Study on convection and dispersion characteristics of dense gases in urban environment considering trees

Although several studies on the dispersion of heavy toxic gas released from ruptured tanks on vehicles during transportation have considered complex terrain such as urban buildings, the influence of trees on the flow field in urban areas during gas dispersion tends to be ignored. In this study, a Computational Fluid Dynamics (CFD) model was proposed to investigate the characteristics of gas release and dispersion from loaded vehicle in the urban environment. In this model, the tree crown was treated as a porous medium, and the influence of drag due to the crown was incorporated into the model by a momentum source term through a user-defined function. In this study, the dynamic characteristics of chlorine (Cl₂) dispersion under the conditions of building distribution, tree species and porosities were comprehensively analysed, to cover the influence of urban complexity, leaf density, and tree planting configuration. The results show that compared with flat terrain, the presence of urban buildings will prolong the dense gas retention time and increase the dangerous distance. It is found that the horizontal dispersion distance can increase by 63% and the isosurface of 25 ppm hazardous gas can increase by 130% with the introduction of buildings. Compared with the terrain with only buildings, the introduction of arbors or shrubs can result in a 147% or 359% increase in the maximum concentration. Also, trees will prolong the dispersion duration. It is also found that the higher the porosity, the less the wind blocking effect, and the weaker the ability of capturing gas. The wind field affected by arbores and shrubs are different in height, and arbores capture more Cl₂. Planting short shrubs around buildings can effectively reduce the spread of harmful gases.     

简易升降类机械式停车设备安全隐患探析

随着人们生活水平的提高,单个家庭购买多部汽车的情况在逐年增加,停车位一位难求的矛盾比较突出。住宅小区家庭用户购买的单个平面停车位向立体2个停车位拓展情况成为趋势。本文从防载车板坠落装置设置、同步检测装置、载车板升降过程中视线盲区三个方面分析其安全隐患,并有针对性地提出一些建议,旨在减少简易升降类机械式停车设备的安全隐患提供有益帮助。     

Geo-spatial and log-linear analysis of pedestrian and bicyclist crashes involving school-aged children

PROBLEM: There is a growing concern with the safety of school-aged children. This study identifies the locations of pedestrian/bicyclist crashes involving school-aged children and examines the conditions when these crashes are more likely to occur. METHOD: The 5-year records of crashes in Orange County, Florida where school-aged children were involved were used. The spatial distribution of these crashes was investigated using the Geographic Information Systems (GIS) and the likelihoods of crash occurrence under different conditions were estimated using log-linear models. RESULTS: A majority of school-aged children crashes occurred in the areas near schools. Although elementary school children were generally very involved, middle and high school children were more involved in crashes, particularly on high-speed multi-lane roadways. Driver's age, gender, and alcohol use, pedestrian's/bicyclist's age, number of lanes, median type, speed limits, and speed ratio were also found to be correlated with the frequency of crashes. DISCUSSION: The result confirms that school-aged children are exposed to high crash risk near schools. High crash involvement of middle and high school children reflects that middle and high schools tend to be located near multi-lane high-speed roads. IMPACT ON INDUSTRY: The pedestrian's/bicyclist's demographic factors and geometric characteristics of the roads adjacent to schools associated with school children's crash involvement are of interest to school districts.     

Graduated driver licensing: review of evaluation results since 2002

Unintentional injury from motor-vehicle crashes is the number one cause of death among teenagers in the United States. Increasingly, jurisdictions have adopted three-stage graduated driver licensing (GDL) systems for young novice drivers. Since a previous review of U.S. GDL evaluation results, many more U.S. states and Canadian provinces have implemented GDL and/or had enough time pass that additional evaluation results are now available. Twenty-one studies of GDL within 14 individual jurisdictions, and six studies of GDL in the U.S. nationwide, were collected, reviewed, and summarized. Positive results (usually crash reductions) of varying degrees were reported from nearly all the studies. Given differences in approaches, study goals, methods, and analyses, the results are surprisingly consistent. Overall, GDL programs have reduced the youngest drivers' crash risk by roughly 20 to 40%. Research on teen driving and comprehensive GDL enhancements could further reduce teen drivers' motor-vehicle crashes, injuries, and fatalities. IMPACT ON INDUSTRY: Policy-makers, as well as the motor vehicle, insurance, and other industries have been involved in teen driving safety and could enhance and coordinate their roles.     

Reducing emissions from in-use vehicles: an evaluation of the Phoenix inspection and maintenance program using test results and independent emissions measurements

Various federal regulations require states to evaluate the effectiveness of their vehicle inspection and maintenance (I/M) programs in reducing in-use emissions. One method to evaluate program effectiveness is to compare initial and final program test results of individual vehicles. Unscheduled emissions measurements, from remote sensing measurement or roadside pullover testing, can also be used to provide an independent assessment of program effectiveness. We compared emissions reductions from the Arizona IM240 program measured by program data and a large set of remote sensing measurements. Remote sensing measurements indicate smaller emission reductions from the program than those calculated directly from program test results. We discuss some possible causes of the differences obtained from the two sets of measurements.     

Fatal motorcycle crashes in wide urban area of Zagreb,Croatia—A 10-year review

Objective: The objective of our study was to determine the prevalence of alcohol and drug intoxication among fatally injured motorcyclists in a wide urban area of Zagreb, Croatia.

Methods: We conducted a single-center observational retrospective study over a 10-year period (2007–2016) in 3 counties covering an area including 1.2 million residents. We reviewed the records on fatally injured motorcyclists, collecting information relating to sex, age, cause of death, time of death in relation to the time of the crash, and the circumstances of the crash (time of day, day of the week, season). Blood alcohol concentration (BAC) and toxicology analysis results were collected and analyzed.

