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    <title>Transport Research International Documentation (TRID)</title>
    <link>https://trid.trb.org/</link>
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    <language>en-us</language>
    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Transport Research International Documentation (TRID)</title>
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      <link>https://trid.trb.org/</link>
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    <item>
      <title>Edible cannabis use on simulated driving performance</title>
      <link>https://trid.trb.org/View/2772174</link>
      <description><![CDATA[To assess driving performance after consuming edible cannabis using a driving simulator, examining frequency of use, THC dose, and rural versus urban settings. Adults in Denver, Colorado (N = 88), between 25 and 55 years old, were recruited from November 2023 to July 2024 and assigned to groups based on past 90-day cannabis use: daily (N = 29), occasional (N = 30), or no recent use (i.e., comparison group; N = 29). This within-subjects study compared driving performance (i.e., speed, lane departures per minute, and standard deviation of lateral placement (SDLP)) using a validated driving simulator (miniSim™) at baseline and two post-consumption tests (52 and 119 min). Linear mixed models were used to evaluate performance. Daily-use group drove slower than the occasional-use group (decrease in average speed from pretest of 2.49 mph (urban, p <0.01 post-1); 1.80 mph (p = 0.02 post-2)) and the comparison group (decrease in average speed from pretest of 2.70 mph (urban, p <0.01 post-1); 2.68 mph (urban, p < 0.01 post-2)). Lane departures increased in the occasional-use group from 0.17 at pretest to 0.47 in post-1 and 0.40 in post-2 (p < 0.01). Their rural SDLP increased: post-1 (29.37 cm, p <0.01), post-2 (29.81 cm, p <0.01), versus pretest (25.45 cm). This group had significantly greater change in lane departures than both the comparison group (0.26, p <0.01) and daily-use group (0.34, p <0.01) in post-1. In post-2, the change remained greater than the daily-use group (0.20, p = 0.02). The study found significant changes in driving performance following edible cannabis use, including findings related to effect duration, use frequency, and road settings. The occasional-use group showed greater impairment than daily-use group, suggesting tolerance contributes to outcomes beyond THC concentration alone.]]></description>
      <pubDate>Fri, 25 Sep 2026 10:51:25 GMT</pubDate>
      <guid>https://trid.trb.org/View/2772174</guid>
    </item>
    <item>
      <title>Predicting drowsy driving impairment using ocular-motor metrics: A pre-drive assessment approach using the BrainEye app.</title>
      <link>https://trid.trb.org/View/2704082</link>
      <description><![CDATA[Driver drowsiness is a leading contributing factor to vehicle crashes, although loss of sleep impacts individuals to different degrees. While in-vehicle technologies can monitor a driver for signs of tiredness and distraction while on the road, there is obvious benefit in predicting impairment before a driver even enters the vehicle. Here we sought to examine whether driver impairment can be predicted using subjective reports of drowsiness and using ocular-motor behaviour recording using the BrainEye mobile phone app. Eighteen participants took part in a 20-min baseline drive in a driving simulator along a highway, followed by a restricted sleep for four hours between 10 p.m. and 2 a.m. Participants returned to the driving simulator after 9 a.m. to complete a second drive while sleep deprived. An increase in subjective reports of drowsiness predicted reduced average and maximum driving speed, while an BrainEye derived ocular-motor model predicted deviations in lateral position (swerving) and speed variability. Reducing a vehicle's speed to counteract the impact of drowsiness has been previously shown as a compensatory driving mechanism. Our findings reveal that ocular-motor parameters may predict impairment in driving that is associated with reduced cognitive capacity (meaning driving requires increased cognitive effort) and decreased attentional vigilance. While these results are preliminary, being able to use a mobile phone app to predict driver impairment may assist individuals to decide whether they are competent to get behind the wheel.]]></description>
      <pubDate>Fri, 28 Aug 2026 08:34:58 GMT</pubDate>
      <guid>https://trid.trb.org/View/2704082</guid>
