macro level (emission of greenhouse gases and global warming). Such impacts have led to increased interest in reducing motor vehicle emissions. A household automobile type choice model was developed at a disaggregate level. The model can provide a direct forecast of consumer demand for personal-use vehicles given the available choices. A well-developed form of discrete choice modeling techniques, the nested logit model, was used to investigate the process of household automobile type choice decisions given that a transaction has occurred.
Simulation of Regional Freight Movement with Trade and Transportation Multinetworks
Authors: Xu Jinghua , Hancock Kathleen L. , Southworth Frank
Published: April 2007

A simulation model called Trade and Transportation Multinetworks (TTMNet), constructed for the purpose of studying the effects of highly developed information technologies and logistic strategies (e.g., electronic commerce and real-time information) on freight transportation, is described. TTMNet is formulated as a multilevel product supply chain system that integrates the financial, informational, logistical, and physical aspects of transportation networks and allows interactions between each of these networks. Several simulators, including a freight traffic simulator, a supply chain decision-making simulator, and a pseudo-real-time information simulator, are involved. The freight traffic simulation is the focus of the present study. As part of this simulator, a learning model is set up to help decision makers estimate transportation costs on the basis of past experiences. Given the stochastic nature of these transportation costs and of the freight demands simulated by the system, the route for an origin–destination shipment may not remain optimal during a trip and may change along the way. A vehicle redirection procedure that handles this is presented. A numerical example is designed to compare a set of freight movements under two scenarios, one supported by and the other not supported by pseudo-real-time information on traffic conditions.
Integration of Qualitative and Quantitative Methodologies Framework and Quick Examples
Authors: Al-Jammal Rana , Parkany Emily
Published: April 2007

A framework that integrates qualitative and quantitative data analysis methodologies of trip-chaining behavior research was developed. The proposed qualitative methods include analysis of descriptive statistics and visual analysis of space–time prisms. The results of the qualitative analysis help in the quantitative modeling process. The proposed integrated qualitative and quantitative framework incorporates both logit models and hazard duration models as quantitative analysis tools. Qualitative examples, what was learned from them, and how the qualitative data affect the quantitative methodology are described. The qualitative examples show that aggregate and individual trip-chaining behaviors are not easy to model. Integration of the results from both qualitative and quantitative methods lead to a better understanding of how people make their trip-chaining and travel behavior decisions.
Predicting Travel Times for the South Jersey Real-Time Motorist Information System
Authors: Chien Steven I. J. , Liu Xiaobo , Ozbay Kaan
Published: April 2007

A dynamic travel-time prediction model was developed for the South Jersey (southern New Jersey) motorist real-time information system. During development and evaluation of the model, the integration of traffic flow theory, measurement and application of collected data, and traffic simulation were considered. Reliable prediction results can be generated with limited historical real-time traffic data. In the study, acoustic sensors were installed at potential congested places to monitor traffic congestion. A developed simulation model was calibrated with the data collected from the sensors, and this was applied to emulate traffic operations and evaluate the proposed prediction model under time-varying traffic conditions. With emulated real–time information (travel times) generated by the simulation model, an algorithm based on Kalman filtering was developed and applied to forecast travel times for specific origin-destination pairs over different periods. Prediction accuracy was evaluated by the simulation model. Results show that the developed travel-time predictive model demonstrates satisfactory performance.
Improving a Travel-Time Estimation Algorithm by Using Dual Loop Detectors
Authors: van Lint J. W. C. , van der Zijpp N. J.
Published: April 2007

An algorithm is presented for off-line estimation of route-level travel times for uninterrupted traffic flow facilities, such as motorway corridors, based on time series of traffic-speed observations taken from the sections that constitute a route. The proposed method is an extension of the widely used trajectory method. The novelty of the presented method is that trajectories are based on the assumption of piecewise linear (and continuous at section boundaries) vehicle speeds rather than piecewise constant (and discontinuous at section boundaries) speeds. From these assumptions, mathematical expressions are derived that describe the trajectories within each section. These expressions can be used to replace their existing counterparts in the traditional trajectory methods. A comparison of the accuracy of the new method and of the existing method was carried out by using simulated data. This comparison showed that the root-mean-square error ( RMSE) value for the new method is about half the RMSE value for the existing method. When this RMSE is decomposed in a bias and a residual error, it turns out that the existing method significantly overestimates the travel time. However, the largest part of the reduction of the RMSE value is still caused by a reduction of the residual error. In other words, if both methods are corrected for their bias, the new method performs significantly better.
Estimating Corridor Travel Time by Using Transit Vehicles as Probes
Authors: Cathey Frederick W. , Dailey Daniel J.
Published: April 2007

