The required supporting strength of a buried pipe is affected by the total load imposed upon the pipe and the manner in which the pipe is supported by the surrounding soil. The classic procedure for designing reinforced concrete pipe is the indirect design method, which is based on: (1) Determining the moment that will occur at the pipe invert under the specified loading conditions; (2) determining a three‐edge bearing load or D‐load that produces the same moment; and (3) designing the pipe reinforcing for that D‐load. Direct design methods determine the actual moments, thrusts, and shears in the entire buried pipe and they design the reinforcing to carry these forces. The advent of finite element modeling of soil behavior now allows an even more direct design method in which the actual soil conditions around a pipe are accurately modeled. This paper will demonstrate the differences between the various design methods by analyzing an actual installation with both methods. The finite element analyses are completed with the computer program SPIDA (Soil Pipe Interaction Design and Analysis).

This paper presents a pavement maintenance management system (PMMS) composed of the following modules: (1) Pavement‐network identification; (2) pavement condition survey and rating procedures; (3) distress‐prediction models; (4) maintenance activities and strategies; and (5) economic analysis and prioritized maintenance programs. Modules 1 and 2 follow the PAVER procedures. The distress‐prediction models are developed from local network data for load associated distress and climate/durability related distress. These models predict the extent of distress—not condition indexes. Nineteen different maintenance activities are defined in module 4. Each distress is assigned the most appropriate maintenance activity in order to bring any given pavement section up to target condition for each year. In module 5, the PMMS incorporates a unit‐cost analysis of all maintenance activities and a cost‐benefit scheme that permits the determination of the most economic order of maintenance activities in terms of work quantity and dollar value. The proposed PMMS is fully computerized in Microsoft FORTRAN 77 and runs on any personal computer with 640 KB of random‐access memory (RAM) and an arithmetic processor.

The efficient use of semi‐actuated control requires careful selection of phasing plan, timing design, and detector configuration. Computer simulation can be used to assist in the search for efficient ways of operating such a control, but it has not been widely employed by practicing engineers. Analytical methodologies for the operational design of signal control are potentially easier to use than are simulation models. Their development, however, has not reached a mature stage. The objective of this study is to use a simulation model to develop an easily accessible knowledge base for the use of semi‐actuated control at individual intersections. This knowledge base concerns semi‐actuated operations that rely on inductive loop detectors for presence detection of vehicles and that do not accommodate pedestrian timing. It focuses on the following aspects of the signal operations: choice of phasing plan, timing design for nonactuated phase and actuated phase, timing setting of call‐delay for delayed‐call detectors, and the choice between semi‐actuated and full‐actuated control.

A prototype knowledge‐based expert system for assisting engineers in selecting, locating, and designing construction and retrofit projects for traffic barriers, such as roadside barriers, median barriers, bridge rails, and crash cushions is described. The system uses design principles of traffic barriers, information provided through interviews with experts, and information on a particular site to generate feasible candidate designs. These designs are processed by an evaluation system that includes finite‐element analysis, a weighting mechanism, and a cost‐benefit model. Color graphics and an exaplanation module illustrate the design. An integrated rule‐ and frame‐based expert‐system shell facilitates implementation of the knowledge‐based system on a microcomputer with the help of external routine links, data‐base access, and a graphical interface. Visual knowledge, which is preserved through scanned images, is replete with educational benefits to highway engineers. An example bridge‐rail‐retrofit procedure demonstrates the approach to development of the knowledge‐based system.

Collision of vehicles with fixed objects adjacent to the roadway has been a concern of traffic engineers for many years. One solution to prevent or reduce the number of accidents of this type is to install a traffic barrier to shield the objects from being hit directly. However, because the barrier itself is a fixed object, the question is whether a barrier is more effective at a particular location than no barrier at all. If a barrier is needed, where should it be located and what type of barrier would satisfy the design criteria? Issues of this nature are ill‐structured and difficult to address using normal computing technology since many factors contribute to the problem. For roadside safety, the primary factors are diverse and interrelated. This paper presents a demonstration prototype knowledge‐based expert system (Roadside) for roadside‐safety analysis. In particular, this system is developed to evaluate whether a traffic barrier is necessary for a particular site in analysis. Development of this demonstration prototype shows an expert‐system approach for roadside safety analysis is feasible. The artificial‐intelligence (AI) programming language Prolog is used for developing the system. The use of Prolog provides greater flexibility and adaptability in developing the system. However, much more programming time is required to develop the expert system.

This paper reports on the evaluation of a dispersion simulation model that predicts carbon monoxide (CO), concentrations in urban street canyons. The distribution characteristics of vehicle‐generated carbon monoxide concentrations measured at six major urban arterials in Riyadh, Saudi Arabia are presented. The maximum 1‐hour and 8‐hour CO concentrations monitored annually over a three‐year period, are shown. The structure of the composite street canyon model that was used to predict the hourly concentrations of carbon monoxide at study arterials is discussed. A comparative analysis of predicted versus measured concentrations is made. The model, although unsophisticated, predicts CO levels that agree reasonably well with the values measured in Riyadh. The model is felt to be generally applicable to the conditions of the rapidly developing urban areas of the Persian Gulf.

This paper describes a network design approach to the selection and programming of alternative route improvements to the U.S. highway network of interstates, four‐lane urban highways, and principal rural arterials. Alternative route‐improvement strategies are defined as mutually exclusive sets of link improvements that can be programmed for construction within any decade of a multidecade planning horizon. The two improvement strategies considered for each route are: (1) To make every link median divided with controlled access and at least four lanes; or (2) to make every link at least four lanes, but without any changes to median division or access control. The examples of this paper evaluate 536 potential improvements to 289 major highway routes between adjacent Bureau of Economic Analysis (BEA) regions, or nearly two improvement strategies per route. Route‐improvement strategies programmed for each decade are constrained by 10‐year funding allocations. A trip distribution model is used to distribute commodity shipments forecast for each decade among regions. Route‐improvement benefits are computed as changes in the value of the objective function, which is the total discounted interregional shipment cost for all years of the planning period. Since different routes and interregional shipments can share common links, a rank‐add‐and‐swap heuristic solution procedure was developed and applied that accounts for the interdependent costs and benefits of route improvements. Implications of this network design approach for planning future expansions and improvements of the interstate highway network are discussed.