bluuebunny/crossref_metadata_2025 huggingface dataset:
Freeway Detector Assessment
Authors: Coifman Benjamin
Published: May 2018

Loop detectors have been the preeminent detection technology for several decades, but they require closing of the right-of-way during installation and potentially undermine the integrity of the pavement surface if they are not installed before paving. As a result, there is great interest in emerging technologies that promise traffic detection without the liabilities of loop detectors, many of which have already been deployed in large numbers. The remote traffic microwave sensor (RTMS) is among the most widely deployed noninvasive traffic detectors. This study evaluates the performance of the RTMS in side-fire mode relative to loop detectors in freeway applications. First, the aggregated data reported by the RTMS using its internal controller emulation are compared with data from nearby dual-loop detectors. It is shown that the RTMS measures are noisier than loop detectors for occupancy (percentage of time the detector is occupied by vehicles) and flow (number of vehicles per unit time), although the RTMS velocity estimates are almost as good as those from single-loop detectors (but inferior to direct measurement from dual-loop detectors). Second, the study considers aggregate measurements from contact closure data and compares the RTMS against the dual-loop detectors. For reference, the work also compares one loop against another in a dual-loop detector, with the spacing between loops being greater than the spacing between the reference loops and the RTMS detection zone.
Vehicle Classification Model for Loop Detectors Using Neural Networks
Authors: Ki Yong-Kul , Baik Doo-Kwon
Published: May 2018

Vehicle class is an important parameter in the process of road traffic measurement. Inductive loop detectors (ILD) and image sensors are rarely used for vehicle classification because of their low accuracy. To improve their accuracy, a new algorithm is suggested for ILD using backpropagation neural networks. In the developed algorithm, inputs to the neural networks are the variation rate of frequency and occupancy time. The output is five classified vehicles. The developed algorithm was assessed at test sites, and the recognition rate was 91.7%. Results verified that, compared with the conventional method based on ILD, the proposed algorithm improves the vehicle classification accuracy.
Connectionist Approach to Improving Highway Vehicle Classification Schemes
Authors: Kwigizile Valerian , Mussa Renatus N. , Selekwa Majura
Published: May 2018

The mechanistic–empirical pavement design methodology being developed under NCHRP Project 1–37A will require accurate classification of vehicles to develop axle load spectra information needed as the design input. Scheme F, used by most states to classify vehicles, can be used to develop the required load spectra. Unfortunately, the scheme is difficult to automate and is prone to errors resulting from imprecise demarcation of class thresholds. In this paper, the classification problem is viewed as a pattern recognition problem in which connectionist techniques such as probabilistic neural networks (PNN) can be used to assign vehicles to their correct classes and hence to establish optimum axle spacing thresholds. The PNN was developed, trained, and applied to field data composed of individual vehicles’ axle spacing, number of axles per vehicle, and overall vehicle weight. The PNN reduced the error rate from 9.5% to 6.2% compared with an existing classification algorithm used by the Florida Department of Transportation. The inclusion of overall vehicle weight as a classification variable further reduced the error rate from 6.2% to 3.0%. The promising results from neural networks were used to set up new thresholds that reduce classification error rate.
Trip-Chaining Trends in the United States
Authors: McGuckin Nancy , Zmud Johanna , Nakamoto Yukiko
Published: May 2018

This paper uses data from the 1995 Nationwide Personal Transportation Survey and the 2001 National Household Travel Survey to examine trip-chaining trends in the United States. The research focuses on trip chaining related to the work trip and contrasts travel characteristics of workers who trip chain with those who do not, including their distance from work, current levels of trip making, and the purposes of stops made within chains. Trends examined include changes in the purpose of stops and in trip-chaining behavior by gender and life cycle. A robust growth in trip chaining occurred between 1995 and 2001, nearly all in the direction of home to work. Men increased their trip chaining more than women, and a large part of the increase was to stop for coffee (the Starbucks effect). It was found that workers who trip chain live farther from their workplaces than workers who do not. It was also found that, in two-parent, two-worker households that drop off children at school, women are far more likely than men to incorporate that trip into their commute and that those trips are highly constrained between 8:00 a.m. and 9:00 a.m. An analysis was done of workers who stopped to shop and those who did not but made a separate shopping trip from home; a large potential to increase trip-chaining behavior in shopping trips was found. Results of these analyses have important policy implications as well as implications for travel demand forecast model development. Finally, this paper uses these analyses to develop conclusions about the utility of transportation policies and programs that use the promotion of trip chaining as a primary travel demand management strategy.
Field Testing of Intrusion Detection Technologies for High-Speed Rail Crossings
Authors: Blacketer Ron , Zaworski J. R. , Hunter-Zaworski K. M.
Published: May 2018