    </item>
    <item>
      <title>Prevalence of cannabis, alcohol, and simultaneous use among drivers in states with and without recreational cannabis laws, 2021–2023</title>
      <link>https://trid.trb.org/View/2714780</link>
      <description><![CDATA[The present study investigated trends in the prevalence of alcohol use, cannabis use, and their simultaneous use among drivers in states with and without recreational cannabis laws.  Telephone interviews were conducted with 9,146 adult drivers across six states in 2021–2023 with a 27% cooperation rate. Four states legalized cannabis for recreational use shortly before or during the study period (Connecticut, Delaware, New York, and Virginia), and two states did not have recreational cannabis laws (North Carolina and South Carolina).  In the states with recreational cannabis laws, past-year cannabis use was 21%–29% in 2021 and 30%–36% in 2023, past-year drinking was 67%–75% in 2021 and 67%–79% in 2023, and simultaneous use was 10%–15% in 2021 and 14%–20% in 2023. In the other states, the prevalence of past-year cannabis use was 21%–22% in 2021 and 25–28% in 2023, past-year drinking was 65%–70% in 2021 and 62%–66% in 2023, and simultaneous use was 9%–10% in 2021 and 12–14% in 2023. Although past-year cannabis use and simultaneous alcohol and cannabis use rose in states with recreational cannabis laws, most time trends did not differ significantly across states with recreational cannabis laws compared with other states.  Drivers in all study states reported higher prevalence of cannabis use and simultaneous alcohol and cannabis use in 2023 compared with 2021, but results were inconclusive regarding the association of recreational cannabis laws with these changes.  The increased prevalence of simultaneous substance use is concerning due to the possibility of heightened risk behavior and poorer driving performance, suggesting a need for increased awareness among drivers about the risks of using alcohol and cannabis together.]]></description>
      <pubDate>Fri, 21 Aug 2026 14:01:30 GMT</pubDate>
      <guid>https://trid.trb.org/View/2714780</guid>
    </item>
    <item>
      <title>Metacognitive judgments of alcohol-related intoxication and impairment: The Mellanby effect and alcohol myopia in low-risk drinkers</title>
      <link>https://trid.trb.org/View/2714767</link>
      <description><![CDATA[The decision to drive after alcohol consumption is largely influenced by an individual’s interpretation of their alcohol intoxication and level of driving impairment. However, such perceptions may be influenced by the level and duration of intoxication. This study investigated the effect of alcohol intoxication on drivers’ judgments of their impairment and driving capabilities across different blood alcohol concentration (BAC) levels.  One hundred and sixty blinded participants were randomly allocated into low (∼.025%), mid (∼.055%), or high (∼.085%) BAC condition groups and completed surveys about their perceived alcohol intoxication and driving capabilities at various time points.  The results showed that the mid BAC condition group was most accurate in estimating the number of standard drinks consumed, whereas the low condition group overestimated, and the high condition group underestimated their alcohol consumption. While participants overestimated their BAC, they became more accurate when their BAC was falling. Between-group comparisons showed that participants rated their driving capabilities lower in the higher BAC condition groups. However, prior to consuming alcohol, the mid and high condition groups were significantly more confident in their ability to drive over the legal limit. Despite having a higher average actual BAC, the high condition group reported greater driving capabilities when their BAC was falling and a lower estimated BAC compared to the mid condition group when BAC was rising. Finally, logistic regression analysis revealed that estimated BAC and estimation confidence, rather than perceived driving impairment, significantly predicted the decision to drive after drinking.  These findings suggest that the level and duration of alcohol intoxication may influence a driver’s perception of impairment and their subsequent decision to drive.]]></description>
      <pubDate>Fri, 21 Aug 2026 14:01:30 GMT</pubDate>
      <guid>https://trid.trb.org/View/2714767</guid>
    </item>
    <item>
      <title>Driving under the influence of cannabis (DUIC): A risky proposition?</title>
