Enhancing our understanding of teen-driver crashes.

Whileprogresshasbeenmade in reducing thenumberof teens killedinmotorvehiclecrashes,crashescontinuetobetheleading causeofdeathfor teens intheUnitedStates.1Thehighcrashrate for teens isowing in largepart to theirlackofdrivingexperience.2,3 Continued identificationof specific characteristicsof teens that leadtoelevatedcrashriskcan informinterventions forhigh-risk subgroups.Thismonth’sissueofJAMAPediatrics includesastudy byOuimetetal4 thatexaminedtheassociationbetweencortisol reactivity and subsequent occurrence of crash and near-crash (CNC) events among newly licensed teens. As part of theNaturalisticTeenDrivingStudy,salivarycortisolreactivity inresponse toa stress-inducing taskwasassessedatbaseline ina sampleof 42 healthy, typically developing 16-year-old participants, after which they drove instrumented vehicles for 18months. Ouimetetal4 foundthat teenswith lowercortisol reactivity in response to the stressorhadhigherCNC ratesduring the first 18monthsof licensure. Inaddition, thosewith lowercortisol reactivityhadaslowerdecreaseinCNCratesovertime.Theauthors positedthattheassociationsobservedintheirstudycouldbeowingtoindividualdifferencesinoptimalphysiologicalarousaland/ or tothemannerbywhichteensprocessemotional information. The extent to which the authors believe these are competing, complementary,or interactiveprocesses remainsunclear.Most compelling,andsupportedbyotherliterature, istheideaofanormativeemotional learningpathway,whereby individualdifferences in hypothalamic-pituitary-adrenal (HPA) axis reactivity affect thesensitivityofdrivers to stimuli in thedrivingenvironment,whichsubsequentlyaffectslearning.5Forexample,asteens gain independent driving experience, they are exposed to a varietyofemotionallyevocativestimuli—suchasnearmisseswith unexpected hazards—which enables them to better anticipate, avoid, and react more effectively in the future. In this hypothesizedpathway, theemotional response (as indicatedbygreater cortisol reactivity) to stressorsandchallengesexperiencedduring the learning-to-driveprocesspromoteseffective learningof necessaryskills.ThefindingsbyOuimetetal4wouldsuggestthat, althoughall teensgainexperienceover timeandthisexperience is associatedwithdecreasingCNCs, individual variation in cortisol reactivity—specificallyaweakeremotional reactivity in responsetohazards—mightattenuate theassociationbetweenexperienceandlowercrashrisk.Furthersupport for theemotional learninghypothesis among teendrivers isprovidedbyprior experimental research. In a small convenience sample of experienced and novice drivers, Kinnear et al6 found that themagnitude of skin conductance response, a physiologicalmeasure of autonomic arousal, to simulateddrivinghazards increased as a function of real-world driving experience. Implications for Researchers Themost immediate implicationof the findingsof theOuimet et al4 study is for continued research tobetter characterize the relationship between cortisol reactivity in response to stressors and crash risk in the general population of healthy teens and among those teenswhomight be at higher crash risk owing to preexisting conditions or history of risky behaviors. For example, variation in function of the HPA axis has been implicated in clinical samples of youthas apotential factor in the development of antisocial disorders, aswell as a variety of internalizing and externalizing disorders.7-9 Although thecurrent studybenefited fromstrongdata collection methods, generalizations are difficult to make owing to the small and likely nonrepresentative sample of healthy, typically developing teens; very few actual crash events; and limited characterization of the near crashes. It remains unclear what proportion of novice teen-driver crashesmight be explained by individual differences in HPA regulation. Previous research has suggested that most crashes involving teen drivers aredue to inexperienceandnotovert risk takingon the part of teens,2,3 lending additional support to an emotional learning pathway. Further research is needed to explicate the mechanisms by which individual differences in the HPA systemcovarybydevelopmental factors, driving experience, and other individual difference variables (eg, attention-deficit/ hyperactivity disorder and conduct disorder) to affect driving behaviors and outcomes.