排序方式: 共有26条查询结果,搜索用时 15 毫秒
21.
Traffic forecasts provide essential input for the appraisal of transport investment projects. However, according to recent
empirical evidence, long-term predictions are subject to high levels of uncertainty. This article quantifies uncertainty in
traffic forecasts for the tolled motorway network in Spain. Uncertainty is quantified in the form of a confidence interval
for the traffic forecast that includes both model uncertainty and input uncertainty. We apply a stochastic simulation process
based on bootstrapping techniques. Furthermore, the article proposes a new methodology to account for capacity constraints
in long-term traffic forecasts. Specifically, we suggest a dynamic model in which the speed of adjustment is related to the
ratio between the actual traffic flow and the maximum capacity of the motorway. As an illustrative example, this methodology
is applied to a specific public policy that consists of suppressing the toll on a certain motorway section before the concession
expires. 相似文献
22.
Lasse Moklegaard Maria Druzhinina Anna Stefanopoulou 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2001,36(2):179-201
A unified engine torque actuator for heavy-duty vehicles is developed in this paper. Based on averaging and identification of the instantaneous torque response for changes in brake valve timing and fuel flow, we derive a control oriented engine model of a six cylinder, 350 Hp turbocharged diesel engine, equipped with a compression brake. This work bridges the gap between the detailed compression crank angle based models developed in the engine design community, and the first order lag representation of diesel engine torque response used in the vehicle dynamics community. Moreover, we integrate the compression brake actuator with the service brakes and design a PI-controller that emulates the driver's actions during long descends on grades. The controller simply uses the engine speed measurement to activate the service brakes only when needed. 相似文献
23.
The aim of the present study is twofold. First, to provide new information concerning the technical characteristics of urban bus companies on the basis of a sample of medium and large-size cities in Spain. Second, to analyze the degree of efficiency of those companies and to quantify the reasons for this efficiency. The results should be useful in evaluating possible changes in public policies relating to urban transport, specifically changes in the way the market is organized and in pricing.The analysis is carried out by estimating a cost function. The sample is made up of a panel data set consisting of observations of nine Spanish companies that operated during the period 1983–1995. The specified functional form is translogarithmic. The output unit of measure adopted is bus*kms run. The cost function includes the network length for each company, thus permitting evidence concerning economies of density and economies of scale.The use of panel data allows us to estimate the cost function, taking into account that each company is affected by the specific characteristics of each individual city, the different features of the network in question and by different levels of efficiency. The economies of scale have been calculated, taking into account that the features of the network and of the city – represented by their specific individual effect – will vary with the company's level of output.Finally, an analysis is made of the relative productive efficiency of the companies, as well as of the variables likely to influence that efficiency. 相似文献
24.
Guido Friebel Sergei Guriev Russell Pittman Elizaveta Shevyakhova Anna Tomová 《运输评论》2013,33(3):251-271
Abstract Railways restructuring takes place under very different circumstances and with very different goals in Western Europe, Central and Eastern Europe, and Russia. There are some improvements in productivity associated with the reforms in the European Union (among others access to infrastructure and vertical separation). But they are not certain to be replicated following similar restructuring in transition economies, especially if one takes account of the much higher shadow price on government subsidies in the latter. The current and proposed reforms in the railways of Central and Eastern Europe and Russia are described in detail; the likely outcomes of reforms in the special economic, regulatory and legal environments of these countries are analysed; and an alternative proposal for restructuring in Russia is presented. 相似文献
25.
Shipping is increasing today along with the sector's emissions of greenhouse gases. The awareness of the emissions has increased the pressure for regulations of the shipping industry. Regulating the sector is far from simple due to the complexity of the market and the evasive characteristics of the industry. We know from studies of road pricing that attitudes among stakeholders are important for a successive policy implementation. The objective of this paper is to capture the Swedish ports’ attitudes towards regulations of the shipping sector's emissions of CO2 . This has been done by conducting a survey among commercial ports in Sweden. To our knowledge, this is the first study of this kind. Our analysis indicates that ports in Sweden are generally positive towards an implementation of regulations to reduce carbon dioxide (CO2) emissions from the shipping industry. The ports where most positive towards CO2 differentiated port due (97%), followed by a technical standard (92%), CO2 taxation (84%) and EU ETS (The European Union Emissions Trading Scheme; 74%). 相似文献
26.
Anna Lavoie Kim Sparks Stephen Kasperski Amber Himes-Cornell Kristin Hoelting Conor Maguire 《Coastal management》2013,41(5):359-387
AbstractCommunity vulnerability is increasingly evaluated through quantitative social indices, typically developed using secondary data sources rather than primary data collection. It is necessary to understand the validity of these indices if they will be used to inform policy and decision making. This paper presents a ground-truthing effort to validate quantitative indices that characterize the well-being of Alaska fishing communities. We utilized ethnographic data collected from 13 representative communities and a capital assets framework to ground-truth the indices, in which qualitative ranks of vulnerability were compared against quantitative indices. The majority (73.8%) of ranks were in complete or moderate agreement and the results indicate that most of the indices are representative of community vulnerability; yet some variables utilized to create the indices could be modified to better reflect realities in Alaska. Indices of commercial fishery engagement and reliance appeared to be more reliable than socio-economic indicators, particularly for smaller fishing communities. We also confirmed that the indices do not capture political, or ecological factors that affect levels of community vulnerability. We conclude that quantitative indices of community vulnerability are useful rapid assessment tools; however, they should be validated, and complemented with ethnographic data prior to their implementation as policy making and management tools. 相似文献