High-speed passenger rail is becoming a more common form of mass transit. A concern when high-speed rail systems are implemented is the provision of intrusion detection at rail crossings. High-speed rail equipment is lighter and faster than traditional rail equipment, and even small objects can damage or derail it. The goal of this project was to field-test two intrusion detection technologies–-a video detection system and a microwave detection system–-and determine whether they could effectively be used for intrusion detection at rail crossings. The tests used objects of varying size, color, and material composition to serve as intruders. The detection systems used were chosen as a result of several previously performed laboratory studies that suggested that both systems, though designed to detect automobiles and pedestrians, could meet the specified requirements. Field testing, however, showed that the performance level of both systems was lower than expected. Therefore, the conclusion was drawn that the technologies would require much testing and refinement before either could be implemented as a stand-alone rail crossing intrusion detection system. This report describes the field testing that was done to evaluate these systems. It includes a description of the detection systems, the test methods and results, and conclusions about the viability of these technologies for this particular application.
A Model for Evaluating Countermeasures at Highway–Railway Grade Crossings
Authors: Saccomanno Frank F. , Lai Xiaoming
Published: May 2018

Current collision prediction models fail to account for the full spectrum of relevant factors affecting the number of collisions at specific highway– railway grade crossings. A number of reasons contribute to this failure, including biases in model parameters resulting from collinearity in the model inputs, absence of important variables in the prediction model caused by lack of statistical significance, the inability of models to consider higher-order interactions, and the presence of unexplained variation in the prediction estimates. These problems have compromised the use of collision prediction models in decisions concerning the development and evaluation of cost-effective safety treatments or countermeasures for application at specific crossings. This paper introduces a stratified collision prediction model for highway–railway grade crossings. The development of this model involves three steps: ( a) crossing inventory variables are expressed in terms of a limited number of orthogonal (nonlinear) underlying attributes or factors; ( b) factor scores are estimated for each crossing and factor, and these scores are used as “seed points” in a subsequent clustering exercise to yield groups or clusters of crossings with similar underlying attributes; and ( c) for each cluster, separate collision prediction models are developed and include important treatment input variables of interest to decision makers and planners. The paper describes an application of a stratified collision prediction model to Canadian highway–railway grade crossing inventory and collision occurrence data for the period 1993 to 2001. The usefulness of the model in estimating collision reduction benefits of selected treatments is illustrated with reference to two countermeasure strategies: upgrades in the type of warning device and the removal of whistle prohibition.
Maximizing Legibility of Unlit Freeway Guide Signs with Clearview Font and Combinations of Retroreflective Sheeting Materials
Authors: Carlson Paul J. , Holick Andrew
Published: May 2018

The legibility of full-scale guide signs was evaluated in a controlled field study. The objective was to determine how the legibility of unlit guide signs could be maximized with combinations of font and retroreflective sheeting. Two fonts were tested: Series E (Modified) and Clearview 5WR, a modified version of Clearview 5W. Five combinations of retroreflective sheeting were also evaluated. The study included 30 subjects split into three age groups. Without informing the subjects, the researchers varied headlamp output to evaluate the legibility of various sign lighting levels. The results of the study clearly show that the most legible combination of font and retroreflective sheeting (of those tested) is the Clearview 5WR font and microprismatic legends on beaded, high-intensity backgrounds. Although the combination of microprismatic legends and backgrounds performed statistically equivalently to microprismatic legends on beaded, high-intensity backgrounds (in term of legibility distances), the research shows that the higher luminance contrast and lower costs associated with the latter combination make it a much more attractive application.
Evaluation of Flashing Yellow Arrow in Traffic Signal Displays with Simultaneous Permissive Indications
Authors: Knodler Michael A. , Noyce David A. , Kacir Kent C. , Brehmer Christopher L.
Published: May 2018

The results of a comprehensive study on protected and permissive left-turn (PPLT) operations showed that the flashing yellow arrow (FYA) indication was an acceptable and recommended application for permissive left turns. As documented in NCHRP Report 493, an FYA permissive indication was recommended for implementation in the FHWA Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Research findings suggested that the FYA be implemented in an exclusive four-section vertical signal display centered over the left-turn lane, which differs from the most common application of PPLT signal displays. Many traffic engineers currently use a five-section clustered-arrangement shared signal head to meet MUTCD requirements of two signal heads per major approach. FYA implementation in the five-section display would require an interim retrofit requiring the FYA to be displayed simultaneously with the through-movement circular green (CG), circular yellow, or circular red indication. This research evaluated driver comprehension of the retrofit display and the resulting simultaneous indications by using a dynamic driving simulator and computer-based static experiments. A comparison of seven permissive left-turn scenarios featuring the CG or FYA permissive indications, or both, was completed. In total, 264 drivers evaluated 3,457 permissive left-turn scenarios. Results showed that simultaneous indications in the retrofit display did not affect the drivers’ understanding of the permissive indications. The drivers demonstrated an understanding of the yield requirement with simultaneous indications (with a 65% to 89% correct responses), providing evidence to suggest that the simultaneous indications would be suitable as an interim display to ease FYA implementation.
Effectiveness of Lane Direction Arrows as Pavement Markings in Reducing Wrong-Way Movements on Two-Way Frontage Roads
Authors: Schrock Steven D. , Hawkins H. Gene , Chrysler Susan T.
Published: May 2018

