How do you increase capacity of transportation systems without new construction? Through improved planning. Gathering data
on who is traveling where, when, and why is being made possible through the use of the Global Positioning System Automated
Travel Diary (GPS-ATD). The intuitive user interface captures trip information, with minimal user input and burden, and wireless
ties personal and vehicular GPS-ATD units together. The result? A unit that could prove useful for the 2010 California Statewide
Household Travel Survey.
Most current transportation systems are at or have exceeded their maximum capacity, and adding capacity through building is
no longer a viable option due to space or environmental constraints. Better planning — at the city, regional, and state levels
— can reduce the demand on the transportation system.
But improved planning requires a better understanding of traveler behavior. Traditional cross-sectional survey methods measure
traffic at a single point of a road or intersection, providing traffic loading at a specific location over time. While this
may support conclusions regarding capacity at a point, it does not provide needed information on traveler behavior such as
trip purpose, trip frequency and schedule, route selection, and speed profiles throughout the entire route. In comparison,
longitudinal surveys directly measure traveler behavioral change at the level of the individual traveler, and provide information
leading to a better understanding of the factors that influence and direct personal travel behavior. Such data are critical
in:
- developing travel demand models and forecasting future demand;
- predicting the number of trips generated by households as a function of demographics, socioeconomics, and location relative
to employment and commercial centers;
- estimating travel-mode choice and traffic volumes on specific roads;
- assessing the impact of changes in the transportation system or policies;
- predicting emissions from motor vehicles and input for air-quality analysis; and
- calibrating regional travel models.
Household longitudinal travel surveys collect three categories of data: household information, household member personal information,
and travel activity information for particular days. Travel diaries are filled out by survey respondents or the surveyors
after questioning the respondents; diaries are the standard method used to capture participating household travel activity
information. But gathering complete information in this way has been problematic. The drawbacks of self-administered paper-based survey
designs are well known, and this approach is not suited for long-term mobility pattern observations. Computer-assisted self-interview
methods, in which respondents input information into a computer, are an improvement over paper-based surveys, but respondents
need access to a computer and the Internet. Moreover, multi-day personal surveys often suffer from responents' survey fatigue
and low response rates typical in longer survey durations. It is common for respondents to underreport or to provide incorrect
data due to poor memory, misunderstood instructions, or carelessness. Short or infrequent day trips are the type most often
not reported.
To accurately capture the full spectrum of travel behavior, surveys need to be carried out over several weeks while maintaining
data accuracy and minimizing the respondents' burden. Earlier longitudinal surveys using GPS have shown great potential. GPS-based
surveys are more accurate and minimize the respondent burden. In one study, 75 percent of respondents took less than one minute
to enter all required trip information into the travel diary, compared to 10 minutes on a paper diary or 20 minutes on a follow-up
phone call. In addition, GPS digital data can be readily imported into computer analysis programs. This approach captures
route choice, path, and speed profile information — items not feasible with traditional paper surveys. Such data may be used
to measure the level of congestion of a particular highway, for instance.
Previous GPS travel diaries may be classified into two types: interactive and passive. Some previous GPS travel diaries were
interactive, requiring the respondent to input survey information such as marking trip start and end, trip purpose, trip cost,
and travel mode. The majority of previous GPS travel diaries were passive GPS data loggers requiring no interaction with the
respondent. The respondents only needed to carry and turn on the device whenever they traveled. Other trip information is
collected through paper diaries or follow-up phone call, or is estimated by computer-aided software based on the GPS data.
