Testimony for Presentation at the Subcommittee on Highways and Transit Hearing on Driver Distractions: Electronic Devices in the Automobile

Wednesday, May 9, 2001

Jane C. Stutts, Ph.D.
Manager, Epidemiological Studies
University of North Carolina Highway Safety Research Center
Chapel Hill, NC

Driver inattention is a major contributor to highway crashes. The National Highway Traffic Safety Administration estimates that at least 25% of police-reported crashes involve some form of driver inattention. Driver distraction is one form of inattention, and is a factor in over half of these crashes. Distraction occurs when a driver is delayed in the recognition of information needed to safely accomplish the driving task, because something within or outside the vehicle draws his attention away from driving. The presence of a triggering event distinguishes a distracted driver from one who is simply inattentive or "lost in thought."

The AAA Foundation for Traffic Safety awarded a contract to the University of North Carolina Highway Safety Research Center to conduct research on the role of driver distraction in traffic crashes. The goal of the project is to identify (using both crash and field data) the major sources of distraction to drivers and the relative importance of the distractions as potential causes of crashes. As a part of this project, we have recently completed a descriptive analysis of five years of Crashworthiness Data System (or CDS) data, made available to us by NHTSA's National Center for Statistics and Analysis.

The CDS is a national, annual probability sample of approximately 5,000 police-reported crashes involving at least one passenger vehicle that has been towed from the crash scene. Data are collected by trained professional crash investigation teams that visit the scene of the crash, examine the crash-involved vehicles, interview the crash victims and other witnesses, and review available medical records. Beginning in 1995, "Driver's Distraction/Inattention to Driving" was added to the CDS variable list. The variable includes codes for "attentive," "looked but did not see," and "sleepy or asleep," along with more than a dozen specific distractions (eating or drinking, other occupants in vehicle, moving object in vehicle, talking on cellular phone, etc.).

For the current analysis two variables were defined – one identifying the attention status of the driver (attentive, distracted, sleepy/asleep, or unknown), and the second the specific distracting event for those drivers identified as distracted. For the overall 1995-1999 CDS data, 48.6% of the drivers were identified as attentive at the time of their crash; 8.3% were identified as distracted, 5.4% as "looked but did not see," and 1.8% as sleepy or asleep. The remaining 35.9% were coded either as unknown or no driver present. This high percentage of drivers with unknown attention status dilutes the percentages in the other categories. Without the unknowns, the percentage of drivers identified as distracted increases to 12.9%. The percentage of actual crashes involving driver distraction would be still higher.

The specific sources of distraction identified were as follows:

Specific Distraction % of Distracted Drivers
Outside person, object or event 29.4
Adjusting radio, cassette, CD 11.4
Other occupant in vehicle 10.9
Moving object in vehicle 4.3
Other device/object brought into vehicle 2.9
Adjusting vehicle/climate controls 2.8
Eating or drinking 1.7
Using/dialing cell phone 1.5
Smoking related 0.9
Other distractions 25.6
Unknown distraction 8.6
Total 100.0 %

Young drivers (under 20 years of age) were the most likely to be involved in distraction-related crashes. In addition, certain types of distractions were more prominent in certain age groups, for example, adjusting the radio, cassette or CD among the under 20-year-olds; other occupants (e.g., young children) among 20-29 year-olds; and outside objects and events among those age 65 and older. Variations by driver sex were less pronounced, although males were slightly more likely than females to be categorized as distracted at the time of their crash.

In addition to these driver factors, a number of roadway, environmental, vehicle, and crash variables were also examined to determine their relationship to driver distraction. Although these results were less clear, they nevertheless underscore the importance of considering specific contextual factors in collecting and analyzing driver distraction data. A few illustrative examples include the higher proportion of adjusting radio/cassette/CD events occurring in nighttime crashes, the higher proportion of moving object in vehicle events occurring in crashes on non-level grade roadways, and the higher proportion of other occupant distractions occurring at intersection crashes.

When interpreting these results, one should keep in mind both the stated purpose of the analysis, and the limitations inherent in crash data such as the CDS. The primary purpose of this analysis was to provide input for developing a taxonomy of driver distractions that would guide subsequent real-world observations in people's vehicles. Our analysis was not intended to provide definitive answers as to which distractions pose the greatest risk to drivers. Additional data are needed to address this question, including information on how often and under what conditions drivers engage in different distracting behaviors.

It is also important to consider the limitations of the CDS data. Despite the in-depth nature of the data collection activities, there is potential underreporting of distracted driving in general, as well as differential underreporting of specific distracting events. Crashes involving cellular phones offer a good example. Given the huge increase in reported ownership and use of cellular phones nationwide, one might expect an increase in the reported number of crashes involving cell phones over the five years covered by the analysis. No such increase occurred, however. The actual recorded number of cases involving cellular phones was 8 in 1995, 10 in 1996, 8 in 1997, 10 in 1998, and 6 in 1999. It may be that as more attention has been drawn to the potential role of cellular phones in unsafe driving and crashes, drivers have become less willing to reveal this information when involved in a crash. People may believe that admitting to cell phone use at the time of their crash puts them in more legal or financial (insurance) jeopardy than admitting to spilling a cup of coffee or dropping a CD.

The larger issue here is that of potential biases in identifying sources of driver distraction, not only in the CDS data, but in any crash data that relies on information accessible to officials investigating a crash. As suggested above, a differential willingness by drivers to report a particular distraction could very well influence these results. In addition, distracting events that leave some form of "evidence" (drink containers, loose CDs, pets, spilled packages, etc.) may be more likely to trigger an inquiry and subsequently get reported than those (such as adjusting climate controls) that do not entail evidence. When cellular phones were first introduced in the mid-1980s, they were much larger than the small hand-held models popular today, and potentially more likely to be observed and reported by officers investigating a crash.

Clearly better crash data are needed to clarify and quantify the magnitude of the driver distraction problem and the relative contributions of different sources of driver distraction. Equally important, however, are empirical data on how often drivers engage in potentially distracting behaviors and what it is about these behaviors that increases crash risk. For example, does a particular distraction lead to reduced vehicle control (in the form of lane wandering, reduced headways, lower speeds, braking, etc.), reduced situational awareness (measured by eye gaze direction, longer response times, fewer mirror checks to monitor surrounding traffic, etc.), or both? To date, these kinds of data have primarily been collected in laboratory settings, but there is growing recognition that they also need to be collected in real-world driving environments, with people driving their own vehicles.

I appreciate the opportunity to speak before the Subcommittee, and applaud its efforts to address the safety concerns related to the proliferation of new in-vehicle technologies.