A corridor approach to travel-time estimates by using transit vehicles as probes is presented. These estimates increase the information density along the corridor, compared with use of only probe information at specified points. Speed estimates are provided that track the significant changes identified in inductance-loop data, but the estimate of the speed appears to be conservative. Comparison of instantaneous travel times, often used for real-time applications, and travel time computed by using a corridor speed surface indicates that the instantaneous travel times have a delay in tracking changes in the corridor and have higher maximum travel time.
Evaluation of an Artificial Neural Network Technique Applied to Multiple-Sensor Weigh-in-Motion Systems
Authors: González Arturo , Papagiannakis A. Thomas , O’Brien Eugene J.
Published: April 2007

Weigh-in-motion (WIM) accuracy in measuring static axle loads is affected by vehicle dynamics and noise. Neural networks can identify underlying relationships, such as the spatial repeatability in axle dynamics, and can efficiently remove noise. Furthermore, they can adapt to changing circumstances (e.g., traffic characteristics, road profile, or sensor failure), unlike conventional WIM calibration algorithms. The paper performance of a multilayer feed-forward artificial neural network algorithm applied to a multiple-sensor WIM is analyzed. Numerical simulations of the axle forces applied on a smooth road profile are used to train, validate, and test the artificial neural network algorithm. This dynamic axle load variation is predicted with the vehicle simulation model VESYM. The mechanical parameters of the truck models and their speeds are randomly varied over a range established from real traffic measurements. Once the theoretical WIM data are obtained at the sensor locations, the measurements are artificially corrupted with noise up to the typical level of WIM accuracy. Details are given on the process of the neural network design, the size of the training sample, and the length of the training period. The artificial neural networks approach resulted in higher accuracy than the traditional average-based calibration method, especially at high noise levels. As a result, it shows promise for estimating static axle loads from multiple WIM measurements.
Algorithm for Detecting and Correcting Errors in Archived Traffic Data
Authors: Wall Zachary R. , Dailey Daniel J.
Published: April 2007

An algorithm is presented for correcting errors in archived loop data from freeway traffic-management systems that are the result of poorly calibrated sensors. These errors pose a significant difficulty when archived data are used in off-line analysis because the calibration errors are difficult to detect by using traditional methods. In the presented work, consistency of vehicle counts is used to judge the validity of the data: if vehicles counts are balanced, the data are valid; if vehicle counts are not balanced, the data are not valid. The method also can determine a correction factor. This correction factor is used to create a time series that can be combined with the original data to adjust the volume to create a consistent data set. To illustrate the methodology, an example case is presented that details the process of identifying a pair of reference stations that are properly calibrated. After the reference stations are identified, a poorly calibrated station is identified, and the data from this station are corrected. The result of the correction process is discussed.
Freeway On-Ramp Metering, Delay Savings, and Diverge Bottleneck
Authors: Cassidy Michael J.
Published: April 2007

An effort was made to clarify certain issues concerning freeway onramp metering and its potential for saving commuter delay. Simple analogies were used toshow that delay is reduced if ramp metering increases the rates at which commuters exit the freeway. Contrary to what is frequently reported in the literature, higher travel speeds and flows on links within a freeway system are not evidence of diminished delay and this too was made clear by the analogies. The discussion explains why a metering scheme should be specially tailored to the freeway it serves, and why no single metering logic will suffice for all situations. This idea was emphasized by demonstrating that some of the best known on-ramp metering algorithms can actually reduce freeway outflows (and therefore increase delay) when the freeway is plagued by a diverge bottleneck with a congested off-ramp. Other more effective strategies for dealing with the (commonly occurring) diverge bottleneck are described, as are methods of field-testing these strategies. Changes in commuter travel behavior brought by metering, and possible effects of these changes, are discussed as well.
Finding Near-Optimal Locations for Variable Message Signs for Real-Time Network Traffic Management
Authors: Huynh Nathan , Chiu Yi-Chang , Mahmassani Hani S.
Published: April 2007

