Outcomes of Variability in Teen Driving Experience and Exposure Evidence from Naturalistic Driving Studies (2025) / Chapter Skim
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3 Results
3 Results
Pages 14-35
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From page 14... ...
For Research Objective 1b, various risky driving behaviors (e.g., percentage of time speed ing, passenger presence) were explored using descriptive statistics, regression models, and/or chi-square statistics to assess differences in driving behavior for teen drivers with more or less driving exposure during the learner's permit driving phase for the SPDS and during the early independent driving phase for the SHRP 2 NDS.
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From page 15... ...
In the SHRP 2 dataset, the overall SCE rate was similar during the early and later independent driving phases. 4,500 4,000 3,500 3,000 Total driving hours 2,500 2,000 1,500 1,000 500 0 Learner's permit Early driving Later driving Less exposure More exposure Figure 5. SPDS total driving time by driving phase and exposure group.
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From page 16... ...
For the less-driving-exposure group, this represents an average of 17 hours of practice driving per participant, and for the more-driving-exposure group, an aver age of 52.7 hours of practice driving per participant. The state of Virginia, where the SPDS was 7,000 0.014 6,000 0.012 5,000 0.01 Total driving hours 4,000 SCE rate 0.008 3,000 0.006 2,000 0.004 1,000 0.002 0 0 Learner's permit Early driving Later driving SPDS Driving time SHRP2 Driving time SPDS SCE rate SHRP2 SCE rate Figure 7. Driving hours and SCE rate in two datasets.
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From page 17... ...
. For both driving exposure groups, approximately 40% of all 1,400 1,200 1,000 Total traveled hours 800 600 400 200 0 Weekday Weekend Less exposure More exposure Figure 9. Total learner's permit phase driving hours by DOW and exposure group (SPDS)
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From page 18... ...
. The research team categorized route familiarity during the learner's permit phase into the categories of familiar and unfamiliar based on a binary familiarity score.
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From page 19... ...
. 30 25 Percentage of unfamiliarr trips 20 15 10 5 0 Learner's permit Early driving Later driving Less exposure More exposure Figure 13. Percentage of unfamiliar trips by driving phase and exposure group (SPDS)
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From page 20... ...
Teens with more exposure to driving during the learner's permit phase had lower CNC rates in early and later independent driving phases. 0.02 0.018 0.016 0.014 CNC rate per hour 0.012 0.01 0.008 0.006 0.004 0.002 0 Learner's permit Early driving Later driving Less exposure More exposure Figure 15. CNC rates by driving phase and exposure group (SPDS)
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From page 21... ...
The breakdown by sex for SHRP 2 NDS teen drivers in each exposure group is provided in Table 2. More teen females agreed to participate in the SHRP 2 NDS earlier in their driving experience than teen male drivers.
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From page 22... ...
For both the less-driving-exposure and more-driving-exposure groups, approximately 90% of driving was on these lower-speed road ways, whereas ∼9% of hours traveled was on controlled-access and high-speed highways. Figure 19 shows the CNC rates for the less-driving-exposure and more-driving-exposure groups during the early independent phase of driving.
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From page 23... ...
This is similar to the pattern observed for the SPDS teen drivers in independent driving phases. In the later independent driving phase, the more-driving-exposure group had a higher CNC rate than the less-driving-exposure group, as opposed to in the early independent driving phase (see Figure 19)
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From page 24... ...
The SPDS NDS had a fairly complete set of data for the learner's permit and early independent driving phases, whereas the SHRP 2 NDS had no data for the learner's permit phase and limited driving data for the first 6 months post licensure. Statistical Model To compare driving exposure in the learner's permit phase and early independent driving to safety outcomes in later independent driving, the research team first grouped the participants into more and less driving exposure based upon learner's permit and early independent driv ing experience, as described above.
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From page 25... ...
KRD: Driving Phases 3 TOD 3 DOW 3 Route Familiarity TOD and DOW were not significant in the Poisson regression model using CNC; the research team evaluated these factors using KRD event rates. CNCs were infrequent and thus it was difficult to assess some variables that may have required a more sensitive dependent measure.
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From page 26... ...
The Poisson regression model indicated that hard braking events occurred more frequently during nighttime driving, which may also suggest that nighttime driving is higher risk. Hard braking also occurred sig nificantly more frequently during early and later independent driving phases compared to the learner's permit phase.
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From page 27... ...
250 Weekday Weekend Acceleration and brake rate 200 (per 1,000 hours) 150 100 50 0 Learner's Early driving Later driving Learner's Early driving Later driving permit permit Fast start Hard braking Figure 25. Hard braking and fast start rates by DOW and driving phase.
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From page 28... ...
Research Objective 1b Research Objective 1b was to evaluate how exposure to driving in diverse traffic and road environments earlier in the learning-to-drive process is associated with variability in teen driver behavior or safety-relevant performance measures in later independent driving, corrected/ normalized for exposure. This section evaluates whether the prevalence of known teen risky driving behaviors is impacted by the amount of driving exposure or diversity during the learner's permit phase.
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From page 29... ...
The first column lists the predictor variables and their comparisons, while the subsequent columns provide the estimated odds (estimates) , the 95% confidence intervals, 45 40 Percentage of time speeding 35 30 25 20 15 10 5 0 15 20 25 30 35 40 45 50 55 60 65 70 Speed limit Figure 29. Percentage of time speeding in all trips by speed limit (SPDS)
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From page 30... ...
Passenger Presence The chi-square analysis indicated a significant difference in passengers across driving phases and between driving exposure groups (p < 0.01)
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From page 31... ...
In the two independent driving phases, teens driving without passengers accounted for the highest percentage. For the teen passengers, the percentage increased with more driving exposure.
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From page 32... ...
Research Objective 2 Research Objective 2 was to develop recommendations/strategies for improving teen driving safety for State Highway Safety Offices. Despite the challenges in accessing the naturalistic driving data needed to fully test the research hypotheses of this project, the findings suggest some potential changes in how graduated driver's licensing programs are implemented that would be likely to improve teen driver performance and safety.
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From page 33... ...
• Put in place and enforce requirements for improved documentation of supervised driving time/experience. This could be accomplished via a state-provided "supervised driving app" to be downloaded to the teen's and parent's smartphones -- with appropriate privacy controls -- that creates time-stamped, continuous driving history files that can be provided to the licensing authority when the supervised driving phase is completed and the teen wishes 100 Percentage of seatbelt use 80 60 40 20 0 Early driving Later driving Early driving Later driving Less exposure More exposure Figure 34. Percentage of seatbelt use by exposure group and driving phase (SHRP 2)
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From page 34... ...
Female teens with less driving exposure during the learner's permit phase experienced higher SCE rates during the early inde pendent phase relative to males. This is the first analysis to find statistically significant results indicating that more practice during the learner's permit phase does reduce CNC involvement for the teen driving population and has direct implications for policy and practice.
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From page 35... ...
. More focused attention on teen driver speeding behavior on highways and in residential areas and enforcement during key time periods during the academic year (e.g., the beginning of school year, high school events)
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