The principal objective of this research was to conduct a before-and-after study of the impacts of using lane direction arrows on a two-way frontage road to determine if the arrows could reduce wrong-way movements for vehicles exiting the freeway. A recent national survey related to all-white pavement markings indicated that 94% of the 851 drivers surveyed correctly interpreted the intended meaning of the arrows to indicate the proper lanes for travel. The authors believed that this high comprehension rate could be useful in helping drivers at locations where a potential for driving in the wrong direction exists. Video surveillance of a two-way frontage road before and after installation of lane direction pavement marking arrows was conducted. It was observed that at the selected location, approximately one of every 13 drivers exiting the freeway to the frontage road acted as though the frontage road were a one-way section and incorrectly chose the left lane for travel. Significant reductions were observed in wrong-way driving after the installation of two lane direction pavement marking arrows downstream from the exit ramp. After the installation, only one of 150 vehicles selected the incorrect lane. Researchers concluded that lane direction pavement marking arrows had a beneficial effect on safety at the study location and recommended expanded efforts to determine other locations that could benefit from this treatment. Although the evaluation was limited to one study site, the strength of the results suggests that the treatment would be beneficial at other similar locations.
Comparison of Radius-Estimating Techniques for Horizontal Curves
Authors: Carlson Paul J. , Burris Mark , Black Kit , Rose Elisabeth R.
Published: May 2018

Techniques to obtain horizontal curve radii were identified and tested in a controlled experimental study. Ten techniques were identified and pilot tested. Eight of those initial 10 were then used to measure 18 horizontal curves on two-lane rural highways in Texas to evaluate fully their accuracy, precision, cost, ease of use, and safety. Statistically, all eight techniques produced equivalent accuracies, but they displayed a wide range in their precision. The costs varied as a function of the number of times each technique would be used in the field, with those techniques with high initial costs becoming more cost-competitive over the long run with many uses. Ease of use was gauged on the basis of the experience gained during this research. Safety was measured on the basis of whether a technique required personnel on the roadway or roadside or whether it allowed personnel to work from an office or inside a vehicle. The recommendations were based on the expected needs of three different groups that use radii information: transportation agencies, accident investigators, and transportation researchers. Within transportation agencies, engineers and planners in the office will probably benefit most from the plan sheet method, whereas field personnel will probably benefit most from using either the advisory speed or a Global Positioning System (GPS) method. Those who estimate only occasionally, such as accident investigators, will benefit most from the compass method. Finally, researchers or others who may have difficulty accessing plan sheets but still require accurate data will benefit from using a GPS.
Evaluation of Dynamic Speed Display Signs
Authors: Ullman Gerald L. , Rose Elisabeth R.
Published: May 2018

This paper describes an analysis of the effectiveness of dynamic speed display signs (DSDSs) installed in several permanent locations. Sites evaluated included a school speed zone, two transition speed zones in advance of a school speed zone, two sharp horizontal curves, and two approaches to signalized intersections on high-speed roadways. Data were collected before the DSDSs were installed, about one week after installation to determine initial effects of the signs upon vehicle speeds, and again about four months after installation to determine how well the initial speed reductions were maintained. Researchers analyzed average speeds, 85th percentile speeds, and the percentage of the sample exceeding the speed limit. In addition, least-squares regression analyses between the speed of a vehicle upstream of the DSDS and that vehicle's speed measured again at the DSDS were performed to determine whether the sign affected higher-speed vehicles more substantially than lower-speed vehicles. Overall, average speeds were reduced by 9 mph at the school speed zone. Elsewhere, the effect of the DSDS was less dramatic, with average speeds reduced by 5 mph or less depending on the location tested. As expected, those motorists traveling faster than the posted speed limit did appear to reduce their speed more significantly in response to the DSDS than did motorists traveling at or below the posted speed limit. The results of this project suggest that DSDSs can be effective at reducing speeds in permanent applications if appropriate site conditions apply.
Measuring the Impacts of Speed Reduction Technologies
Authors: Monsere Christopher M. , Nolan Casey , Bertini Robert L. , Anderson Edward L. , El-Seoud Tarek Abou
Published: May 2018

