Flammability of hydrocarbon and carbon dioxide mixtures

The effect of carbon dioxide (CO₂) concentration on the ignition behaviour of hydrocarbon and CO₂ gas mixtures is examined in both jets and confined explosions. Results from explosion tests are presented using a 20 l explosion sphere and an 8 m long section of 1.04 m diameter pipeline. Experiments to assess the flame stability and ignition probability in free-jets are reported for a range of different release velocities. An empirically-based flammability factor model for free-jets is also presented and results are compared to ignition probability measurements previously reported in the literature and those resulting from the present tests.The results help to understand how CO₂ changes the severity of fires and explosions resulting from hydrocarbon releases. They also demonstrate that it is possible to ignite gas mixtures when the mean concentration is outside the flammable range. This information may be useful for risk assessments of offshore platforms involved in carbon sequestration or enhanced oil recovery, or in assessing the hazards posed by poorly-inerted hydrocarbon processing plant.     

Artificial neural network modelling of As(III) removal from water by novel hybrid material

The present study reported a method for removal of As(III) from water solution by a novel hybrid material (Ce-HAHCl). The hybrid material was synthesized by sol–gel method and was characterized by XRD, FTIR, SEM–EDS and TGA–DTA. Batch adsorption experiments were conducted as a function of different variables like adsorbent dose, pH, contact time, agitation speed, initial concentration and temperature. The experimental studies revealed that maximum removal percentage is 98.85 at optimum condition: pH = 5.0, agitation speed = 180 rpm, temperature = 60 °C and contact time = 80 min using 9 g L⁻¹ of adsorbent dose for initial As(III) concentration of 10 mg L⁻¹. Using adsorbent dose of 10 g L⁻¹, the maximum removal percentage remains same with initial As(III) concentration of 25 mg L⁻¹ (or 50 mg L⁻¹). The maximum adsorption capacity of the material is found to be 182.6 mg g⁻¹. Subsequently, the experimental results are used for developing a valid model based on back propagation (BP) learning algorithm with artificial neural networking (BP-ANN) for prediction of removal efficiency. The adequacy of the model (BP-ANN) is checked by value of the absolute relative percentage error (0.293) and correlation coefficient (R² = 0.975). Comparison of experimental and predictive model results show that the model can predict the adsorption efficiency with acceptable accuracy.     

Electrostatic ignition of sensitive flammable mixtures: Is charge generation due to bubble bursting in aqueous solutions a credible hazard?

Experiments have been conducted to gain insight into the credibility of sparging aqueous solutions as an electrostatic ignition hazard for sensitive hydrogen/air or fuel/oxygen mixtures (Minimum Ignition Energies of ∼0.017 mJ and ∼0.002 mJ, respectively, compared to ∼0.25 mJ for hydrocarbon/air mixtures). Tests performed in a 0.5 m³ ullage produced electric field strengths between 125 and 560 V m⁻¹ for air flows of 5–60 l min⁻¹, respectively, comprised of 2–4 mm diameter bubbles. Field strength can be related to the space charge and fitting to an exponential accumulation curve enabled the charge generation rate from the air flows to be estimated. This was observed to be directly proportional to the air flow and its magnitude was consistent with literature data for bubble bursts. The charge accumulation observed at laboratory scale would not be a cause for concern. On the basis of a simple model, the charge accumulation in a 27 m³ ullage was predicted for a range of air flows. It is apparent from such calculations that ignition of hydrocarbon/air mixtures would not be expected. However, it would seem possible that field strengths might be sufficient to cause a risk of incendive spark or corona discharges in moderately sized vessels with sensitive flammable mixtures.     

Pb(II) adsorption from aqueous solutions by raw and treated biomass of maize stover – A comparative study

The potential to remove Pb(II) ion from wastewater treatment systems using raw and treated maize stover through adsorption was investigated in batch experiments. To achieve this, batch mode experiments were conducted choosing specific parameters such as pH (2–8), dosage concentration (2–30 g L⁻¹), contact time (5–180 min), temperature (20–45 °C) and metal ion concentrations (10–50 mg L⁻¹). Adsorption was pH-dependent showing a maximum at pH value 5. The equilibrium sorption capacities of raw and treated maize stover were 19.65 and 27.10 mg g⁻¹, respectively. The adsorption data fitted well to the Langmuir isotherm model. Kinetic studies revealed that the adsorption process followed pseudo-second-order model. The calculated thermodynamic parameters showed that the adsorption of Pb(II) was spontaneous and exothermic in nature. Consequently, this study demonstrated that both raw and treated maize stover could be used as adsorbents for the treatment of Pb(II) from industrial wastewaters.     