This study addressed the problem of finding the best locations for portable variable message signs to divert traffic to alternative paths when an incident occurs so that impact on the network is minimized. The study proposed and evaluated a solution procedure for finding such locations in the context of real-time network traffic management. In this context, it was essential that the procedure find the solution to the formulated mathematical program in a relatively short time. The procedure relied on a heuristic to guide the search and a simulation-based dynamic traffic assignment program to evaluate the solution. The proposed heuristic combined principles of greedy and drop heuristics. To evaluate the proposed solution procedure, four sets of experiments were conducted on the Fort Worth, Texas, network. The results from the proposed solution procedure are compared with those obtained by other methods—( a) an a priori solution to a stochastic programming formulation, and ( b) the optimal solution with an exact (but slow to execute) procedure. It is found that the solutions obtained from the proposed solution procedure consistently outperform the a priori solutions and that they are consistently within 15% of the optimal solutions.
Series of New Local Ramp Metering Strategies: Emmanouil Smaragdis and Markos Papageorgiou
Authors: Smaragdis Emmanouil , Papageorgiou Markos
Published: April 2007

The local ramp metering strategy ALINEA is the only available feedback strategy that is based on powerful and robust automatic control methods. A number of modifications and extensions were proposed to address specific issues and needs not covered by ALINEA. More specifically, the following new local ramp metering strategies are presented: FL-ALINEA is a flow-based strategy, UP-ALINEA is an upstream-occupancy-based version, and UF-ALINEA is an upstream-flow-based strategy. X-ALINEA/Q is a combination of any of the preceding strategies with efficient rampqueue control to avoid interference with surface street traffic. The new local ramp metering strategies are discussed with respect to their features, their limitations, and their relation to available strategies. Macroscopic simulation investigations demonstrate the capabilities and limitations of the new strategies.
Measuring Recurrent and Nonrecurrent Traffic Congestion
Authors: Skabardonis Alexander , Varaiya Pravin , Petty Karl F.
Published: April 2007

A methodology and its application to measure total, recurrent, and nonrecurrent (incident related) delay on urban freeways are described. The methodology used data from loop detectors and calculated the average and the probability distribution of delays. Application of the methodology to two real-life freeway corridors in Los Angeles, California, and one in the San Francisco, California, Bay Area, indicated that reliable measurement of congestion also should provide measures of uncertainty in congestion. In the three applications, incident-related delay was found to be 13% to 30% of the total congestion delay during peak periods. The methodology also quantified the congestion impacts on travel time and travel time variability.
Incident Occurrence Models for Freeway Incident Management
Authors: Konduri Sravanthi , Labi Samuel , Sinha Kumares C.
Published: April 2007

Incident prediction models are presented for the Interstate 80/Interstate 94 (Borman Expressway in northwestern Indiana) and Interstate 465 (northeastern Indianapolis, Indiana) freeway sections developed as a function of traffic volume, truck percentage, and weather. Separate models were developed for all incidents and noncrash incidents. Three model types were considered (Poisson regression, negative binomial regression, and nonlinear regression), and the results were compared based on magnitudes and signs of model parameter estimates and t-statistics. Least-squares estimation and maximum-likelihood methods were used to estimate the model parameters. Data from the Indiana Department of Transportation and the Indiana Climatology Database were used to establish the relationships. For a given session and incident category, the results from the Poisson and negative binomial models were found to be consistent. It was observed that, unlike section length, traffic volume is nonlinearly related to incidents, and therefore these two variables have to be considered as separate terms in the modeling process. Truck percentage was found to be a statistically significant factor affecting incident occurrence. It was also found that the weather variable (rain and snow) was negatively correlated to incidents. The freeway incident models developed constitute a useful decision support tool for implementation of new freeway patrol systems or for expansion of existing ones. They are also useful for simulating incident occurrences with a view to identifying elements of cost-effective freeway patrol strategies (patrol deployment policies, fleet size, crew size, and beat routes).
State of the Practice in High-Occupancy Vehicle System Performance Monitoring
Authors: Henderson Darren
Published: April 2007

Performance monitoring has been an integral element of high-occupancy vehicle (HOV) system development since the first HOV facilities were opened in the late 1960s. Much of the current HOV guidance has evolved from the lessons learned from performance reporting during these initial projects, and performance monitoring remains the only effective way to determine whether a particular facility or system has accomplished desired goals and achieves benefits. The state of the practice in HOV system performance monitoring in the United States reveals that generally all areas conduct some form of performance monitoring, although the range of goals and objectives, performance measures, and analysis methodologies varies widely among areas. Often there is a disconnect between HOV goals and performance monitoring, resulting in monitoring programs that do not focus on appropriate expectations for the HOV system, making it inherently difficult to adequately address the legitimacy of the HOV system through performance or to appropriately respond to changing performance conditions. Disparities in HOV performance monitoring programs need to be addressed to establish an analogous range of goals, data collection techniques, and performance measures. Appropriate goals and performance measures can then be articulated for each region as the basis for ongoing monitoring. Current experience demonstrates that meaningful HOV system performance can be accomplished for relatively limited resources when goals and performance measures are focused, data collection is automated, and data analysis sampling is applied. Recognizing the need to demonstrate the benefits of HOV facilities to address public expectations, monitoring agencies call for a commitment to advance data collection technologies and to provide the necessary resources to sustain and enhance the state of the practice in HOV system performance monitoring.
Life-Cycle Graphical Representation of Managed High-Occupancy Vehicle Lane Evolution
Authors: Swisher Myron , Eisele William L. , Ungemah David , Goodin Ginger Daniels
Published: April 2007

