Cellphone laws and teens’ calling while driving: analysis of repeated cross-sectional surveys in 2013, 2015, and 2017

Abstract

and the District of Columbia (D.C.) have also enacted laws to ban phone conversation using a handheld mobile phone for drivers of all ages (i.e., handheld calling bans). 20,21In addition, 38 states and D.C. have implemented young driver bans that restrict any type of cellphone use while driving for novice drivers (≤ 18 years or drivers with a permit/intermediate driver license). 20 assess the effectiveness of these laws, studies have investigated the association between cellphone laws and driving outcomes including driver cellphone use and fatal crash rates. 4,22When speci cally looking at young drivers, previous research has found that handheld calling bans were related to a 55% reduction of self-reported calling while driving, 23 a 58% decrease of roadside-observed phone conversations, 24 and a signi cant reduction in driver fatalities and the rate of involvement in fatal crashes. 25,26When assessing texting bans, studies have reported no signi cant associations between the enactment of texting bans and the reduction of self-reported engagement in texting 23,27 and have seen inconclusive ndings with reducing crash fatalities among young drivers. 26,28Furthermore, studies have found young driver bans lack effectiveness in reducing both short-term ( ve months after enactment) and long-term (two years after enactment) observed cellphone use. 29,30However, none of these studies assess the combined effect of a handheld calling ban and a young driver ban in reducing self-reported talking on a phone while driving among teen drivers.To ll the research gap, our study aimed to estimate the association between cellphone laws and the prevalence of talking on a phone while driving among teen drivers by using state level Youth Risk Behavior Surveys data from multiple states and years.

Methods
Data source and study population Data was obtained from state Youth Risk Behavior Surveys (YRBSs), which are repeated cross-sectional surveys using a two-stage cluster sample design.9]31 Only state with a response rate ≥ 60% would be weighted and access to public.
States that asked a question about talking on a cellphone while driving in at least one of the years from 2013 to 2017 were included in this analysis.Participating states are listed in Additional File Table 1.The study inclusion criteria were students who had reached their state's minimum age to obtain a learner's permit license and had driven at least once 30 days prior to the survey administration date.
State cellphone bans and components of their graduated driver license system (GDL) were obtained from the Insurance Institute for Highway Safety. 20,32The ban amendments and effective dates were identi ed using the LexisNexis Academic database and state legislative documents. 33The total number of public school districts and the number of districts in rural areas were obtained from the National Center for Education Statistics. 34Detailed values of these variables for each state are listed in Additional File Table 2.

Measures
The study outcome was self-reported talking on a phone while driving (we used calling while driving, CWD as an abbreviation not TWD because TWD usually refers to texting while driving), which was measured with the question: "During the past 30 days, on how many days did you talk on a cell phone while driving a car or other vehicle?"Response options included seven ordinal categories ranging from 0 to 30 days.Students who responded "I did not drive" were excluded from the analysis.For the descriptive analysis, we categorized responses into never (0 days), sometimes (1-9 days) and frequent (10-30 days)   engagement in CWD.For multivariable analysis, we created a binary outcome (never versus at least once) as any exposure to talking on a phone while driving may increase crash risk for teen drivers.A similar categorization was consistent with a previously published study using YRBSs data on texting/emailing while driving. 35e state status of handheld calling bans and young driver bans were classi ed as 1) the absence of a handheld calling ban and a young driver ban (no ban); 2) the absence of a handheld calling ban but an enacted young driver ban (young driver ban); and 3) the enactment of both a handheld calling ban and a young driver ban (concurrent bans).No YBRSs participating state had an enacted handheld calling ban but an absence of a young driver ban during the study period.Cellphone law information for each state is listed in Additional File Table 2.
6][37] For our study, urban/rural status was presented by the proportion of state's public school districts that were in rural areas, which was calculated by dividing the number of public school districts in rural areas by the total number of public school districts in that states.We categorized the district proportion into three groups by approximately equal tertiles (17%-50%; 51%-78%; 79%-90%).9][40][41][42] The strength of the GDL system for each state was based on scores suggested by Steadman et al., 43 and categorized as: fair to moderate (<8 points); good (=8 points); and excellent (>8 points; see Additional File Table 2).

Statistical analysis
The association of cellphone laws and CWD was examined by adjusting for student demographics, the state GDL score, the proportion of state's public school districts in rural areas, and survey year.Crude and adjusted prevalence ratios (PRs) with 95% con dence intervals (CIs) for CWD were estimated using Poisson regression models with robust variances estimation. 44Complete case analysis was used to handle missing data as the percentage of missing was small (approximately 3% of students reached permit age but did not answer the question on CWD).
All reported results were weighted and considered the survey design. 31Data analyses were performed in 2019 using SAS Enterprise Guide 7.1 (SAS Institute Inc., Cary, NC) and STATA 14.0 (StataCorp LLC, College Station, TX).

