Research and Development Branch

Sacramento, CA, United States

Research and Development Branch

Sacramento, CA, United States

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Chand S.S.,University of Vic | Tory K.J.,Research and Development Branch | Ye H.,Research and Development Branch | Walsh K.J.E.,University of Melbourne
Nature Climate Change | Year: 2017

The El Niño/Southern Oscillation (ENSO) drives substantial variability in tropical cyclone (TC) activity around the world. However, it remains uncertain how the projected future changes in ENSO under greenhouse warming will affect TC activity, apart from an expectation that the overall frequency of TCs is likely to decrease for most ocean basins. Here we show robust changes in ENSO-driven variability in TC occurrence by the late twenty-first century. In particular, we show that TCs become more frequent (â 1/420-40%) during future-climate El Niño events compared with present-climate El Niño events - and less frequent during future-climate La Niña events - around a group of small island nations (for example, Fiji, Vanuatu, Marshall Islands and Hawaii) in the Pacific. We examine TCs across 20 models from the Coupled Model Intercomparison Project phase 5 database, forced under historical and greenhouse warming conditions. The 12 most realistic models identified show a strong consensus on El Niño-driven changes in future-climate large-scale environmental conditions that modulate development of TCs over the off-equatorial western Pacific and the central North Pacific regions. These results have important implications for climate change and adaptation pathways for the vulnerable Pacific island nations. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.


Masten S.V.,Research and Development Branch | Foss R.D.,University of North Carolina at Chapel Hill | Marshall S.W.,University of North Carolina at Chapel Hill
Accident Analysis and Prevention | Year: 2013

Graduated driver licensing (GDL) programs are specialized licensing systems for beginner drivers adopted in all U.S. states, Australia, Canada, and New Zealand. GDL programs reduce novice drivers' exposure to high-risk driving situations while they gain driving experience. Several studies document the success of GDL programs overall in reducing young teen crash rates. However, little is known about which specific components of these programs (e.g., nighttime driving restrictions) and which calibrations of these components (e.g., 10 PM, 11 PM, 12 AM, or 1 AM), are associated with the largest crash reductions. The goal of this study was to identify the GDL component calibrations associated with the largest reductions in fatal crash involvements for 16-17-year-olds. Driver fatal crash involvements for all U.S. states from 1986 to 2007 were analyzed using Poisson regression models to estimate the association of various GDL component calibrations with 16- and 17-year-old driver fatal crash incidence, after adjusting for potential confounders. We found clear evidence that (a) a minimum learner permit holding period of 9-12 months and (b) a passenger restriction allowing only one teen passenger for 6 months or longer are the calibrations for the learner permit holding period and passenger restriction components associated with the largest reductions in 16-17-year-old driver fatal crash involvements. Additionally, the data suggest that (a) disallowing learner driving until age 16, (b) disallowing intermediate licensure until age 16 to 17, and (c) a nighttime driving restriction starting at 10 PM or earlier are the calibrations for these components associated with the largest reductions in 16-year-old driver fatal crashes. There was no clear evidence to support particular calibrations for supervised driving hours or unrestricted license ages. © 2013 Elsevier Ltd. All rights reserved.


O'Brien N.P.,University of North Carolina at Chapel Hill | Foss R.D.,University of North Carolina at Chapel Hill | Goodwin A.H.,University of North Carolina at Chapel Hill | Masten S.V.,Research and Development Branch
Accident Analysis and Prevention | Year: 2013

Most states require teens to complete a certain number of hours of supervised driving practice to obtain a license to drive unsupervised. Although widely implemented, the effect of requiring supervised practice is largely unknown. Using auto-regressive integrated moving average (ARIMA) interrupted time-series analysis, we found no change in fatal and injury crash involvement of 16-17-year-old drivers in Minnesota following enactment of a 30 h supervised driving requirement. To supplement and provide insight into these findings, we conducted telephone interviews with parents of newly licensed teenage drivers in five states with varying amounts of required supervised driving, including Minnesota. Interviews revealed awareness of supervised driving requirements was limited. Only a third of parents (32%) overall could correctly identify the number of hours their state required. In Minnesota only 15% of parents could identify the amount of supervised driving their teen was required to complete. Awareness of the number of hours required was substantially higher (55%) in Maryland. Unlike the other states, Maryland requires submission of a driving log detailing the hours of supervised driving. The findings suggest states need to develop more effective mechanisms to ensure parents are aware of supervised hours requirements. © 2012 Elsevier Ltd.