High-occupancy vehicle (HOV) lanes usually go through an evolution of stages in their life cycle. The typical evolution includes changes in demand levels from several modes including 2+ or 3+ carpools and vanpools, transit, and general-purpose vehicles. To ensure adequate usage, most facilities have started out with a designation of HOV2+. In some cases, over time, HOV2 volumes have exceeded the capacity of the facility, which has caused delays for transit vehicles. Therefore, there is an inevitable need for managing the hierarchy of facility users over time. A graphical tool is presented that indicates the life span of a managed HOV lane, and it can be applied to a variety of existing and planned managed HOV lane projects. The graphic was used in Colorado, Florida, and Texas in communicating the managed lane concept to transportation professionals. Further, the graphic was used to explain the historical operation of a managed HOV lane facility and the likely progression if current management policies remain in effect, based on experiences in similar facilities. Alternative management strategies can also be evaluated and compared with the graphical tool. The graphical representation of this managed HOV lane concept is anticipated to be valuable for transportation professionals in many areas (e.g., highway, tolling, and transit) in presenting and understanding operating scenarios for managed lanes over time and how they meet the goals of the facility. Applications of the life-cycle graphic to various facilities in the United States are also presented.
Multicommodity Maximal Covering Network Design Problem for Planning Critical Routes for Earthquake Response
Authors: Viswanath Kannan , Peeta Srinivas
Published: April 2007

A multicommodity maximal covering network design problem (MCNDP) is formulated for identifying critical routes for earthquake response and seismically retrofitting bridges. MCNDP seeks routes that minimize the total travel time over the selected routes and maximize the total population covered, subject to a budget constraint on bridge retrofitting costs on the selected routes. The problem is formulated as a two-objective integer programming model and solved with the branch-and-cut module in the CPLEX optimizer. The model performance is analyzed with the transportation network of a seismically prone region in southwestern Indiana. A problem reduction strategy is introduced to reduce computational times by recognizing that the critical routes usually are not circuitous. Thereby, the search for the critical routes for an origin–destination (O-D) pair is confined to a limited geographical region around it. To further reduce computational costs, the formulation is extended to incorporate valid inequalities that exploit the problem structure. Computational experiments are conducted to investigate the effects of varying the budget and the relative weights of the two objectives. Noninferior frontiers that illustrate the trade-offs between the conflicting objectives for different budgets are constructed to provide practical insights to decision makers. In addition, a vulnerability analysis is performed for the various solution instances to infer their ability to ensure connectivity between all O-D pairs after an earthquake.
Modeling Integrated Lane-Changing Behavior
Authors: Toledo Tomer , Koutsopoulos Haris N. , Ben-Akiva Moshe E.
Published: April 2007

The lane-changing model is an important component within microscopic traffic simulation tools. Following the emergence of these tools in recent years, interest in the development of more reliable lane-changing models has increased. Lane-changing behavior is also important in several other applications such as capacity analysis and safety studies. Lane-changing behavior is usually modeled in two steps: ( a) the decision to consider a lane change, and ( b) the decision to execute the lane change. In most models, lane changes are classified as either mandatory (MLC) or discretionary (DLC). MLC are performed when the driver must leave the current lane. DLC are performed to improve driving conditions. Gap acceptance models are used to model the execution of lane changes. The classification of lane changes as either mandatory or discretionary prohibits capturing trade-offs between these considerations. The result is a rigid behavioral structure that does not permit, for example, overtaking when mandatory considerations are active. Using these models within a microsimulator may result in unrealistic traffic flow characteristics. In addition, little empirical work has been done to rigorously estimate the parameters of lane-changing models. An integrated lane-changing model, which allows drivers to jointly consider mandatory and discretionary considerations, is presented. Parameters of the model are estimated with detailed vehicle trajectory data.
Real-Time Optimization Model for Dynamic Scheduling of Transit Operations
Authors: Fu Liping , Liu Qing , Calamai Paul
Published: April 2007

