SUMMARY

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

Background

According to the latest data available from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System, 2,883 teens aged 13–19 were killed in motor vehicle crashes in 2022 (Insurance Institute for Highway Safety 2024). Crash rates during the learner’s permit period are low and are similar to crash rates for adult drivers. When teenagers start driving independently, crash risk dramatically increases at licensure and remains elevated during the first several months of independent driving. Ehsani et al. (2020) suggested that consistent driving practice during the learner’s permit period could reduce teen drivers’ crash risk during the first year of independent driving. Klauer et al. (2011) suggested that crash rates may be higher when teen drivers are exposed to known risk factors (e.g., nighttime, teenage passengers, speeding). The relationship between amount of practice and crash rates is largely unknown. Further research is necessary to fully understand how driving exposure and diversity during the learner’s stage and/or early independent stage of driving affects subsequent crash risk.

Objectives

This research was conducted to evaluate how exposure to driving in diverse traffic and road environments during the learner’s permit period and early independent driving is associated with crashes and/or other safety surrogates as well as teen driver behavior in later independent driving.

Project Approach

Two naturalistic driving datasets—the second Strategic Highway Research Program (SHRP 2) and the Supervised Practice Driving Study (SPDS)—were employed to evaluate how exposure to driving in more diverse traffic and road environments during the learner’s permit period and first 6 months of independent driving is associated with teen driver behavior in later independent driving. Independent variables and dependent variables analyses are summarized in Table S-1. Crash/near-crash (CNC), safety-critical event (SCE) rate, kinematic risky driving (KRD), and percentage of time speeding were analyzed across different exposure groups and driving phases. KRD and percentage of time speeding were further analyzed using regression models.

Table S-1. Independent and dependent variables analysis summary in two datasets.

Results

The group with more driving exposure had lower rates of SCEs and KRD events in independent driving phases compared to the groups with less exposure to driving. In regression models, exposure group, driving phase, sex, and vehicle access significantly impacted the SCE rate. Exposure group, driving phase, and familiarity significantly impacted acceleration and hard braking rates. Yaw rate and hard cornering rate were not significantly different across route familiarity or time of day (TOD).

A key finding from this study was that teens who had accumulated more practice driving during the learner’s permit phase had significantly lower SCE rates during independent driving phases relative to those teenagers who had little practice driving during the learner’s permit phase. This association was particularly pronounced for females. Female teens with less driving exposure during the learner’s permit phase experienced higher SCE rates during the early independent driving 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.

Another key finding from this study was that teenage drivers with primary access to a vehicle had higher SCE rates than those teens who shared a family vehicle. This was especially pronounced for teen drivers who had accumulated less practice driving during the learner’s permit stage. This result is an important finding that should be included in educational materials for parents of teen drivers and driver’s education instructors.

To understand factors associated with driving diversity, the research team used a range of measures, including TOD and day of week, as well as a novel measure, route familiarity, which captured whether the individual had driven a particular route before. The research findings confirm that teens had higher rates of hard braking events during nighttime driving and on unfamiliar routes, but also had higher rates of fast starts on familiar routes. Hard braking events were associated with a higher SCE occurrence. These results suggest that more exposure to diverse and unique routes during early independent driving can improve safety.

Conclusion

Teens with more driving exposure during the learner’s permit phase and thus a greater number of driving hours had lower CNC rates and KRD event rates in the independent driving phases compared to teens with less supervised practice driving during the learner’s permit phase. This finding leads to a better understanding of how greater driving diversity during the learner’s permit phase reduces crash risk and improves safety outcomes in the independent driving phases. This is the first analysis to demonstrate a positive relationship between more supervised practice driving during the learner’s permit phase and lower CNC rates during independent driving.

Additionally, there were significantly higher rates of hard braking events when teens were driving on unfamiliar routes than when they were driving on familiar routes. This finding provides evidence that teens should be practicing driving in a wide variety of roadway environments during the learner’s permit phase so parents can assist them as they navigate novel road features and infrastructure. With such experience, teens will better handle unfamiliar situations once they are driving independently. More practice and more exposure to new and unique roadways will result in improved safety outcomes.

Teen drivers sped more frequently on roadways with 25–35 mph speed limits and on roadways with 55+ mph speed limits. The lower-speed roadways tend to have more pedestrians and driveways where severe crashes can occur.

These results suggest that regardless of state graduated driver’s licensing requirements for supervised practice driving during the learner’s permit phase, it may be beneficial to require parents to better record/provide evidence of the amount of supervised practice driving that their teen receives prior to licensure. Additionally, providing information to parents and driver’s education instructors regarding the importance of supervised practice driving hours that include driving in nighttime conditions, on a wide variety of road types, with different kinds of roadway infrastructure will reduce crash occurrence for teen drivers.