Masten S.V.,Research and Development Branch | Foss R.D.,University of North Carolina at Chapel Hill | Marshall S.W.,University of North Carolina at Chapel Hill
JAMA - Journal of the American Medical Association | Year: 2011

Context: In the United States, graduated driver licensing (GDL) systems allow full, unrestricted licensure for drivers younger than 18 years only after an initial period of supervised driving and an intermediate period of unsupervised driving that limits driving at night, transporting multiple young passengers, or both. Objective: To estimate the association of GDL programs with involvement in fatal crashes among 16- to 19-year-old drivers. Design, Setting, and Participants: Pooled cross-sectional time series analysis of quarterly 1986-2007 incidence of fatal crashes involving drivers aged 16 to 19 years for all 50 states and the District of Columbia combined. Main Outcome Measures: Population-based rates of fatal crash involvement for 16-, 17-, 18-, and 19-year-old drivers. Rate ratios and 95% CIs comparing statequarters with stronger (restrictions on both nighttime driving and allowed passengers) or weaker (restrictions on either nighttime driving or allowed passengers) GDL programs with state-quarters without GDL. Results: Fatal crash incidence among teen drivers increased with age, from 28.2 per 100 000 person-years (16-year-old drivers) to 36.9 per 100 000 (17-year-olds), before reaching a plateau of 46.2 per 100 000 (18-year-olds) and 44.0 per 100 000 (19-yearolds). After adjusting for potential confounders, stronger GDL programs were associated with lower incidence of fatal crashes for 16-year-old drivers, compared with programs having none of the key GDL elements (rate ratio, 0.74 [95% CI, 0.65-0.84]). However, stronger GDL programs were associated with higher fatal crash incidence for 18-yearold drivers (rate ratio, 1.12 [95% CI, 1.01-1.23]). Rate ratios for 17-year-olds (0.91 [95% CI, 0.83-1.01]), 19-year-olds (1.05 [95% CI, 0.98-1.13]), and 16- to 19-year-olds combined (0.97 [95% CI, 0.92-1.03]) were not statistically different from the null. Conclusions: In the United States, stronger GDL programs with restrictions on nighttime driving as well as allowed passengers, relative to programs with none of the key GDL elements, were associated with substantially lower fatal crash incidence for 16-year-old drivers but somewhat higher fatal crash incidence for 18-year-old drivers. Future studies should seek to determine what accounts for the increase among 18-yearold drivers and whether refinements in GDL programs can reduce this association. ©2011 American Medical Association. All rights reserved.


Masten S.V.,Research and Development Branch | Guenzburger G.V.,Research and Development Branch
Journal of Safety Research | Year: 2014

Objective To determine if cannabinoid prevalence increased among fatal-crash-involved drivers in 12 U.S. states after implementing medical marijuana laws. Methods Time series analyses of 1992 to 2009 driver cannabinoid prevalence from the Fatality Analysis Reporting System. Results Increased driver cannabinoid prevalence associated with implementing medical marijuana laws was detected in only three states: California, with a 2.1 percentage-point increase in the percentage of all fatal-crash-involved drivers who tested positive for cannabinoids (1.1% pre vs. 3.2% post) and a 5.7 percentage-point increase (1.8% vs. 7.5%) among fatally-injured drivers; Hawaii, with a 6.0 percentage-point increase (2.5 vs. 8.5) for all drivers and a 9.6 percentage-point increase (4.9% vs. 14.4%) among fatally-injured drivers; and Washington, with a 3.4 percentage-point increase (0.7% vs. 4.1%) for all drivers and a 4.6 percentage-point increase (1.1% vs. 5.7%) among fatally-injured drivers. Changes in prevalence were not associated with the ease of marijuana access afforded by the laws. Discussion Increased prevalence of cannabinoids among drivers involved in fatal crashes was only detected in a minority of the states that implemented medical marijuana laws. The observed increases were one-time changes in the prevalence levels, rather than upward trends, suggesting that these laws may indeed provide marijuana access to a stable population of patients as intended, without increasing the numbers of new users over time. Although this study provides some insight into the potential impact of these laws on public safety, differences between states in drug testing practices and regularity, along with the fairly recent implementation of most medical marijuana laws, suggest that the long-term impact of these laws may not yet be known. Practical applications It is recommended that nationwide standardization of drug testing procedures and criteria be considered to improve the consistency of testing both between and within jurisdictions. © 2014 National Safety Council and Elsevier Ltd. All rights reserved.


