Web-Based Tools Help With Travel Data Analysis
Why do people travel? What modes of transportation do they use? How long are their trips? Where do they go? The answers to these questions and more are what the Federal Highway Administration's National Household Travel Survey (NHTS) seeks to collect and provide to the transportation community. The NHTS data enable transportation decisionmakers to assess initiatives, review programs and policies, study current mobility issues, and plan for the future.
The NHTS serves as an inventory of the Nation's daily travel. The 2009 NHTS dataset contains data for more than 150,000 households across the United States with information on household characteristics, vehicles, and daily trips. The 2009 survey marked 40 years of data collection, with previous surveys conducted in 1969, 1977, 1983, 1990, 1995, and 2001.
The NHTS Web site at http://nhts.ornl.gov provides readily available data to a wide range of individuals and organizations. Hosted by the Center for Transportation Analysis at the Oak Ridge National Laboratory, the site provides a full range of services, including access to disaggregate datasets in a variety of formats, publications, survey methods, materials and data documentation, news briefs, a user forum, and browser-based data analysis tools.
"The NHTS is the most important national survey for transportation planners," says Jana Lynott, senior strategic policy advisor for AARP, whose organization is using the survey to examine changes in the travel patterns of older adults. "The robust sample size and questionnaire enable researchers to answer an almost unlimited number of transportation policy questions."
Analyzing Data With NHTS's Online Tools
Online tools accessible from the home page of the NHTS Web site support data analysis for the three most recent surveys (1995, 2001, and 2009). From readymade tables of frequently requested data to customized data tabulations, the tools help a variety of users with differing data analysis experience meet their needs.
For the casual NHTS user, the Frequently Asked-for Tables feature provides more than 25 tables populated with data such as the number of vehicles by household income and the number of trips by mode and purpose. For users who require more specific data tables, NHTS Table Designer facilitates creation of customized tabulations of travel behavior and characteristics of households, household members, and vehicles. Advanced options enable users to customize response categories (such as income level) by collapsing responses and to subset the records of analysis (such as add-on State data). Table Designer users can save their table specifications. Users can view both Frequently Asked-for Tables and tabulations generated with the Table Designer in HTML format and export them to Microsoft® Excel®. To date, NHTS has approximately 6,000 registered users who generate an average of 900 custom tables per month.
Another popular tool is the online Codebook Browser, which provides the list of dataset variables and their characteristics, including ways to sort, filter, and search. For example, a keyword search of "inc" will locate all variables related to household "income." Codebook information includes the data type, question number, data file membership, and variable values and meanings.
The Web site also features a transferability tool, which uses statistical methods to transfer NHTS data to small geographic areas such as Census Tracts and Transportation Analysis Zones. This tool helps transportation planners estimate regional or local travel, including vehicle trips and miles of travel, and person trips and miles of travel, by trip purposes.
Introducing the Data Extraction Tool
NHTS staff recently created a data extraction tool that provides an easier way to dig into the datasets and generate trend analysis statistics ready for export. This tool enables users to obtain data from the 1995, 2001, and 2009 surveys to examine total travel (person trips and miles traveled, and vehicle trips and miles traveled), and easily extract data from all three surveys.
To use the data extraction tool, which is accessible from the NHTS home page, the user chooses elements using selection criteria—essentially a menu of parameters—to generate a customized dataset. The user then can download the customized dataset in comma separated values format for additional analyses.
"FHWA strives to enhance its ability to transform numbers into information and knowledge and to democratize all complex data," says David Winter, director of the FHWA's Office of Highway Policy Information. "The NHTS online analysis tools offer a portal for not only the professional data analyst, but more important, for the general public to understand travel behavior in the United States."
Adella Santos is the NHTS program manager at FHWA.