Air-transport demand forecasting constitutes an important determinant of airport planning, design, and operations. Errors in forecasting can be very costly. Underestimating demand may lead to increased congestion, delay, and inadequate airport facilities. Overestimating demand may also create serious economic problems for airport authorities. It is, therefore, very important for airport planners to develop reliable forecasting models and to understand possible limitations in the forecasting accuracy of these models. The objective of this paper is to examine the predicting ability and forecasting accuracy of air-travel demand models. In particular, an analytical framework for developing econometric models is presented and postfact analysis is used to test the accuracy of the models. Statistical data describing air-travel demand patterns for two major international airports, the Frankfurt and the Miami International Airports, are used to demonstrate the effectiveness of the proposed models. In addition, the effect of external factors such as the deregulation of the air-transport industry is examined. The results suggest that simple models with few independent variables perform as well as more complicated and costly models, and that external factors have a pronounced effect on air-travel demand.

Traffic accidents at urban intersections result in a huge cost to society in terms of death, injury, lost productivity, and property damage. Unfortunately, the elements that effect the frequency of intersection accidents are not well understood and, as a result, it is difficult to predict the effectiveness of specific intersection improvements that are aimed at reducing accident frequency. Using seven-yr accident histories from 63 intersections in Bellevue, Washington (all of which were targeted for operational improvements), this paper estimates a negative binomial regression of the frequency of accidents at intersection approaches. The estimation results uncover important interactions between geometric and traffic-related elements and accident frequencies. The findings of this paper provide exploratory methodological and empirical evidence that could lead to an approach to estimate the accident reduction benefits of various proposed improvements on operationally deficient intersections.

Vehicle delay is one of the most serious impacts of highway workzones on existing traffic operations. The present study provides a comprehensive and detailed estimation of traffic delay due to a freeway workzone where the roadway in one direction is closed and the traffic usually on the closed roadway is diverted to share the roadway in the opposite direction. The total delay was decomposed into speed reduction delay and congestion delay. Different procedures were developed to estimate speed reduction delay for several roadway conditions. A mathematical model was developed to find the length of the queue upstream of a workzone and a procedure was generated to estimate daily congestion delay under any given condition. Alternative roadway closure patterns along the length of a given project were evaluated in terms of traffic control cost and additional road user costs. The optimal workzone length for a given project was studied. Procedures were developed to determine the optimal workzone length.

For level-of-service analysis, the 1994 Highway Capacity Manual divides freeways into basic sections, ramps and ramp junctions, and weaving areas. Different criteria are applied to these components to define levels of service. This use of nonuniform criteria makes it difficult to assess operating consistency in terms of the spatial change of traffic operations throughout a freeway system. This problem can be alleviated by using vehicle speed to establish a set of uniform criteria for the systemwide evaluation of freeway design and operation. Toward this end, the relationships between speed and other related geometric design and traffic parameters should be established. The spatial variations of flow characteristics on freeways, and the need to account for such variations in capacity and level-of-service analysis, are discussed first by analyzing observed speed-flow relationships. This is followed by a discussion on the selection and application of uniform criteria for planning and design.

A new asphalt layer modulus degradation model for use with flexible-pavement analysis procedures is described. The model is capable of determining the reduction in stiffness of the asphaltic material in a flexible pavement due to cumulative fatigue damage. Measured surface deflection bowls from a number of test pavements are used with a pavement parameter back-calculation procedure, to determine the reduction in stiffness of the asphaltic material throughout the life of the pavement. Results show an exponential relationship between the reduction in asphalt layer stiffness and cumulative fatigue damage. This type of relationship does not agree with an earlier theoretical continuum damage mechanics model, where the relationship between the reduction in asphalt layer stiffness and cumulative fatigue damage was predicted to be linear.

