Do parking requirements significantly increase the area dedicated to parking? A test of the effect of parking requirements values in Los Angeles County

Minimum parking requirements (MPRs) are the norm for urban and suburban development in the United States (Davidson et al., 2002). The justification for MPRs is that overflow parking will occupy nearby street or off-street parking. Shoup (1999a) and Willson (1995) provide cases where there is reason to believe that parking space requirements have forced parcel developers to place more parking than they would in the absence of parking requirements. However, to our knowledge the existing literature does not test the effect of parking minimums on the amount of lot space devoted to parking beyond a few case studies. This paper tests the hypothesis that MPRs bind for most land uses using data on suburban office, commercial, industrial and retail property sales from Los Angeles County using both direct and indirect approaches. Our indirect test of the effects of parking requirements is similar to the one used by Glaeser and Gyourko (2003). A simple theoretical model shows that the marginal value of additional parking to the sale price of a building should be equal to the cost of land plus the cost of parking construction. We estimate the marginal values of parking and lot area with spatial methods using a large data set from the Los Angeles area non-residential property sales and find that for most of the property types the marginal value of parking is significantly below that of the parcel area. In addition, we directly examine required and supplied parking and find that on average parking supplied is quite close to the required amount.     

高速公路隧道洞口除雪防滑工作

结合京沪高速济莱段,首先分析了高速公路隧道口的特点,其次阐述了冬季隧道口开展除雪防滑的过程和应当注意的安全事项。     

Are Longer and Heavier Vehicles (LHVs) Beneficial for Society? A Cost Benefit Analysis to Evaluate their Potential Implementation in Spain

Abstract

In this paper we carry out a thorough review of the current research related to the benefits and costs arising from the implementation of longer and heavier vehicles (LHVs). From this review we concluded that despite the many studies available, little has been said about the sensitivity of the benefits and costs to the ultimate performance of the key variables related to the evolution of the economy, road transport performance, safety, and so on. In order to fill this gap, we have designed a sensitivity approach based on a cost benefit analysis tool to determine which variables demonstrate the greatest influence on the benefits and costs stemming from the implementation of LHVs. In order to test the methodology, we have used it in an analysis of the Spanish trunk network. The results show that the benefits of LHVs for society are significant. Even in the least favorable scenario, the economic benefits are greater than €3500 million over 15 years, and the environment enhanced as well, for CO₂ emissions are reduced by 2 Million tonnes. Overall we noted how the results are not very sensitive to the evolution of key variables in determining the final outcome. However, we found that the variables that have the greatest affect on the final benefit, such as traffic growth and social discount rate, depend basically on the performance of the overall economy. Moreover, the private cost for haulers seems to be more important in determining the final benefit than externality costs.     

基于卡尔曼滤波法修正的灰色系统理论在桥梁施工控制中的应用

文章运用卡尔曼滤波法修正的灰色系统理论对桥梁悬臂施工过程中出现的节段挠度实测值与设计值不一致的情况进行分析修正,并以某预应力混凝土连续梁结构为工程实例,运用灰色系统控制理论以及卡尔曼滤波法修正的灰色系统理论分别对其进行挠度的预测,结果表明:经过卡尔曼滤波修正的灰色系统理论能够更有效地减小预测值与实测值的偏差,更好地对成桥线形进行控制。     

Toward regional transportation governance: a case study of Greater Vancouver

This paper discusses the evolving institutional structure and governance of transportation planning, policy development and transit delivery within one major North American city-region, the Greater Vancouver area. Various methods of transportation governance are explored from complete independence to full regional integration. The move away from a direct provincial role in transportation management to a greater regional transit authority is discussed and critiqued. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于机器视觉的球笼保持架窗口位置检测方法

介绍了一种基于视觉检测技术的球笼保持架窗口位置在线检测方法.采用具有独特双光源照明的成像系统的同时获取了窗口边缘和基准面的图像信息,以VC++为平台对数字图像信息进行处理和分析,频域高斯滤波完成图像去噪后,采用形态学边缘检测算法获得窗口边缘点和基准点,利用两直线的平行关系开展最小二乘直线拟合确定窗口边缘位置.实际应用证明该系统稳定可靠,检测效率高,具有良好的应用前景.     

