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How Freight Moves: Estimating Mileage and Routes Using an Innovative GIS Tool
by Stephen M. Lewis and Felix Ammah-Tagoe, Ph.D.
The Bureau of
Transportation Statistics (BTS) has
developed an innovative software tool,
called GeoMiler, that is helping
researchers better estimate freight travel. GeoMiler is being used to compute mileages along likely routes for the nearly 6 million
freight shipments expected to be reported in the 2007 Commodity Flow Survey (CFS), the nation’s largest
survey of freight movements. These computations are used in estimating modal ton-miles of freight —a key measure for understanding the use and performance of our nation’s freight transportation system.
BTS, part of the Research
and Innovative Technology
Administration (RITA) of the
U.S. Department of Transportation (USDOT), developed GeoMiler using current Geographic Information
System (GIS) technology to assign
routes and calculate mileage from the true origin to the true
destination of each freight shipment even when more than one freight mode is used. While developed for
use in the CFS, the tool’s
integration of core GIS technology and
its modeling approach can be used for any multimodal freight
movement at all geographic levels.
Background
The Commodity Flow Survey,
a nationwide survey of
U.S. businesses that generate freight shipments, is the primary source of national data on the flow of goods —from where to where, how far, and by what means. The
2007 survey, sponsored by BTS and conducted by the Census Bureau, is currently underway; it
covers 100,000
U.S. business establishments primarily engaged in manufacturing, mining, and wholesale activities. Visit www.bts.gov/cfs for additional information about the survey.
For the prior CFSs, conducted in 1993, 1997, and 2002,
shipment distances were estimated by using a set of routing modules
that are now dated and do not fit within the current USDOT Enterprise
Architecture. There were individual modules for air cargo, surface modes, and exports. As a result, the CFS records had to be
processed multiple times. Because GIS technology was not
used, the models relied on flat ASCII-file representations of the transportation networks. These networks were cumbersome to maintain. Without the GIS component,
there was no way to visualize on a
map the routes that were
generated.
For the 2007 CFS, BTS
wanted a tool that met CFS’
operational requirements while being easy to maintain and upgrade. This effort was part of a major
performance push to improve overall efficiency, methods, and quality of mileage information in the 2007 CFS.
Why the Need for Mileage Estimation?
CFS shipment mileage is
estimated by BTS after the survey data have been collected from respondents. The respondents were shippers and not
transportation providers (carriers). Shippers know the actual origin and destination of their shipments but may know little about the specific modes of transportation used by carriers, the ultimate routes
taken, and the distance traveled. The survey asks for origin and
destination ZIP Code and the mode sequence (e.g., highway-railhighway) used for each shipment.
From this information, BTS
must calculate the mileage traveled by single mode (highway,
rail, water, air, parcel, and pipeline) and by many
multimodal combinations.
Few, if any, off-the-shelf
national-level multimodal transportation networks are available for
use in a GIS. In addition, there are
almost no commercial routing modules capable of
seamlessly handling intermodal transfers in the specific modal sequence provided by shippers. For example,
routing a grain shipment by truck, rail, inland
waterway, and truck is not a simple shortest path
problem. It requires routing logic that allows the shipment
to transfer at commodity-appropriate intermodal terminals and water docks. This routing logic is built
into GeoMiler.
The absence of a readily
available commercial solution for such multimodal routing
led BTS to develop the GeoMiler network routing tool, using current GIS technology and robust spatial network
data. It integrates map visualization features
with route solvers to handle many alternative
multimodal combinations from the following list of
modes represented in the CFS:
- parcel delivery, courier,
U.S. postal post;
- private truck; for-hire truck;
- railroad;
- shallow-draft (Inland Water) Vessel;
- deep-draft (Ocean) Vessel;
- great Lakes vessel (generated by
routing models);
- air;
- pipeline;
- unknown (don′t know or missing);
- other; and
- multimode (any combination of the
above).
GIS Platform and System Architecture
The operational
requirements for accurately estimating mileages for the nearly 6 million
shipments, of which over one-tenth
involved some multimodal transfer, required a multitier logical and physical design (figure 1). This design allowed data pre-processing separate from the route solver,
modeling logic, and mapping interface.
