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Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies (2025)

Chapter: Appendix: Supporting Tables

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Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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APPENDIX

Supporting Tables

Table A-1. List of key independent variables.

Variable Levels Operational Definition
Driving Phase Learner’s Permit Phase Driving time while holding learner’s permit.
Early Independent Driving Phase Driving time during first 6 months of independent driving.
Later Independent Driving Phase Driving time during months 7 through 12 of independent driving (SHRP 2)/Driving time during months 6 through 12 of independent driving (SPDS).
Driving Exposure Less Exposure Driving exposure that is less than the median normalized total hours of driving during learner’s permit phase for SPDS and early independent driving phase for SHRP 2 NDS.
More Exposure Driving exposure that is more than the median normalized total hours of driving during the learner’s permit phase for SPDS and early independent driving phase for SHRP 2 NDS.
Functional Road Classification FC 1 and 2 Driving that occurs on controlled -access highways and/or high-speed highways that connect distant cities/communities.
FC 3, 4, and 5 Driving that occurs on shorter distance connectors, arterials, and/or residential streets.
Vehicle Access Primary access to vehicle Primary access to vehicle means that the teen was the driver for more than 50% of all trips in that vehicle.
Share family vehicle Share family vehicle means that the teen drove less than 50% of all trips in the vehicle.
Time of Day Daytime There is some sunlight visible in the environment (6:00am–8:00pm).
Nighttime There is no sunlight visible in the environment (8:00pm–6:00am).
Day of Week Weekday Day of week is Monday, Tuesday, Wednesday, Thursday, or Friday.
Weekend Day of week is Saturday or Sunday.
Route Familiarity Familiar/Unfamiliar Familiar was defined as 70% of the GPS data overlap with a prior trip and the trip length was within .02 miles of a prior trip.
Page 42
Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Variable Levels Operational Definition
Sex Female/Male Participants indicated on self-reported demographic data that they were female or male.
Seatbelt Yes/No Seatbelt was observed in use or seatbelt was observed as not in use.
Passenger Presence Adult Any passenger in the front passenger seat who appeared older than 20 was labeled an adult.
Teen A front seat passenger who appeared to be younger than 20 but older than 13 was deemed a teenager.
Child A front seat passenger who appeared younger than 13 was labeled a child.
No Passenger No passenger meant no passenger in front seat.

Table A-2. The total driving time for less-driving- and more-driving-exposure groups for both SPDS and SHRP 2 NDS.

SPDS (learner’s permit) SHRP 2 (early independent driving)
Less Exposure More Exposure Less Exposure More Exposure
Total traveled hours 698.227 2,160.54483 333.241 1,277.61
Traveled hours in daytime 620.483 1,858.258 207.1299 1,096.247
Traveled hours in nighttime 77.744 302.287 26.8298 158.944
Traveled hours in weekday 409.386 1,290.645 248.359 924.712
Traveled hours in weekend 288.841 869.899 84.88 352.895
Traveled hours on road classes 1 and 2 103.502 323.691 43.45 256.593
Traveled hours on road classes 3, 4, and 5 446.059 1,423.485 714.437 2,710.175
Number of familiar road trips 2,194 6,269
Number of unfamiliar road trips 356 714
Passenger presence 633.588 1,883.57 116.670 458.725
Rate of CNC 0.005729 0.00555 0.015 0.00783
Rate of hard braking 0.0578 0.0581 0.33 1.47
Rate of cornering 0.023 0.023 0.41 1.033
Page 43
Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Table A-3. Driving time, miles, number of crashes/near-crashes (CNCs), and CNC rate per hour and per mile by driving phase (SHRP 2 and SPDS datasets).

SHRP 2
Driving time (hours) Driving distance (miles) CNCs CNC rate per hour CNC rate per mile
Early Independent Driving 1,610.85 36,681.01 15 0.0093 0.000409
Later Independent Driving 4,361.81 106,379.99 40 0.00917 0.000376
SPDS
Driving time (hours) Driving distance (miles) CNCs CNC rate per hour CNC rate per mile
Learner’s Permit Driving 2,859.104 79,175.958 16 0.005596 0.000202
Early Independent Driving 6,436.875 176,648.222 92 0.014293 0.000521
Later Independent Driving 5,807.141 166,804.631 77 0.01326 0.000462

Table A-4. CNC Poisson regression model.

