Car-following models NETSIM, INTRAS, FRESIM, and CARSIM have been extensively used for simulation of traffic conditions, including congested conditions. The car-following algorithms of these models are well known and available in the literature. However, the stability, performance, and characteristic car-following behavior of these models have not been investigated in the literature. Since the model outcomes are used in place of real data in most circumstances, it is important to know the individual vehicle behavior and car-following stability of these models. In this paper, the car-following algorithms of the above mentioned models and a recently introduced model, INTELSIM, are examined for their stability and performance in congested traffic conditions. The performance of the car-following models and the individual vehicle behavior are evaluated for accuracy, stability, problem areas, and overall model behavior for the congested conditions. Moreover, this paper aims to help the users utilize the models correctly and understand the outputs better by showing insights to the individual vehicle behavior simulated in the above models. It was found that vehicles in NETSIM and CARSIM models car-follow at separation time headways approximately equal to their reaction times. In addition, INTRAS and FRESIM presented unrealistic acceleration fluctuations and a large number of maximum decelerations. INTELSIM model presented speed and spacing profiles similar to those of the drivers.

An empirical, three-regime, freeway queuing duration model is developed from a database of 161 observations. The explanatory variable is the ratio of the annual average daily traffic volume to hourly capacity (AADT/C). The daily recurring queuing duration, in hours, is estimated to within 0.5 h of the actual at 51% of the 161 observations. The model potentially represents an improvement to the volume-delay function traditionally used in traffic assignment, because the entire peak period, not just the peak hour, is considered. The model may be useful where resources prevent the direct measurement of recurring congestion. The model's form may be considered for application in real-time traffic management. A residuals analysis indicates recommendations for model improvement, including additional explanatory variable, a larger database, careful identification of bottlenecks, circumstantial freeway capacity calculations, consideration for the day-to-day variability of recurring congestion, and nonlinear regression.

Achieving consistent geometric design is an important goal in highway design to ensure obtaining safe, economical, and smooth traffic operation. Existing operating speed models for design consistency in North America and Europe are mainly based on two-dimensional (2D) analysis of highway horizontal alignments. This paper develops operating speed models for two-lane rural highways that account for the three-dimensional (3D) nature of highways. The models will help highway designers to predict operating speed and evaluate design consistency more accurately, and thus aid highway safety. Two types of 3D combinations were considered: a horizontal curve combined with a sag vertical curve and a horizontal curve combined with a crest vertical curve. Regression analysis was used to develop the operating speed models based on data collected on Highway 61 and Highway 102 in Ontario. The results show that there is a significant difference between the predicted operating speed using the 2D and 3D models. Therefore, it is recommended that the developed 3D models be used in highway consistency analysis and evaluation.

Because a statewide transportation planning model covers a much larger area than an urban transportation planning model, land-use inventories and a household survey, which are often used to collect socioeconomic and traffic data for a UTP model, are prohibitively expensive for a STP model. The literature suggests alternatives of using the geography of census such as census tracts or block groups as Traffic Analysis Zones (TAZs) and using decennial Census for the socioeconomic data needed for statewide traffic demand modeling. The use of these alternatives raises new research questions for transportation planners. Which level of the census geography is better for statewide planning? Where should the centroids of TAZs be located given that the TAZs are heterogeneous in land-use activities? How much difference will the change of TAZ size and centroid location make in the results? Would the difference justify the extra effort in using more detailed TAZs and network? The primary purpose of this study is to determine how different TAZ structures and different roadway network details affect the ability of a STP model to replicate annual average daily traffic counts on the network. Idaho statewide traffic demand model is adopted as a case study. Results of this study can provide transportation planners a quantitative guide in selecting a zoning system for their statewide traffic demand models.

The quest for developing a payment adjustment plan for contractors considering several distress indicators simultaneously is hindered by three issues: (1) different measurement units for the distress indicators; (2) possible correlation among those indicators; and (3) variation in each of the indicators. In this study, three procedures are compiled together to cope with the preceding issues. First, normalization of each distress indicator is employed to create a dimensionless indicator. Second, principal components analysis, a multivariate statistical technique, is applied to eliminate the possible correlation among the distress indicators. Finally, through a proposed reliability analysis procedure, the pay factor is determined by the ratio of the reliability of the uncorrelated principal components of the as-built pavement over that of the as-designed pavement. Reliability refers to the level of confidence that exists in the distress indicators, not to exceed a certain limit. The results showed that pay factors based on multiple distress indicators are usually lower than those based on one single indicator when the variation in influencing factors such as asphalt concrete thickness is large.