This paper provides a time-domain solution to the problem of viscoelastic pavement response under moving dynamic loads. It assumes linear material behavior and uses Boltzman's principle to superimpose the effect of a loading function with time-dependent amplitude to the influence function of a pavement response parameter. The unique element of this formulation is that it takes into account the variation of the dynamic load within the area of influence of the moving load at any particular location. This formulation is applied in evaluating the effect of two suspension types, generically referred to as air and rubber. Dynamic load data for these suspensions was experimentally obtained with an instrumented vehicle. The accumulation of strain cycles along the road was translated into number of repetitions to fatigue failure assuming spatial repetitiveness of dynamic loads. Overall pavement section failure was defined as the number of repetitions corresponding to the 90th percentile of the subsection survival curves. The relative damaging effect of the two suspensions was evaluated in terms of the ratio of the number of repetitions to failure for a load of constant magnitude divided by the number of repetitions to failure for the dynamic load.

Westergaard solutions for maximum bending stress and deflection are derived by assuming infinite slab width and length, and ignoring possible thick-plate behavior of slab under loading. This paper examines the effects of these two factors on Westergaard solutions by comparing with thick-plate solutions for rectangular slabs derived by the writers. The infinite slab assumption is found valid if the slab length is more than four times the radius of relative stiffness. However, because of thick-plate action, not all solutions for slab responses converge to Westergaard values when slab sizes are large. For large slabs where the effect of slab dimensions is negligible, the difference of thick-plate solutions and Westergaard solutions for maximum bending stress are less than 15% for square slabs, and less than 20% for 3.66 m (12 ft) wide rectangular slabs. For these large slabs, the values of maximum deflection obtained from the two solutions show good agreement in the case of square slabs. However, for 3.66 m wide rectangular slabs, Westergaard solutions underestimate maximum deflection by 10–70%, depending on the value of radius of relative stiffness of the slab-on-grade system.

There are two techniques for constructing longitudinal joints allowed by the Wisconsin Department of Transportation (WISDOT): (1) sawing; and (2) insertion of polyethylene parting strips during construction. Secondary cracks parallel to the longitudinal joint and concrete spalling have been observed in several portland cement concrete (PCC) pavement projects constructed using parting strips. To evaluate the performance of parting strips in the formation of longitudinal joints in PCC pavements, an extensive database was developed. This database involved visual observation and laboratory analysis of cores taken from distressed and nondistressed areas. Visual observation involves collecting data regarding traffic condition and the distress type and severity. Laboratory analysis involves the collection of cores and their analysis to determine the possible causes of distress. An investigation of 60 core samples taken from 20 sites, a positive statistical correlation was found between the amount of spalling and parting strip installation variables including depth, angle, and variance. A statistical model developed verifies the assumption that an improperly installed parting strip leads to spalling along the longitudinal joint.

This paper first reviews the large displacement formulation of the soil-beam pipeline interaction problem. It then demonstrates that two methods of integration, namely, one-dimensional integration of section-property-deformation relationships and three-dimensional volume integration, yield the same results for finite element analysis of pipe that does not buckle and for deformation paths of typical settlements, even though the section-property-deformation relationships are, theoretically, nonintegrable. Similar results are demonstrated for a softening material. Based on the fact that the characteristics of section-property-deformation curves that include the effect of wrinkling can be simulated by this latter type curve, it argues that the analyses have established a reliable method of analysis for a pipe that deforms into the local buckling range. It also demonstrates that the effect of softening is to create a localized area in which the curvatures concentrate, that is, a wrinkle forms, while curvatures at other locations decrease. The section-property-deformation relationships used in the solution of the problems are extracted from three-dimensional shell analyses.

A dynamic analysis of a new track system, developed for a light rail transit vehicle powered by linear induction motors (LIMs) is made by a specially developed computer package. The track system, which incorporates steel crossties, is modeled by the finite-element method, while the vehicle is modeled separately as a combination of masses, springs, and dampers. The two models, which are linked through wheel loads, are applied to at-grade guideways in a study of the influences of a number of parameters on the dynamic behavior of the track and on the variation of the LIM air gap. The important parameters include vehicle-track interaction, nonlinearity, and stiffness of the tie pads, rail surface profile, and vehicle speed. The dynamic distributions of the LIM and wheel loads among the crossties are also discussed. It is shown that both the surface profile of the rail and the vehicle-track interaction affect the displacement response of the track significantly, while the wheel loads are mainly affected by the rail profile.