Anaerobic digestion modeling of the main components of organic fraction of municipal solid waste

The organic fraction of municipal solid waste (OFMSW) is composed of several heterogeneous organic and inorganic wastes. The diversity of composition, the high volatile solid content and the biodegradable material that this waste offers make it quite an interesting option for anaerobic digestion (AD). Depending on the substrate composition, the biological degradation and kinetics of the AD could vary. Biochemical methane potential (BMP) tests are used as a tool to evaluate the methane production of several fractions of OFMSW, in order to study the influence of each fraction in the final mixture. The kinetic parameters of methane curves and the prediction of final productions are studied by different approaches to model equations using linear, exponential, logistic and Gaussian models. The analyses of the fractions indicate that organic substrates such as meat/fish which are in a small proportion in the final mixture, obtain major productivities (291 ± 3 mlCH₄/gVS), however others such as paper (217 ± 5 mlCH₄/gVS) could have their productivity enhanced due to their high VS present in the final mixture. Both the Gomperzt and the first order model fit reasonably with all the fractions, although substrates with lag phase adjust only to the Gompertz model explaining 99% of the experimental results.     

Stochastic modeling of accident risks associated with an underground coal mine in Turkey

In this study, a methodology is proposed towards development of an uncertainty model that includes randomness in the occurrence of days-lost accidents in a coal mine. The accident/injury data consists of 1390 days-lost accident cases recorded at GLI-Tuncbilek underground lignite mine from January 1994 to December 2002. In the first step of proposed methodology, the frequency and the severity of the accidents have been modeled statistically by fitting appropriate distributions. The test done by BestFit software yields a chi-square value of 21.53 (p = 0.089) with 14 degrees of freedom and estimates the parameter of lambda for Poisson distribution as 12.87 accidents/month. For the severity component, a lognormal distribution is fitted to days-lost data and chi-square goodness-of-fit test calculates a value of 40.44 (p = 0.097) with 30 degrees of freedom. The parameters of lognormal distribution are estimated as a mean of 14.3 days and standard deviation of 23.1 days, respectively. Then, two distributions are basically combined by Monte Carlo simulation in order to construct relative risk levels in yearly base referring to the final cumulative distribution. Finally, a simple forecasting modeling is carried out in order to quantitatively predict the expected risk levels by using decomposition technique in time series analysis. Stochastic model estimates that although, there would be substantial reduction in the expected number of accidents in the near future, the higher level of risks still should be a concern for the mine management.     

Degradation of Rhodamine B by an electrochemical ozone generating system consist of a Ti anode coated with nanocomposite of Sn–Sb–Ni oxide

An ozonation process was performed using a recycled electrochemical ozone generator system. A titanium based electrode, coated with nanocomposite of Sn–Sb–Ni was applied as anode in a laboratory-made electrochemical reactor. A constant flow rate of 192 mg/h of generated ozone was entered to an ozonation reactor to contact with a typical target pollutant, i.e., Rhodamine B (Rh.B) molecules in aqueous solution. Four operational parameters such as: initial dye concentration, pH, temperature and the contact time were evaluated for the ozonation process. Experimental findings revealed that for a solution of 8 mg/L of the dye, the degradation efficiency could reach to 99.5% after 30 min at pH 3.7 and temperature of 45 °C as the optimum conditions. Kinetic studies showed that a second order equation can describe the ozonation adequately well under different temperatures. Also, considering to the importance of process simulation, a three-layered feed forward back propagation artificial neural network model was developed. Sensitivity analysis indicated order of the operational parameter's relative importance on the model output as: time ≫ pH > Rh . B initial concentration > temperature.     