      <link>https://trid.trb.org/View/2737002</link>
      <description><![CDATA[When non-medical cannabis use was legalized in Canada in 2018, there was concern that prevalence of driving under the influence of cannabis (DUIC) would rise. Post-legalization survey data has revealed potentially interesting patterns. Prevalence of cannabis use rose among the adult population following legalization. Among cannabis users, prevalence of DUIC decreased. Yet across the full population (cannabis users and non-users), prevalence of DUIC did not increase in the years immediately following legalization, though more recent survey data (2022 and 2023) identified a slight rise in DUIC prevalence across the general population. In the first few years post-legalization, there was some mixed data suggesting a rise in motor vehicle collision (MVC)-related injuries and fatalities involving delta-9-tetrahydracannabinol (THC; the psychoactive compound in cannabis); however, some more recent data suggest that this rise in MVC-related injuries and fatalities involving THC has begun to return to pre-legalization levels. Why did prevalence of cannabis use increase, yet most data suggest that DUIC did not? Public health initiatives aimed at influencing risk perceptions of cannabis use may provide part of the answer. The authors explore here survey data examining cannabis users’ perceptions of health and safety risks of cannabis and DUIC. The assessment supports continued use of health promotion materials and campaigns, but calls for more rigorous evaluation of the effectiveness of these health promotion campaigns. If the number of people who choose to use cannabis continues to rise, Canada may still see an increase in the number of DUIC cases despite the lower prevalence of DUIC among cannabis users.]]></description>
      <pubDate>Fri, 21 Aug 2026 08:37:10 GMT</pubDate>
      <guid>https://trid.trb.org/View/2737002</guid>
    </item>
    <item>
      <title>Sleep-deprived and behind the wheel: Exploring the impact of sleep patterns on new parents’ driving behavior</title>
      <link>https://trid.trb.org/View/2736972</link>
      <description><![CDATA[New parents commonly experience sustained sleep disruption in the postpartum period, yet their road-safety risk remains under-examined. This study investigated sleep patterns, the prevalence of fatigued driving, risk awareness, and fatigue-management strategies among Australian parents with at least one child under 12 months.  A cross-sectional design using an online survey was conducted using Qualtrics. Measures included sleep quantity and quality (modified Pittsburgh Sleep Quality Index), frequency and symptoms of fatigued driving, self-reported driving behavior (Driver Behavior Questionnaire), comparative risk awareness, and use of behavioral and technological fatigue-mitigation strategies.  Among the 1,160 responses included in the analysis, participants reported substantial sleep disruption, averaging six hours of sleep per night with generally poor sleep quality. Over 90% reported driving while fatigued at least once in the past 30 days. Common self-observed symptoms included poor concentration, tired eyes, increased blinking, and an increased likelihood of driving errors. Participants who reported fatigued driving also reported significantly higher levels of aberrant driving behaviors (Aggressive Violations: t (1015) = -2.59, p = 0.01; Violations: t (1015) = -4.71, p < 0.001; Lapses: t (1015) = -6.23, p < 0.001; Errors: t (103) = -7.17, p < 0.001). Fatigued driving was reported more frequently than speeding, mobile phone use, or alcohol- and drug-impaired driving. Fatigue management relied primarily on short-term behavioral strategies such as caffeine intake and in-vehicle stimulation, while uptake and perceived effectiveness of fatigue-detection technologies were limited.  New parents experience pronounced sleep disruption and frequently engage in fatigued driving associated with higher crash-risk behaviors. These findings highlight the need for greater attention to fatigue-related driving risk during early parenthood.  Targeted road-safety messaging, healthcare-provider advice, supportive workplace policies, and clearer communication about fatigue-detection technologies may reduce fatigue-related driving risk during early parenthood.]]></description>
      <pubDate>Thu, 20 Aug 2026 15:10:27 GMT</pubDate>
      <guid>https://trid.trb.org/View/2736972</guid>
    </item>
    <item>