Chapman E.A.,Research and Development Branch | Masten S.V.,Research and Development Branch | Browning K.K.,Impact Teen Drivers
Journal of Safety Research | Year: 2014

Introduction How do crash and traffic violation rates for novice 16-17-year-old drivers change over the months before and after licensure under a graduated driver licensing (GDL) program relative to those for older novices who are not subject to GDL? Method Plots and Poisson regression comparing overall rates and subtypes of crashes and traffic violations among California novice drivers ages 16 to 35 years over time before and after unsupervised licensure. Results Majorities of 16-year-olds (57%) and 17-year-olds (73%) actually hold their learner permits longer than the required 6 months; majorities (67%-81%) of age 18 or older novices hold their learner permits less than 6 months. Crash rates of novice 16- and 17-year-olds - as well as most other age groups - are highest almost immediately after they are licensed to drive unsupervised, after which their rates decline quickly during their first year of licensure and at a slower rate for the second and third years. Novice 16- and 17-year-olds' traffic violation rates reach their zenith long after their total crash rates peak and decline, whereas violation rates for older novices peak during their first year of licensure. Over 70% of 16- and 17-year-old novices are crash-free for the first 3 years of licensure. Conclusions While novice 16- and 17-year-olds' highest crash rates occur almost immediately after they are licensed, their peak traffic violation rates are delayed until around the time they turn age 18. Both pre-licensure crash rates and post-licensure crash peaks were more pronounced for some older age groups of novices than was the case for 16-17-year-olds. Practical Applications Extending learner permit holding periods for 16-17-year-old novices appears consistent with their actual behavior; requiring older novices - particularly those ages 18 to 20 - to hold permits for minimum periods may reduce their initial crash rates. © 2014 National Safety Council and Elsevier Ltd.


Brar S.S.,Research and Development Branch
Journal of Safety Research | Year: 2014

Introduction and Method Quasi-induced exposure analysis was used to estimate annual fatal crash involvement rates for validly licensed, suspended or revoked (S/R), and unlicensed drivers in California from 1987 through 2009 using fatal crash data obtained from the National Highway Traffic Safety Administration's Fatality Analysis Reporting System and crash culpability determinations from the California Highway Patrol's Statewide Integrated Traffic Records System. Results Although there was some year-to-year fluctuation in the annual estimates, S/R and unlicensed drivers were over-involved as at-fault drivers in fatal crashes during every year of the 23-year time period relative to validly licensed drivers. The fatal crash involvement ratios combined across all years were 0.86 for validly licensed drivers, 2.23 for S/R drivers, and 2.34 for unlicensed drivers. Hence, compared to validly licensed drivers, the odds of being at-fault for a fatal crash were 160% higher for S/R drivers (involvement ratio = 2.60) and 173% higher for unlicensed drivers (involvement ratio = 2.73). The excess risks of S/R and unlicensed drivers are somewhat lower than estimates found in a prior study using the same technique, but the results nonetheless provide evidence that S/R and unlicensed drivers are much more hazardous on the road than are validly licensed drivers and emphasize the importance of using strong countermeasures - including vehicle impoundment - to reduce their high crash risk. These findings support interventions to help reduce driving among S/R and unlicensed drivers. © National Safety Council and Elsevier Ltd.