A new transit operating strategy is presented in which service vehicles operate in pairs with the lead vehicle providing an all-stop local service and the following vehicle being allowed to skip some stops as an express service. The underlying scheduling problem is formulated as a nonlinear integer programming problem with the objective of minimizing the total costs for both operators and passengers. A sensitivity analysis using a real-life example is performed to identify the conditions under which the proposed operating strategy is most advantageous.
Optimization of Multiple-Route Feeder Bus Service: Application of Geographic Information Systems
Authors: Chien Steven I-Jy , Tsai Feng-Ming , Hou Edwin
Published: April 2007

A genetic algorithm (GA) was developed to optimize a bus transit system serving an irregularly shaped area with a grid street network. The developed objective total cost function was minimized subject to realistic demand distribution and street pattern. The service area in New York City was selected as an example to demonstrate the application of the developed model. With the application of geographic information systems, the street network within the service area was obtained and applied, while the passenger demand information was approximated based on the New York City census report of 1990. The optimal number of bus routes and their locations were found by applying the proposed GA, while the optimal headways of the routes were analytically derived. The method developed here can be applied to dynamic routing buses under various incident situations.
Forecasting Traffic Flow Conditions in an Urban Network: Comparison of Multivariate and Univariate Approaches
Authors: Kamarianakis Yiannis , Prastacos Poulicos
Published: April 2007

Several univariate and multivariate models have been proposed for performing short-term forecasting of traffic flow. Two different univariate [historical average and ARIMA (autoregressive integrated moving average)] and two multivariate [VARMA (vector autoregressive moving average) and STARIMA (space–time ARIMA)] models are presented and discussed. A comparison of the forecasting performance of these four models is undertaken with data sets from 25 loop detectors located in major arterials in the city of Athens, Greece. The variable under study is the relative velocity, which is the traffic volume divided by the road occupancy. Although the specification of the network’s neighborhood structure for the STARIMA model was relatively simple and can be further refined, the results obtained indicate a comparable forecasting performance for the ARIMA, VARMA, and STARIMA models. The historical average model could not cope with the variability of the data sets at hand.
Optimal Toll Design in Second-Best Link-Based Congestion Pricing
Authors: Yang Hai , Zhang Xiaoning
Published: April 2007

In the traffic assignment literature, it is well known that a marginal-cost toll is charged on each link to drive a user equilibrium flow pattern toward a system optimum in a general network. Although this principle is theoretically reasonable, it is not practically appealing for many reasons. In real life, a second-best pricing scheme is more attractive, where only a subset of links is subject to toll charge. Previously most studies in the research area of second-best pricing concern the determination of optimal toll levels on predetermined toll links, whereas very little attention has been devoted to the selection of toll locations. The second-best link-based pricing scheme that involves optimal selection of both toll levels and toll locations is described here. Travel cost minimization or social welfare maximization with and without inclusion of the implementation cost of the toll charge is sought in general networks. Optimization models with mixed (integer and continuous) variables are formulated for determining toll levels and toll locations simultaneously. A binary genetic algorithm is used to search optimal toll locations dynamically and a simulated annealing method is used to search optimal toll levels.
Study of Solution Approach for Dynamic Vehicle Routing Problems with Real-Time Information
Authors: Hu Ta-Yin , Liao Tsai-Yun , Lu Ying-Chih
Published: April 2007

Recent advances in commercial vehicle operations (CVO), especially in communication and information technologies, allow the study of dynamic vehicle routing problems under new and updated information, such as traffic conditions and new customers. Two major operational benefits of CVO include ( a) dynamically assigning vehicles to time-sensitive demands, and ( b) efficiently rerouting vehicles according to current traffic conditions. In this research, stochastic vehicle routing problems (SVRP) are considered and extended to incorporate real-time information for dynamic vehicle routing problems. The SVRP model is formulated by a chance-constrained model and is solved by CPLEX with branch-and-bound techniques. Numerical experiments are conducted in a Taichung city network to investigate dynamic vehicle routing strategies under real-time information supply strategies and to assess the effectiveness of such strategies in a dynamic perspective.
Real-Time Dynamic Origin-Destination Matrix Adjustment with Simulated and Actual Link Flows in Urban Networks
Authors: Tsekeris Theodore , Stathopoulos Antony
Published: April 2007

