Household Travel Surveys At A Glance

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September 2013

Overview of Surveys

Motivating factors

Metropolitan planning organizations (MPOs) and state departments of transportation (DOTs) use data collected from household travel surveys (HTS) to better understand residents' travel patterns and use the results to update and/or calibrate their travel demand models. Travel behavior trends are examined for forecasting vehicle miles traveled (VMT), greenhouse gas (GHG) emissions, and new public transit investments.

Implementation

Comprehensive one- and two-day travel diaries collect information about the household, its members, and all the trips completed on a pre-assigned travel date. A pilot study is typically used to test the methods and materials, so that the full study benefits from improvements and refinements (e.g., modifications to question wording or response rate assumptions). Planning and public outreach for the HTS is critical because of declining response rates. Outreach methods increasingly include social media posts, videos, project websites, and targeted materials or contacts with certain hard-to-reach populations in the study region.

Methods and Datasets

HTS typically use the following methods:

• Sampling: Address-based sampling (ABS)
  • Sample is randomly selected from geographic subareas within the study region
  • Oversampling is possible and typically done at the geographic subarea level
  • Non-probability sampling is an option for hard-to-reach groups such as vanpoolers
• Recruitment: First-class mail or telephone
  • Households are notified and provided with instructions for how to complete the survey
  • Special incentives for hard-to-reach households, such as zero-vehicle, low-income, and large families are often used
• Data retrieval: Online survey instrument, paper-based survey, and/or computer-assisted telephone interview (CATI)
  • Most studies provide respondents with at least two of the above options to reduce response bias
• GPS sub-sample: Added to an increasing percentage of travel diary data collection efforts (described in more detail on reverse side)

The survey instruments typically collect the following information:

• Household data (e.g., location, number of vehicles, number of members)
• Person data (e.g., age, employment status, relationship)
• Vehicle data (e.g., year, make, and model of each vehicle)
• Trip data (e.g., start time, duration, mode, purpose)

Example Survey Interface with GPS Trip Data

The image to the right is a screen capture of an example web-based survey instrument. This particular prompt asks the respondent to provide details corresponding to the trip captured by GPS data.

GPS Data

For the last decade, about 20 of the larger agencies have included a 5% or 10% GPS sub-sample as part of their region's HTS. The primary purpose of the GPS sub-sample has been to generate trip rate correction factors for the other sampled households and account for trip under-reporting often found in diary-based HTS.

The GPS approach is typically conducted as follows:

• Households are assigned to a GPS subsample and recruited into HTS
• Households are sent wearable GPS or vehicle-based

GPS devices and each household member is asked to use the device for a pre-defined number of days

• Households return devices so that data can be downloaded and processed
• Respondents complete the "recall survey" to verify and provide additional data about their trips collected on the wearable device.

Most recently, tests on using 100% GPS-only diaries have been conducted in Ohio, and smartphones with embedded GPS and accelerometers are now being tested.

Household Travel Survey References

The following list of references can be used to learn more about the topic of HTS: methods, developments/technologies, trends, and data uses.

• National Household Travel Survey (NHTS)
• Transportation Research Board's (TRB) Travel Survey Methods Committee
  • On-line Travel Survey Manual
• Texas A&M Transportation Institute's (TTI) Household Travel Survey Symposium

Recent publications on survey methods:

• Stopher et al (2008). NCHRP Report 571: Standardized Procedures for Personal Travel Surveys.
• Stopher (2012). Collecting, Managing, and Assessing Data Using Sample Surveys.
• Zmud, Lee-Gosselin, Munizaga, Carrasco (Eds.) (2013). Transport Survey Methods - Best Practice for Decision Making.

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