Examining teen driver crashes and the prevalence of distraction: Recent trends, 2007–2015

IntroductionTeen drivers crash at a much higher rate than adult drivers, with distractions found as a factor in nearly 6 out of 10 moderate-to-severe teen crashes. As the driving environment continues to rapidly evolve, it is important to examine the effect these changes may be having on our youngest and most vulnerable drivers.MethodThe purpose of this study was to identify types of vehicle crashes teens are most frequently involved in, as well as the distracting activities being engaged in leading up to these crashes, with a focus on identifying changes or trends over time. We examined 2,229 naturalistic driving videos involving drivers ages 16–19. These videos captured crashes occurring between 2007 and 2015. The data of interest for this study included crash type, behaviors drivers engaged in leading up to the collision, total duration of time the driver's eyes were off the forward roadway, and duration of the longest glance away from forward.ResultsRear-end crashes increased significantly (annual % change = 3.23 [2.40–4.05]), corresponding with national data trends. Among cell phone related crashes, a significant shift occurred, from talking/listening to operating/looking (annual % change = 4.22 [1.15–7.29]). Among rear-end crashes, there was an increase in the time drivers' eyes were off the road (β = 0.1527, P = 0.0004) and durations of longest glances away (β = 0.1020, P = 0.0014).ConclusionsFindings suggest that shifts in the way cell phones are being used, from talking/listening to operating/looking, may be a cause of the increasing number of rear-end crashes for teen drivers.Practical applicationsUnderstanding the role that cell phone use plays in teen driver crashes is extremely important. Knowing how and when teens are engaging in this behavior is the only way effective technologies can be developed for mitigating these crashes.     

Nursing student evaluation of NIOSH workplace violence prevention for nurses online course

Introduction: As primary targets of workplace violence in health care settings, nurses may suffer negative physical and psychological consequences. NIOSH created an online course to educate nurses about violence prevention techniques. Method: A mixed-methods approach assessed workplace violence awareness and knowledge among nursing students. A pre/post/post-test survey and focus group discussions evaluated participant awareness and knowledge, assessed course design, and solicited recommendations for increasing participation and strategies for improving message retention. Results: The mean awareness scores differed significantly between pre-course and both post-course time points (Wilk's λ = 0.319, F(2, 46) = 49.01, p < 0.001). Post hoc tests using the Bonferroni correction revealed that course participation increased awareness of workplace violence from pre-course scores (M = 0.75, SD = 0.438) to immediate post-course (M = 2.13, SD = 0.789) and four-week post-course (M = 1.96, SD = 0.771) scores on a 3-item measure. Similarly, mean knowledge scores increased between pre-course and both post-course time points (Wilk's λ = 0.495, F(1.57, 73.66) = 37.26, p < 0.001). Post hoc tests using the Bonferroni correction revealed that course participation increased knowledge of workplace violence from pre-course scores (M = 6.65, SD = 1.45) to immediate post-course (M = 8.56, SD = 1.32) and four-week post-course (M = 8.19, SD = 1.42) scores on a 10-item measure. Qualitative data from the focus groups reinforced the quantitative findings. Participants citing benefits from the content strongly recommended including the course in nursing curriculums. Incorporating the course early in the nursing educational experience will better prepare students to deal with workplace violence when they enter health care professions. Conclusions: The results indicate that NIOSH and its partners created an effective online workplace violence awareness and prevention course. Practical applications: Nursing students and professionals can be effectively educated about workplace violence using an online format.     

Comparison studies of adsorption properties of MgO nanoparticles and ZnO–MgO nanocomposites for linezolid antibiotic removal from aqueous solution using response surface methodology

In this investigation, the adsorption measure of linezolid antibiotic onto MgO nanoparticles and ZnO–MgO nanocomposites were performed. The adsorbents were characterized by different techniques such as XRD, SEM, TEM and BET. The parameters influence such as the pH, adsorbent dosage and temperature was tested and evaluated by Box–Behnken Design combined with response surface methodology. Performing adsorption tests at optimal conditions set as 0.5 g L⁻¹ of adsorbent, pH 10 and 308 K make admit to obtain high adsorption turnover (123.45 and 140.28 mg g⁻¹ for MgO nanoparticles and ZnO–MgO nanocomposites, respectively). A good compromise between predicted and experimental data in this research was observed. The experimental equilibrium data fitting to Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich models indicate that the Langmuir model is a best model for evaluation of adsorption behavior. Kinetic evaluation of experimental data indicated that the adsorption operations followed well pseudo-second-order models. The adsorption capacity of ZnO–MgO nanocomposites is higher than MgO nanoparticles that because of the ZnO–MgO nanocomposites have high specific surface area.     

