This paper includes the results of an analytical study of the effects of automobile tire loads on thin asphalt pavements over granular bases. Two different methods of calculating the tire contact pressure are used and the strains induced in the pavement structure are evaluated. The uniform pressure tire model assumes that the tire contact pressure is equal to the tire inflation pressure. The Tielking tire model is a finite element computer program that models the tire as a shell of revolution and calculates the contact pressure distribution by using the tire carcass properties and the tire load. The contact pressure distributions are used in ILLIPAVE to calculate the strains at various locations in a pavement having a surface of thickness ranging from 2.54 to 10.16 cm (1 to 4 in.) and moduli ranging from 345 to 5,516 MPa (50 to 800 ksi). A granular base 20.32‐crn (8‐in.) thick with two different moduli is over a subgrade soil with a modulus of 34.5 MPa (5 ksi). The results are analyzed and the findings indicate that automobile tire loads can produce high pavement strains for certain combinations of surface thickness moduli over weak bases. The best performance occurs when stiff bases are used.

The conventional approach for determining load on buried concrete pipe for trench installation is summarized. A finite element computer model's capabilities are demonstrated by examining cases of trench installations for which some field experience is available. Comparisons are made between predictions using the conventional method and the new computer method. The conventional method estimated higher load on the pipe than the computer model for trench installations. This is partly because the conventional trench method neglects the support capability of the sidefill soil. The computer method is shown to have advantages over the conventional method in its ability to represent a variety of actual installation conditions and to provide information on soil pressure distribution needed for pipe design.

This study attempts to identify the mode and the factors that contribute to the selection of a particular mode for commodity movements provincially based on average shipment size, control, loads, hire, and type of commodity. The main objective of this study is to propose a more comprehensive and statistically credible method to analyze the vast data required in transportation planning. It involves the application of standard statistical techniques such as the log‐linear and logit models. The data are collapsed to form multidimensional contingency tables in order to develop these models. The data from both shippers and consignees are taken from a survey conducted by Alberta Transportation, Canada. From the analysis it is found that truck and rail are the only two major carriers of freight across the province. Truck mode dominates over rail in transporting all commodities. The less‐than‐full‐load market belongs exclusively to truck mode. The rail mode shares a very small percentage $(<15\%)$ of the full‐load market, and is used to transport specific bulk commodities under higher average shipment size.

Portland cement‐stabilized soil is widely used as a base material for roads, airfields, and similar structures. Cracking in this material is studied using fracture mechanics concepts. Fracture toughness in the form of the plane strain stress intensity factor and in the form of the J‐integral are used as primary descriptors in the study. A simple power law is used in the case of fatigue loading to describe the relationship between the change in crack length per load cycle and the fluctuation in the stress intensity factor. An increase in static toughness occurs with an increase in strength and this relationship is explained. Physical models are developed that define the relationship between the physical and chemical nature of the material and its engineering usage. These relationships consider cement content, compactive effort, and fracture toughness. Initial results and future requirements for relationships between creep and fatigue and between static toughness and fatigue are discussed.

The modulus of soil reaction, $E\prime \text{,}$ characterizes the stiffness of soil backfill placed at the sides of buried flexible pipelines for the purpose of evaluation deflection caused by the weight of backfill above the pipe. In this study, the nature of $E\prime$ is investigated in detail to determine whether its magnitude increases with increasing depth of embedment. The development of $E\prime$ in the literature is reviewed, and data from field installations are presented to establish that $E\prime$ can be shown to increase with depth on the basis of previous research. Analytical methods, based on elastic theory and finite element techniques, are also used to demonstrate the dependence of $E\prime$ on depth. Design values of $E\prime \text{,}$ which vary with depth, are presented, together with recommendations regarding the use of $E\prime$ in the Iowa formula.

The object of this investigation was to develop a procedure for making optimal maintenance decisions for a deteriorating system. The particular system chosen for study is a pavement, and a methodology is developed to ensure that pavements meet certain performance criteria while minimizing the expected maintenance cost. A cumulative damage model based upon a Markov process was developed to model pavement deterioration. The optimal repair action for each possible pavement state in the planning horizon was found by means of probabilistic dynamic programming. Sample sequences of repair actions were generated during a simulation in which the optimal repair policy was applied to sample pavement condition histories. Several sensitivity studies were performed to study the variation in expected cost, including the effect of delaying the optimal program.

The 1985 Highway Capacity Manual suggests the use of an adjustment factor called f_p to reflect the influence of driver population on the highway capacity analysis for freeways and multilane highways. The manual recommends a value of f_p equal to 1.0 for commuter traffic streams or other regular users of a facility and a range of f_p between 0.75 and 0.90 for ``other'' types of traffic streams. As a prerequisite to an appropriate application of the factor f<sub>p</sub>, a systematic and objective method that can be used for classification of highways according to driver population characteristics is described. Using data from two Canadian provinces, seven classes of roads are identified on the basis of trip purpose and trip length distribution. Suggested values of f<sub>p</sub> are listed that can be used as a ``guide'' in exercising an engineering judgment in selecting a specific f_p value for a particular type of traffic stream.