The relative settlement of a rigid box buried in a nonlinear medium is simulated by the trapdoor model. The nonlinear compressibility and shear‐displacement relationships are idealized by piecewise linear curves for which closed form solutions for each branch of the curve are obtained. A one‐dimensional finite element is defined for which stiffness terms are determined from the analytical solutions. The iterative solution of the finite element system yields results such as: displacement field, normal stress and strain variations, and shear stresses along the slip planes.

Midair collisions are often perceived as the number‐one safety issue in aviation. Though the actual incidence of such accidents is (thankfully) small, public perception of the problem, and the government's reaction to it, may threaten the very future of general aviation. Midair collisions are primarily a general aviation problem. Its solution starts with the review of accident statistics and nearmidair report data, an exploration of prior art, and an understanding of the capabilities and limitations of TCAS (Threat alert and Collision Avoidance System), the FAA's supplement to visual traffic avoidance. This paper contemplates the need for an “ideal” general aviation collision avoidance system—one which is selfcontained, noncooperative in nature (requiring no equipment in the “other” plane), transparent to the Air Traffic Control System, and fully compatible with TCAS and all other FAA proposals.

Results of full‐scale accelerated traffic tests conducted by the U.S. Army Corps of Engineers were studied. It was found for similar pavements that relationships between observed failure coverages for different loads and gear assemblies provided a better correlation for flexible pavements than for rigid pavements. The analyses suggest that there may be variables in the tests that could adversely affect either the performance in rigid pavements more than in flexible pavements, or only the performance of rigid pavements. It was inferred that inconsistent test track results can be expected in similar rigid pavements due to: (1) The presence of joint system itself and difference in the material and construction variabilities in the joint system; (2) the possible difference in the geometrical layout of the joint system relative to the applied traffic pattern in each test traffic lane; and (3) temperature and moisture differentials in the concrete slabs, which may not be repeatable from one test to another. The analyses may suggest that the reliability of the failure criteria established from field‐test data may be inherently lower for rigid pavements than for flexible pavements.

An analysis of the errors involved in both the nondestructive testing data collection and the modeling of a pavement structure is presented. The errors are separated into: (1) Random errors associated with the measuring devices; (2) random errors due to the intrinsic variability of the materials and pavement structures; and (3) systematic errors associated with the modeling of pavement structure, loading conditions, and material characterization. An analysis of the backcalculation process is conducted to investigate the effect of the errors on the backcalculated moduli. An experimental design approach is applied, using the first‐order approximation for the expected values and variance of the layer moduli. It is shown that (1) Mean values can be backcalculated from an average deflection bowl in which all random errors are reduced to a negligible value; and (2) the intrinsic variability of the materials can be correctly estimated only if the random errors associated with the measuring devices are eliminated. In recognition of these two findings, two testing programs are proposed, denoted as programs I and II. A case study with measured deflection data illustrates and supports the findings of the analysis and of the experimental design approach: (1) The backcalculated modulus of the upper layer depends strongly on the accuracy of the sensor at the center of the loading plate; (2) the number of tests per location required for obtaining a set of reliable moduli is about 4; and (3) testing program I is superior to testing program II.

Data, collected correctly and analyzed systematically, provide a solid basis for understanding the traffic system. This paper discusses recent developments in the collection and analysis of video data. It is particularly directed towards applications in low‐speed environments: car parks and pedestrian crossings. The paper discusses the collection of data on behavior, speed, travel time, headway, parking‐duration, and parking (and unparking) times. It concludes that video enables the accurate determination of changes in maneuvers, removes errors due to the reaction time of the observer, provides a permanent record for repeated analysis, enables the impact of remedial measures to be observed, and, when combined with automatic detection procedures, allows considerable reductions in data extraction times.

This research studied the accuracy of borrowed synthetic models for estimating through trips in small urban areas. Three sets of models—NCI, NC2, and KY, which were previously developed in North Carolina and Kentucky, were evaluated as a part of this study. All three models were essentially two‐stage models. The first stage estimated the number of through trip ends at each cordon station. The second stage distributed the through trip ends calculated in the first stage from each station to all other destination stations. The basic features of all the models were compared to bring out their similarities and differences. The models were then tested with the help of data obtained from 14 small urban areas in North Carolina. The trip end estimation models were tested on all the 14 urban areas, and the trip distribution models were tested on six of these urban areas. The estimated through trips were compared with the actual through trips obtained from origin‐destination (O‐D) surveys to assess the accuracy of the models. Additional analyses were performed to determine the sensitivity of functional classification for all three models, and the sensitivity of route continuity on the NC2 model. The accuracy of the models in predicting large volumes of through trips was found to be acceptable. It was concluded that the models are useful tools for quick estimation of through trip patterns in small urban areas.

A revised flexible pavement design equation has recently been published by the American Association of State Highway and Transportation Officials. The revised equation contains new input parameters: resilient modulus, $M_R$, to characterize subgrade support; reliability, R to allow the designer to introduce the concept of risk analysis into the design process; and standard error, $S_o$, to represent variability in design input values. This paper summarizes the results of a significance study performed using the revised flexible pavement design equation. The study demonstrates the relative importance of design equation input parameters and provides insights into the relative change in required pavement structure thickness resulting from variations or errors in input parameter values. Study results show that variation in subgrade resilient modulus, $M_R$, has the most pronounced effect on thickness structural number, SN. Variation in the predicted number of 18-kip equivalent single-axle loads, W₁₈, has a lesser effect, and variation in combined standard error, $S_o$, has a minimal effect on $S_n$. Selection of the highest values for design reliability, R, results in significant increases in Sn.