School transportation mode,by distance between home and school,United States,ConsumerStyles 2012

IntroductionMotor-vehicle crashes are a leading cause of death among children in the United States, and almost one-fourth of all trips by school-aged children are trips to and from school. This study sought to determine how children (5–18 years) travel to and from school and, among those living ≤ 1 mile of school, to explore the role of school bus service eligibility on school travel mode.MethodsWe used national 2012 survey data to determine prevalence of usual school travel mode, stratified by distance from school. For those living ≤ 1 mile of school, multivariable regression was conducted to assess the association between bus service eligibility and walking or bicycling.ResultsAlmost half (46.6%) of all children rode in passenger vehicles (PV) to school and 41.8% did so for the trip home. Results were similar among those living ≤ 1 mile (48.1%, PV to school; 41.3%, PV to home). Among those living ≤ 1 mile, 21.9% and 28.4% of children walked or bicycled to and from school, respectively. Ineligibility for school bus service was strongly associated with walking or bicycling to school [adjusted prevalence ratio (aPR: 5.36; p < 0.001)] and from school (aPR: 5.36; p < 0.001).ConclusionsRegardless of distance from school, passenger vehicles were a common mode of travel. For children who live close to school, the role that school bus service eligibility plays in walking or bicycling deserves further consideration.Practical applicationsGiven the large proportion of children who use passenger vehicles for school travel, effective interventions can be adopted to increase proper child restraint and seat belt use and reduce crash risks among teen drivers. Better understanding of conditions under which bus service is offered to children who live close to school could inform efforts to improve pedestrian and bicyclist safety for school travel.     

Removal of a cationic bisbiguanide using Functionalized Activated Carbons (FACs)

Functionalized Granular Activated Carbons (FACs) are used as adsorbents for treating pharmaceutical wastewaters containing Chlorhexidine Gluconate. Chemical modifications of Granular Activated Carbons (GACs) using functionalizing agents like HCl and HF produce FACs. The adsorption capacity of each of FAC-HCl and FAC-HF is found to be higher than GAC. The modelled maximum adsorption capacity for FAC-HCl is 1.02 g/g of adsorbent, 3.49 g/g of adsorbent for FAC-HF and 0.0682 g/g of adsorbent for GAC. This is mainly due to the additional chemisorptions by surface complexation at the functionalized surface sites of the modified GACs. This is also supported by the well-known pseudo-second-order kinetic model. Formation of surface complexes with the functional groups and weakly polar Chlorhexidine Gluconate is well supported by the physical characterization using Energy dispersive X-ray spectroscopy (EDAX), Brunner–Emmett–Teller (BET) test and Fourier Transform Infrared spectroscopy (FTIR) analysis after adsorption. The adsorption capacity of GAC and the FACs increases in the order of FAC-HF > FAC-HCl > GAC conforming to the proportion of the total acidity of the carbon surfaces. Intra-particle diffusion is not the sole rate-controlling factor. An agreement to pseudo-second-order kinetic model, Elovich kinetic model and Boyd's film diffusion model proves that chemisorption is the rate-controlling parameter in this adsorption study.     

Characterization of fall patients: Does age matter?

IntroductionEvaluating age-specific fall characteristics is important for prevention programs. The aim was to characterize fallers who presented to our trauma center. We hypothesized that fall characteristics and outcomes would vary with age.MethodsData were retrospectively collected from the trauma registry and electronic medical records during January 1st, 2014-December 31st, 2015. Data were analyzed by Chi-square test with Yates’ continuity correction and one-way ANOVA with Bonferroni’s multiple comparisons test.ResultsThere were 1541 fallers, 814 (52.8%) were male. Ages ranged from 11 months to 100 years. The admission rate was high at 86%, with an average hospital stay of 5.7 days. Patients in the 0-18 and 19-45 age groups spent significantly less time in the hospital (p < 0.0001). Elderly patients had the highest average injury severity score (p < 0.0001). However, the youngest patients required surgery more often (p = 0.0004). The overall mortality rate was 3.6% and 52.8% were male. The mortality rate increased with age, from 0% for the 0-18 age group to 6.9% for patients ≥ 65 years of age. Remarkably, fallers in the 19-45 and 46-64 age groups predominantly died from ground level falls even though the average fall height in these groups was the highest (p < 0.0001). More fallers in the 19-45 and 46-64 age groups tested positive for alcohol/drug use (p < 0.0001). Middle-aged and elderly patients were more likely to be discharged to a skilled nursing or rehabilitation facility compared to younger patients who were discharged home.Conclusions and practical applicationsFall characteristics and outcomes varied with age. Data on age-specific characteristics, outcomes, and risk factors of falls will help in developing targeted interventions and may lead to better approaches to treat patients.     