This paper presents the results of a quantitative and qualitative evaluation of a dynamic curve warning system deployed at one site on Interstate 5 in Oregon. On a dynamic message sign, the system displays messages directed to drivers on the basis of the observed speed of approaching vehicles. For the evaluation, three measures of effectiveness were selected: ( a) the change in mean speed for passenger cars and commercial vehicles, ( b) the change in the speed distribution for both passenger cars and trucks, and ( c) public response to the sign. Speed samples were taken of vehicles with a laser ranging and detection device recording both speed and distance information over 7 days: four in the before period and three in the after period. The quantitative evaluation indicated that the advanced curve warning system was effective in reducing the mean speeds of passenger cars and trucks by approximately 3 mph for the southbound direction and 2 mph for the northbound direction. After the system was installed, the distribution of vehicle speeds was statistically different, with a lower number of vehicles in the higher speed bins. Because the system was installed only recently, crash reduction impacts have not yet been evaluated. Intercept surveys of motorists at nearby rest areas revealed a positive perception of the system. Overall, the results of the evaluation indicate that the advanced curve warning system is effective.
Onset Times and Detection of Colored Signal Lights
Authors: Bullough John D.
Published: May 2018

Light sources used in signal lights for transportation applications have a variety of temporal onset characteristics, including a wide range of onset times. These characteristics, along with luminous intensity and color characteristics, can have important impacts on the ability to detect and respond to colored signal lights. Studies of the impact of these factors on responses to colored signals are reviewed, along with potential implications for the selection of light sources used in traffic and vehicle signals. The onset characteristics of recently developed light sources might offer significant potential to improve visual detection of signal lights. Nonetheless, it is important to understand the context in which a signal light is presented to determine whether such improvements in visual detection have practical significance.
Engineering Solution for the Uniform Strength of Partially Cracked Concrete
Authors: Jensen Elin A. , Hansen Will , Brincker Rune
Published: May 2018

Significant computational resources are required to predict the remaining strength from numerical fracture analysis of a jointed plain concrete pavement that contains a partial depth crack. It is, therefore, advantageous when the failure strength can be adequately predicted with an engineering solution. Current engineering or closed-form solutions are based on the elastic effective crack approach with the fracture parameters toughness and critical crack tip opening of concrete. The solutions do not directly consider the effect of the distance to the boundary conditions (restrained slab length) and the cracking process caused by stress softening across the crack. A proposed engineering solution methodology includes these latter variables. The application of the solution is demonstrated on a slab containing a partial depth midslab crack and subjected to in-plane tension. The solution captures the effects of material fracture properties and structural size in terms of crack length and distance from boundary to the crack. The model assumes a bilinear stress–crack width relationship for the fracture process zone. The concrete characteristic length, determined from the fracture energy represented by the first part of the stress–crack width relationship, controls the failure load of a partially cracked concrete slab. A unique master curve between slab strength and crack depth was developed using the results from the numerical analysis. The master curve was verified with results from laboratory testing of large-scale slabs subjected to in-plane tension. The solution methodology can readily be extended to other loading cases.
Improvements of Testing Procedures for Concrete Coefficient of Thermal Expansion
Authors: Won Moon
Published: May 2018

The coefficient of thermal expansion (CTE) of concrete has a significant effect on the performance of portland cement concrete pavement. Concrete with a higher CTE is more prone to cracking, additional warping, and spalling. To improve PCC pavement performance, several districts of the Texas Department of Transportation (TxDOT) currently limit the CTE of concrete. To support this policy, efforts have been made to improve the accuracy and repeatability of the testing procedures for CTE. The current AASHTO Test Method TP 60 has been evaluated, its shortcomings identified, and improvements made. The improvements include CTE determination from regression analysis of temperature and displacement measurements. The effects of a number of variables on concrete CTE were investigated. The effect of the rate of heating and cooling is negligible. Concrete age and specimen size also have a negligible effect. Coarse aggregate content in the concrete mix has an effect on the test results. This test procedure was used to evaluate coarse aggregates from 32 sources in Texas. The results show that coarse aggregate type has a significant effect on concrete CTE. The proposed testing procedure for concrete CTE provided more accurate results than the AASHTO TP 60. TxDOT plans to implement this test procedure and to develop appropriate steel design standards for continuously reinforced concrete pavement and other construction-related requirements such as different curing methods for concrete with varying CTEs. This implementation should result in better concrete pavement performance.
Enhanced Portland Cement Concrete Fatigue Model for StreetPave
Authors: Titus-Glover Leslie , Mallela Jagannath , Darter Michael I. , Voigt Gerald , Waalkes Steve
Published: May 2018

