How We Travel A Sustainable National Program for Travel Data (2011) / Chapter Skim
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3 New Approaches for Meeting Travel Data Needs
3 New Approaches for Meeting Travel Data Needs
Pages 45-74
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. This section focuses on survey data because the flagship passenger and freight travel surveys -- the National Household Transportation Survey (NHTS)
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for recent household travel surveys conducted for the Washington and Baltimore metropolitan areas. The estimated cost of the 2010 Travel Behavior Inventory, a local travel survey conducted by the Minneapolis-St.
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T Tang, Federal Highway Administration (FHWA)
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The accuracy of survey responses is also a problem; for example, only 58.7 percent of the total number of establishments sampled in the 2007 CFS provided complete and usable responses.9 More generally, data providers in the private sector are most concerned about protection of proprietary data.10 In the context of growing interest in detailed travel data by transportation planners and modelers, companies are worried about the risk of revealing such data to competitors. Many businesses also are skeptical of data collection by the federal government, particularly for open-ended purposes.
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First, the cost of data collection is increasing, often just to keep response rates constant. Second, declining response rates may introduce bias, calling into question the representativeness of survey results.11 For household surveys, the difficult-to-reach nonrespondents are a key problem.
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. The use of incentives Box 3-1 Approaches to Overcoming Barriers to the Collection of Passenger Travel Data Most approaches to overcoming barriers to the collection of passenger travel data are focused on boosting response rates to household travel surveys.
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Many advances in household travel surveys, including greater use of technology, especially GPS tracking, have become commonplace within the United States over the past decade (Zmud 2010b)
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Travel surveys using paper travel diaries can take a long time to complete and process.14 Web-based diaries not only can "remember" and automatically populate repetitive information, but also are typically linked to interactive maps (such as Google Maps) that allow easy identification of exact locations.
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Opt-in respondents are the hallmark of many web surveys but are not a suitable sample for travel surveys because of self-selection bias, among other issues. To date, use of technologies that are becoming state-of-the-practice for data collection in local travel surveys is limited for the flagship NHTS.
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In summary, a wide range of methods are being explored, including greater use of technology, to reduce respondent burden and improve survey response rates and increase the accuracy and efficiency of both passenger and freight travel data collection. However, use of these methods, particularly technology, requires the resolution of numerous issues, which often involves further research and testing before the effectiveness of the methods can be confirmed and they can be widely adopted.
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To date, the major focus has been on new ways of tracking vehicle movements. INRIX, a leading provider of traffic and navigation services in North America, aggregates traffic data from more than 2 million GPS-enabled vehicles and cellular probes in its Smart Driver Network, along with other traffic-related data sources, to provide real-time traffic information to both private- and public-sector clients (INRIX 2010a)
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Applications of the data range from real-time, in-vehicle traffic information and advisories for drivers, to more aggregated data on traffic flows combined with information on incidents and weather alerts, used by transportation agencies for daily operational purposes. Data also are archived for future retrieval, for example, by public agencies wishing to measure traffic flows and bottlenecks for safety and emergency planning and evacuation purposes and for investment analyses for new capacity.
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Working with trucking companies and third-party vendors protected by contractual arrangements and nondisclosure agreements that maintain the confidentiality of the data, ATRI currently collects data from approximately 600,000 GPS-instrumented trucks throughout North America (Jones and Murray 2010) .24 The core FPM initiative centers on data on travel speeds and reliability for some 25 significant Interstate freight corridors, border crossing times and reliability for 15 major U.S.
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Either spot-speed or processed speed data can be used to calculate travel time reliability measures such as buffer time indices, variability measures, and simple standard deviations from mean speeds. Since the Freight Performance Measurement (FPM)
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27. Most recently, FHWA, in partnership with ATRI, launched a free web tool -- FPMWeb -- that enables state and local transportation agencies, as well as businesses and freight companies, to access data on where and when trucks are moving at slower than free-flow speeds, to visualize the results in a web-based GIS environment, and to probe the data more deeply through a customized query option (FPMweb undated; AASHTO Journal 2010)
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Finally, much of the data is focused on vehicle movements and speeds but not connected to information on traffic volumes, trips, people, or vehicle characteristics; travel behaviors; or the condition of the infrastructure on which the travel occurs.29 28. Traffax Inc., for example, uses its proprietary Blufax traffic surveillance units, together with in-vehicle Bluetooth technology, to provide state and local governments with continuous real-time measure ment of travel times (between data collection stations)
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continuous surveys with responsive design, (b) panel surveys, and (c)
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Continuous data must often be aggregated over time to obtain the same sample sizes for small groups that would be obtained from periodic surveys conducted at one point in time. Continuous surveys thus require pooling data over several years to increase confidence 30.
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Some suggest that team fatigue and waning motivation with continuous surveying lead to declining response rates, while limited evidence suggests that response rates that have been declining could actually be stabilized by more consistent staffing and methods (Lepkowski et al.
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. The smallest geographic units for which the data are generally published are the nine Government Office Regions.35 Panel Surveys Panel surveys are another way of collecting data that can be particularly useful in understanding the dynamics of travel behavior, although experience with these surveys in transportation research, particularly in the United States, is limited.
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The data are coded and entered into a data system, and quality checks are performed. Response rates are high -- around 60 percent overall, but lower in inner and outer London (46 percent and 49 percent, respectively, in 2008)
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. Panel surveys pose challenges, not the least of which are initial recruitment in the face of the continuing nature of the survey, imposing a heavier respondent burden; natural attrition of the panel and declining response rates over time; and panel fatigue and poorer quality of responses in later
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Panel attrition is not a trivial problem. The Puget Sound Transportation Panel experienced about a 20 percent attrition rate between the first two survey waves, the German Mobility Panel a 43 percent attrition rate, and the Dutch National Mobility Panel a 44 percent attrition rate (Zmud 2009, 3)
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2008) .44,45 The panel surveys are part of a family of personal travel surveys, described in the following subsection.
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The United States should consider adopting an approach similar to the German model -- using a portfolio of surveys at the core of comprehensive data programs to meet future travel data needs, both passenger and freight. This approach should include • Consideration of continuous surveys to replace or supplement the federal flagship surveys to provide more timely travel data or, at a minimum, a regular cycle of periodic surveys with updates in interim years using a smaller sample; • Establishment of a national panel survey to improve understanding of the dynamics of household travel behavior and to track national travel trends over time, which could be supplemented by periodic surveys targeting traveler response to particular policies and investments; • Partnerships with state and local governments to expand national surveys to collect more state- and regional-level data and to work toward more common formats for state and local travel surveys so as to encourage pooling of data, or substitution of modeled data, particularly for use across small metropolitan areas with common characteristics; and 47.
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Experience with such approaches is limited in the transportation sector, however, and the learning curve for properly collecting, analyzing, and using the data is likely to be steep. In addition, more evidence is needed on whether these methods will improve or stabilize response rates compared with periodic surveys.
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Federal Highway Administration, Matteson, Ill. Briefing presented to the Committee on Strategies for Improved Passenger and Freight Travel Data, Washington, D.C., Dec.
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Federal Highway Administration, Wash ington, D.C. Briefing presented to the Committee on Strategies for Improved Passenger and Freight Travel Data, Washington, D.C., Feb.
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Briefing presented to the Committee on Strategies for Improved Passenger and Freight Travel Data, Washington, D.C., May 6. Short, J., R
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2007. Mobility Panel Surveys: The German Experience.
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