Increasing the United States' air‐transportation system capacity is a need expressed by air passengers, airlines, and aviation policymakers. This paper addresses the advantages and disadvantages of adding superhub (or wayport) facilities to the existing California air‐transportation system. To reach a conclusion, the feasibility of adding either two airports, one in the San Francisco Bay Area and the other in the Los Angeles basin, or one facility located between these regions was studied. Results indicate that the addition of two new airports would reduce traffic through the state because the presence of two facilities would divide potential markets, which would cause flight‐frequency advantages to be lost, effectively making California a less‐attractive hub. If stage‐length restrictions were placed on the existing airports, increases in traffic through the state could be expected with the addition of one centrally located superhub (or wayport). However, such restrictions may be politically unacceptable, and economically undesirable as well. On the other hand, if no restrictions were enforced, little traffic would be expected through the superhub unless high‐speed (supersonic) aircraft were allowed to use the new airport. Thus, the market niche for the superhub (or wayport) concept in California may be for high‐speed aircraft that can't use existing airports, because of environmental and physical constraints.

The present paper introduces some basic concepts and terminology of distributed planning, and describes a novel coordinator‐coworker structure—a control mechanism that can dynamically reorganize the planning system in response to the tasks at hand. Coordinators get either self‐appointed in unambiguous situations or selected through a unique and inexpensive nomination/confirmation process. The matching of tasks and coworkers is accomplished with minimum message passing and processing, by using appropriate meta‐knowledge about the status of the network of nodes. Connections can be initiated by both coordinators and coworkers, leading to optimum load balancing. A hierarchically organized set of distributed scratch pads supports the coordinator‐coworker mechanism. It is the medium for information exchange and also provides the basis for self‐repairing in a graceful degradation mode whenever individual nodes become inoperational. We discuss the problems of air‐traffic control and describe the kernel design of the airborne processors in a location‐centered cooperative planning system. Finally, we explain the simulation‐based planning process and its timing and selection considerations. A companion paper follows in the journal.

This is the second of two companion papers dealing with distributed planning for air‐traffic control. Three different organizational structures have been implemented: the local centralized architecture, and location‐centered cooperative planning system with one‐ and two‐level coordinator‐coworker hierarchies. We present an initial, simplified analysis of the speedup obtainable by using the latter two organizational structures. The vehicle of our empirical studies, the distributed air‐traffic control test bed is then introduced. We discuss the design and the results of a series of experiments performed. We compare in the test‐bed performance measures of the three systems using the respective organizational structures. The comparisons are made at different levels of traffic density and problem size, in terms of communication overhead and processing time needed for planning.

Some of the most significant factors in determining runway capacity are air traffic control regulations. Interaircraft separation regulations have been established to provide maximum safety to the travelling public. Thus any modification of these regulations, in an attempt to increase capacity, must have sufficient benefits to outweigh any increase in risk. A simulation indicated that the required separation between two arriving aircraft of 5,490 m could be reduced to 4,570 m, with a modeled 15% increase in capacity and a 1.5% increase in risk. Further simulations indicated that parallel runways spaced as close as 914 m apart could be operated independently, with capacity increases of between 38% and 95% and no estimated increase in risk. Reducing the present requirement to separate arriving aircraft from departing aircraft by 3,560 m to 1,825 m was estimated to result in a 25% increase in capacity with only a 1.5% increase in risk.

This paper examines the ability of conventional travel‐forecasting models to respond to forecasting needs created by the Clean Air Act Amendments (CAAA) of 1990 and the air‐quality lawsuit brought against the Metropolitian Transportation Commission, San Francisco. Initially, the probable response of travel behavior to the various transportation control measures of the CAAA are reviewed. The ability of the travel‐forecasting models to reflect each of the various responses is examined, concluding that only those transportation‐control measures (TCMs) resulting in a change in travel mode, auto occupancy, or destination can be modeled. Most remaining TCMs require significant model changes. Similarly, with capacity changes, three of the seven potential changes in travel behavior can be modeled, if the models are run through a series of feedback loops. For emissions modeling, the inputs cannot be obtained with the required specificity. Short‐run and longer‐run changes are identified that should be made to current modeling procedures to add further to the abilities of the models to produce good travel forecasts.

This paper outlines a methodology for bridge project selection based on reliability methods and optimization procedures, which could serve as part of a bridge management system. The Markovian model is used to decay the structural components. Then, a reliability index is determined for each element using either subjective assessment or first‐order reliability methods. The overall reliability of the bridge is calculated as a system reliability by combining the individual reliability of the components in a series system. Risk is obtained from the reliability of the bridge and the consequence of closure. Repairs can be modeled in any year. The optimum set of repairs is defined as that which minimizes the total network risk in the planning horizon. Methods for finding the optimum set of repairs are discussed, and a near‐optimum algorithm is selected.

In a comprehensive two‐year research project, traffic noise was monitored at 42 locations in 13 districts in Riyadh, Saudi Arabia. A total of 2,095 individual heads of household were interviewed at the noise monitoring sites for their perceptions and attitudes toward urban traffic noise. The socioeconomic characteristics of the sample population were identified, and the perceived impact of noise on their welfare and health was determined. The maximum mean district equivalent noise levels by road type are presented. While a significant number of individuals were aware of the interference of traffic noise with their daily activities, only a few pointed to the long‐range impact of noise on hearing damage. The degree of awareness of the health impact of traffic noise increased with an increase in the respondents' income and level of education. The extent and degree of annoyance with traffic noise varied with the change in the functional classification of urban roadway. People living and working along major arterials and freeways were considerably more annoyed than those residing along local or collector streets.

Nonlinear finite element analysis of dowel‐jointed concrete pavements is presented. The nonlinearities considered are cracking of concrete in tension, compressive yielding of concrete, and loss of support due to lift‐off of pavements because of temperature gradients. Smeared cracking representation of cracks in concrete and a plasticity‐based material model are employed. Loss of support due to removal of subgrade material through pumping is considered. Analysis of a doweled joint subjected to shear loading is performed to obtain dowel‐concrete interface response characteristics. Analyses of plain concrete pavements subjected to self‐weight, temperature gradients, and static wheel loads are performed with four different extent of loss of subgrade support and two different dowel‐concrete interface characteristics. The loss of subgrade support may lead to a rapid deterioration of pavements through fatigue, by increasing the tensile stress level in concrete. Faulting of slabs may also be due to loss of support at the far end of the slabs. Softening of the dowel‐concrete interface stiffness significantly affects the efficiency of the joint in transferring the loads. Nighttime temperature curling further increases the stresses due to lift‐off of slabs at the ends, while daytime temperature curling is found to be less critical.