Frank Southworth

INTERMODAL AND INTERNATIONAL FREIGHT NETWORK MODELING

The authors describe the development and application of a single, integrated digital representation of a multimodal and transcontinental freight transportation network. The network was constructed to support the simulation of some five million origin to destination freight shipments reported as part of the 1997 United States Commodity Flow Survey. The paper focuses on the routing of the tens of thousands of intermodal freight movements reported in this survey. Routings involve different combinations of truck, rail and water transportation. Geographic information systems (GIS) technology was invaluable in the cost-effective construction and maintenance of this network and in the subsequent validation of mode sequences and route selections. However, computationally efficient routing of intermodal freight shipments was found to be most efficiently accomplished outside the GIS. Selection of appropriate intermodal routes required procedures for linking freight origins and destinations to the transportation network, procedures for modeling intermodal terminal transfers and inter-carrier interlining practices, and a procedure for generating multimodal impedance functions to reflect the relative costs of alternative, survey reported mode sequences.

A technical review of urban land use - transportation models as tools for evaluating vehicle travel reduction strategies

The continued growth of highway traffic in the United States has led to unwanted urban traffic congestion as well as to noticeable urban air quality problems. These problems include emissions covered by the 1990 Clean Air Act Amendments (CAAA) and 1991 Intermodal Surface Transportation Efficiency Act (ISTEA), as well as carbon dioxide and related {open_quotes}greenhouse gas{close_quotes} emissions. Urban travel also creates a major demand for imported oil. Therefore, for economic as well as environmental reasons, transportation planning agencies at both the state and metropolitan area level are focussing a good deal of attention on urban travel reduction policies. Much discussed policy instruments include those that encourage fewer trip starts, shorter trip distances, shifts to higher-occupancy vehicles or to nonvehicular modes, and shifts in the timing of trips from the more to the less congested periods of the day or week. Some analysts have concluded that in order to bring about sustainable reductions in urban traffic volumes, significant changes will be necessary in the way our households and businesses engage in daily travel. Such changes are likely to involve changes in the ways we organize and use traffic-generating and-attracting land within our urban areas. The purpose of this review is to evaluate the ability of current analytic methods and models to support both the evaluation and possibly the design of such vehicle travel reduction strategies, including those strategies involving the reorganization and use of urban land. The review is organized into three sections. Section 1 describes the nature of the problem we are trying to model, Section 2 reviews the state of the art in operational urban land use-transportation simulation models, and Section 3 provides a critical assessment of such models as useful urban transportation planning tools. A number of areas are identified where further model development or testing is required.

Mitigating climate change through green buildings and smart growth

Energy-efficient buildings are seen by climate change experts as one of the least-cost approaches to mitigating greenhouse gas emissions. This paper summarizes a study carried out for the Pew Center on Global Climate Change that takes a broader look at the potential role of a climate-friendly built environment including not only considerations of how buildings are constructed and used, but also how they interface with the electric grid and where they are located in terms of urban densities and access to employment and services. In addition to summarizing mechanisms of change (barriers and drivers) the paper reviews a set of policies that could bring carbon emissions in the building sector in 2025 almost back to 2004 levels. By the middle of the century the combination of green buildings and smart growth could deliver the deeper reductions that many believe are needed to mitigate climate change.

ON THE MEASUREMENT AND VALUATION OF TRAVEL TIME VARIABILITY DUE TO INCIDENTS ON FREEWAYS

Incidents on freeways frequently cause long, unanticipated delays, increasing the economic cost of travel to motorists. This paper provides a simple model for estimating the mean and variance of time lost due to incidents on freeways. It also reviews methods for assigning a monetary value to the variability that such incidents introduce into the daily travel. The paper offers an easy-to-implement approach to measuring the performance of freeway incident reduction strategies, an approach that should be useful in early project selection exercises where a sketch planning process is used to identify promising actions.

The geography of metropolitan carbon footprints

Abstract The worlds metropolitan carbon footprints have distinct geographies that are not well understood or recognized in debates about climate change, partly because data on greenhouse gas emissions is so inadequate. This article describes the results of the most comprehensive assessment of carbon footprints for major American metropolitan areas available to date, focusing on residential and transportation carbon emissions for the largest 100 metropolitan areas in the United States. These findings are put into the context of efforts across the country and the globe to characterize carbon impacts and policy linkages.

