PASSENGER AND CELL-PHONE CONVERSATIONS IN SIMULATED DRIVING
Frank A. Drews, Monisha Pasupathi, and David L. Strayer
University of Utah, Salt Lake City, Utah
Previous work on use of cell phones while driving compared cell phone conversations while driving with
driving only conditions. This study investigated how conversing on a cell phone differs from conversing
with a passenger. Participants conversed about close-call situations they experienced. We compared how
well drivers followed task instructions when driving only, when driving and conversing on a cell phone,
and when driving and conversing with a passenger. The results show that the number of driving errors was
highest in the cell-phone condition. Analyzing the conversations we found that in passenger conversations
more references were made to traffic and more turn taking followed those references than in cell phone
conversations. The results show that passenger conversations differ from cell phone conversations because
the surrounding traffic becomes a topic of the conversation, helping driver and passenger to share situation
awareness, and mitigating the potential effects of conversation on driving.
There is ample evidence that conversing on a cell-phone
while driving affects driving performance negatively.
Previous studies have found that cell phone use impairs the
driving performance of younger adults (Alm & Nilsson, 1995;
Briem & Hedman, 1995; Brookhuis, De Vries, & De Waard,
1991; Brown, Tickner, & Simmonds, 1969; Goodman et al.,
1999; McKnight & McKnight, 1993; Redelmeier &
Tibshirani, 1997; Strayer & Johnston, 2001; Strayer, Drews,
& Johnston, 2003), and older adults (Strayer & Drews, 2003).
The level of impairment can be compared to being intoxicated
at a blood alcohol level of .08 (Strayer, Drews, & Crouch,
2003). Still unexamined is whether and how conversing on a
cell phone differs from a conversation with a passenger.
There are at least two competing hypotheses: One hypothesis
is that there is no difference between cell-phone
conversations and passenger conversations, and that both
negatively affect driving performance. An alternative
hypothesis is that the passenger in a passenger conversation
shares the same situation as the driver. The passenger may
monitor the surrounding traffic, and respond to changes in
driving demands. This supportive behavior can be explicit,
for example by referring to traffic dangers, or more implicit
by moderating the conversational flow in response to
increased difficulty of the driving task. Of course, this
assumes that the passenger has at least a rudimentary
understanding of potential dangers of traffic and the driving
task. Directing the driver’s attention towards potential danger
creates situation awareness (Endsley, 1995) of the
surrounding traffic that is shared by the driver and the
passenger. Contrary to this, in a cell-phone conversation, the
person not driving lacks awareness of the traffic surrounding
the driver. As a consequence, he or she is unlikely to support
the driver with regard to the driving task.
One of the major problems for research on impact of cell-
phone conversations on driving performance relates to the
issue of naturalistic conversations. Some investigators have
used conversations in which confederates converse with the
driver about some topic of interest identified earlier, others
have use word repetition tasks to create a situation which is
equivalent to a conversation. These approaches are frequently
criticized because of their failure to mimic naturalistic
conversations. An alternative to these approaches in studying
the impact of conversations on driving is to use close call
stories (Bavelas, Coates, & Johnson, 2000) as the topic of the
conversation. Close call stories are defined as stories about
times when “your life was threatened.” The advantage of
using close call conversations is that they involve the kinds of
stories that are often told among friends, and the type of story
which is engaging for participants. In the current study this
paradigm was chosen with the intention to create a situation
which comes as close as possible to naturalistic
The goal of this research is to increase the understanding
of how conversing on a cell-phone while driving differs from
conversing with a passenger while driving.
Participants. 96 adults participated in the study.
Participants ranged in age 18 from to 49, with an average age
of 20 years. 49 participants were male and 47 participants
were female. All participants had normal or corrected-to-
normal visual acuity, normal color vision (Ishihara, 1993),
and a valid Utah driver’s license. Participants were recruited
in friend dyads, and received course credit for participating.
Stimuli and Apparatus. A PatrolSim™ high-fidelity
driving simulator, manufactured by GE Capital I-Sim was
used in the present study (Figure 1). For the purpose of this
study the computer panel and the radio were removed from
the dashboard of the simulator. The simulated vehicle bases
on the vehicle dynamics of a Crown Victoria® model with
automatic transition build by the Ford Motor Company.
PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 48th ANNUAL MEETING—2004 2210
Figure1. I-Sim driving simulator.
A freeway road database simulated a 24-mile multi-lane
beltway with on and off-ramps, overpasses, and two-lane
traffic in each direction. Participants were driving under an
irregular-flow driving condition (Drews, Strayer, Uchino, &
Smith, in press) where vehicles changed lanes and speeds
frequently, making it difficult for the participant to proceed
smoothly and requiring varying attentional demands.