The efficiency and robustness of different real-time dynamic origin–destination (O-D) matrix adjustment algorithms were investigated when implemented in large-scale transportation networks. The proposed algorithms produce time-dependent O-D trip matrices based on the maximum-entropy trip departure times with simulated and actual observed link flows. Implementation of the algorithms, which are coupled with a quasi-dynamic traffic assignment model, indicated their convergent behavior and their potential for handling realistic urban-scale network problems in terms of both accuracy and computational time. The main factors influencing the numerical performance of each algorithm were identified and analyzed. Their relative efficiency was found to be particularly dependent on the level at which the assigned flows approximate the observed link flows. These results may provide insights into the suitability of each algorithm for diverse application domains, including freeways, small networks, and large-scale urban networks, where a different quality of O-D information is usually available.
Modeling Stress- and Moisture-Induced Variations in Pavement Layer Moduli
Authors: Richter Cheryl , Schwartz Charles W.
Published: April 2007

The in situ moduli of unbound pavement materials vary on a seasonal basis as a function of temperature and moisture conditions. The development of empirical models to predict backcalculated pavement layer moduli as a function of moisture content and stress state is addressed. The work is based on data collected via the Seasonal Monitoring Program of the Long-Term Pavement Performance Program. This research identified fundamental incompatibilities between the stress states computed from layer moduli backcalculated using linear layered-elastic theory and those used in laboratory resilient modulus testing. Important implications of this finding are that (a) application of laboratory-derived constitutive model coefficients in combination with stress states computed using linear layered-elastic theory may yield inaccurate stress-dependent modulus values and (b) meaningful advances in the state of the art for backcalculation of pavement layer moduli cannot be achieved without addressing the inaccuracies and limitations inherent in the use of linear layered-elastic theory to model nonlinear pavement response. Other important findings include the following: (c) variation in moisture content is not always the most important factor causing seasonal variations in pavement layer moduli and (d) a constitutive model form suitable for approximately incorporating the stress and moisture sensitivity of layer moduli backcalculated using linear layered-elastic procedures for practical design purposes is identified.
Direct Method for Evaluating Structural Needs of Flexible Pavements with Falling-Weight Deflectometer Deflections
Authors: Hoffman Mario S.
Published: April 2007

A direct and simple method (YONAPAVE) for evaluating the structural needs of flexible pavements is presented. It is based on interpretation of measured falling-weight deflectometer (FWD) deflection basins using mechanistic and practical approaches. YONAPAVE estimates the effective structural number (SN) and the equivalent subgrade modulus independently of the pavement or layer thicknesses. Thus, there is no need to perform boreholes, which are expensive, time-consuming, and disruptive to traffic. Knowledge of the effective SN and the subgrade modulus together with an estimate of the traffic demand allows the determination of the overlay required to accommodate future needs. YONAPAVE’s simple equations can be solved using a pocket calculator, making it suitable for rapid estimates in the field. The simplicity of the method, and its independence from major computer programs, make YONAPAVE suitable for estimating the structural needs of a road network using FWD data collected on a routine or periodic basis along network roads. YONAPAVE can be used with increased experience and confidence as the basis for nondestructive testing structural evaluation and overlay design at the project level.
Application of Wavelets in Detection of Cavities Under Pavements by Surface Waves
Authors: Shokouhi Parisa , Gucunski Nenad , Maher Ali
Published: April 2007

Application of wavelet transforms in the detection of underground shallow cavities is investigated. Wave propagation is simulated through a transient response analysis on an axisymmetric finite element model. Cavities in a homogeneous half-space and a pavement system of a variety of shapes and embedment depths are considered. The continuous wavelet transform is introduced as a new tool for cavity detection. Effects of different types of cavities on power spectral surfaces (power spectral amplitudes versus frequency and receiver location) and Gaussian wavelet time-frequency maps (wavelet transform coefficients versus time and frequency) are studied. Results show strong energy concentration in power spectral surfaces right in front of a cavity in certain frequency bands. Time and frequency signatures of waves reflected from near and far faces of the cavity can be clearly observed in the wavelet time-frequency maps. These observations are used to locate and estimate the size of the cavity. It is demonstrated that the wavelet transform is a promising analysis tool for cavity detection and characterization.
Using the Asphalt Pavement Layer Condition Assessment Program: Case Studies
Authors: Xu Bing , Ranjithan S. Ranji , Kim Y. Richard
Published: April 2007

