Caffeine, a central nervous system stimulant, is arguably the most frequently ingested pharmacologically active substance in the world. Occurring naturally in more than 60 plants, including coffee beans, tea leaves, cola nuts, and cocoa pods, caffeine has been part of innumerable cultures for centuries. But the caffeine-in-food landscape is changing. From waffles to sunflower seeds, jelly beans to syrup, and even bottled water, the array of new caffeine-containing energy products, including energy drinks and supplements entering the marketplace, is, in the words of U.S. Food and Drug Administration (FDA) commissioner Margaret Hamburg, truly mind boggling. Years of scientific research have shown that moderate consumption by healthy adults of products containing naturally occurring caffeine is not associated with adverse health effects. But the changing caffeine landscape raises concerns about safety and whether any of these new products might be targeting populations not normally associated with caffeine consumption, namely, children and adolescents, and whether caffeine poses a greater health risk to those populations than it does to healthy adults. At the request of the FDA, on August 56, 2013, the Institute of Medicine (IOM) convened a workshop in Washington, DC, to review the available science on safe levels of caffeine consumption in foods, beverages, and dietary supplements and to identify data gaps. See Box 1-1 for a detailed list of specific workshop objectives. Workshop participants included scientists with expertise in food safety, nutrition, pharmacology, psychology, toxicology, and related disciplines; medical professionals with pediatric and adult patient experience in cardiology, neurology, and psychiatry; public health professionals; food industry representatives; regulatory experts; and consumer advocates.

关键词：咖啡因；中枢神经系统；饮食

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Shared spaces are being implemented in many countries to deal with safety concerns and traffic flow problems on busy urban streets and street crossings. However, shared space concepts could not be tested before they were built because of the lack of a functioning microscopic shared space simulation. Lane-based car-following models, currently used in traffic simulation, cannot reproduce the high heterogeneity of a mixed traffic mode's nonchannelized flow. This paper's novel approach introduces an extended social force model for vehicles and pedestrians that incorporates social interactions between different modes of transport rather than following a purely rule-based approach. The calibration of such a microscopic traffic simulation model with real-world data from two shared space sites is presented. The simulation can reproduce real-life shared space behavior by comparing it with trajectory and interaction data collected at implemented shared space road designs.

关键词：汽车；仿真系统；模拟比较

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Mobility attributes such as driver's license, car ownership, reserved parking at work, and transit pass have a very strong impact on travel choices, in particular, mode choice. Mobility attributes are not acquired for a particular trip but rather are driven by the entire set of individual travel needs (commuting being the most basic of them). Some mobility attributes, for example, car ownership and transit pass, are substitutable; others, for example, car ownership and reserved parking at work, are complementary. For this reason, mobility attributes have to be analyzed and modeled jointly. The purpose of the current research is to analyze a wide set of mobility attributes and incorporate them in an operational activity-based model as a set of midterm choices. The approach suggested in this paper is based on an iterative application of three interlinked choice submodels: (a) joint choice of person driver's license, usual driver role (priority in using one of the household cars), car type choice, reserved or reimbursed parking at work, and transit pass; (b) household car ownership choice by type; and (c) intrahousehold car allocation by type. Model estimation results confirmed strong cross-attribute effects as well as revealed many impacts of person, household, and travel accessibility variables. In particular, historical and cultural differences between three population sectors in Jerusalem-secular Jewish, Orthodox Jewish, and Arab-manifested themselves quite strongly. Application of these models for future scenarios is discussed.

