Tuesday, March 18, 2014
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Barrett Whitener: From the National Institutes of Health, I’m Barrett Whitener. And this is Research Developments, a podcast from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the NICHD.
Driving while impaired by alcohol and/or drugs is one of the major causes of driving fatalities for young drivers. A recent study found that teenagers who reported riding in a vehicle with a driver who was intoxicated from either alcohol or drugs were much more likely to later report that they had driven a vehicle while intoxicated themselves. And the earlier and more frequently teens reported driving with an impaired driver, the more likely they were to later drive impaired. The study also found that a teenager who obtains his or her driver’s license early may be more likely to engage in impaired driving. My guest today is Dr. Bruce Simons-Morton, one of the authors of the study. Dr. Simons-Morton is senior investigator in the Health Behavior Branch of the Division of Intramural Population Health Research at the NICHD. Thank you for joining us, Doctor.
Dr. Bruce Simons-Morton: You’re welcome.
Whitener: First, how common is it for young drivers to drive while they are impaired by drugs, alcohol, or both? What are the trends for this age group?
Dr. Simons-Morton: Fortunately, the trends are downward over the past decade. The prevalence of drinking—of driving while intoxicated—has declined nearly 50 percent. However, in our surveys of 10th to 12th graders, we found teens reported, 12 to 14 percent of teens reported, driving while intoxicated at least once in the last 30 days.
Whitener: Can you tell us a little more about the impact of driving while impaired on driving-related deaths among young drivers?
Dr. Simons-Morton: Yes, a very large percentage of fatal crashes among teen drivers are alcohol-related—nearly 30 percent of fatal crashes in fact. So, alcohol is a major factor in fatal and injurious crashes among teen drivers.
Whitener: Why did you decide to study the possible association between riding while impaired by drugs or alcohol and driving while impaired?
Dr. Simons-Morton: The NEXT Generation Study follows adolescents, who we recruited in the 10th grade, for several years; and among the variables of interest to us include teenagers, substance use, and their driving behavior. And so it was natural for us to look at both driving and drinking, and we realized that the risk of an alcohol-impaired crash and injury is the combination of both driving and riding with an intoxicated driver.
Whitener: Now, you mentioned also in the study that there’s a body of evidence that shows the social norms of novice teenage drivers are influenced by their parents and their peers’ driving. Can you say a little more about that?
Dr. Simons-Morton: Well, the evidence is certainly greatest that teens are highly influenced in the way they drive by how their friends drive. If you ask a teenager about the driving behavior of their close friends, that’s highly associated with their own driving behavior, including risky driving and the likelihood of drinking and driving. So, there’s a very substantial peer influence. There’s also parent influences. These are not as dramatic, but clearly parents are very important in terms of their ability to establish expectations and monitor the behavior of their youth.
Whitener: And you even found, you mentioned that the previous studies had shown that the timeframe can be pretty brief in terms of the effect of that. Like within 1 year of being exposed to that kind of driving, a young person can then be DWI themselves.
Dr. Simons-Morton: So, here what we found primarily was that teenagers’ exposure to riding with an intoxicated driver, what we call RWI, was highly predictive of later DWI, driving while intoxicated, among those teens. And we found not only an association, but it was an effect of how early that exposure occurred and how frequently it occurred, and the association—the predictive potential of RWI—was surprisingly high.
Whitener: How did you measure the connection of riding while intoxicated with driving while intoxicated?
Dr. Simons-Morton: So, each year we conducted surveys, and in the 10th grade, 11th grade, and 12th grade, we asked teenagers how often they had ridden with a driver who had been intoxicated in the past year, and we asked them had they driven while intoxicated in the past month. So, those were our measures of RWI and DWI.
Whitener: And how did you go about measuring this effect with young people over time?
Dr. Simons-Morton: In the NEXT Generation Study, we recruited a nationally representative sample of 10th graders, collected a lot of data from them, and then we followed them and measured them each year through the 12th grade.
Whitener: And what specifically did you find about the connection between riding and driving while intoxicated?
Dr. Simons-Morton: We found several interesting things. One, we found that adolescents who reported being exposed to riding with an intoxicated driver in the 10th grade were considerably more likely to report driving while intoxicated as 12th graders. And if they had reported this in the 10th grade—that was much more predictive than if they reported it later in the survey, like in the 11th grade. So, the earliness of their exposure to riding with an intoxicated driver was highly predictive; and if they reported it at all three surveys riding with an intoxicated driver, they were extremely likely—120 times more likely than those who had never ridden with an intoxicated driver to report driving while intoxicated in the 12th grade.
Whitener: Now you also studied the possible connection between how early a teenager receives their driver’s license and how likely he or she is to drive while intoxicated. Why did you look into that and what did you find?
Dr. Simons-Morton: Well, there’s lots of interest in timing of licensure, and so here we had some adolescents got licensed in the 10th grade, some in 11th, and some in the 12th grade. And earliness can reflect two things; here we found an association between earliness of licensure and DWI in the 12th grade. Adolescents who were licensed in the 10th grade were about twice as likely to report DWI in the 12th grade than those who were not licensed until the 11th or 12th grade. So why might this be? Well, early licensure probably reflects early exposure. The earlier one is licensed, the more they drive so the more potential there is for them to have a DWI experience, but adolescents who were licensed earlier might also be somewhat more precocious or risk-taking, which also may be associated with DWI.
Whitener: And you also mentioned possible lack of parental supervision among those teenagers, etc., some other potential factors.
Dr. Simons-Morton: Exactly. Teenagers who get licensed at their first opportunity tend to be more independent than those who are licensed later and probably experience less parental supervision.
Whitener: What do you think the implications of your study are for reducing the incidence of teenagers driving while intoxicated?
Dr. Simons-Morton: Most prevention programs have primarily focused on DWI, which we know from our study and other studies is highly, is much more likely among those who drink or have a lot of drinking experiences. So, most prevention programs have focused on drinking, and drinking and driving. What our study has pointed out is that riding with an intoxicated driver seems to be a very good predictor and so this provides a new focus for some prevention programs where we can identify those who are not at risk for DWI yet, but are gaining this kind of exposure to something through a behavior that sort of normalizes the idea of DWI.
Whitener: And what do you feel the implications may be of your research for parents?
Dr. Simons-Morton: Well, as difficult as it can seem to be the parent of an adolescent, what parents do really matters, and I think most parents are very concerned about when their teen starts driving, about the possibility that they would drink and drive, and therefore they discourage this as much as possible. What our study points out is that parents also need to pay attention to all of their teen’s behavior to really monitor not only when their teen drives, but also with whom they ride and everything about their transportation experience.
Whitener: And for policymakers, do you have any implications there?
Dr. Simons-Morton: Policies regarding drinking and driving are now quite advanced in most states and generally can be considered quite good. I don’t think we’re going to make too much more progress in drinking and driving and riding with an intoxicated driver through policy. The policies are now in place that really empower parents to act very strongly to discourage their teens from driving while intoxicated and to riding with those who are intoxicated.
Whitener: We’ve been speaking with Doctor Bruce Simons Morton of the NICHD. Thank you so much for joining us today to discuss your research, doctor.
Dr. Simons-Morton: Thank you.
About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit the Institute’s website at http://www.nichd.nih.gov/.