Flight schedule punctuality control and management: a stochastic approach

The insufficiency of infrastructure capacity in an air transport system is usually blamed for poor punctuality performance when implementing flight schedules. However, investigations have revealed that ground operations of airlines have become the second major cause of flight delay at airports. A stochastic approach is used in this paper to model the operation of aircraft turnaround and the departure punctuality of a turnaround aircraft at an airport. The aircraft turnaround model is then used to investigate the punctuality problem of turnaround aircraft. Model results reveal that the departure punctuality of a turnaround aircraft is influenced by the length of scheduled turnaround time, the arrival punctuality of inbound aircraft as well as the operational efficiency of aircraft ground services. The aircraft turnaround model proposed is then employed to evaluate the endogenous schedule punctuality of two turnaround aircraft. Model results, when compared with observation data, show that the operational efficiency of aircraft ground services varies among turnarounds. Hence, it is recommended that the improvement of departure punctuality of turnaround aircraft may be achieved from two approaches: airline scheduling control and the management of operational efficiency of aircraft ground services.     

Rehabilitating the Mangrove Resources of Cogtong Bay,Philippines: A Comanagement Perspective

The local management of mangrove resources in Cogtong Bay, Philippines, dates back to the 1940s and 1950s when some families informally designated mangrove areas under their care and management. The 1960s and 1970s saw several exogenous events that led to the progressive denudation of mangrove stands and the decline in fish catch per fishing trip. This article draws attention to the forces that prompted coastal villages and external agents to collaborate with the national and local government units in resource rehabilitation. It also assesses the performance of a coastal resources comanagement project at Cogtong Bay.     

The Effectiveness of Coastal Zone Management in the United States

The Coastal Zone Management Effectiveness Study was undertaken between 1995 and 1997 to determine how well state coastal management programs in the United States were implementing five of the core objectives of the U.S. Coastal Zone Management Act (CZMA). The five core objectives studied were: (1) protection of estuaries and coastal wetlands; (2) protection of beaches, dunes, bluffs and rocky shores; (3) provision of public access to the shore; (4) revitalization of urban waterfronts; and (5) accommodation of seaport development (as an illustration of the policy to give priority to coastal-dependent uses). Separate articles in this issue of Coastal Management report the findings of the five studies, each dealing with one of the core objectives. Each of the articles assesses issue importance, processes and tools used, and the limited outcome data available for that objective. This article provides an overview of the purposes of the study, the methodology used, the summary findings of each study, and overall conclusions and recommendations of the study team. State coastal programs are found to be effective in addressing the five CZMA objectives examined, but this conclusion is based on very limited information about program outcomes. A more definitive conclusion will require better outcome information. Coastal managers in the United States have not agreed upon indicators of success, which severely inhibits systematic and sustained collection of outcome information. A national outcome monitoring and performance evaluation system is recommended to address these deficiencies and allow better determinations of program effectiveness in the future.     

Coastal Zone Management: Using No-Build Areas to Protect the Shorefront

Five coastal counties in Florida were studied to assess the effect of state-mandated local comprehensive plan policies on hurricane evacuation clearance times and public shelter demand. Numbers of residential units in 2002 and at the time of plan approval were estimated from property parcel data. Abbreviated transportation models were used to calculate 2002 evacuation times and shelter demand and to ascertain the impacts of post-plan residential growth within hurricane hazard areas. Calculated increases in clearance times and shelter demand are not in concert with the state's mandate to maintain or reduce clearance times. State law currently limits the leverage of the state planning agency to compel local governments to implement the required comprehensive plan policies. We recommend a concurrency management strategy that parallels the state's requirement to provide adequate transportation facilities to accommodate the impacts of future residential growth. Such a policy could be employed in other states as well.     

Dynamic system-optimal traffic assignment using a state space model

We propose a new mathematical formulation for the problem of optimal traffic assignment in dynamic networks with multiple origins and destinations. This problem is motivated by route guidance issues that arise in an Intelligent Vehicle-Highway Systems (IVHS) environment. We assume that the network is subject to known time-varying demands for travel between its origins and destinations during a given time horizon. The objective is to assign the vehicles to links over time so as to minimize the total travel time experienced by all the vehicles using the network. We model the traffic network over the time horizon as a discrete-time dynamical system. The system state at each time instant is defined in a way that, without loss of optimality, avoids complete microscopic detail by grouping vehicles into platoons irrespective of origin node and time of entry to network. Moreover, the formulation contains no explicit path enumeration. The state transition function can model link travel times by either impedance functions, link outflow functions, or by a combination of both. Two versions (with different boundary conditions) of the problem of optimal traffic assignment are studied in the context of this model. These optimization problems are optimal control problems for nonlinear discrete-time dynamical systems, and thus they are amenable to algorithmic solutions based on dynamic programming. The computational challenges associated with the exact solution of these problems are discussed and some heuristics are proposed.     

Optimal Linear Active Suspensions with Derivative Constraints and Output Feedback Control

In optimally controlled active suspensions with either full or incomplete state feedback there is tradeoff between system performance and overall stiffness. It is sought to remove this limitation by incorporating integral action which results in a system with infinite stiffness towards static loading, but which is soft with respect to road inputs. The system is also able to eliminate the steady state deflections due to step and (potentially) ramp type inputs at the wheel. Optimality is retained at the cost only of a derivative constraint and the system can be physically realised using output feedback control.     

A composite attitude-behavior model of traveler decision making

A general model for the behavioral analysis of traveler decision making is described. The model is one which blends research in human information processing with probabilistic choice theory. The model is used as a basis for discussing two studies of grocery store choice behavior. In these studies, algebraic models of individuals' grocery store preferences which are derived using controlled hypothetical choice situations are related to real-world choice behavior. Results show a high monotonic correspondence between laboratory and real-world behavior. Implications of the research for existing approaches to behavioral modeling are described.     

A methodology to estimate travel time using dynamic traffic assignment (DTA) under incident conditions

This paper presents results from a research case study that examined the distribution of travel time of origin–destination (OD) pairs on a transportation network under incident conditions. Using a transportation simulation dynamic traffic assignment (DTA) model, incident on a transportation network is executed under normal conditions, incident conditions without traveler information availability, and incident conditions assuming that users had perfect knowledge of the incident conditions and could select paths to avoid the incident location. The results suggest that incidents have a different impact on different OD pairs. The results confirm that an effective traveler information system has the potential to ease the impacts of incident conditions network wide. Yet it is also important to note that the use of information may detriment some OD pairs while benefiting other OD pairs. The methodology demonstrated in this paper provides insights into the usefulness of embedding a fully calibrated DTA model into the analysis tools of a traffic management and information center.