Sensitivity analysis
Several sensitivity analyses were conducted to assess potential bias: 1) restricting the analysis to the ve states that participated in all three survey years (Connecticut, Massachusetts, Missouri, Montana, North Dakota); 2) excluding Utah, which enacted their young driver ban during the same year the survey was conducted (2013), thus limiting the sample to states that enacted young driver bans before survey administration; 3) excluding Texas, which was weighted as 41% of the total study population (the total population in Texas is much larger than other participating states); 4) excluding Maryland, which conducted a census instead of a two-stage cluster survey.
We further restricted our analysis to students who had reached the state-dependent age to begin unsupervised driving under certain driving conditions as driving under the supervision of an adult driver may prohibit teen's CWD behavior. 29,32Lastly, to estimate how cellphone laws are associated with a nominal outcome, we tted Poisson regression models to estimate the prevalence ratio for 1) sometimes CWD vs. never CWD, and 2) frequent CWD vs. never CWD.

Results
In total, 109,069 high school students participated in the surveys during 2013, 2015 and 2017 from 14 states.Approximately 56% (56, 492) of total participants reached the minimum permit age in their states and indicated that they had driven in the past 30 days.Among students who met the inclusion criteria, 46% engaged in CWD during the past 30 days.The prevalence of CWD was highest among older students (≥ 18 years, 63%) and lowest for the youngest students (14 years, 27%).A higher prevalence of White students (53%) reported CWD compared to students of other races/ethnicities (38% for Black students, and 40% for Hispanic students).(Table 1) CWD prevalence varied across states, from 29% in Maryland to 62% in North Dakota (Table 1).States with concurrent bans had a higher percentage of students who never engaged in CWD (63%) compared to states with a young driver ban or states with no ban (53% and 47% respectively) (Fig. 1).Students in states with a young driver ban had a lower prevalence of CWD compared to states with no ban (47% vs 53%), but this difference was not statistically signi cant in the adjusted model (Table 2).
Multivariable analysis showed that students in states with concurrent bans were 14% less likely to report CWD compared to students in states with no ban (adjusted PR = 0.86, 95% CI: 0.77-0.97)(Table 2).Similarly, students in states with concurrent bans were 15% less likely to engage in CWD compared to students in states with only a young driver ban (adjusted PR = 0.85, 95% CI: 0.79-0.93;data not shown).
Results of the sensitivity analyses were similar to the main analysis (Additional File Table 3 and Table 4).When categorizing CWD as a nominal outcome, students in states with concurrent bans had a lower risk of sometimes engaging in CWD compared to students in states with no ban (adjusted PR = 0.83, 95% CI: 0.72-0.95).The concurrent bans were associated with a 13% decrease in frequent CWD, but the decline was not statistically signi cant perhaps due to the limited sample size.(adjusted PR = 0.87, 95% CI: 0.69-1.09)(Additional File Table 4).

Discussion
This study is the rst to assess the combined effect of two types of state cellphone legislation (concurrently enacted handheld calling bans and young driver bans) on teens' self-reported CWD.We found that nearly half of teen drivers engaged in CWD at least once during the 30 days prior to the survey.Compared to states with no bans, the prevalence of CWD was 14% lower in states with concurrent bans.
Our ndings on the association between the presence of a handheld calling ban and CWD support and extend previous ndings.Rudisill et al., found the percentage of adolescent drivers (16-18 years) engaging in self-reported CWD was lower in states with a handheld calling ban compared to states without a ban. 23The association was stronger than what was seen in this study, PR= 0.45 (95% CI: 0.32-0.63)versus PR=0.86 (95% CI: 0.77-0.97).This difference could result from differences between selected study populations.For example, our study population was comprised of high school students aged ≥ 14 years whereas the study population in Rudisill et al., was comprised of adolescents aged ≥16 years from household samples where the parent was a liated with an online probability-based research panel.
Depending on the state, our study population may include more teens in the permit or intermediate license phases, resulting in a more novice group of teen drivers.It is important to include teen drivers in the earlier phases of licensure into the analysis as nearly one in four students aged 14-15 years engaged in CWD.They are the most inexperienced and youngest drivers under the restriction of both young driver bans and GDL.Furthermore, the two studies adjusted for different covariates.For example, our study controlled for the strength of the state GDL system, which could adjust the bias resulting from exposed driving time and supervised driving period.Since states with a stronger GDL system tend to have stricter nighttime driving restrictions and longer supervised driving practice, teens have fewer opportunities to engage in risky driving behaviors like CWD.One possible explanation for the lack of an association between young driver ban and self-reported CWD may include the level of ban awareness teen drivers possess.A survey conducted in North Carolina found that less than two-thirds of teens were aware of the cellphone restriction in their state as far as two years after the implementation of the young driver ban. 30Another issue is the challenge of enforcing cellphone laws.Analysis of citation data from 14 states and D.C. has found that overall enforcement of cellphone bans was low, with cellphone-related distracted driving citations comprising only 1% of all written citations. 45Young driver ban violations accounted for only 2.7/1000 of all teen tra c citations, less than handheld violations for young drivers (9.6/1000). 45Qualitative research also has shown that police o cers have a sense of discomfort in ticketing for cellphone-related distracted driving, as it can be ambiguous what drivers are actually doing with their phone while driving along with the low rate of admittance from drivers on their engagement in distracted driving. 46,47ong with the effectiveness of cellphone bans, culture and environment have critical roles in shaping young drivers' behavior. 48,49As driving is a learned behavior, parents/guardians serve as the primary role models for teen drivers and contribute to the overall tra c safety culture. 48,50,51Survey results from Carter et al. reported that teens with parents who engaged in distracted driving had a higher percent of engaging in distraction tasks. 52In states with a young driver ban only, teen passengers may be more likely to observe their parents and other adults engaging in CWD.This could potentially send a mixed message that once driving is "mastered," engagement in CWD is safe.On the other hand, in states with handheld calling bans, irrespective of driver age, adults were less likely to engage in CWD, 53 and their teen drivers would potentially be less likely to be exposed to adult drivers engaging in cellphone-related distracted driving.
From a clinical and policy perspective, these ndings, in combination with previous ndings on cellphone bans provide further support for the utility of handheld bans for drivers of all ages.Pediatricians should routinely discuss avoidance of distracted driving with teens during yearly physical exams.Promotion of safer alternatives such as hands-free options or technology which blocks cellular use while driving (e.g.Do Not Disturb mode), should be recommended as motor vehicle crashes remain a leading cause of injury and death for this age group.Although young driver bans target a population of vulnerable road users, legislative effort that acknowledges unsafe driving behavior irrespective of age will promote a safer driving culture and will translate into safer roads for all drivers.