The main objective of the most recent Mobile Load Simulator (MLS) test program was to conduct a comparative study of two rehabilitation processes, Rehabs A and B, constructed on the south- and northbound lanes of US281 near Jacksboro, Tex., in 1995 and 1996, respectively. The underlying pavements have composite asphalt layers with the first construction done in 1957. Performance was evaluated in terms of surface rutting, loss of stiffness in pavement layers, and permanent deformation in the layers. Tools used during the study included an on-site weather station, nondestructive testing equipment (FWD, SPA, PSPA, SASW), and in situ instrumentation (MDD). The findings of this study provided conclusive results on the relative performance of the two rehab strategies. Rehab A performed well with its sound underlying structure. The Dallas District has elected to use this recycling process based, in part, on the results of the MLS tests in Jacksboro. The study serves as an example of how the MLS program has yielded a variety of products and increased pavement engineering knowledge.

Fatigue behaviors of several different materials are studied by means of a numerical methodology presented in the basic formulation part of the paper. Fatigue crack growth rate and S-N curve are established; fatigue lives are evaluated; crack length variations and relative modulus changes with the number of load cycles is examined, respectively, for three kinds of materials. The influence of material properties as well as temperature on fatigue behavior is studied. These numerical results show a good agreement with available experimental results.

The study of applying the C–ϕ (cohesion and angle of friction) concept to asphalt paving mix design was once an active area of research in the early 1950s. Further research, however, was not pursued subsequently probably due to the complexity and long duration of the laboratory triaxial tests, and the difficulties encountered in relating the test results to field behavior of paving mixtures. Today, with much more advanced test equipment and powerful analytical and computation tools, another look at this theoretically sound approach is justified. By means of a C–ϕ finite element model, this paper illustrates that a link between Marshall test results and the triaxial test properties of C–ϕ can be established analytically. This presents a useful tool for analyzing past pavements that were designed on the basis of Marshall criteria. The analytical model is also used to reestablish the C–ϕ based asphalt paving mix design concept proposed by Smith in 1950, and to show that Smith's analysis model is a poor representation of multilayer asphalt pavement systems. Of special interest is that the proposed analytical C–ϕ model is able to analyze the behavior of asphalt pavement under load, thereby permitting the incorporation of mechanistic or semimechanistic distress models into asphalt mix design as well as pavement thickness design. It thus offers a potentially useful basis for an integrated procedure for asphalt paving mix design and asphalt pavement design.

This paper describes research carried out to investigate pavement material-stiffness modulus variability. Detailed pavement surface deflection data were obtained from two sections of newly constructed flexible pavement in the United Kingdom, by performing tests with a falling weight deflectometer. The deflection data were back-analyzed using the computer program PADAL to obtain estimates of the in situ pavement layer stiffness moduli. The results were statistically analyzed to identify suitable test sampling regimes for end product specifications using the falling weight deflectometer. Results show that the mean values of key deflection parameters are not very sensitive to test spacing for a nominally uniform (as specified) pavement construction. However, more variability in the standard deviations of these parameters, particularly when data were sampled at more than 50 m centers (<10 samples) was found. Results from a statistical analysis of the layer stiffness moduli showed that mean layer stiffness moduli could be reasonably estimated from a low number of samples. However, many more samples would be required for a reasonable estimation of standard deviation of the layer stiffness moduli. For lengths of pavement around 500 m, tests would be required every 10 m.

This paper presents the soil friction restraint on oblique pipelines in loose sand. A series of experimental tests are conducted in a prefabricated large-scale drag box with dimensions 1.83 m × 1.83 m × 1.22 m. Model pipes 0.61 m long with diameters of 152.4, 228.6, and 304.8 mm are obliquely moved from an axial-longitudinal to lateral-transversal direction in the drag box to study the associated soil restraints of the oblique pipes with various shallow embedded depths. All the test results indicate that for the axial pipes, the longitudinal soil restraint could be estimated as the product of the average of the vertical and horizontal earth pressures at the centerline of the pipe and the tangent value of soil-pipe friction angle, whereas for the lateral pipes, the transversal soil restraint could be predicted by using the limit equilibrium model with the assumption of the planar sliding failure surface. The longitudinal and transversal soil restraints of the oblique pipes could geometrically be obtained by multiplying the corresponding cosine and sine values of the oblique angle with the associated longitudinal soil restraint of axial pipe and the transversal soil restraint of the lateral pipe, respectively. The findings also indicate that the scale effects are not significant for the size of the pipes tested herein.

From the perspective of vehicles with a suspension system, some conventional highway design criteria do not adhere to vehicle characteristics. In particular, the relationship between minimum radius, superelevation, side friction, and design speed should be modified to incorporate modern vehicle design in body rolling. This study addresses the limitations of conventional design criteria for horizontal curves. A more appropriate equation is derived. From the revised equation, roughly 12–30% of the deflected fraction of the conventional minimum radius criteria was found. In order to ensure driving safety based on the values obtained from the revised equation, an evaluation of existing highway curves is proposed. This study also suggests that highway agencies should improve unsatisfactory sections and install speed calming measures at places that cannot be modified.