      <title>Cannabis, self-ratings of cognition and driving behaviour among older adults: An exploratory study</title>
      <link>https://trid.trb.org/View/2735216</link>
      <description><![CDATA[Despite cannabis use increasing among older adults, scant research has explored the subjective effects of cannabis (both prescribed and non-prescribed) on cognitive and driving-related skills in older adults, and how these relate to driving following cannabis consumption. This study explored the nature of cannabis use (both prescribed and non-prescribed) in older adults and self-ratings of perceived cognitive and driving-related competence. In addition, this study aimed to identify factors that predict driving wait times following cannabis consumption among this cohort. A total of 283 participants aged 60 to 78 years (M age = 66 years) completed an online survey, comprising of questions relating to cannabis use (both prescribed and non-prescribed), self-ratings of perceived cognition and driving behaviors/competence following cannabis consumption, and driving wait times following consumption. Participants reported using cannabis for the first time at the age of 20 years. Ninety-six per cent reported using cannabis regularly (at least weekly). Further, 58% of the sample reported current prescribed medicinal cannabis use and 70% of the sample reported non-prescribed use. Earlier age of onset of cannabis use and higher self-ratings of perceived cognition/driving competence significantly increased the odds of driving within four hours of consuming cannabis (by 3% and 22% respectively). Further, holding a medicinal cannabis prescription reduced the odds of driving within four hours of consuming cannabis by 46%. The findings from this study provide insights into the nature of cannabis use in older adults, and the factors that influence driving wait times following cannabis consumption among this cohort.]]></description>
      <pubDate>Fri, 14 Aug 2026 15:04:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/2735216</guid>
    </item>
    <item>
      <title>Preventing Alcohol and Cannabis-Impaired Driving among Adolescents: Effects of a Web-Intervention in a Driver Education Program</title>
      <link>https://trid.trb.org/View/2714453</link>
      <description><![CDATA[Adolescence is a critical period during which teens initiate and escalate substance use, as well as begin learning to drive. Limited research has evaluated programs to prevent impaired driving behaviors in this age group. The authors tested effects of adding a single-session web intervention to existing driver education curriculum. Driving school staff recruited participants aged 15.5 to 17 from 12 driver education programs. Participants were randomized to driver education only (usual care, 30 h) or driver education plus a single-session web intervention (webCHAT, ∼30 min). Participants completed surveys at baseline and six months. The sample (N = 198) was 60% female, 80% White, and averaged 15.7 (SD = 0.8) years old. At baseline, 25% and 8% reported past three-month alcohol and cannabis use, respectively, and 19% and 10% reported ever riding with someone under the influence of alcohol or cannabis, respectively. At follow-up, webCHAT participants reported significantly lower perceived peer alcohol (−1.14, 95% CI: −1.915, −0.372, p = 0.004) and cannabis (−1.09, 95% CI: −1.866, −0.306, p = 0.007) use norms compared to usual care participants. Both webCHAT and usual care participants significantly reduced past month alcohol and cannabis use and viewed impaired driving as riskier and less acceptable at follow-up. Driver education programs offer a unique opportunity to prevent substance use and impaired driving when adolescents are motivated to participate to secure their driver's license. These programs should continue updating curricula to reflect the state of science for alcohol and drug prevention.]]></description>
      <pubDate>Tue, 21 Jul 2026 09:49:55 GMT</pubDate>
      <guid>https://trid.trb.org/View/2714453</guid>
    </item>
    <item>
      <title>The Grand Rapids Dip: Could It Be Real?</title>
      <link>https://trid.trb.org/View/2724963</link>