The Asphalt Pavement Layer Condition Assessment Program (APLCAP) is developed in this research to help highway agencies assess layer conditions of asphalt pavements. APLCAP implements a new integrated procedure for condition assessment from falling-weight deflectometer (FWD) deflections. The main components of this procedure include screening of FWD raw deflections, predictions of condition indicators from FWD measurements, structural adjustments for the predicted condition indicators, and layer condition evaluation based on the adjusted condition indicators. This procedure was developed on the basis of dynamic nonlinear finite element analysis and calibrated using field measurements. The three case studies presented show that the APLCAP algorithms can predict the asphalt concrete modulus, pavement critical strains, and strengths of the base and subgrade quite well, but not the compressive strain in the aggregate base layer. Although the APLCAP procedure includes the complicated dynamic effect of FWD loading and nonlinear behavior of unbound materials, the time to obtain results from this procedure is insignificant and therefore suitable for real-time evaluation of pavement conditions.
Approaches to Evaluation of Profiler Accuracy
Authors: Li Yongqi , Delton James
Published: April 2007

The inadequacy of the existing ASTM E950 method for definition of the bias of an inertial profiler in the measurement of a pavement profile is analyzed. An improved bias calculation method is proposed. An analysis of the profile measurements and international roughness indexes (IRIs) of four pavement locations was conducted, and the results show that there is no statistical correlation between the profile biases and IRI bias. This analysis demonstrates that a profiler classified as having high accuracy in measuring profiles by ASTM E950 or other proposed bias criteria does not necessarily provide an accurate measurement of IRI. Therefore, it is recommended that the accuracy of a profiler in the measurement of IRI be evaluated independently when IRI, instead of profile, is used for a smoothness specification or other purposes. A criterion to evaluate profilers’ accuracy to measure IRI is developed based on the concept of probability.
Variation of Pavement Smoothness Between Adjacent Lanes: Implications for Performance-Based Contracting
Authors: Dougan Charles E. , Aultman-Hall Lisa , Choi Soon-Nam , Overturf Bradley , Hobson Christine
Published: April 2007

There is a need to understand how pavement smoothness varies over space and time and with other environmental factors. Information from a large set of international roughness index (IRI) field data together with traffic and pavement design and age data is used to consider IRI variation across the lanes of multilane highways and freeways in the state of Connecticut. The objective is to determine to what extent IRI varies over all lanes through time in order to consider the amount of field data that will have to be collected for departments of transportation to adequately measure or predict pavement rideability for newer performance-based contracting agreements, particularly those involving contractor warranties. Results indicate that on the basis of IRI, small average roughness differences exist between adjacent lanes. IRI values are highest in the outer right lanes. Lateral differences are relatively consistent and random but small in magnitude. No strong effects could be found between pavement age, composition, or traffic loading and IRI. However, some preliminary evidence suggests that the influence of these factors may also vary by lane. These results have implications for future research as well as the logistics of pavement monitoring by agencies for warranty-based contract payments. First, the difference in IRI between lanes is small and consistent (0.1 to 0.2) when averaged over longer sections, and therefore it is not necessary to repeat measurements for all lanes along longer projects or whole routes. Second, the variation in these field IRI measurements is unpredictable, especially over smaller spatial areas, suggesting that IRI data should be collected in all lanes when shorter projects are being considered.
Implementation of New Ride Quality Specification in Maryland: Incentive-Based Profile Specification
Authors: Stephanos Peter , Withee Jeffrey , Andrews John
Published: April 2007

The Maryland State Highway Administration (MDSHA) has developed a new, performance-based construction specification for ride quality. The new specification was developed as a strategy to meet an objective in the MDSHA business plan that requires the percentage of smoother pavements to increase statewide over the next 5 years. The new specification allows the use of inertial profiler testing devices as well as California-style rolling-wheel profilographs and includes incentive- and disincentive-based pay adjustments for asphalt paving. The specification includes an innovative approach to establishing acceptable ride quality values that considers many of the factors that affect the ability to construct a smooth riding surface. In addition, the specification includes clear identification of pay adjustments that are calculated using a software application developed by MDSHA. The new specification is to be included in all projects advertised after July 1, 2001, and implementation involves efforts to train construction project personnel in the use of the specification. Future implementation efforts phase out the use of the California-style profilograph by 2004. The efforts completed to date to develop the new specification are described, and highlights of the new specification are provided.
Pavement Surface Macrotexture Measurement and Applications
Authors: Flintsch Gerardo W. , de León Edgar , McGhee Kevin K. , AI-Qadi Imad L.
Published: April 2007

