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Chapter 6 - The State of Transportation Statistics

  • We have extensive data on local passenger travel but limited data on long distance travel; conversely, we have extensive data on long distance freight movement but limited data on local freight movement.
  • We have extensive data on the condition and performance of highways, bridges, airports, and waterway facilities, but little data on the condition of privately owned railroads and pipelines.
  • We have extensive data on accidents and air emissions, but limited data on noise and other forms of environmental and community disruptions caused by transportation.
  • We have information about transportation's share of gross domestic product, but little knowledge of the impact of transportation on our nation's economy and on our citizens' quality of life.
  • Alternatives to increasingly expansive surveys, such as the use of administrative records and technologybased monitoring, are needed to develop transportation statistics. The digital revolution presents opportunities and challanges for improving transportation statistics.

Congress underscored the importance of statistical information for transportation investment decisions, policy initiatives, and other public actions when it established the Bureau of Transportation Statistics (BTS) and required BTS to assess the state of statistics in an annual report. The transportation community's current emphasis on performance measurement underscores the continuing importance of data for decisions two decades after the creation of BTS.

The diversity of information needed to support the wide range of transportation decisions makes the development of useful and timely transportation statistics a challenging task. Some of these decisions require data on transportation infrastructure, vehicles, and traffic flows. Other decisions require data on the human factors involved in transportation.

For example, to help meet the Administration's National Export Initiative goal of doubling U.S. exports by the end of 2014, information is needed to identify bottlenecks in our Nation's transportation infrastructure that impede the timely and most economical movement of exports through the system. The information needs include, but are not limited to, the wait time at different transportation facilities (e.g., a lock on the Ohio River, a railroad yard in Chicago, a border crossing in Arizona); the time it takes for intermodal transfers (i.e., transferring shipments from one mode to the next); system capacity and capability to handle different commodities at different ports and terminals; and the investment needed to meet future demand.

In contrast to the geographic focus of exports, combating distracted driving requires statistics involving individual's behavior. Data is needed to answer questions such as:

  • What activities distract a driver's attention?
  • Which activities are more distracting than others?
  • What age group is most likely to engage in activities that distract attention while driving?
  • How effective are enforcement actions, outreach, and educational strategies?
  • What has been the progress over time in addressing distracted driving?

The challenge in developing useful and timely transportation statistics is further complicated by the enormous size and complex nature of our Nation's transportation system.

Progress made in compiling and distributing statistics on passenger travel, freight transportation, transportation's role in the economy, and transportation and its unintended consequences are briefly summarized below. This chapter also highlights the major transportation data gaps and the challenges and opportunities facing future transportation statistics programs.

Passenger Travel

Passenger travel data are collected by various government agencies, some on a periodic basis and others on a continual basis. The collection of these data can be categorized into two groups.

The first group collects overall system usage data without collecting data on individual travelers' characteristics. The data programs in this group include, but are not limited to, the Highway Performance Monitoring System [USDOT FHWA HPMS 2010]; the Federal Transit Administration's National Transit Database [USDOT FTA NTD 2012]; and the Bureau of Transportation Statistics' monthly passenger enplanement data [USDOT RITA BTS 2012a], National Census of Ferry Operators [USDOT RITA BTS NFCO 2010], and Intermodal Passenger Connectivity Database [USDOT RITA BTS IPCD 2012b]. These data programs are crucial in the development of baseline information, the analysis of overall usage trends over time, and for understanding how changes in the economy influence the use of our transportation systems.

The second group of passenger travel data programs collects data at the individual traveler's level (without identifying personal identifiable information) from which travel patterns and traveler characteristics for the population as a whole can be estimated. The most prominent program in this group is the National Household Travel Survey (NHTS), sponsored mainly by the Federal Highway Administration (FHWA) and with increased co-sponsorship by states and metropolitan planning organizations [USDOE ORNL 2012]. The NHTS collects not only information on individual trips but also demographic, household vehicle ownership, neighborhood characteristic data, and other factors that influence a household member's decision on when, how, and how far to travel. Although the NHTS collects all personal travel taken by all modes of transportation, it mainly captures local travel. The high cost of conducting this type of nationwide survey has limited the frequency of this survey to once every 5 to 8 years. Despite these limitations, NHTS remains the only source that provides the comprehensive data needed to understand travel decisions and predict travel demand.

The Census Bureau's American Community Survey (ACS) is another commonly used source of passenger travel information. The ACS collects commute-to-work data from an annual survey of the population. This survey provides small-area information every year, unlike the once-per-decade information formerly provided by the decennial census. The ACS also provides statistics for small units of geography averaged over several years, while the NHTS provides national statistics by size of place [USDOC ACS 2011].