The Portland Cement Association (PCA) pavement thickness design method for jointed concrete pavements is mechanistically based and consists of both fatigue and erosion analyses. It determines the minimum slab thickness required for a given set of site and design conditions on the basis of both fatigue and erosion criteria. At the heart of the fatigue analysis is the fatigue model, which establishes the number of allowable load repetitions for a given stress ratio [ratio of flexural edge stress caused by the application of wheel loads to the portland cement concrete (PCC) slab flexural strength]. The PCA fatigue model is based on data derived from beam fatigue tests conducted in the early 1950s and 1960s. The model estimates the conservative lower-bound estimate of the allowable number of load applications at a given stress ratio (i.e., it incorporates a high degree of reliability–-approximately 90% or higher). Although this may be desirable for high-volume, high-traffic pavements, it is too conservative for low-volume roads or street pavements. The PCA pavement thickness design method currently is being used in the American Concrete Pavement Association (ACPA) pavement design software, StreetPave. StreetPave incorporates the PCA's pavement thickness design methodology in a Windows-based user platform. ACPA commissioned a study to expand, improve, and broaden the current PCA fatigue model by including reliability as a parameter for predicting PCC fatigue damage and by calibrating the enhanced model with additional fatigue data from recently completed studies. An enhanced fatigue model was then developed.
Stress Prediction for Cracking of Jointed Plain Concrete Pavements, 1925–2000
Authors: Ioannides Anastasios M.
Published: May 2018

The evolution of analytical methods for the prediction of cracking in jointed plain concrete pavements was traced over the period from the publication of Westergaard's early work until the year 2000. This development was accomplished in parallel with the birth and coming of age of geotechnical engineering and was likewise pioneered by a number of colorful and distinguished personalities. Westergaard's limiting assumptions have defined the task for generations of pavement engineers who, with road tests and laboratory studies, jerry-rigged equipment, and sophisticated electronic tools, have eventually managed to eliminate each one of them. As a new era of mechanistic–empirical pavement design is ushered in, it behooves the profession to undertake a concerted and serious effort to eliminate the most crucial remaining stumbling block to their efforts: Miner's fatigue hypothesis. Fracture mechanics, similitude concepts, and the principles of dimensional analysis hold the brightest promise of a future worthy of the pioneers celebrated here.
Concrete-Filled, Glass Fiber–Reinforced Polymer Dowels for Load Transfer in Jointed Rigid Pavements
Authors: Murison Scott , Shalaby Ahmed , Mufti Aftab
Published: May 2018

Smooth, round steel dowels have been used for nearly a century to transfer wheel loads across concrete pavement joints. Dowels are subjected to shear and bending stresses caused by traffic loads in addition to curling stresses caused by temperature gradients in pavement slabs. Over time, the use of deicing salts corrodes steel dowels and causes damage to concrete pavement joints. Alternative dowel materials, such as stainless steel and glass fiber–reinforced polymer (GFRP), have been introduced in recent years. The dominant size of dowels for highway pavements has remained the same, typically 38 mm in diameter, and costs can be considerably higher for stainless steel compared with epoxy-coated steel dowels of the same size. Experimental tests at the University of Manitoba, Canada, examined the performance of four dowel types, including the standard 38-mm epoxy-coated steel; 38-mm solid, pultruded GFRP dowels; and 50-mm and 63.5-mm concrete-filled GFRP tube dowels. The dowels were cast in small concrete slabs of typical pavement thickness and instrumented with strain and displacement gauges. Behavior of the dowels was evaluated on the basis of measured displacements, bending strains, and performance for more than 1 million load cycles. Concrete-filled GFRP tube dowels exhibited considerably smaller displacements and, therefore, lower bearing stresses than 38-mm steel and solid GFRP bars. After 1 million load cycles, concrete-filled dowels and concrete slab showed no signs of fatigue damage or loss of load transfer, indicating a reasonable potential for replacing steel dowels, particularly in corrosive environments.
Estimating the Sensitivity of Design Input Variables for Rigid Pavement Analysis with a Mechanistic–Empirical Design Guide
Authors: Hall Kevin D. , Beam Steven
Published: May 2018

Many highway agencies use AASHTO methods for the design of pavement structures. Current AASHTO methods are based on empirical relationships between traffic loading, materials, and pavement performance developed from the AASHO Road Test (1958–1961). The applicability of these methods to modern-day conditions has been questioned; in addition, the lack of realistic inputs regarding environmental and other factors in pavement design has caused concern. Research sponsored by the NCHRP has resulted in the development of a mechanistic–empirical design guide (M-E design guide) for pavement structural analysis. The new M-E design guide requires more than 100 inputs to model traffic, environmental, material, and pavement performance to provide estimates of pavement distress over the design life of the pavement. Many designers may lack specific knowledge of the data required. A study was performed to assess the relative sensitivity of the models used in the M-E design guide to inputs relating to portland cement concrete materials in the analysis of jointed plain concrete pavements. Twenty-nine inputs were evaluated by analysis of a standard pavement section and change of the value of each input individually. The three pavement distress models (cracking, faulting, and roughness) were not sensitive to 17 of the 29 inputs. All three models were sensitive to six of the 29 inputs. Combinations of only one or two of the distress models were sensitive to six of the 29 inputs. These data may aid designers in focusing on inputs that have the most effect on desired pavement performance.
Calibration of Alligator Fatigue Cracking Model for 2002 Design Guide
Authors: El-Basyouny Mohamed M. , Witczak Matthew
Published: May 2018