Removal mechanism of trace oxytetracycline by aerobic sludge

To investigate the mechanism of removal of selected pharmaceuticals in activated sludge systems, laboratory-scale batch experiments were conducted to assess the adsorption and degradation behavior of trace oxytetracycline (OTC). The adsorption equilibrium of OTC was observed in 30 min and the adsorption process could be well described by a pseudo-second-order model with a rate of 0.362 L μg^?1 min^?1. The OTC adsorption rate decreased with increasing temperature and could be fitted by the Freundlich isotherm. The linear partition coefficients (K_d) were 1.19, 0.999, and 0.841 L g^?1 at temperatures of 15, 20, and 25 °C, respectively. Thermodynamic analysis revealed that the adsorption of OTC onto the inactivated sludge was spontaneous (ΔG = ?16.7 to ?17.0 kJ mol^?1), enthalpy-driven (ΔH = ?24.9 kJ mol^?1), entropy-retarded (ΔS = ?27.4 J (mol K)^?1), and predominantly a physical adsorption.     

Investigation on removal of p-nitrophenol using a hybridized photo-thermal activated persulfate process: Central composite design modeling

The aim of this work is the study of p-nitrophenol (PNP) removal, as a nitroaromatic compound, using a hybridized photo-thermally activated potassium persulfate (KPS) in a fully recycled batch reactor. Response surface method was used for modeling the process. Reaction temperature, KPS initial dosage and initial pH of the solution were selected as variables, besides PNP degradation efficiency was selected as the response. ANOVA analysis reveals that a second order polynomial model with F-value of 41.7, p-value of 0.0001 and regression coefficient of 0.95 is able to predict the response. Based on the model, the process optimum conditions were introduced as initial pH of 4.5, [KPS]₀ = 1452 mg/L and T = 66 °C. Also experiments showed that using thermolysis and photolysis of the persulfate simultaneously, the role of thermolysis is not considerable. A pseudo first order kinetic model was established to describe the degradation reaction. Operational cost, as a vital industrial criterion, was estimated so that the condition of initial pH of 4.5, [KPS]₀ = 1452 mg/L and T = 25 °C showed the highest cost effective case. Under the preferred mild condition, the process will reach to 84% and 89% of degradation and mineralization efficiencies, after 60 and 120 min, respectively.     

Assessing the impact of risk-taking behavior on road crash involvement among University students residing in two Mediterranean countries

Surveillance systems are indispensable for injury prevention; yet, detailed electronic records are rarely available. The “Student’s Health Card” is a self-reporting electronic tool addressing health issues of University students, while aiming to actively involve them in preventive practices and health promotion. Utilizing data from the injury prevention related section, this study sought to investigate the impact of risk-taking behavior on road crash involvement among University students residing in two Mediterranean countries. A total of 978 University students, 451 Greek and 527 Italian, provided information on prior road crash involvement, as well as on eight behavioral variables, comprising a risky behavior score. Multiple logistic regression analysis was performed. The already known tendency for clustering of risky behaviors was evident. One degree increment in the risky behavior score was found to increase the risk of road crash involvement by 35%. Driving after drinking (OR = 2.55, CI = 1.53–4.26), riding with a drunk driver (OR = 2.19, CI = 1.08–4.45) and tobacco smoking (OR = 1.95, CI = 1.18–3.22) significantly multiplied the risk. Despite their better compliance with safety measures, Italian students, compared with Greek, reported worse alcohol-related driving habits and engaged more frequently in mobile phone use while driving. Clustering of risky behaviors was found to be an important predictor of road crash involvement. Screening and awareness of risk-taking propensity of University students could guide early intervention. The “Student’s Health Card” could provide, at minimal cost, reliable risk-taking and road crash involvement information, which is needed for both personal risk assessment and surveillance purposes.     