Based on these national statistics and on information from metropolitan area studies, the FHWA is exploring options to develop a national picture of passenger movements from county to county and state to state by all transportation modes. The robustness of the final results depend heavily on estimation models because the last physical measure of intercity passenger traffic is the BTS American Travel Survey conducted almost two decades ago. Costs of repeating the American Travel Survey are prohibitive.

Freight Transportation

The U.S. transportation system moves more than 4.6 trillion ton-miles of freight annually. Due to the complexity of freight transportation, there is no single data source capable of providing a comprehensive picture of annual freight movement from origin to destination, by all modes of transportation, and by all commodity types. Among the various data sources, the Commodity Flow Survey (CFS) serves as the backbone for developing a comprehensive picture of U.S. freight flows. The CFS is the only source of national- and state-level data on domestic freight shipments by major U.S. business establishments and selected retail industries. It also provides comprehensive data on domestic hazardous material shipments. The CFS, sponsored mainly by the Bureau of Transportation Statistics (BTS) and cosponsored by the Census Bureau, is conducted every 5 years as part of the Economic Census.

To develop an integrated national picture of freight movement, FHWA's Freight Analysis Framework (FAF) relies on CFS data as the base and supplements it with multiple, publicly available data sources, such as the data on freight flows across U.S. land borders and data on the international movement of air cargo collected by BTS [USDOT RITA BTS 2012c]. This comprehensive picture is updated with annual statistics on railroad and waterway freight flows and foreign trade statistics. The FAF also includes forecasts.

The performance of our Nation's freight transportation system in handling the 4.6 trillion ton-miles that move through it annually is primarily measured by freight travel time, including, but not limited to:

  • average train speed and average waiting time for loaded train cars to proceed for each major railroad,
  • vessel delay times for each lock on the inland waterway system,
  • truck speed and reliability on major highways and at border crossings, and
  • throughput measures for selected ports.

The major national data sources for freight movement and performance are described at USDOT's freight transportation website (

Transportation's Role in the Economy

In 2010, transportation-related expenditures as part of final demand accounted for nearly 9.8 percent of U.S. gross domestic product (GDP) and enabled linkages among natural resources, manufacturing, distribution centers, and consumers [USDOT RITA BTS NTS 2013, table 2-2].

Transportation's direct economic contribution is derived from statistics on the costs paid by households and businesses for transportation services, employment in transportation industries and occupations, and the value of transportation infrastructure and equipment. These statistics come from the Census Bureau, the Bureau of Economic Analysis (BEA), and the Bureau of Labor Statistics (BLS), each of which treats transportation as a significant sector of the economy.

For-hire transportation is one of the many sectors covered in the Economic Census, conducted every 5 years. This sector is also covered in the Census Bureau's Services Annual Survey, which collects operating revenue and other industry-specific data. These data are used by the BEA to estimate the flow of expenditures among sectors of the economy in order to understand how changes in the costs in a specific sector affect the rest of the economy. However, accounting for only the for-hire transportation sector misses the sizable contribution to the economy made by in-house transportation services within nontransportation industries, such as truck fleets operated by large retail companies (see box 6-A). Chapter 4 discusses the differences between for-hire and in-house transportation employment.

Transportation is not often highlighted in monthly national economic statistics. To provide a perspective on transportation's role in a dynamic economy, BTS developed the monthly Freight Transportation Services Index (TSI) [USDOT RITA BTS TSI 2012d]. This index is based on activity in all modes of for-hire freight transportation services and affords a better understanding of the relationship between transportation and the current and future course of the economy. After adjusting for long-term growth and seasonal variation, it appears that declines in freight movements proceeded the two most recent recessions (figure 6-2). The March 2001–November 2001 recession followed an extended period of decline in the Freight TSI index. The December 2007–June 2009 recession [NBER] was preceded by a general decline in the index beginning in late 2005. Although there was a short upward movement in the freight TSI for several months before and during the start of the most recent recession, the declines in the index continued during both recessions. The drop in the TSI was especially precipitous during the December 2007–June 2009 recession. The increases in the index slightly lag the end of the recessions.

Transportation and its Unintended Consequences

In addition to the intended economic activity that transportation creates, its notable unintended consequences are in the areas of safety, energy consumption, environmental issues, and community impacts. Of these, safety dominates the statistical activities of the USDOT. The National Highway Traffic Safety Administration (NHTSA) and the Federal Motor Carrier Safety Administration account for 40 percent of the expenditures on major statistical programs in the Department [USEOP OMB 2011]. One of the major safety data efforts is the modernization of NHTSA's Fatal Accident Reporting System to ensure the reliability and timeliness of safety data collection and analysis. The Pipeline and Hazardous Materials Safety Administration and FHWA also have large-scale safety programs. Altogether, the Department's annual expenditures on safety data exceed $50 million.