In AASHTO's 2002 design guide, the classic fatigue cracking mechanism, which normally initiates at the bottom of the asphalt layer and propagates to the surface (bottom-up cracking), was studied. The prediction of bottom-up alligator fatigue cracking was based on a mechanistic approach to calculate stress and strain. An empirical approach then related these strains to fatigue damage in pavement caused by traffic loads. To provide credibility to the new design procedure, the theoretically predicted distress models must be calibrated to “real-world” performance. In fact, calibration of these distress models is considered to be the most important activity to facilitate implementation, acceptance, and adoption of the design procedure and to establish confidence in the entire procedure. The procedure followed for the national calibration of the alligator fatigue–cracking model used in the AASHTO 2002 design guide is discussed. This calibration study used data from all over the United States, with different environments, material, and traffic. A total of 82 pavement sections from 24 different states were used in the calibration. Tensile strain at the bottom of each asphalt layer was calculated using a linear layer elastic analysis procedure. The initial (base) reference model used in the calibration was the Asphalt Institute MS-1 model. This model was used to compute the damage caused by traffic loads and pavement structure. Predicted damage was then correlated to the measured fatigue cracking in the field, and a transfer function was obtained for the alligator fatigue–cracking distress.
Field and Theoretical Evaluation of Thermal Fatigue Cracking in Flexible Pavements
Authors: Al-Qadi Imad L. , Hassan Marwa M. , Elseifi Mostafa A.
Published: May 2018

Thermal cracking in flexible pavement occurs when the tensile stress exceeds the tensile strength of hot-mix asphalt at a given temperature or when fluctuating stresses and strains caused by temperature variation lead to a buildup of irrecoverable deformations over time. The objective of this study was twofold: ( a) to quantify the measured strain magnitude associated with thermal fatigue through field measurements and ( b) to present a three-dimensional, finite element (FE) model that accurately simulated thermal fatigue in flexible pavement. Results of the experimental program indicated that pavement response to thermal loading was associated with a high strain range, reaching a maximum recorded value of 350 μm/m. This finding confirms the hypothesis that the criticality of thermal fatigue arises from the high stress–strain level exhibited in each cycle rather than its frequency, which is usually the critical factor in load-associated fatigue cracking. Moreover, the developed FE model accurately simulated pavement response to thermal loading by conducting a sequential coupled heat transfer analysis. Results of the developed FE model were in agreement with field measurements and demonstrated the model's capability to simulate both the temperature and stress fields associated with thermal loading. This model may be used to evaluate pavement performance against transverse cracking induced by thermal fatigue.
Analytical Study of Effects of Truck Tire Pressure on Pavements with Measured Tire–Pavement Contact Stress Data
Authors: Machemehl Randy B. , Wang Feng , Prozzi Jorge A.
Published: May 2018

Truck tire inflation pressure plays an important role in the tire–pavement interaction process. As a conventional approximation method in many pavement studies, tire–pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and to be simply equal to the tire pressure. However, recent studies have demonstrated that the tire–pavement contact stress is far from uniformly distributed. Measured tire–pavement contact stress data were input into an elastic multilayer pavement analysis program to compute pavement immediate responses. Two asphalt concrete pavement structures, a thick pavement and a thin pavement, were investigated. Major pavement responses at locations in the pavement structures were computed with the measured tire–pavement contact stress data and were compared with the conventional method. The computation results showed that the conventional method tends to underestimate pavement responses at low tire pressures and to overestimate pavement responses at high tire pressures. A two-way analysis of variance model was used to compare the pavement responses to identify the effects of truck tire pressure on immediate pavement responses. Statistical analysis found that tire pressure was significantly related to tensile strains at the bottom of the asphalt concrete layer and stresses near the pavement surface for both the thick and thin pavement structures. However, tire pressure effects on vertical strain at the top of the subgrade were minor, especially in the thick pavement.
Implementation Initiatives of the Mechanistic–Empirical Pavement Design Guides in Indiana
Authors: Nantung Tommy , Chehab Ghassan , Newbolds Scott , Galal Khaled , Li Shuo , Kim Dae Hyeon
Published: May 2018