Results: We identified 163 deaths (95.7% males, 4.3% females). Overall, 64.2% of the victims were 20 to 39 years old. The majority (50.9%) of those fatally injured were responsible for causing the traffic crash; the rest were determined not to be responsible or the responsibility could not be determined. The most frequent causes of death were multiple injuries (55.8%) and isolated head trauma (23.3%). The rider’s BAC was above the legal limit for driving (>0.50?g/kg) in 53.8% of cases, with a mean BAC of 1.91?g/kg. There was no difference in riding a motorcycle with a BAC above the legal limit between groups defined as younger (≤39 years of age) and older (≥40 years of age). The number of people with an illegal BAC was significantly higher during weekends than during the work week. The BAC of riders who were responsible for the crash was significantly higher than that of those who were not responsible or whose responsibility could not be determined. Use of illegal drugs or nontherapeutic use of legal drugs was not common and was detected in 10.4% of fatally injured riders.

Conclusions: Alcohol intoxication has a major role in motorcycle crash–related mortality. A significant difference in BAC between fatally injured riders responsible for the accident and those who were not responsible implies that measures directed toward prevention of drinking and driving behavior could lower the number of fatal motorcycle crashes. Weekend measures, especially during spring and summer, could have particularly significant effects.     

不同类型机动车尾气中芳香烃化合物含量分析

首次对北京市9种车辆、5种燃料在不同工况下排放芳香烃化合物的特征．进行了定量研究。结果表明,车型、燃料、净化器及工况等因素对排放量产生影响,电喷车比化油器车芳香烃化合物排放量低;汽油车排放量最高,柴油车其次,LPG及CNG车排放量最低;使用净化器可以降低芳香烃排放量;不同工况对排放量的影响随车型,燃料类型的不同而不同。     

汽车内微环境空气污染的初步探究

为了研究车内的污染水平,在2004-04-10至2004-06-20对车内空气进行了采样和分析.对车龄在2年内的91种型号轿车的车内微环境进行了静态检测,有效检测车辆共计802辆,同时对比检测20辆2002年以前出厂的旧车.检测项目包括甲醛、苯、甲苯、二甲苯和CO等.参照国家室内空气质量标准,新车中甲苯浓度超标率达82%,苯和甲醛浓度的超标率分别为75%和24%.在被检测车辆中,甲醛、苯、甲苯和二甲苯浓度均是新车比旧车高,只有CO浓度是旧车比新车高.初步分析判断苯系物主要来源于车内的胶粘剂,甲醛来自于车椅座套和座垫等,CO来源于发动机排放残留.     

Determination of VOC source signature of vehicle exhaust in a traffic tunnel

This study describes the methodology used to obtain the volatile organic compound (VOC) source signature of vehicle exhaust. To accomplish this, C(2)-C(9) VOCs were measured in a traffic tunnel located in Seoul, South Korea. The effect of VOC concentrations from the outside ambient air was considered in the determination of the source signature. To examine the effects of ambient air on VOC concentrations inside the tunnel, the ratio of propane to the total VOC concentrations was compared between the entrance and middle sites in the tunnel. Propane was used as a standard not only because of its insignificant contribution to vehicle exhaust gas, but also the fact that propane is the most abundant VOC in the atmosphere of Seoul. The ratio of propane to the total VOC concentrations was higher at the entrance site than at the middle location by, on average, 60%. This suggests that ambient air affects the inside tunnel air to a greater extent at the entrance site as compared to the middle site. The contribution of ambient air to the air inside the tunnel at the entrance location varied from 30% to 67%, with an average of 55%. This is 1.5 times higher than the value measured at the middle location, which ranged from 20% to 48%, with an average of 36%. This shows that ambient air substantially affects the inside air of the tunnel. Excluding the effects of ambient air on the air inside the tunnel can provide an improved chemical composition for vehicle exhaust using tunnel measurements. We believe that the concentration difference between the two sites within the tunnel provides a more accurate chemical composition of vehicle exhaust as compared to that obtained from a measurement taken at only one point inside the tunnel.     

Does time of day matter at highway work zone crashes?

Introduction: It is widely agreed that highway work zones pose significant threats to road users because driving conditions in work zones are quite different from the normal ones, particularly when traffic volumes approach a highway capacity. Therefore, work zone safety is a critical aspect for state agencies and traffic engineers. Method: In the current study, a total of 10,218 crashes that occurred in highway work zones in the state of Washington for the period between 2007 and 2013 were used. Time of day is disaggregated into four subgroups: (1) Morning from 6:00 to 11:00 a.m. (2) Midday from 12:00 to 5:00 p.m. (3) Night from 6:00 to 11:00 p.m., and (4) Late night from 12:00 to 5:00 a.m. Then, four mixed logit models were estimated to account and correct for heterogeneity in the crash data by considering three injury severity levels: severe injury, minor injury, and no injury. Results: The estimation results reveal that most contributing factors are uniquely significant in a specific time of day period, whereas three factors affect injury severity regardless of time of day such as the indicators of not deployed airbag, one passenger vehicle involved in the crash, and rear-end collision. Further, some factors were found to affect injury severity into two or three time periods, such as female drivers that found to decrease the probability of no injury in morning and night time periods, while increasing severe injury outcome in midday time. Conclusions: The effect of time of day on injury severity of work-zone related crashes should be modeled separately rather than using a holistic model. Practical applications: As a starting point, findings of the current study can be used by transportation officials to reduce fatalities and injuries of work zone crashes by identifying factors that uniquely contribute to each time of day period.