      <description><![CDATA[The “Grand Rapids dip” refers to a finding in the Grand Rapids study of drinking-and-driving, indicating that drivers with a low blood alcohol concentration had a lower risk of accident involvement than drivers with a zero-blood alcohol concentration. In the Grand Rapids study, it was found that this was a statistical artefact only and did not indicate a real decline in accident risk. This paper asks if a decline in accident risk at a low blood alcohol concentration could be real. It is concluded that it could but is likely to be uncommon. It may occur if: (1) There is a comparatively large a group of drivers who are experienced both in driving and in drinking alcohol; (2) This group of drivers drive regularly with a low blood alcohol concentration, and (3) The drivers can predict how a low blood alcohol concentration will influence them and adapt behavior so as to avoid an increase in accident risk.]]></description>
      <pubDate>Tue, 21 Jul 2026 09:49:51 GMT</pubDate>
      <guid>https://trid.trb.org/View/2724963</guid>
    </item>
    <item>
      <title>The effects of methamphetamine on driving performance and behavior: A thematic linking of consumption patterns and cognitive-behavioral outcomes from in-depth interviews with methamphetamine users</title>
      <link>https://trid.trb.org/View/2708315</link>
      <description><![CDATA[This study sought to investigate the thematic links between methamphetamine (MA) users’ consumption patterns; their perceptions about the effects that MA has on their thoughts, feelings, and behavior; and their tendency to drive following MA consumption. Seventeen MA users were recruited through a combination of social media advertising and third-party outreach. Participants completed a semi-structured interview lasting approximately 30 min. Interview data were analyzed using thematic analysis to identify key patterns undermining impaired driving behavior. An overarching theme revealed that participants’ beliefs about MA use and their tendency to drive while intoxicated were largely dependent on their history and patterns of MA use. Three primary profiles of MA users were identified: (a) sporadic users, who used “speed” infrequently and in the context of social situations; (b) progressed users, who described similar initial patterns but had progressed to frequent use of more potent “crystal” MA and displayed characteristics of substance dependency; and (c) regressed users, who acknowledged a previous history of problematic use, but had since reduced their use patterns significantly. Where sporadic users tended to perceive MA as detrimental to their attention and behavior on the road, progressed users commonly believed that MA positively influenced their driving. However, it was typically acknowledged among all users that regardless of intoxication, extended MA use could lead to significant driving risk due to the severe cognitive (erratic thinking) and behavioral (aggression) symptoms associated with fatigue and the ‘come down’ of MA. Finally, the analysis showed that the tendency to drive while intoxicated was contextual to participants’ beliefs about the associated cognitive-behavioral outcomes of MA use. The findings highlight how MA use patterns and perceptions contribute to impaired driving behaviors. These insights can inform the development of more targeted interventions addressing the interconnected issues of substance dependence and drug-impaired driving.]]></description>
      <pubDate>Tue, 23 Jun 2026 13:50:27 GMT</pubDate>
      <guid>https://trid.trb.org/View/2708315</guid>
    </item>
    <item>
      <title>The COVID-19 pandemic influence on fatal car crashes and impaired driving in Arkansas</title>
      <link>https://trid.trb.org/View/2708313</link>
      <description><![CDATA[The COVID-19 pandemic had a profound impact on motor vehicle traffic patterns, leading to a noticeable decrease in traffic volume during the peak of the pandemic. Previous studies have highlighted an increase in risky driving behaviors during the pandemic, such as impaired driving and not wearing seatbelts. Despite reduced traffic, many states, including Arkansas experienced an increase in motor vehicle crash fatality rates. This trend highlights the need to better understand the factors associated with this trend. This study aimed to examine the potential role of impaired driving and the lack of restraint use in the rise of fatal crashes during the pandemic. Record-level data from fatal car crashes occurring in Arkansas between 2018 through 2021 were obtained from the Fatality Analysis Reporting System (FARS). Multivariable logistic regression analyses were conducted to compare restraint use among both deceased drivers and passengers before (January 1, 2018 through March 10, 2020) and during the pandemic (March 11, 2020 through December 31, 2021), as well as impaired driving among drivers who died in a crash and all drivers