Prediction of the dimensional deformation of the addendum and dedendum after the warm shrink fitting process using a correction coefficient

The warm shrink fitting process is generally used to assemble automobile transmission parts (shafts/gears). However, this process causes a deformation in the addendum and dedendum of the gear depending on the fitting interference and gear profile, and this deformation causes additional noise and vibration between the gears. To address these problems, the warm shrink fitting process is analyzed by considering the error in the dimensional deformation of the addendum and dedendum found when comparing the results of a theoretical analysis and finite element analysis (FEA). A correction coefficient that reduces this error is derived through an analysis of the difference in the cross-sectional area between the shapes used for the theoretical analysis and that of the actual gear, and a closed-form equation to predict the dimensional deformation of the addendum and dedendum is proposed. The FEA method is proposed to analyze the thermal-structural-thermal coupled field analysis of the warm shrink fitting process (heating-fitting-cooling process). To verify the closed-form equation using the correction coefficient, measurements are made of actual helical gears used in automobile transmissions. The results are in good agreement with those given by the closed-form equation.     

Major sources of hydrocarbon emissions in a premixed charge compression ignition engine

Although premixed charge compression ignition (PCCI) combustion engines are praised for potentially high efficiency and clean exhaust, experimental engines built to date emit more hydrocarbons (HCs) and carbon monoxide (CO) than the conventional machines. These compounds are not only strictly controlled components of the exhaust gas of road vehicles but are also an energy loss indicator. The prime objective of this study was to investigate the major sources of the HCs formed in the combustion chamber of an experimental PCCI engine in order to suggest some effective technologies for HC reduction. In this study, to explore the dominant sources of HC emissions in both operation modes, a single cylinder engine was prepared such that it could operate using either conventional diesel combustion or PCCI combustion. Specifically, the contributions of the top-ring crevice volume in the combustion chamber and the bulk quenching of the lean mixture were investigated. To understand the influence of the shape and magnitude of the crevice on HC emissions, the engine was operated with 12 specially prepared pistons with different top-ring crevices installed one after another. The engine emitted proportionally more HCs as the depth of the crevice increased as long as the width remained narrower than the prevailing quench distance. The top-ring-crevice-originated exhaust HCs comprised approximately 31% of the total HC emissions in the baseline condition. In a series of tests to estimate the effects of bulk quench on exhaust HC emissions, intake air was heated from 300K to 400K in steps of 25K. With the intake air heated, HC and CO emissions decreased with a gradually diminishing rate to zero at 375K. In conclusion, the most dominant sources of HC emissions in PCCI engines were the crevice volumes in the combustion chamber and the bulk quenching of the lean mixtures. The key methods for reducing HC emissions in PCCI engines are minimizing crevice volume in the combustion chamber and maximizing intake air temperature allowed based on the permissible NOx level.     

刚性索自锚式悬索桥主缆锚固区局部应力分析

以平顶山建设路立交桥——刚性索自锚式悬索桥为工程实例,分别运用有限元计算程序Midas/Civil和Ansys建立其整体计算模型和边跨主缆锚固区梁段的局部计算模型,对锚固区进行空间局部应力分析,研究其受力状态,得出结论:箱梁绝大部分位置的应力均在规范允许范围内,且主梁压应力储备充足;箱梁主梁梁段切开截面端与顶板交接处的正中心位置顺桥向正应力和最大主拉应力均较大,局部超过规范要求,建议在桥梁设计和施工过程中考虑在边跨顶板中心位置配置压重或顶板纵向预应力钢束,防止箱梁顶板开裂;主缆锚固位置处的最大主压应力较大,锚固位置附近的最大主拉应力超限,需要在锚固位置附近局部加强或改变锚固方式;所有倒角部位在施工时应尽量平顺,避免应力集中。     

Fusion Framework of Urban Traffic Control and Route Guidance Based on CPS Theory

以避免交通拥堵和提高交通效率为目标,同时满足交通用户要求和交通系统交通流均衡要求,对城市交通控制与诱导融合框架进行研究.分析城市交通控制与诱导系统和信息物理融合系统(CPS)的特性及两者关联.探讨CPS理论应用于城市交通控制与诱导系统的各项技术要求.根据动态城市交通流诱导系统和城市交通信号控制系统的内容,针对两者相关性、冲突性与解决方法,考虑信息物理融合系统的人机系统特点,提出一种基于信息物理融合系统理论的城市交通控制与诱导融合框架.该框架包含计算部分、通讯部分、控制部分和物理世界部分,增强了城市交通流诱导系统和城市交通信号控制系统的融合度,侧重从技术层面分析两者深度融合的可行性,为智能交通系统中交通控制与诱导融合的实施提供理论依据.