The release of the Mechanistic–Empirical Design Guide for New and Rehabilitated Pavement Structures (M-E design guide) generated a new paradigm for designing and analyzing pavement structures. It is expected to replace the commonly used empirical design methodologies. The M-E design guide uses a comprehensive suite of input parameters deemed necessary to design pavements with high reliability and to predict pavement performance and distresses realistically. However, the considerable amount of input needed and the selection of the corresponding reliability level for each might present state highway agencies with complexities and challenges in its implementation. An overview is presented of ongoing investigative studies, sensitivity analyses, and preimplementation initiatives conducted by the Indiana Department of Transportation (INDOT) in an effort to accelerate the adoption of the new pavement design guide by efficiently using existing design parameters and determining those parameters that influence the predicted performance the most. Once the sensitive inputs are identified, the large amount of other required design input parameters can be significantly reduced to a manageable level for implementation purposes. A matrix of trial runs conducted with the M-E design guide software suggests that a higher design level input does not necessarily guarantee a higher accuracy in predicting pavement performance. The software runs also confirmed the need to use input values obtained from local rather than national calibration. Such findings are important for state highway agencies such as INDOT in drafting initiatives for implementing the M-E design guide.
Strategic Plan of the Texas Department of Transportation for Implementing NCHRP 1–37A Pavement Design Guide
Authors: Uzan Jacob , Freeman Thomas J. , Cleveland Gregory S.
Published: May 2018

The Texas Department of Transportation (TxDOT) used the recently released NCHRP 1–37A guide and software to develop a strategic plan for its implementation of operations. The new guide includes all possible variables that may affect the performance of the pavement. A general sensitivity study of these variables was conducted with an early version of the software. A few focused studies were conducted, including ( a) a preliminary local calibration of the guide with 11 Strategic Highway Research Program General Pavement Studies sections in Texas, ( b) traffic composition effect compared with that of the traditional 80–kN equivalent single-axle loads (ESALs) and of the design load, and ( c) effect of the choice of the weather station and of changing the water table depth on the performance of the pavement. The results indicate that ( a) the use of the 80–kN ESALs leads to underdesigning the structure, ( b) the design load concept can be used in screening runs to determine a preliminary design, and ( c) in the case analyzed, changing the depth of the water table resulted in changing the moduli of the unbound material but did not affect the performance. Finally, a strategy for implementation was recommended to TxDOT, including ( a) training, ( b) laboratory testing and equipment acquisition, ( c) field forensic studies for calibration, ( d) calibration and validation of the guide, and ( e) additional studies.
Evaluation of Predicted Pavement Response with Measured Tire Contact Stresses
Authors: Park Dae-Wook , Fernando Emmanuel , Leidy Joe
Published: May 2018

A uniform circular vertical contact stress is commonly assumed in representing wheel loads in pavement analysis procedures. However, experimental measurements have shown that actual loading conditions are nonuniform and depend on tire construction, tire load, and tire inflation pressure. Predicted pavement response from three-dimensional (3D) finite element (FE) and layered elastic programs were compared to establish guidelines for modeling wheel loads in current layered elastic pavement analysis programs to provide a better approximation of pavement response parameters for design and evaluation. Tire contact pressure was measured with the stress-in-motion pad. In addition, tire contact pressure measurements from a previous study conducted at the University of California at Berkeley were obtained. Available contact pressure measurements on four tires were used to predict pavement response with a 3D FE program, which permitted input of measured tire contact pressures at various tire loads and tire inflation pressures. Horizontal strain at the bottom of the asphalt layer, compressive strain at the top of the subgrade, and principal stresses at different depths were predicted. Similar predictions were generated with layered elastic theory with two different representations of contact pressure and contact area. From predicted strains, service life for a range of pavements, tire load, and tire inflation pressures were estimated with limiting strain criteria. In addition, Mohr-Coulomb (MC) yield function values were calculated from predicted principal stresses at different depths. The MC yield function values and pavement life estimates from 3D FE and layered elastic analyses were compared with established guidelines for modeling wheel loads using existing layered elastic procedures.
Urban Commercial Vehicle Movement Model for Calgary, Alberta, Canada
Authors: Stefan K. J. , McMillan J. D. P. , Hunt J. D.
Published: May 2018

Commercial vehicle movements compose perhaps 15% of all urban vehicle trips and produce large impacts in key areas, such as congestion, emissions, road wear, and industrial area traffic. A system for modeling such movements was developed for Calgary, Alberta, Canada. It is a novel application of an agent-based microsimulation framework that uses a tour-based approach and emphasizes important elements of urban commercial movement, including the role of service delivery, light commercial vehicles, and trip chaining. The microsimulation uses Monte Carlo techniques to assign tour purpose, vehicle type, next-stop purpose, next-stop location, and next-stop duration. Tours are “grown” with a return-to-establishment alternative within the next-stop purpose allocation, which is consistent with the nature of tour making in urban commercial movements. The Monte Carlo probabilities are established with the use of a series of logit models, with coefficients estimated on the basis of observed behavior of different commercial movement segments. The estimation results in themselves provide insights into the revealed behavior that have not been available previously.
Incorporating Trip-Chaining Behavior into Network Equilibrium Analysis
Authors: Maruyama Takuya , Harata Noboru
Published: May 2018

