Carlos Zozaya-Gorostiza

THE PROBLEM OF CYCLIC FLOWS IN TRAFFIC ASSIGNMENT

A fundamental property of traffic assignment is that cyclic flows from a common origin or to a common destination cannot exist in an equilibrium solution. However, cyclic flows can easily be created by the Frank-Wolfe (F-W) assignment procedure, especially during its first several iterations. The PARTAN technique--a more rapidly converging derivative of the F-W method--can also create cyclic flows during its procedure. We show in this paper that once cyclic flows become part of a combined assignment, they are difficult to correct, thus presenting one impediment to convergence. We then present modifications to the F-W and PARTAN procedures that prevent cyclic flows from being created between adjacent pairs of nodes. The avoidance of cyclic flows in test problems is shown to accelerate the convergence of both the F-W and PARTAN techniques, particularly in the first several iterations. While the impossibility of cyclic flows in a true equilibrium solution is an important property of traffic assignment, this paper shows that (1) the F-W and PARTAN procedures eventually reduce cyclic flows to zero if they occur, (2) avoiding cyclic flows can be most helpful in the early iterations of these procedures, and (3) avoiding cyclic flows in large networks is very difficult because of large computational requirements.

A knowledge-intensive planner for construction projects

Abstract This paper reviews the capabilities and application of the CONSTRUCTION PLANEX system. This knowledge-based expert system assists in the selection of construction technology, the definition of work tasks, the estimation of required resources and durations, the estimation of costs, and the preparation of a project schedule. The system has been applied in laboratory simulations in three ways: interactively as an intelligent assistant, independently as an automated planner, and as part of an integrated building design environment. CONSTRUCTION PLANEX can plan for the excavation and structural erection of concrete and steel buildings; example applications have ranged from two to twenty stories. Provisions are included in the system for expanding the knowledge base to consider other functional elements or facility types. Descriptions of the system architecture, knowledge representation scheme, control procedures, and applications are included.

Construction Planex: A Knowledge Intensive Planner for Construction Projects

This paper reviews the capabilities and application of the CONSTRUCTION PLANEX system. This knowledge-based expert system assists in the selection of construction technology, the definition of work tasks, the estimation of required resources and durations, the estimation of costs, and the preparation of a project schedule. The system has been applied in laboratory simulations in three ways: interactively as an intelligent assistant, independently as an automated planner, and as part of an integrated building design environment. CONSTRUCTION PLANEX can plan for the excavation and structural erection of concrete and steel buildings; example applications have ranged from two to twenty stories. Provisions are included for expanding the knowledge base to consider other functional elements or facility types. Descriptions of the system architecture, knowledge representation scheme, control procedures, and applications are included.

An Expert System for Construction Planning

Among other concerns, construction planning involves the choice of construction technology, the definition of work tasks, the estimation of required resources and durations, the estimation of costs, and the preparation of a project schedule. A prototype knowledge intensive expert system to accomplish these tasks, CONSTRUCTION PLANEX, is described in this paper. This system generates project activity networks, cost estimates and schedules, including the definition of activities, specification of precedences, selection of appropriate technologies and estimation of durations and costs. The CONSTRUCTION PLANEX system could be useful as an automated assistant in routine planning, as a laboratory for the analysis and evaluation of planning strategies, and as a component for more extensive construction assistance systems involving design, site layout or project control. The current application for CONSTRUCTION PLANEX is to plan modular high rise buildings, including excavation, foundation and structural construction.