车钩改进与互换的管理

在美国,车钩几乎是铁路装备中既要受美国联邦铁路管理委员会管理,又要受美国铁路协会监督的仅有部件,要求各制造商生产的车钩必须具有良好的互换性。这一要求适用于车钩的几乎每一单件,即钩舌、钩锁和钩体。机、货车的可靠连接完全取决于整个车钩的互换性。这一要求使得ABC     

正确认识牵引杆的选择

介绍了无间隙牵引杆和关节连接器在北美货车联运中的运用情况，比较分析了其与常规车钩缓冲装置运用上的互换性和可维修性，同时阐述了牵引杆的结构特点和性能特征。     

车辆用缓冲装置

介绍了近10年来缓冲装置的发展情况,以及几个供货商研究开发的车钩缓冲装置。     

下一代新型货车

介绍了美国几家主要货车制造商开发的新型有盖漏斗车、双层棚车、大载重平车、铝合金煤炭漏斗车、双层汽车运输车、冷藏车和可交换车体货车等车型的主要特点和结构参数,其共同目标是延长车辆寿命、减轻车辆自重、提高有效运载能力.     

Assessing economic activity in coastal areas: A shift‐share approach

Abstract

An essential aspect of economic analysis associated with planning efforts is identifying the composition of existing economic activity and understanding historical trends in economic change. The shift‐share model is a useful and inexpensive tool for this purpose. Shift‐share analysis evaluates changes in local economic activities relative to changes in a reference area (usually the state or nation). Economic change is separated into a reference area component, an industry mix component, and a local share component. These measure, respectively, the effect on the local economy due to changes in the reference area, factors specific to the local mix of industries, and the changing competitive position of the local area relative to the reference area.

A shift‐share analysis of Florida's coastal counties reveals that all grew much faster over the 1965–1975 period than did the national economy. This rapid growth is primarily a result of a net shift of economic activity toward the study area relative to the nation. However, a few coastal counties did exhibit a mix of slow‐growing industries. Specific industry results for Florida counties at the eighty‐industry level reveal that many industries showed significant shifts toward Florida's coastal counties. The performance of individual industries in the coastal counties generally exceeded that of the same industries in noncoastal counties.     

Federal consistency and state expectations

Abstract

The requirement in the Coastal Zone Management Act of 1972 that federal projects be consistent with approved state coastal zone management programs is an important incentive for states to complete their programs. As a condition of program approval, states must first consult with the federal agencies concerned and provide opportunities for comment, with the hope of avoiding conflicts. The consistency requirement is also subject to various exceptions whose scope remains to be determined. One such exception of uncertain extent is the exclusion from the coastal zone of federal lands “the use of which is subject solely to the sole discretion ... of the Federal Government....”; Despite these uncertainties, however, the consistency provision represents a major change in federal policy, which has traditionally allowed federal agencies to operate largely without concern for state land or water use requirements.     

Tragedy of the San Francisco bay commons

Abstract

Although the early efforts to save San Francisco Bay in the 1960's provided the role model for protection of California's 1100 mile ocean coastline, neither Proposition 20 of 1972 nor the California Coastal Act of 1976 provided any benefits to San Francisco Bay. One result is that the Bay is locked into its urban, shoreline‐use dominated plan of 1969 while every other estuary and coastal wetland in California receives much stronger protection of its resources. Furthermore, due to the complexity of California's water laws, there is no instream flow protection for receiving waters such as San Francisco Bay. This is particularly critical considering that 70% of the Bay's freshwater inflow has been diverted. The Bay's present decline as the largest and most important estuary on the West Coast, as well as its possible death as an estuary, may be irreversible. The problem requires the immediate attention of engineering, scientific, economic and legal disciplines if San Francisco Bay is to be saved.     

Determining the optimal number of seasonal adjustment factor groupings when estimating annual average daily traffic and investigating their characteristics

Although cluster analysis is recommended by the US Traffic Monitoring Guide (TMG) to supplement the development of seasonal adjustment factor groupings (SAFGs), the relationships among SAFGs' characteristics remain undiscovered, while the determination of the optimal number of clusters is an ambiguous task exposed to great subjectivity. Statistical indicators provide a mathematical solution by removing engineering judgment without taking into consideration any guidelines or other criteria, necessary for transportation planners to generate ‘practical and sensible’ groupings. The method examined in this study aims to overcome the above weaknesses incorporating into the methodology a series of statistics, recommendations, and previous research findings. The investigation of the relationships among (1) the within-group variation, (2) the total number of sites, (3) the minimum number of stations within a cluster, (4) the optimal number of clusters, and (5) the geographical size of the groups constitutes the main objectives of this research. According to the results, the cluster variability declines as the available number of stations increases. When the minimum number of stations within a cluster increases, the weighted coefficient of variation inflates as well, with the rate of increase depending on sample size. The average number of automatic traffic recorders per cluster is analogous to the sample size, while the optimal number of clusters varies conversely with the minimum number of stations within a cluster. The application developed for the conduct of the analysis minimizes the computational time needed, while it can be easily implemented by engineers to automate the process recommended by the TMG, enhancing the current state of practice.