Parrish K.E.,Research and Development Branch | Masten S.V.,Research and Development Branch
Traffic Injury Prevention | Year: 2015

Objective: Although driver license suspension and revocation have been shown to improve traffic safety, suspended or revoked (SR) drivers who continue to drive—which appears to be the majority—are about 3 times more likely to be involved in crashes and to cause a fatal crash. In California and many other U.S. states, drivers are typically mailed notices requesting that they surrender their licenses when they are SR for reasons other than driving under the influence of alcohol or drugs (DUI), yet they frequently do not comply. Typical procedures at DUI checkpoints in California and other U.S. states include inspecting driver licenses and checking for signs of intoxication during brief contacts with law enforcement officers. Hence, these checkpoints are in fact DUI/license checkpoints in California and many other states. The purpose of this study was to estimate the extent to which SR drivers avoid being detected at DUI/license checkpoints for SR driving, because they illegally retained possession of their license cards.Method: Law enforcement officers used electronic license card readers at DUI/license checkpoints in Sacramento, California, to record data for 13,705 drivers. The SR status of all contacted drivers was determined after the checkpoints and compared to law enforcement citation records from the checkpoints.Results: Although only 3% of the drivers contacted at the checkpoints were SR, about 41% of SR drivers were able to pass through undetected because they presented license cards that they illegally retained. Drivers SR for DUI-related reasons were more likely to be detected, whereas those SR for failure to provide proof of financial responsibility (insurance) were less likely to be detected.Conclusion: The fact that many SR drivers are able to pass through DUI/license checkpoints undetected weakens both the specific and general impacts of checkpoints for deterring SR driving and may diminish the effectiveness of suspension and revocation actions for reducing the crash risk posed by problem drivers. Using license card readers that can quickly identify SR drivers in real time during routine traffic stops and at DUI/license checkpoints warrants further consideration. © 2015, Copyright © Taylor & Francis Group, LLC.


Hope P.,Research and Development Branch | Lim E.-P.,Research and Development Branch | Wang G.,Research and Development Branch | Hendon H.H.,Research and Development Branch | And 2 more authors.
Bulletin of the American Meteorological Society | Year: 2015

The record warm Australian spring of 2014 would likely not have occurred without increases in CO2 over the last 50 years working in concert with an upper-level wave train. © 2015 American Meteorological Society.


Camp B.J.,Research and Development Branch
Journal of Safety Research | Year: 2013

Introduction: In 2007, the California Department of Motor Vehicles (DMV) undertook a pilot study of the 3-Tier Assessment System, the purpose of which was to examine, in a large-scale real-time public agency setting, the effectiveness of this method for both reducing the crash risk of individual drivers and for extending the safe driving years of Californian drivers of all ages. Method The 3-Tier Assessment System consisted of tiered series of screening tools incorporated into the in-office driver's license renewal process. These screening tools identified drivers with various kinds of functional limitations (physical, visual, and cognitive/perceptual), that might impact safe driving. Paired with the screening tools were educational materials designed to improve drivers' knowledge of their own limitations, including compensating techniques. The present study is a population-based evaluation of the effects of the pilot on subsequent crash risk and mobility outcomes (including delicensure) of participating drivers age 70 and older. Pilot participants were compared with two control groups processed according to standard California DMV license renewal procedures. Because the 3-Tier Assessment System was designed to identify limitations normally associated with aging, the present analyses focus on drivers age 70 and older. However, it should be emphasized that during the 3-Tier pilot the screening tools were applied to drivers of all ages. Results There were two main findings. First, there were no consistent, statistically significant differences between the pilot and control groups in crash risk in the two years following screening. Second, pilot participants experienced statistically significant effects on mobility. These effects included delays in time to complete their license renewal, an increase in the number of assigned license restrictions, and an increase in the number of customers failing to renew their driving privilege. Conclusions Based on these findings, suggestions for further research are made. Impact on industry None. © 2013 National Safety Council and Elsevier Ltd. All rights reserved.

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