Limitations
There are several limitations in our study.First, the questionnaire was framed to inquire about CWD and information was not available for differentiating handheld or hands-free calling behavior.Environmental factors such as the use of Bluetooth while driving would affect the proportion of drivers engaging in handheld calling.The proportion of smartphone owners that have access to Bluetooth or other hands-free devices that work in their vehicles increased about 12% from 2012 to 2015. 36,54Self-reported data also showed that the enactment of a handheld cellphone ban reduced overall handheld cellphone use while driving, but increased the use of hands-free technology. 55,56Therefore, our analysis might underestimate the effect of a handheld calling ban as drivers in states with the ban may switch to hands-free technology to avoid a ticket.Second, due to social desirability, students in a state with a cellphone ban may be less likely to report CWD compared to a state without a ban, which may overestimate the effectiveness of a ban.Third, since this was a cross-sectional study, the analysis cannot imply causality of legislation on drivers' behavior.Fourth, limited states adapted the question on CWD, restricting the analysis to 14 states with only ve states having data for all three years.The difference of CWD across law types may also be attributed to differences between states.In an effort to account for this potential bias, we controlled for two state-level covariates and conducted several sensitivity analyses which yielded similar results between law type and the prevalence of CWD.As none of the participating states had a handheld calling ban without a young driver ban, we cannot estimate the association of a handheld calling ban versus no ban, or directly compare the handheld calling ban versus a young driver ban.However, the prevalence ratio between concurrent bans versus no ban was similar to the prevalence ratio between concurrent bans versus a young driver ban, and the young driver ban was non-statistically associated with a reduction in CWD.It is reasonable to believe that a handheld calling ban only would also be associated with a reduction in CWD, but further data and investigation is needed.

Conclusions
Overall, teens in states with concurrent bans (handheld calling ban and young driver ban) had a lower prevalence of CWD.While the overall effectiveness of cellphone laws need further investigation, it is apparent that restricting drivers of all ages, including teens, may in uence the tra c safety culture on distracted driving.Further research with more states and more years of data to compare the concurrent bans and handheld calling ban in reducing CWD among teens would provide more insight into the effectiveness of different types of cellphone laws.Risk Behavior Survey data.We thank Melody L. Davis and Kayleigh Humphries for their valuable edits on this manuscript.

Tables
CI: Con dence interval D.C.: District of Columbia GDL: Graduate driver license PR: Prevalence ratio U.S.: United States YRBS: Youth Risk Behavior Survey Declarations Ethics approval and consent to participate: This study did not include personal identi ers and was exempt from IRB review at Nationwide Children's Hospital.Consent for publication: Not applicable.

d.
Concurrent bans: handheld calling ban along with young driver ban; e.Other included: American Indian/Alaskan Native, Asian, Native Hawaiian or Other Pacific Islander, and Multiple-Non-Hispanic/Latino.

Figures
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Table 1
Study population characteristics and prevalence of calling while driving (CWD) a Data were from state Youth Risk Behavior Surveys in 14 states (2013, 2015 and 2017), the United States; b.Weighted percentage of calling while driving (CWD): Percentage of students that reported talking on a phone while driving at least once during the 30 days before the survey (among students who drove); c.Model adjusted for cellphone laws, age, sex, race, the proportion of state's public school district in rural areas, strength of state's graduated driver license system, and survey year;