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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.

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.
Driving Exposure	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.
Functional Road Classification	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.
Vehicle Access	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).
Time of Day	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.
Day of Week	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.

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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

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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

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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

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

Chapter: Appendix: Supporting Tables

APPENDIX

Supporting Tables