关键词：汽车；设计风格；个性化

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In the past decade, the development and the application of traffic micro-simulation to replicate real-world traffic behavior have become pervasive among traffic and transport researchers. The modeling of a driver's car-following behavior, which forms the fundamental component of traffic microsimulation, has meanwhile been an important research direction leading to the sophistication of traffic microsimulation. However, recent studies have pointed out that a driver's following behavior varies when the lead vehicle is a passenger car as opposed to a heavy vehicle. Nevertheless, existing models do not precisely address those differences. This oversight could diversely affect the accuracy of traffic microsimula-tions, particularly with the current trend of an increasing number of heavy vehicles in the traffic stream. A novel car-following model that considered the heterogeneity of lead vehicles was developed. Two types of lead vehicles were considered in this study: passenger cars and heavy vehicles. The model was developed on the basis of the local linear model tree approach. This approach is able to incorporate human perceptual imperfections into a car-following model. The input space is partitioned incrementally, and a linear model is developed for each locality (partition). The final output is calculated by the fuzzy combination of local models according to the validity function of each model. For training and testing purposes, two real-world data sets were obtained from a U.S. freeway under congested traffic conditions. The results showed very close agreement between the real data and the outputs of the proposed model.

关键词：汽车；车辆类型；模型

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The Netherlands is well known for its large share of bicycle use and for its relatively compact cities; these conditions suggest that transport poverty may be less of a problem than in other developed countries. This paper explores the role of the bicycle in the avoidance of transport poverty on the basis of two exploratory studies. The first study focused on low-income households and showed that the bicycle did curb transport poverty but was of limited importance as a means of access to the labor market. The second study explored the ability of households without cars to maintain social networks. The study findings underlined the importance of the bicycle but also showed that the bicycle was used selectively by elderly residents and was of limited relevance to households with a social network that extended beyond urban borders.

关键词：汽车；自行车；角色

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Transportation accounts for about 33% of total U.S. greenhouse gas emissions. To reduce petroleum consumption, vehicle air pollution, and noise emissions, the hybrid electric vehicle (HEV) was introduced to the U.S. market in 1999 and offered new efficiency-improving technologies. However, the current market share and adoption rate of HEVs are still low. HEV sales are not spatially and temporally uniform. The HEV spatial diffusion process is investigated, and the influence of the neighborhood effect (NE) on HEV adoption is analyzed. A cluster analysis is conducted with Florida add-on data from the 2009 National Household Travel Survey to display the spatial clusters of the households that purchased HEVs from 2005 to 2008. More HEV clusters emerge over time. Geographic patterns demonstrate increasing numbers of clusters featuring households with hybrid vehicles and surrounding HEV adopters. Furthermore, the relationships between hybrid vehicle adoption, NEs, and sociodemographic factors are analyzed with weighted and unweighted binary logit models. NEs are confirmed to be significant in both urban and rural models, especially the factors of 1- and 5-mi neighborhood coverage. This finding indicates that potential buyers are more likely to purchase HEVs when HEV exposure is high in the surrounding areas, and this measurement of exposure is proved reasonable for NEs. Of the sociodemographic attributes, household income is the most significant variable and plays a dominant role in affecting the propensity to buy hybrid vehicles. Factors such as vehicle ownership, household structure, and education attainment level also significantly affect a household's choice to buy a hybrid car.

关键词：汽车；混合动力；噪音

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Rear-end crashes on freeways contribute significantly to nonrecurring congestion. Reducing these events would significantly improve freeway capacity, particularly during peak hours. Although promising coun-termeasures, such as variable speed limits, changeable message signs, and vehicle-based improvements, are under consideration, currently there is a shortage of demonstrably proven countermeasures targeted at freeway rear-end crashes. Liability rules, in which the direct cost associated with a crash is divided between the drivers, their insurance companies, or both, are a primary mechanism for influencing the occurrence of freeway rear-end crashes. An exploratory effort uses concepts from evolutionary game theory to predict the effects of liability rules on rear-end crashes. In a typical two-vehicle car-following scenario, driving behavior can be associated with a utility that each driver expects to achieve depending on his or her and the opponent's actions. Such interactions between leader and follower are modeled as the outcome of an evolutionary process in which drivers with different driving behaviors are randomly and repeatedly matched against each other to play a two-player game. The outcome of these games determines the fraction of drivers pursuing a particular driving strategy for the next phase of the game. The stable long-run distribution of driving strategies is then used to predict the proportion of drivers who are more likely to be involved in a rear-end accident. It turns out that when direct crash costs are allocated evenly to the involved drivers, a population in which all drivers act to avoid crashes is not evolutionarily stable.