Different techniques for measuring pavement surface macrotexture and their application in pavement management are discussed. The main applications of surface macrotexture are to measure the frictional properties of the pavement surface and to detect hot-mix asphalt (HMA) construction segregation or nonuniformity. Since surface macro-texture can be measured quite efficiently using noncontact technologies and provides important information regarding pavement safety and HMA construction quality, this parameter may be included in the quality assurance or control procedures. Correlations between different measuring devices were investigated utilizing different HMA wearing surfaces. Excellent correlation was found between the circular track meter and sand patch measurements. In addition, the macrotexture determined using a laser profiler correlates well with that determined with sand patch measurements. Consistent with previous studies, it was found that the skid number gradient with speed is inversely proportional to the pavement macrotexture. However, there was a noticeable difference in speed dependency when smooth and ribbed tires were used. Oscillations in the percent normalized gradient with time due to seasonal variations were also observed. Macrotexture measurements hold great promise as tools to detect and quantify segregation for quality assurance purposes. A standard construction specification was proposed in a recent NCHRP study. However, the equation proposed for computing the nonsegregated estimated (mean) texture depth could not be applied to the mixes studied. An alternative equation has been proposed, which estimates the surface macrotexture using the mix nominal maximum size and voids in the mineral aggregate. The study was based on the mixes used at the Virginia Smart Road. Further investigation using other mixes is recommended.
Use of a Ride Quality Index for Construction Quality Control and Acceptance Specifications
Authors: Swan Mike , Karamihas Steven M.
Published: April 2007

Profilographs have traditionally been the tool of choice for measurement of newly constructed pavement roughness. Although only a modest relationship exists between profilograph output and ride quality, the construction industry has been reluctant to consider other methods of measurement. In part, this is because a well-established method exists for using a profilograph trace to pinpoint locations that require diamond grinding. In contrast, inertial profilers offer a way to obtain measurements with proven relevance to ride quality and overall pavement performance via analysis by ride quality indexes. A major drawback to using a ride quality index, as cited by the construction industry, is the lack of a method for pinpointing hot spots in pavement that should be corrected by a diamond grinder. A method for locating isolated rough spots on new pavement and a basis for prioritizing the use of a grinder to improve new pavement smoothness by using the inertial profiler output are presented. Rough spots are identified by using an adapted version of the roughness profile, called continuous reporting of ride quality. Isolated irregularities are located by reporting a ride quality index on all possible road segments of a given length. The rough spots located by this method provide a direct snapshot of where events that penalize the overall ride quality most occurred on the pavement. This snapshot provides the road builder feedback that can be used to examine the paving process. A diamond grinding simulation is used to ensure that corrective action is implemented only at locations where a grinder would actually improve ride quality.
Investigation of Tender Zone in Compaction of Coarse-Graded Superpave® Hot-Mix Asphalt Mixtures
Authors: Buchanan M. Shane , Cooley L. Allen
Published: April 2007

Tender hot-mix asphalt mixtures have been observed and experienced by paving contractors for many years. However, during the field compaction of coarse-graded Superpave® mixes, a "tender zone," not a true tender mix, is sometimes experienced. The tender zone is a range of mix compaction temperatures during which the mixture exhibits instability during roller action. Many possible causes of the tender zone have been presented, including differences in laboratory and production absorption, mix moisture, a low dust-to-asphalt ratio, increased asphalt binder film thickness, and a temperature differential with the lift. A study was conducted to document and evaluate field mixtures exhibiting the tender zone to determine the possible cause(s) of its occurrence. Documentation included mix-, production-, and construction-related items. Laboratory evaluation consisted of mixture gradation and volumetric testing along with Superpave asphalt binder testing with the project asphalt binder before and after steam distillation. Project results failed to clearly identify one particular reason for the occurrence of the tender zone. However, it is believed that the tender zone was a result of field absorption being less than the design absorption and increased asphalt binder film thickness acting in conjunction with an inherent temperature differential within the lift.
Multicharacteristic Performance-Related Specification for Hot-Mix Asphalt Pavement: Complete Development Process
Authors: Weed Richard M.
Published: April 2007

At a time when there is great interest in developing performance-related specifications incorporating multiple quality characteristics and several highly complex approaches are under development, it is questioned whether these procedures will be capable of providing the degree of practicality and ease of application sought by most practitioners. Alternatively, it is claimed that there is a simple, straightforward procedure that is suitable for most practical purposes. The components of this procedure have been successfully applied by the New Jersey Department of Transportation over a period of many years, and it is argued that additional complexity is rarely necessary or beneficial. An example is presented illustrating how readily obtainable data can be used, first to develop the performance model and then to develop the acceptance procedure for a specification for in-place air voids, thickness, and smoothness of hot-mix asphalt pavement. The example is presented in sufficient detail to demonstrate the ease with which this procedure can be learned and applied by individuals with only a basic background in engineering mathematics.