involved in fatal crashes during the study period. During the study period, there were 1,226 deceased drivers, 369 deceased passengers, and 2,200 drivers involved in fatal crashes. Among the 1,226 deceased drivers, there was a 34% decrease in the odds of seatbelt use during the pandemic compared to before the pandemic (p = 0.001). There were no significant changes in impaired driving among deceased drivers during the pandemic (AOR: 1.24; p = 0.09).Seatbelt use among the 369 deceased passengers did not change (AOR: 0.99; p = 0.96).Among the 2,200 drivers involved in fatal crashes, there was a 31% decrease in the odds of seatbelt use (p < 0.0001) and a 38% increase in the odds of impaired driving (p = 0.0002) during the pandemic when compared to before the pandemic. The increase in fatal car crashes during the pandemic may be attributed to the increase in impaired driving and decrease in restraint use. These findings highlight the need for public health interventions, such as sobriety checkpoints, public awareness campaigns, and strengthened enforcement to address impaired driving and promote restraint use.]]></description>
      <pubDate>Tue, 23 Jun 2026 13:50:27 GMT</pubDate>
      <guid>https://trid.trb.org/View/2708313</guid>
    </item>
    <item>
      <title>Beyond just intoxication: An exploration of the potential links between problematic cannabis use, self-reported psychological dysfunction, and subjective driving capabilities</title>
      <link>https://trid.trb.org/View/2698519</link>
      <description><![CDATA[Problematic cannabis use has been linked to cognitive impairment and psychopathology, which may adversely affect an individual’s ability to regulate attention and drive safely. This study examined associations between likely cannabis dependency, cannabis-related psychological symptoms, subjective general driving efficacy, and general driving inattention. It also aimed to compare these factors between specific cohorts of active cannabis users and a comparative sample of low-frequency substance users. An online survey was disseminated to Australian residents aged 20–65 years, who drove at least one hour per week, and did not have a physical condition impairing driving. Active users (N = 271) had consumed cannabis within the past month, whereas the comparison group (N = 159) reported minimal substance use. MANOVAs showed that likely dependent cannabis (n = 114) users reported the greatest psychological symptoms and driving inattention, and the lowest subjective driving efficacy, followed by low-frequency substance users, and then likely non-dependent cannabis users (n = 157). However, no significant differences emerged between those who used medically prescribed compared to non-prescribed cannabis. Correlational analyses further revealed significant associations between likely cannabis dependency, psychological symptoms, subjective driving efficacy, and driving inattention. Finally, structural equation modeling showed that likely cannabis dependency was indirectly associated with subjective driving efficacy and driving inattention through its relationship with emotional and cognitive dysfunction. Overall, these findings suggest that problematic cannabis use is associated with poorer driving capabilities, likely linked to greater psychological dysfunction and cognitive-attentional deficits. In turn, the findings highlight the importance of integrating chronic cannabis-related risks into driving research, policy, and regulation.]]></description>
      <pubDate>Wed, 27 May 2026 13:05:20 GMT</pubDate>
      <guid>https://trid.trb.org/View/2698519</guid>
    </item>
    <item>
      <title>Use of Potentially Impairing Medications in Relation to Driving, United States, 2021</title>
      <link>https://trid.trb.org/View/2701053</link>
      <description><![CDATA[Many prescription and over-the-counter medications have potential effects that adversely impact driving, including dizziness, sleepiness, fainting, blurred vision, slowed movement, and problems with attention. Drivers may take one or more potentially driver impairing medications but may not be aware of the possible impacts on driving. This study utilized data from a survey of driving behavior in the United States in 2021 to quantify the prevalence of recent use of potentially driver impairing medication and driving after use, and to assess the association of healthcare provider warnings regarding medication effects with drivers’ likelihood of driving shortly after use.]]></description>