This system design and the development platform meet USDOT’s Enterprise Architecture
requirements.
- In this multitier configuration, the entire
tool, including the data pre-processor and
post-processor, was developed with a
software tool that uses the BASIC programming
language.
- With the exception of
pipelines, the route solver module for all modes – highway,
rail, water, air, parcel, and multimodal shipments –
was based on the analytical logic and
route solvers from off the shelf GIS software. Due to
restrictions on use of the national pipeline
network, GeoMiler calculates great circle distance (GCD) for
all pipeline shipments.
- The mapping visualization
interface was also based on off the shelf GIS
software, which was customized to allow the assigned
paths to be checked and corrected.
The use of GIS in GeoMiler allows the most likely paths taken by shipments from
ZIP Code to ZIP Code to be displayed on a computer
screen. GIS was used to create a series of
programming and modeling routines that allowed for analysis of
the individual freight transportation networks for roads, rail,
waterways, and air cargo. More
importantly, it allowed for analysis across all of these modes. specifically, GeoMiler creates connectivity rules among
the different networks, models the impedance factors
based on cost descriptors and network hierarchies,
and defines the routing logic that uses these
impedances. Each link in the multimodal network is
assigned an impedance value, which represents the
likelihood of flow on each link. The higher the impedance
value, the less likely the link will be selected for
the path. By leveraging and customizing GIS
technology, GeoMiler allows estimation of the optimal paths for all
modes and allows each path to be displayed for
analysis or decision making.
Developing Multimodal Spatial Network Data
GeoMiler uses a series of spatially
referenced individual transportation networks (highway, rail,
waterway, and airway) linked at points
(airports, seaports, and intermodal transfer facilities) with straight line access and egress connections
that we call "spatial joins."1 This approach makes it
unnecessary to merge the individual mode-specific networks into one large integrated
multimodal network. Keeping the modal networks separate
and connecting them with spatial joins allow
distance estimation for both single-mode shipments and any
combination of multimodal shipments from any ZIP
Code to any ZIP Code.
It also allows calculations
for export shipments by any mode to
Canada and
Mexico as well as by air freight and maritime vessel to all
U.S. overseas trading partners.
This spatial network
database includes ZIP Code centroids, the
U.S. highway network, Canadian
and Mexican highway and rail
networks, national rail network, national waterway and docks network
(including inland, coastal, and Great
Lakes), global seaway network, intermodal truck-rail-ports terminals, and North
American border crossing locations. BTS constructed this geospatial multimodal
network from the following sources:
- Highways and Roads – Highway route data from a commercial source
provided coverage of roads in the
United States. Additional sources were used for
Canada and
Mexico.
- Railroads – Federal Railroad Administration (FRA) maintains the North American rail network used in the Rail Waybill data (enhanced with Waybill ownership, trackage rights, and rail densities).
- Airports and Airways – Federal Aviation Administration sources provided location information for large, medium, and small
hubs that handle freight. For Alaska, it included all hub and nonhub airports. A domestic and
international airway routes network was created from official air cargo data from the BTS office of Airline Information (OAI).
- Waterways – Routable network maintained by
- the
U.S. Army Corps of Engineers
(USACE) and distributed by BTS.
- Water Ports – USACE sources, including dock-to-dock shipment location and
commodity information for all docks on the inland
waterways and seaports.
- Intermodal Facilities – database created and maintained by BTS.
- Zip Code Centroids – United States Postal
Service and a commercial source.
Complementary Input Data
Working together through
interagency cooperation, BTS received official freight data, including
information not available for public use,
from the FRA and the USACE to support the
modeling, validation, and selection of the optimal paths. The
major primary complementary data sources included:
- FRA Waybill Sample Data –
used to determine the link densities,
interlining, and rail station use;
- USACE waterborne traffic data – used to determine the most likely docks by
commodity for multimodal shipments involving the
U.S. waterway system;
- Census Bureau
U.S.-international trade data – used to select and
validate the most likely air and sea routes for all trading
partners, including oceanborne shipments to landlocked countries;
- BTS OAI air cargo data –
used to control cargo traffic among airport pairs for both domestic traffic and exports to all countries;
- BTS TransBorder and Border Crossing data – used to select the most
likely crossing points for exports into
Canada and
Mexico by truck and rail.