Recognizing that roadway safety improvement requires stronger partnerships and collective efforts across all modes of transportation and stakeholders, senior USDOT leadership initiated the development of the Roadway Safety Plan to bring an integrated focus to roadway safety issues [USDOT OST RSP 2012]. One of the priorities of this plan is to improve the systematic collection of safety data and analytical tools. These improvements are intended to help better identify high-risk road users and commercial vehicle operators, prioritize safety investment decisions, and evaluate the effectiveness of safety countermeasures.

The Roadway Safety Plan proposes two programs that are pertinent to safety statistics. First is the Highway Safety Improvement Program in which an electronic base map of all public roads will be developed that can be used to geographically reference and integrate all safety data. Second is the Safety Data Program that will integrate safety data across all modes by reconciling definitional inconsistencies and other data incompatibility issues. Furthermore, the Safety Data Program will identify and address data gaps in existing departmental safety programs.

The lower fatality rates in nonhighway modes, such as commercial aviation, railroads, and transit, do not reduce the need for data to understand risks and maintain or improve safety. The focus of data programs shifts from determining causes of crashes to understanding circumstances surrounding near misses or other mishaps that could have resulted in a serious incident. The National Aeronautics and Space Administration (NASA) provides a close calls reporting system for the Federal Aviation Administration that allows airline employees to make confidential reports that can be used to identify and mitigate safety problems. Nearly 5,000 reports are filed each month [NASA 2012, p. 15]. NASA provides a similar reporting system for Amtrak. BTS developed a similar program for freight railroads [C3RS 2012] and is working with a major transit system to initiate the first urban close calls reporting system.

The transportation sector accounts for more than two-thirds of the petroleum consumed in the country and produces between one-quarter and one-third of all of the carbon dioxide (CO2) emitted by the country's energy consumption. The U.S. Department of Energy has a major data program that tracks energy consumption by the transportation sector [USDOE EIA 2012], and transportation's contributions to greenhouse gases and other emissions are tracked by the Environmental Protection Agency [USEPA OTAQ 2012]. While individual agencies are compiling information to meet their specific needs, integrating the data gathered from multiple perspectives and developing analytical techniques from many disciplines are the keys to effectively using the data sources to bring about a reduction in transportation-related energy consumption and emissions. For example, the relationships between vehicle usage patterns and energy usage intensity are crucial to measuring and assessing the effectiveness of different energy and emission reduction opportunities and policies. Unfortunately, with the discontinuation of the Vehicle Inventory and Use Survey in 2002, much of the data necessary to help make these assessments are now more than 10 years out of date [USDOC CB VIUS 2002].

Information Gaps and Challenges

To understand transportation activity, its contributions to the economy, consequences for the environment, and the potential impacts of policies and investments, it is crucial to estimate the interactions among the following components:

  • Sectors of the economy that produce the demand for transportation and depend on transportation for productivity and health;
  • The response of businesses within supply chains to regulations, private and public investment, and the impact those responses have on both the time and location of transportation activities;
  • Household mobility needs and expenditures that determine the time and location of transportation activity and how travelers respond to transportation investments and regulations;
  • Infrastructure and assets that are needed to serve the mobility requirements of households and businesses, to stimulate local economic growth, and to mitigate the adverse safety and environmental impacts of passenger and freight transportation; and
  • Transportation investments that improve transportation services and promote economic growth and global competitiveness.

Data that are lacking on each of the components are highlighted in table 6-1.

Future Opportunities

The digital revolution presents the biggest opportunities and challenges for improving transportation statistics to support public decisions. Nearly all business transactions are now electronic, and a growing share of personal activity leaves an electronic trail. The databases created by business transactions and credit card purchases, communications systems, traffic management systems, and onboard vehicle diagnostics can be mined to estimate passenger and freight movement, identify the costs to travelers and businesses of those movements, and even measure the emissions created by vehicles in motion or idling. The coverage of databases continues to expand and the tools for mining them, popularly known as Big Data, Data Analytics, and other terms, have improved dramatically. Technology promises timelier, more accurate, and less expensive data, especially when compared to surveys.

Technology-based data typically provide much narrower windows on the phenomena being measured than surveys and place a premium on data integration and statistical representativeness. Technology also raises major privacy, confidentiality, and intellectual property issues. Beyond improved data collection and processing applications, technology shows promise in enhanced understanding of transportation activities and impacts. The processing power of personal computers creates opportunities for widespread use of new analytical and visualization techniques.

The Challenge of Performance Measurement

MAP-21, the Moving Ahead for Progress in the 21st Century Act of 2012 (Public Law 112-141) requires states and the USDOT to publish performance measures and progress toward performance targets for many aspects of surface transportation. These requirements reflect a growing emphasis on accountability and management for improved performance in all fields of public administration. Performance measurement involves many statistical challenges and opportunities in addition to institutional concerns for the transportation community.

