This chapter
provides a brief overview of the GPS-based travel survey experiment that was
conducted by Federal Highway Administration (FHWA) in Lexington, KY. Much of
the material in this chapter is derived from a report prepared by Battelle [1997]
that includes detailed descriptions of the experiment and the databases assembled.

Selection
of MPO

The GPS-based
travel survey experiment required the participation of an MPO. The selected
MPO would need to have an up-to-date and accurate digital map of the test area
and its highway network, with a minimum accuracy satisfying Federal National
Map Accuracy Standards. In addition, the participating MPO would have to be
able to provide about 250-300 hours of total staff support during the field
experiment.

Following
a nationwide solicitation and selection process, the Lexington area MPO was
chosen as the host MPO for the field test. The Lexington area MPO is the principal
planning agency for the two-county area of Fayette and Jessamine in Central
Kentucky. The two counties together encompass an area of approximately 461 square
miles with a total population of approximately 350,000.

Recruitment
of Households

Considering
the specialized nature of the GPS-based field experiment, it was not possible
to utilize a pure random sample for the survey. A special recruitment process
was used to obtain a final sample of 100 participating households for the experiment.

A sample of
nearly 2,000 listed telephone numbers from households in Fayette and Jessamine
counties (weighted by population) was purchased from a commercial source. The
participating households were recruited using a stratified sampling plan based
on several demographic factors. The demographic factors considered included
gender, age, and presence of children in the household. Licensed drivers under
the age of 18 were not permitted to participate as the principal eligible driver
within a household. In addition, principal eligible drivers recruited for the
field test were required to drive at least three days a week. This was done
to ensure that a reasonably large amount of data would be collected despite
the small sample size and short duration of the experiment.

The recruiting
process started by mailing out pre-solicitation letters without any prior contact
with the households. Once the letters were mailed, telephone contacts began
with the households. If the household was responsive to the initial call, they
were asked to participate in a brief screening survey to determine their eligibility
for the field test. Following the screening interview, a pre-usage interview
was conducted to ensure that the household would be able to use the field equipment
without any problems.

A pre-solicitation
letter was sent to a total of about 1,300 households with listed telephone numbers.
Once the telephone interviewers determined that there was an eligible driver
and vehicle in the household, 67 percent of those eligible consented to participate
in the field test. At the end of the recruitment process, a total of 100 households
were successfully recruited for participation in the field test.

Accessories: A SRAM
PCMCIA memory card containing the PTS application software and upto 2 MB of
memory for data collection was provided. In addition, connecting cables that
enabled communication among the devices were also furnished to respondents.

Personal Travel Survey
Software

The Personal Travel Survey
(PTS) software had two primary functions. First, it allowed respondents to easily
enter trip information and second, it facilitated recording of GPS positional
data for each trip. It consisted primarily of three interfaces - administrative,
GPS, and respondent.

The administrative interface
allowed the field test administrator to set the operational parameters of the
data collection devices and personalize the respondent interface for each household.
Household users were not provided access to this interface.

The GPS interface displays
raw GPS output as it is being written to memory in the computer. This interface
provides the mechanism by which the GPS receiver data stream is written and
stored in memory. This interface does not have any user control.

The respondent interface
is the major feature of the PTS software that respondents control and utilize
throughout the field experiment. The interface allows drivers to use a touch-screen
to initiate a trip, identify the driver and his or her activity (trip purpose),
identify passengers and their activities (trip purposes), and end a trip. Note
that time, speed, and positional data are recorded directly through the GPS
receiver.

In general, both the hardware
devices and software interfaces performed well in the field. There were very
few instances of hardware or software malfunction that called for corrective
action. Further details about the hardware and software performance can be found
in Battelle [1997].