Estimate 2.5% (CI) 97.5% (CI) p
Driving Phase: <= 6 Months vs. Learner’s Permit 1.23 3.7 0.009 0.009
Driving Phase: > 6 Months–12 Months vs. Learner’s Permit 2.005 1.191 3.590 0.013
Exposure: Less vs. More Exposure 3.979 1.530 10.462 0.005
Vehicle Access: Shared Vehicle vs. Primary Vehicle Access 0.599 0.365 0.938 0.032
Exposure on FC 3–5: More vs. Less Exposure Groups 1.220 0.813 1.825 0.334
Exposure of Traveling > 55+ mph: More vs. Less Exposure 0.945 0.674 1.325 0.744
Exposure While Driving at Daytime: More vs. Less Exposure 0.807 0.416 1.544 0.522
Exposure While Driving at Night: More vs. Less Exposure 0.691 0.380 1.254 0.227
Exposure While Driving During Weekdays: More vs. Less Exposure 0.828 0.474 1.481 0.515
Exposure While Driving During Weekend: More vs. Less Exposure 1.033 0.714 1.491 0.865
Driver’s Sex: Male vs. Female 2.324 1.514 3.623 0.000
Interaction Between More/Less Exposure and Sex 0.420 0.218 0.798 0.009
Page 44
Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Table A-5. KRD Poisson regression mode—acceleration rate odds ratio estimate, confidence interval (CI), and p value.

Acceleration Rate Estimate 2.5% CI 97.5% CI p
Phase: Early Driving vs. Learner’s Permit 2.895 2.500 3.369 0.000
Phase: Later Driving vs. Learner’s Permit 1.611 1.378 1.892 0.000
TOD: Night vs. Day 0.931 0.823 1.049 0.248
DOW: Weekend vs. Weekday 1.010 0.918 1.109 0.838
Unfamiliar vs. Familiar 0.662 0.521 0.829 0.001

Table A-6. KRD Poisson regression model—hard braking rate odds ratio estimate, CI, and p value.

Hard Braking Rate Estimate 2.5% CI 97.5% CI p
Phase: Early Driving vs. Learner’s Permit 3.236 2.754 3.829 0.000
Phase: Later Driving vs. Learner’s Permit 2.383 2.017 2.833 0.000
TOD: Night vs. Day 1.248 1.114 1.394 0.000
DOW: Weekend vs. Weekday 1.086 0.987 1.194 0.088
Unfamiliar vs. Familiar 1.294 1.081 1.537 0.004

Table A-7. KRD Poisson regression model—hard cornering rate odds ratio estimate, CI, and p value.

Hard Cornering Rate Estimate 2.5% CI 97.5% CI p
Phase: Early Driving vs. Learner’s Permit 16.014 12.582 20.789 0.000
Phase: Later Driving vs. Learner’s Permit 11.649 9.134 15.148 0.000
TOD: Night vs. Day 0.818 0.724 0.900 0.000
DOW: Weekend vs. Weekday 1.177 1.097 1.263 0.000
Unfamiliar vs. Familiar 0.92 0.779 1.078 0.314

Table A-8. KRD Poisson regression model—yaw rate odds estimate ratio, CI, and p value.

Yaw Rate Estimate 2.5% CI 97.5% CI p
Phase: <= 6 Months vs. Learner’s Permit 12.981 11.287 15.026 0.000
Phase: > 6 months–12 months vs. Learner’s Permit 5.777 5.005 6.710 0.000
TOD: Night vs. Day 1.001 0.941 1.064 0.965
DOW: Weekend vs. Weekday 1.226 1.169 1.286 0.000
Unfamiliar vs. Familiar 0.927 0.827 1.035 0.185
Page 41
Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Page 43
Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Suggested Citation:"Appendix: Supporting Tables." National Academies of Sciences, Engineering, and Medicine. 2025. Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies. Washington, DC: The National Academies Press. doi: 10.17226/29066.
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Motor vehicle crash rates for teen drivers during the learner's permit phase are relatively low and comparable to those of adult drivers. However, once teenagers begin driving independently, the crash risk increases significantly at licensure and remains high during the first few months of solo driving.

BTSCRP Research Report 13: Outcomes of Variability in Teen Driving Experience and Exposure: Evidence from Naturalistic Driving Studies, from TRB's Behavioral Traffic Safety Cooperative Research Program, provides insights on how exposure to driving during the learner's permit period and the first months of driving independently, including driving in diverse environments, impacts safety outcomes in later driving.

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