MAP-21 and the Government Performance and Results Act (GPRA) (Public Law 103-62) ask whether government actions are making a difference. The answer requires statistics beyond basic indicators of a general condition, such as the number of fatalities, tied to a generally stated goal, such as improved safety. More detailed statistics and more complex analysis are typically needed to answer the questions identified in table 6-2.

Performance measures are typically defined as output or outcome measures, though many performance measures are actually basic indicators that reflect goals or basic conditions. For example, the number of fatalities is a basic indicator. Fatalities by cause provide a more useful measure against which outputs and outcomes can be considered.

Outputs of government programs should be relatively easy to define, except that programs often involve a variety of specific actions that are difficult to characterize in simple measures. Furthermore, the output of one program may be the input of another. The major output of Federal agencies implementing MAP-21 is spending on safety and other aspects of surface transportation. The outputs of recipients of Federal funds may involve a wide variety of facilities and services purchased with those funds. Statistics on the facilities and services may be lacking for formula grant programs, leaving total expenditures as the only available measure of output.

While outputs should be relatively easy to define in most cases, outcomes are the most difficult to measure. Outcomes are not just changes in an actionable condition following an output. Simple correlation is not enough. To be an outcome, some evidence of causality is required from targeted monitoring, such as before and after studies.

Given resource limitations for expensive new data collection programs, managers of transportation statistics will be challenged to adapt existing data program and analytical techniques to serve performance measurement. For example, current transportation planning models and supporting data are designed to measure problems such as congestion and predict how proposed changes, such as new capacity, will affect those problems. Research is underway to estimate basic indicators and actionable conditions with these models and use forecasting elements to set targets by which actual outcomes can be judged.

Performance measurement will ultimately require some new data collection. MAP-21, GPRA, and the American Recovery and Reinvestment Act of 2009 (Public Law 111-5) all encourage the development and publication of better output and outcome measures. Outcome data from beforeand-after studies and other quasi-experimental designs that measure program effectiveness can both serve performance measurement and become a new source of data for planning models.

Priority Areas Requiring Focused Attention by BTS

MAP-21 establishes priorities for transportation statistics in the years ahead. MAP-21 reaffirms the mandate for BTS and adds the establishment of a safety data program on behalf of the Secretary. MAP-21 requires performance measurement for most surface transportation programs such as safety improvement and infrastructure preservation. MAP-21 also adds new provisions for freight transportation that require data, including designation of freight corridors, development of investment analysis tools, and creation of a national freight strategic plan and state freight plans. MAP-21 also encourages states to maintain a base map of all public roads on which fatal and serious injury accidents can be located and analyzed.

In response to MAP-21 and departmental goals, BTS will emphasize the following areas over the next 2 years:

  • Complete the Intermodal Transportation Database, which includes data on passenger movement by purpose; freight movement by commodity and by origin, destination, and mode; and transportation economic accounts for capital stocks, transportation expenditures, and employment. Central to this activity are completion of the 2012 Commodity Flow Survey and statistical integration of FHWA's Freight Analysis Framework and intercity passenger flow estimates into the Intermodal Transportation Database.

  • Enhance the National Transportation Atlas Database, which includes an analytical network for estimating the routes of passenger and freight movement; link this database to an inventory network file for locating transportation facilities and attributes of those facilities; and link this to population, economic, and environmental data from other Federal agencies. The inventory network, started under the Transportation Network for the Nation initiative of the Federal Geographic Data Committee, will be reviewed as a mechanism for integrating highway safety base maps.

  • Expand the compilation of statistics on transportation performance and impacts to include performance measures developed in response to MAP-21.

  • Establish the safety data program with integrated safety data across all modes, and prepare a safety data improvement action plan.

  • Continue to enhance the quality, timeliness, and efficiency of the airline information program.

  • Expand the functions of the National Transportation Library to serve as a depository and clearinghouse for research as called for in MAP-21.

  • Explore new methods of transportation data collection, analysis, and visualization to support public decision-making, with a particular focus on open data, geospatial data integration, and freight investment data and planning tools.

Some of these BTS initiatives will address several of the gaps and challenges discussed above, and some will explore identified opportunities. Through these and other efforts, BTS will continue to strive toward achieving the vision of Abraham Lincoln who said, in reference to proposed Federal investments in transportation facilities, "Statistics will save us from doing what we do, in wrong places [Lincoln, A; 1848, pp. 709-711]."


Confidential Close Calls Reporting System (C3 RS). Available at as of April 2012.

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National Aeronautics and Space Administration (NASA). Aviation Safety Reporting System, In-Depth ASRS Program Briefing. Available at as of April 2012.

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