Estimating flow times for containerized imports from Asia to the United States through the Western rail network

Abstract

Queuing models are introduced for estimating container dwell times at rail intermodal terminals and transit times through rail line-haul corridors. These models are statistically calibrated on industry data. The intent of these models is to estimate changes in container flow times stemming from changes in infrastructure, staffing levels at terminals, or import volumes passing through given infrastructure. Flow times estimated for individual line segments are aggregated to provide estimates of the total transit time from West Coast rail ramps to inland destination ramps for imports moving from Asia to the Continental United States in marine as well as domestic containers.

Introduction

The substantial growth in waterborne, containerized imports from Asia to the Continental United States experienced until 2007 (i.e., before the onset of the subsequent economic recession) strained the capacities of West Coast ports and landside channels to inland markets. At times, “melt-downs” were experienced at certain West Coast ports and on certain Western rail lines that triggered major shifts in the port and channel volumes of such imports. In response to this trade growth, there have been major expenditures by public agencies and private carriers to expand infrastructure, continuing at the present time. In some cases, new user fees or container fees have been introduced or proposed to pay for such improvements. Rates charged by railroads have in some cases escalated dramatically.

Some of the melt-down events came as a surprise to industry managers and governmental officials. We believe this reflects a lack of practical analytical tools that can be used to predict container dwell and transit times as a function of volume, infrastructure and staffing. While there is much useful literature on simulation models and queuing formulas for operational analysis of individual transportation links and terminals, to our knowledge there is little research on practical congestion analysis of large rail networks to support strategic planning. We aim to fill that need in this article. We provide a queuing model for rail intermodal terminals, the first such model to the best of our knowledge. We develop a new queuing formula for individual rail line-haul segments and combine in a practical way the results of application of the formula to individual rail links into estimates of the total transit times in transcontinental rail container corridors. Combined with results of queuing analyses of terminals, estimates of total container flow times from arrival at origin ramp to train arrival at inland destination ramp are readily developed for multiple transcontinental corridors. To the best of our knowledge, this is the first time a practical queuing-theoretic approach has been developed for estimating transit times through large, general freight rail networks.

Our motivation is the planning for continued growth of containerized imports from Asia to the Continental United States passing through West Coast ports and distributed across the Continental United States. The queuing models we propose are statistically calibrated on industry data for these import flows. There are many terminals and landside channels for which container flow times must be estimated. The desired accuracy of total-channel container flow times is on the order of days.

The structure of this article is as follows. We first provide an overview of the sequence of queues that imports moving in rail channels must negotiate. Next, we review the relevant literature. We then proceed to the development of our proposed queuing models and illustrate their application.