Modeling Simulated Pathfinder Routes
GeoMiler’s basic modeling routines
are straight forward. With data on specific origins and destinations and mode sequence, the tool
determines the set of spatial links and nodes that make
up the "best possible" or optimal route between the
two locations (figure 2). This selected route simulates a typical likely path within the multimodal
network that optimizes a set of pre-defined conditions that are mode and commodity specific.
For the highway (both
for-hire and private) and water (inland shallow draft, deep draft, and Great Lakes) components, the tool finds the least-impedance path from origin point to
destination point over the highway and waterway networks and then
sums the lengths of individual links on these paths.
For rail and rail-inclusive intermodal, the tool estimates a least-impedance path based
on railroad specific operating paths and
selects the most likely route. Rail shipments are routed
over the latest FRA rail network updated with the latest
ownership changes, abandonments, trackage rights, interlining, and track density.
For air shipments, GeoMiler finds the least-impedance truck routes to the origin
airport and from the destination airport. It then uses
airport-to-airport traffic availability to estimate the most likely route, giving priority to direct flights between major hub airports, single carrier routes (circuity constrained), and maximum air cargo lift from
airports, while controlling for the ratio between the truck
mileage and the air mileage.
Because air traffic does not physically cross the U.S. border at designated
gateways, as do the other modes such as rail, GeoMiler measures the
U.S. portion of an international flight by extracting that portion of the flight that extends from the
U.S. airport of exit to the point where the flight path intersects the
U.S. border.
GeoMiler Deployed
As deployed, the GIS-based GeoMiler uses current generation programming languages with
standard commercial GIS software to provide a
fast and efficient data processing module with the capability to estimate and verify shipment
mileages. It offers a dynamic modal routing tool able to
process data and generate shipment distances for
single modes and multimodal shipments.
It also offers a very
user-friendly interface with a consistent diagnostic tool for
reconciling records with problematic origin and
destination state and ZIP Code
information. New route viewing capability, including multimodal routes and information on
choice of intermodal facilities, allows user-analysts to make informed choices when the input
modal information needs correction.
While GeoMiler was developed for the CFS, the approach used in creating the geospatial
databases and modeling the multimodal movements
could be leveraged for other applications.
Figure 3. Example of a GeoMiler Path
Determination
Acknowledgments
A BTS contract team under the management of Stephen Lewis and Michael Margreta developed GeoMiler. The software developing, pro-gramming, and data expertise of Adhi Dipo, Fahim Mohamed, Raquel Wright, and Derald Dudley were critical. The freight modeling and CFS insights were provided by Felix Ammah-Tagoe. The Federal Railroad Administration and the Waterborne Commerce Statistics Center of the Army Corps of Engineers provided critical complementary data and technical support that made this tool possible.
The Bureau of Transportation Statistics is a component of USDOT’s Research and Innovative Technology Administration.
For questions about this or other BTS reports, call 1-800-853-1351, email answers@bts.gov or visit www.bts.gov.
For related data and reports visit www.bts.gov
Data -
- NTAD–National Transportation Atlas Database
- Commodity Flow Survey—value, weight, and ton-miles by commodity, mode, and origins and destinations
- Transborder Freight Data—monthly release of U.S.-Canada and U.S.-Mexico trade data
- Border Crossing/Entry Data—monthly data on incoming vehicle crossings from Canada and Mexico
Reports -
- America’s Container Ports: Delivering the Goods
- North American Freight Transportation 2006
- Freight in America
- America’s Freight Transportation Gateways 2004
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1 Transportation facilities
(e.g., airports, highway/rail transfer yards) can be extensive and contain
many miles of roads or rail. Rather than navigating these labyrinths of rail
and asphalt when connecting two or more different freight
transportation modes, which is cumbersome and time consuming, GeoMiler represents each of these facilities as a single point. The "shortest path
solvers" function in GeoMiler then uses straight-line links, called "spatial
joins," to connect theses points to the appropriate transportation mode(s).
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