The Effects of Commercial Electronic Variable Message Signs ...

B.3 UNOBTRUSIVE OBSERVATION APPROACH
The unobtrusive observation method is different from the on-road instrumented vehicle
method and the naturalistic driving method. The major distinction is that no study participants
are selected, and all data are obtained from the natural flow of traffic past the CEVMS and
other comparison stimuli. The following describes one possible study which might be
conducted using this method.
B.3.1 Method
The unobtrusive observation method employs an array of static cameras or other sensors
mounted near the locations of the CEVMS and other comparison stimuli. The other sensors may
include loops, tubes, or radar to measure vehicle passes and driving parameters. The present
report will focus on video recording of traffic. The cameras are capable of recording the behavior
of vehicles passing the various relevant visual stimuli as a part of the natural flow of traffic. The
drivers are usually completely unaware that their vehicles are being observed. Post-hoc analysis
of the video recordings from these cameras can yield data similar to some of that obtained by the
on-road instrumented vehicle and naturalistic driving methods, which include vehicle speed, lane
position, acceleration, and time. However, the data from distal video cameras are usually far less
accurate than what can be collected by instruments onboard the vehicle. Moreover, with present
measurement technology, such video recordings cannot yield any data concerning driver eye
glance frequency, direction, and duration. The camera arrays are usually left in place for a period
of several months to 1 year at each study site. There would typically be three to four such sites in
the study. At each study site, separate camera arrays would need to be installed at the locations
of all selected CEVMS displays, standard (non-digital) billboards, objects of casual visual
interest (houses, barns, etc.), and natural background control scenery (trees, fields, etc.).
B.3.2 Factors and Measures
As in the on-road instrumented vehicle and naturalist driving studies, the major independent
variables are the presence or absence of CEVMS and other comparison visual stimuli (standard
billboards, buildings, etc.) along the driving path. If possible, the CEVMS should be controlled
according to a prearranged experimental protocol. However, in this instance, the CEVMS
would have to be changed for longer durations because it is possible to predict when vehicles
might pass. In addition, one or more of the primary CEVMS variables of interest to the
community concerned with outdoor advertising control should be represented by varying levels
in the selection of CEVMS stimuli. These constitute the primary independent variables. Since
continuous video recording will be employed, the experimenter can decide to select different
times of data collection for further analysis. This capability can provide insight into some
secondary independent variables such as time of day (day/night) and traffic conditions
(peak, nonpeak).
In contrast to the on-road instrumented vehicle and naturalistic driving studies, the primary
dependent variable is not driver eye glance behavior. Instead, this study method depends
completely on safety surrogate measures associated with driver errors and other measures of
driver performance (headway, lane deviation, and erratic maneuvers). These are subtle driving
behaviors to measure by means of distal cameras mounted along the roadway. Unless the
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