      <pubDate>Tue, 26 May 2026 09:36:41 GMT</pubDate>
      <guid>https://trid.trb.org/View/2701053</guid>
    </item>
    <item>
      <title>Clustering Roadway Departures from Impaired Driving Studies using Derived Features and Shape-Based Methods</title>
      <link>https://trid.trb.org/View/2697857</link>
      <description><![CDATA[Lane departures remain a major contributor to fatal traffic accidents despite the increasing adoption of lane departure warning systems. Existing research has focused on the detection and mitigation of lane departures, while the characteristics of departures and their potential relationships with categories of driver impairment have received less attention. We apply a variety of unsupervised clustering approaches to a comprehensive set of lane departures from three drug-impaired driving studies involving combinations of cannabis and low-dose alcohol, alcohol, and cannabis. We find that departures are more frequent in active-drug conditions, ranging from 26% to 222% increases in mean departures per minute of driving depending on the study and condition. Across all studies, departures are most effectively grouped into two clusters based on duration and peak lateral deviation, with average silhouette scores of the most effective approaches being 0.778, 0.759, and 0.871, respectively, indicating high degrees of cohesion within clusters and separation between them. After clustering on the principal components derived from driving data from before, during, and after each departure we find clusters that differ significantly in their relative proportions of alcohol-dosed drivers (p < 0.001). Shape-based approaches also identify two clusters of departures that differ in duration, maximum deviation, and timing of peak deviation. These clusters contain a significantly different composition of dosing conditions in the combined alcohol and cannabis study (p = 0.015). Our results suggest lane departures can be effectively profiled and that leveraging their characteristics may benefit driver monitoring systems targeting the detection of drug-impaired driving.]]></description>
      <pubDate>Tue, 05 May 2026 10:16:53 GMT</pubDate>
      <guid>https://trid.trb.org/View/2697857</guid>
    </item>
    <item>
      <title>The effects of recreational marijuana legalization on driving under the influence of marijuana in a neighboring state: A cross-border quasi-experiment</title>
      <link>https://trid.trb.org/View/2686782</link>
      <description><![CDATA[This study examines whether recreational marijuana (RM) legalization in neighboring states is associated with driving under the influence of marijuana in a non-legalizing state, as measured by motor-vehicle crashes involving a marijuana-positive driver (MP).   Although Pennsylvania has not legalized RM, it borders five states that legalized RM at different time points in 2021 and 2023. This spatial and temporal variation enables a quasi-experimental stepped wedge design that assesses whether Pennsylvania counties that border a state with RM legalization experienced changes in MP motor-vehicle crash counts. Pennsylvania Department of Transportation data provide crash counts at the county-month level (January 2019–December 2024). Of primary interest are MP crashes where the Pennsylvania State Police (PSP) was the reporting law enforcement agency (MP-PSP). Once RM legalization occurs in a contiguous state, a Pennsylvania county (N=27) bordering that state becomes Post-Exposure. Four Pennsylvania counties eventually bordered two states with RM legalization, becoming Post-Second-Exposure. Poisson regression was used to estimate changes in crashes in the Post-Exposure and Post-Second-Exposure periods relative to the Pre-Exposure period.  On average, a Pennsylvania county experienced a significant 58.41% increase in MP-PSP crashes Post-Exposure and a nonsignificant 55.48% increase Post-Second-Exposure. Where a border county has an interstate highway (N=20), on average, there was a significant 68.95% increase Post-Exposure and a nonsignificant 56.80% increase Post-Second-Exposure. Practical Applications: RM legalization in bordering states may impact traffic safety in a state that has not yet legalized RM. Future research should identify mechanisms for this association as well as actionable strategies to prevent marijuana-impaired driving.]]></description>
      <pubDate>Tue, 28 Apr 2026 11:18:51 GMT</pubDate>
      <guid>https://trid.trb.org/View/2686782</guid>
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