The network equilibrium model is a useful tool for long-term transportation planning and is one promising alternative to the traditional four-step travel forecasting model. However, some issues with the model remain to be considered. For example, almost all variations of the model adhere to the traditional trip-based approach, in which trip chains made by users are treated as separate, independent entities in the analysis. This research aims to develop a simple, tractable model to overcome this problem. One proposed model is based on piston-type trip chaining, and another accommodates any other type of trip chaining and includes congestion phenomena. These proposed models have certain key features: they have been successfully formulated as convex minimization problems, so uniqueness and algorithm convergence are easily proved; traveler behavior is based on theoretically sound random utility models, which allows the benefit of transportation projects to be calculated such that it is consistent with travel demand forecasting; and optimal road pricing can be calculated even in large-scale networks. These models are examined with the use of simple network examples, with special attention paid to the effect of trip-chaining behavior at the level of second-best toll. In a simple two-destination network, the second-best toll of the trip-based model is lower than that of trip chain–based model, indicating one of the biases of the trip-based model.
Path Size Modeling in Multimodal Route Choice Analysis
Authors: Hoogendoorn-Lanser Sascha , van Nes Rob , Bovy Piet
Published: May 2018

Travelers in multimodal networks make many choices (e.g., main mode, access modes, egress modes, boarding nodes, transfer nodes, and egress nodes). One way to address this complexity of choices is to analyze choice sets of multimodal routes. However, choice sets for multimodal networks are large, and overlap of routes within choice sets is substantial. This paper focuses on overlap in multimodal transport networks. An overview of the topic of overlap and route choice modeling is given and is followed by an analysis of how overlap might be defined in the context of multimodal networks. Three definitions of “overlap” are proposed, based on number of legs, time, or distance. The different definitions are analyzed using path size logit estimations, which show that path size must be accounted for. Furthermore, the definition of “path size” for multimodal transport networks should be different from that used for road networks: for multimodal transport networks, a definition using number of legs yields substantially better results. Estimation results suggest that the weighting parameter corresponding with the path size variable should be equal to 1, implying that the path size variable based on number of legs accounts for the correlation of error terms of overlapping parts.
Discrete Choice with Social and Spatial Network Interdependencies
Authors: Dugundji Elenna R. , Walker Joan L.
Published: May 2018

Discrete choice analysis has become an industry standard in land use and transportation models. Such models are fundamentally grounded in individual choice; therefore, the treatment of interdependencies among decision makers is a formidable challenge. Through an empirical application to mode choice, the capture of interdependencies in discrete choice is described and illustrated. Decision makers are assumed to be influenced, for example, by people of similar socioeconomic status who are nearby. Given such social and spatial network relationships, the choice model captures interdependencies in two ways: ( a) including in the systematic utility variables that describe choices of others in the decision maker's social and spatial network and ( b) allowing for correlation across the disturbances of decision makers within the same social and spatial network. Variations of these approaches (including their combination and the use of random parameters) are tested with mode choice and compared with traditional methods of market segmentation. The application results indicate that the proposed methods for capturing interdependencies are significant and superior to traditional methods. Furthermore, capturing the interdependencies in the systematic utility is sufficient: it is better than the model with just correlation and is not significantly worse than the model with both the systematic term and correlation. The systematic term also captures a feedback effect that can propel the adoption of a new mode over time, for example. Models are estimated with the use of a traditional transportation data set and readily available software.
Analysis of Joint Household Decisions about Car and Motorbike Ownership and use in Taiwan
Authors: Jou Rong-Chang , Kou Shih-Chieh , Chen Chih-Cheng
Published: May 2018

Decisions about automobile ownership and use have been the subject of several investigations over the past few decades. However, decisions about car and motorbike ownership and use have not been sufficiently explored. It is important and useful for researchers and government officials in Taiwan to consider joint household decisions about car and motorbike ownership because many motorbikes are used in Taiwan. Therefore, both cars and motorbikes are considered in this study on the basis of microeconomic consumer behavior theory, in which fixed and variable costs are the two main components of budget restriction. A household is assumed to maximize its utility with three parameters: annual kilometers traveled by car, annual kilometers traveled by motorbike, and annual volume of all other goods and services (in monetary units). Probabilities of car and motorbike ownership are derived and calculated from demand functions and indirect utilities. Different scenarios are modeled to investigate the impact of changes in variable and fixed costs of car and motorbike, income, and combinations of these parameters on car and motorbike ownership and use.