Conference Papers 2020

Seminar
Day 1 (9 Sep 2020), Session 3, Model Routing, 15:30 - 17:30

Status
Accepted, awaiting documents

Submitted by / Abstract owner
Howard Slavin

Authors
Andres Rabinowicz
Howard Slavin

Short abstract
In this paper, we describe the design and implementation of a new process for estimating a nationwide origin-destination truck trip table based upon the U.S. Freight Analysis Framework (FAF) commodity flows and for assigning those commodity flows and

Abstract
In this paper, we describe the design and implementation of a new process for estimating a nationwide origin-destination truck trip table based upon the U.S. Freight Analysis Framework (FAF) commodity flows and for assigning those commodity flows and estimated truck trips to a national road network. The objective of this project was to provide the U.S. DOT with a software tool for allocating estimated commodity flows and associated truck trips between counties and major ports in the United States to specific road links, and for that tool to provide a transparent, flexible, and well-documented mechanism for doing so. The new tool and its underlying methodology are also applicable also to interregional models.
The FAF, produced jointly by the Bureau of Transportation Statistics (BTS) and FHWA, combines data from several sources to create an overall picture of freight movement among states and major metropolitan areas by all modes of transportation. Data are reported for 132 domestic FAF zones and eight foreign regions. Extending the FAF estimates to a much more detailed and spatially disaggregate basis is a challenging analytical exercise and is prone to error due to data limitations. Nevertheless, these data are thought to be valuable in understanding the importance of different portions of the national road system in supporting freight flows and in facilitating other analyses.
Caliper was commissioned to create the new FAF tool using TransCAD. TransCAD is a integrated transportation modeling and GIS package that has previously been used for both truck and flow assignments. The new includes methods for:
1. Disaggregating commodity flows to a 3498 zone system of counties, ports, and some sub-county areas
2. Estimating the tonnage of commodity flows between those zones
3. Converting the commodity flow tonnage to annual and daily truck trips, and
4. Assigning flows and trips to specific routes connecting the zones.
In addition, the tool features a flexible, easy to use query engine for retrieving data by origin, destination, route, and selected links.
Considerable thought was given to the choice of an appropriate freight assignment methodology. Conventionally, freight assignments are often done using methods more appropriate for passenger movements. In prior work for example, a stochastic user equilibrium method was used for assigning flows. However, it should be clear that there is no reason why freight movements should be in any sort of equilibrium for any origin-destination pair.
Instead of using a link-based assignment method, we opted for a route choice model. The route choice model uses a new algorithm for identifying alternative paths between origins and destinations. These paths can be viewed, edited, augmented, or deleted should additional information on truck flows become available. A path-size logit model that accounts for the fact that alternative paths often overlap is used for route choice.
The flows from the route choice process are stored by path and network link and can be flexibly queried. Select link analysis is fully available without re-running the assignment and is unique for each scenario.
The new methodological framework was applied to the 2012 FAF flows as a fundamental test of its workability. The work flow was validated as process-worthy and flows were generated on the national network. The query engine was tested and several forms of validation were performed. Data on truck trajectories between city pairs indicated that the method was effective in capturing routes that are actually utilized.

Programme committee
Freight and Logistics