Workers' compensation loss prevention representative contact and risk of lost-time injury in construction policyholders

IntroductionInsurance loss prevention (LP) representatives have access and contact with businesses and employees to provide targeted safety and health resources. Construction firms, especially those smaller in size, are a high-risk population. This research evaluated the association between LP rep contact and risk for lost-time injuries in construction policyholders.MethodsWorkers' compensation data were utilized to track LP rep contact with policyholders and incidence of lost-time injury over time. Survival analysis with repeated events modeling calculated hazard ratios (HR) and 95% confidence intervals (CI).ResultsCompared no LP contact, one contact was associated with a 27% reduction of risk (HR = 0.73, CI = 0.65–0.82), two with a 41% (HR = 0.59, CI = 0.51–0.68), and three or more contacts with a 28% reduction of risk (HR = 0.72, CI = 0.65–0.81).ConclusionsLP reps appear to be a valuable partner in efforts to reduce injury burden. Their presence or contact with policyholders is consistent with reduction in overall incidence of lost-time injuries.Practical applicationsReduction in lost-time injuries, resulting in reduced workers' compensation costs for policyholders and insurance companies, builds a business-case for safety and injury prevention. LP reps are often a low or no-cost benefit for insurance policyholders and may be an important injury prevention resource for small firms and/or those with lack of safety resources and staff.     

Application of Modified Carbon Anodes in Microbial Fuel Cells

The effect of different carbon anodes was examined in a new design of single chambered microbial fuel cell (SCMFC). The new cell design used a low-cost hydrophilic membrane to replace costly proton exchange membranes and carbon felt and a range of carbon and modified carbon anodes were investigated. The fuel for the SCMFC was brewery wastewater which was diluted with domestic wastewater and the presented microflora acts as a source of electro-active bacteria. The membrane acts as a separator between the anode chamber and an air cathode and allows the transfer of ions based on the wastewater's natural conductivity. The air cathode was carbon black (Ketjen Black EC 300J) which was deposited (1 mg cm⁻² concentration) directly onto the surface of the separator (one side of the membrane). Steady state polarization demonstrated maximum power densities of up to 30 mW m⁻² and a steady state power density of 20 mW cm⁻² at a current density of 110 mA m⁻² was achieved. The best performing anodes were made from carbon modified with quinone/quinoid groups. With unmodified graphite felt (the control anode material) as anode, the maximal power density obtained was 9.5 mW m⁻².     

The impact of the 2007 graduated driver licensing law in Massachusetts on the rate of citations and licensing in teenage drivers

ObjectiveWe recently demonstrated that the 2007 Massachusetts Graduated Driving Licensing (GDL) law decreased the rate of motor vehicle crashes in teenage drivers. To better understand this decrease, we sought to examine the law's impact on the issuance of driving licenses and traffic citations to teenage drivers.MethodsCitation and license data were obtained from the Massachusetts Department of Transportation. Census data were obtained from the Census Data Center. Two study periods were defined: pre-GDL (2002–2006) and post-GDL (2007–2012). Two populations were defined: the study population (aged 16–17) and the control population (aged 25–29). The rates of licenses per population were compared pre- vs. post-GDL for the study group. The numbers of total, state, and local citations per population were compared pre- vs. post-GDL for both populations. A sensitivity analysis was performed for the rates of citations using licenses issued as a denominator.ResultsWhile licenses per population obtained by the study group decreased over the entire period, there was no change in the rate of decrease per year pre- vs. post-GDL (2.0% vs. 1.4%; p = 0.6392). In the study population, total, state, and local citations decreased post-GDL (17.8% vs. 8.1%, p < 0.0001; 3.7% vs. 2.2%, p < 0.0001; 14.1% vs. 5.8%, p < 0.0001, respectively). In the control group, total and state citations did not change (26.7% vs. 23.9%, p = 0.3606; 9.2% vs. 10.2%, p = 0.3404, respectively), and local citations decreased (17.5% vs. 13.7%, p = 0.0389). The rates of decrease per year for total, state, and local citations were significantly greater in the study population compared with control (p < 0.0001, p = 0.0002, p < 0.0001, respectively).ConclusionsThe 2007 GDL law in Massachusetts was associated with fewer traffic citations without a change in the rate of licenses issued to teenagers. These findings suggest that 2007 GDL may be improving driving habits as opposed to motivating teenagers to delay the issuing of licenses.