关键词：汽车；交通拥挤；博弈论

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The driver-specific data available from naturalistic driving studies provide a unique perspective from which to test and calibrate car-following models. As equipment and data storage costs continue to decline, the collection of data through in situ probe-type vehicles is likely to become more popular, and thus there is a need to assess the feasibility of these data for the modeling of driver car-following behavior. This study focused on the costs and benefits of naturalistic data for use in mobility applications. Any project seeking to use naturalistic data should plan for a complex and potentially costly data reduction process to extract mobility data. A case study was based on data from the database of the 100-Car Study conducted by the Virginia Tech Transportation Institute. One thousand minutes' worth of data comprising more than 2,000 car-following events recorded across eight drivers from a section of multilane highway located near Washington, D.C., was compiled. The collected event data were used to calibrate four different car-following models, and a comparative analysis of model performance was conducted. The results of model calibration are given in tabular format, displayed on the fundamental diagram, and shown with sample event charts of speed versus time and headway versus time. When compared with the Gipps, intelligent driver, and Gaxis-Herman-Rothery models, the Rakha-Pasumarthy-Adjerid model was found to perform best in matching individual drivers and in matching aggregate results.

关键词：汽车；跟车行为；数据建模

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A reluctance to switch to electric vehicles is observed in various countries despite national efforts to promote them. The question of whether electric cars are capable of meeting daily mobility requirements in Germany is investigated. The analysis is based on data from the German Mobility Panel Survey from 1995 to 2010 and the travel survey of 2009 and 2010 for the Stuttgart, Germany, area and combines a long-term travel behavior analysis with a region-specific verification. The focus is on individuals who exclusively drive a car and walk during the day and who rely on the car as a primary means of transport. For this group, the determinants of the decision to drive an internal combustion engine vehicle versus a battery electric vehicle (BEV) are analyzed, with a focus on driving range and energy costs. Results of the analysis suggest that around 80% of all daily travel by car drivers could be done with currently available models of electric cars and that charging them only at night would be sufficient in most cases. Therefore, the driving range of BEVs cannot be the restricting factor. In contrast, the current cost structure of BEVs (high investment cost, low energy cost) is not favorable for the large share of drivers with low annual mileage because the high investment cost is not compensated for by low operation costs. In the Stuttgart region, drivers from the suburbs would benefit most from such energy cost savings; however, city dwellers would need other cost structures or incentives to switch to BEVs.

关键词：大气；旅游；能源

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In recent years, bikeshare systems have spread throughout the United States. Despite the increase in systems and users, little is known about how bikeshare member demographics and travel patterns compare with those of traditional bicyclists. To bridge the gap, this study investigated bikeshare system user travel behavior and developed a profile of user demographics through the comparison of short-term (1 day) users and annual members of Capital Bikeshare (CaBi) in Washington, D.C., with profiles of area bicyclists. Data originated from a Washington, D.C., regional household travel survey of 2007-2008, an intercept survey of short-term CaBi users, and an online survey of annual CaBi members. The analysis compared gender, race and ethnicity, age, and student status, as well as socioeconomic status across the surveys. The comparison included trip purpose, helmet use, and travel modes for trips that were replaced by bikesharing. Profiles of CaBi and area cyclists differed with respect to many demographic and socioeconomic characteristics. Compared with area cyclists, CaBi short-term users and annual members were more likely to be female and younger, to have lower household incomes, and to own fewer cars and fewer bicycles and were more likely to cycle for utilitarian purposes. CaBi trips mainly replaced trips made by public transport and by walking. CaBi short-term users and members shared similar characteristics, but short-term users were more likely to ride for recreational purposes and were less likely to wear a helmet. The study results indicated that bikesharing can encourage new segments of society to cycle and can help increase the bicycling mode share overall.

关键词：大气；自行车；空气保护

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