Procedure. After providing informed consent, subjects
answered questionnaires assessing their mood and driving
attitudes. Next, participants were familiarized with the driving
simulator using a standardized 20-minute adaptation
sequence. After finishing the familiarization, one participant
was randomly selected to drive the vehicle, the other, based
on condition was either the passenger or talking on the cell-
phone to the driver from a different location. Speaker
(provides the close call story) and listener assignments were
counterbalanced. The participants were instructed to drive
safely and to follow all the traffic rules. Their task was
described as having a conversation about a close call story,
and as leaving the highway once they arrived at a rest area
located approximately 8 miles after the beginning of the
drive. All driving participants additionally drove in a single
task condition, where they were driving only. The dual task
condition consisted of either driving while conversing on a
cell-phone or driving while talking to a passenger. The order
of the single and dual task conditions was counterbalanced.
Measures. As a measure of performance in dealing with
the driving task the number of occasions when the drivers
exited the highway at the designated destination was counted.
In addition, references to the traffic while conversing were
analyzed. The rationale for this measure was that referring to
the surrounding traffic partly directs attention towards an
event, thus participants share situation awareness. A third
measure was the number of turn takes after a reference to
traffic was made. The number of turn takes reflects the
interest both partners have towards conversing about traffic
rather than the close call story.
Design. In the current study a one factorial design
(passenger and cell phone conversation) with conversation as
a between subject factor was used (24 couplets in the
passenger conversation condition, 24 dyads in the cell-phone
conversation condition). In addition every driver had to drive
in a control condition, where they were driving only.
Task completion. One part of the analysis focused on
driving performance, that is successfully accomplishing the
driving task. Table 1 shows the number of participants that
finished the task successfully or failed to finish the task for
the two experimental conditions and the control condition.
Table 1. Successful task completion.
Cell-phone Passenger Control
Correct exit 12 21 46
Missed exit 12 3 2
Analyzing task accomplishment for cell-phone
conversation and passenger conversation a difference
between the two conditions (ȋ2
(1)=7.9; p<.05) was found:
drivers in the cell-phone condition were four times more
likely to fail in finishing the task than drivers in the passenger
condition. No change in performance was observed in the
passenger conversation condition compared to the control
condition (driving only), though the change in performance
between cell-phone condition and control condition was
(1)=8.9; p<.01) .
Shared situation awareness. The transcripts of the
conversations were analyzed for references to traffic and
number of turn takes following such reference. The latter
indicates the extent to which the driving task became a
conversational topic in its own right, temporarily superceding
the close-call stories. The number of references to
surrounding traffic in the passenger conversation condition
and the cell phone conversation condition are shown in Table
2. Fewer references to traffic were made in the cell phone
condition (t(46)=3.0; p<.01).
References 2.1 (1.6) 3.8 (2.4)
Turns at speech 8.6 (6.7) 19.2 (13.8)
Table 2. Mean number (sd) of references to traffic and turns.
The next analysis focused on the number of turns
between the two partners which continued conversing about
traffic after an initial reference to traffic was made. The
number of turns for both conditions is shown in Table 2.
Overall more than twice as many turns occurred in the
passenger condition compared to the cell-phone condition
The present study investigated the question how
driving while talking on a cell-phone differs from driving
while conversing with a passenger. The findings about task
completion demonstrate that a driver who converses on a cell
phone pays less attention to the surrounding traffic as
indicated by the large number of drivers who missed the exit,
because they did not notice it. This failure to successfully
PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 48th ANNUAL MEETING—2004 2211
complete the task in the cell-phone condition can be
explained by the fact that a person on a cell-phone is less
likely to extract information from his environment than
someone who is not conversing on a cell-phone (Strayer,
Drews, & Johnston, 2003). The analysis of the conversation
data suggests that the driver and the passenger are more
frequently talking about the surrounding traffic and that the
traffic and driving task become part of the conversation, as
indicated by the fact that pairs spent more conversational
turns on the traffic topic in the passenger condition. This
indicates that the passenger supports the driver in his task of
driving by directing attention to the surrounding traffic when
necessary and by supporting the driver in devoting attention
to the traffic rather than the storytelling. Thus, the better
driving performance of participants in the passenger condition
is partly due to the fact that the driver and the passenger share
The present findings indicate that when a driver
converses with a passenger, the dyad more often collaborates
in the task of driving safely by referring to traffic and
conversing about it to a larger extent. This helps to maintain a
higher level of shared situation awareness something a person
on the other end of a cell-phone can not do.
One important limitation of this study is that a high
fidelity driving simulator was used to study passenger and
cell-phone conversations. Despite the fact that there is more
and more evidence indicating the validity of driving simulator
based findings with regard to real driving, additional research
investigating passenger conversations and cell-phone
conversations in real driving would be important to show that
the current findings can be generalized beyond simulated
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