Dynamics of Supply Chains: A Multilevel (Logistical–Informational–Financial) Network Perspective

In this paper, we propose a multilevel network perspective for the conceptualization of the dynamics underlying supply chains in the presence of competition. The multilevel network consists of: the logistical network, the informational network, and the financial network. We describe the behavior of the network decisionmakers, which are spatially separated and which consist of the manufacturers and producing firms, the retailers, and the consumers located at the demand markets. We propose a projected dynamical system, along with stability analysis results, that captures the adjustments of the commodity shipments and the prices over space and time. A discrete-time adjustment process is described and implemented in order to illustrate in several numerical examples the evolution of the commodity shipments and prices to the equilibrium solution.

Using decomposition in large-scale highway network design with a quasi-optimization heuristic

The highway network design problem deals with the selection of links from a base network to facilitate the flow of vehicles from origins to destinations. A proper selection of links requires a balance between minimization of travel costs from origins to destinations and minimization of costs incurred in building or improving links in the network. Link construction costs are usually minimized as a part of the objective or constrained by budget availability. National or regional highway network design problems require excessive amounts of computing time, if solved to optimality. This paper presents a variation of the Modified Quasi-Optimization (MQO) heuristic developed by Dionne and Florian (1979). The proposed algorithm solves a large network design problem by decomposing it in a sequence of smaller problems. Additional savings in computation time are achieved by limiting the search in the MQO heuristic to a well-designed set of paths for each OD pair. These paths are generated to suit the network design problem and differ from the K-shortest paths for the OD pairs. The combined use of decomposition and a limited set of paths allows the proposed heuristic to address realistic network design problems. Numerical experience with a problem involving 6563 nodes and 9800 two-ways links is reported.

Estimating departure times from traffic counts using dynamic assignment

Dynamic traffic assignment and observed traffic counts are used to estimate the distribution of departure times in an urban area trip matrix. The objective is to find the maximum entropy distribution of departure times by origin zone subject to observed traffic counts on a subset of network links. The procedure results in the estimated number of trip departures from each origin in 10-15 minute time intervals of the full analysis period. Such an analysis period will typically range from one to three hours long. We first review the dynamic user-equilibrium assignment problem (DUE) and the dynamic traffic assignment algorithm (DTA) from a previous paper, and then describe its use with traffic counts to estimate departure times in a trip matrix. We present an application to a Pittsburgh network in which trip departures are estimated for each 10 minute interval of a peak-hour survey trip matrix. Dynamic assignment and departure time estimation based on traffic counts can be used to examine the impacts of alternative transportation management strategies such as work hour changes and ramp metering. Computational advances such as parallel computing will enable the procedure to be run on large networks while counts are being monitored. Such an application may provide near real-time detection of temporal trip departure profiles by origin zone in emergency evacuations or other special events.

On the potential impacts of land use change policies on automobile vehicle miles of travel

Abstract Recent US traffic growth is summarized and its causes discussed, emphasizing the complex causal linkages between automobile travel and the underlying land use patterns that shape it. This causal framework is used to frame a discussion of how the demands for vehicle travel might be reduced through suitable land use impacting policy instruments. This includes instruments that alter the location, mix and intensity of traffic generating and attracting land use, as well as instruments that affect land development through the supply of added transportation capacity. The existing scientific evidence for the effects of land development patterns on aggregate vehicle miles of travel is found to be of limited use at the present time. For the most part this results from past data limitations and because of the variety of both spatial and temporal scales across which such data needs to be collected and analyzed. It is also concluded that successful travel reduction policies are likely to evolve as part of a broader public policy debate over quality of life issues, notably those involving “urban sprawl” and the balance of economic development against environmental sustainability. The full costs of expanding while also maintaining the current automobile dominated transportation infrastructure may also provide an economic rationale for change.

Quasi-dynamic urban-location models with endogenously determined travel costs

A quasi-dynamic model of residential and job location is fused with the equilibrium trip-assignment model in the manner suggested by the combined model of trip distribution and assignment. The implications of this combined model for assumptions about future levels of interaction are examined. Extensions of the model to include explicit housing stocks and prices and the determination of residential- and job-location attractiveness are considered.