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131.
Leonid Engelson Mogens Fosgerau 《Transportation Research Part B: Methodological》2011,45(10):1560-1571
This paper derives a measure of travel time variability for travellers equipped with scheduling preferences defined in terms of time-varying utility rates, and who choose departure time optimally. The corresponding value of travel time variability is a constant that depends only on preference parameters. The measure is unique in being additive with respect to independent parts of a trip. It has the variance of travel time as a special case. Extension is provided to the case of travellers who use a scheduled service with fixed headway. 相似文献
132.
Maria Börjesson Jonas Eliasson 《Transportation Research Part A: Policy and Practice》2011,45(3):171-184
We investigate how passengers on long-distance trains value unexpected delays relative to scheduled travel time and travel cost. For scheduled services with high reliability and long headways, the value of delays is most commonly assumed to be proportional to the average delay. By exploring how the valuation of train delays depends on delay risk and delay length, using three different stated choice data sets, we find that the “average delay” approach does not hold: the disutility increases slower than linearly in the delay risk. This means that using the average delay as a performance indicator, a guide for operations planning or for investment appraisal will underestimate the value of small risks of long delays relative to large risks for short delays. It also means that estimated valuations of “average delay” will depend on the delay risk level: valuations will be higher the lower the risk levels in the study are. 相似文献
133.
Miroslav Ga
i&#x; Isaac Mancero Mosquera Vedrana Kova
evi&#x; Andrea Mazzoldi Vanessa Cardin Franco Arena Giorgio Gelsi 《Journal of Marine Systems》2004,51(1-4):33
Long-term measurements of the water flow at three Venice Lagoon inlets with the bottom-mounted ADCPs show that the main part of the variance (>90%) is associated with the tidal variability. Semi-diurnal constituents (mainly M2 and S2) are responsible for about 80% of the flow variance. Phase-lag between the axial current and sea-level is on the order of 2 h for M2 and 4 h for the K1, the maximum inflow leading the sea-level maximum. Phase-difference of tidal flows between inlets shows that Chioggia leads both Malamocco and Lido, suggesting that tidal signal progresses northward, thus in the opposite direction of both the semi-diurnal and diurnal tidal signals in the open Adriatic currents. The sea-level slope between the open sea and the lagoon interior controls the inlet flow, which is due to the time lag being constant for all tidal constituents. It was shown that tidal oscillations at Punta Salute (lagoon interior) lag those in Lido by about 45 min. The pressure gradient due to the sea-level slope generates the flow acceleration. Only for large current speeds (>0.5 m/s), the bottom friction term becomes equally important as the local acceleration and the horizontal pressure gradient terms. Wind effects manifest as a remote forcing through Adriatic seiches at semi-diurnal and diurnal scales, and as a local forcing at very long time scales on the order of a month. This latter mechanism is limited to a winter period (November–January). Seiches are present over the entire year, being however, more energetic and frequent during autumn and winter. 相似文献
134.
在船舶航行条件下热带气旋强度变化预报的相似离度方案 总被引：2，自引：1，他引：2
该文提出了在船舶航行条件下利用相似离度作西北太平洋热带气旋６—７２ｈ强度变化预报的方法，并进行了独立样本预报检验和实船试验，基于相似离度利用“形”和“值”两个方面全面去比较实时样本和历史样本之间的相似程度的优．点，采取了一系列相似离度应用技术，从三万多条历史样本曲线库中寻找最相似的样本曲线的未来变压进行强度变化预报，有利于提高预报准确率，减小预报误差，独立样本的预报检验和实船试验表明，该方法具有简便、迅速等特点，还具有较高的预报精度；是现行船舶航行条件下或岸上气象台站及作热带气旋强度变化预报的一种切实可行的途径。 相似文献
135.
This study investigates the repeatability of ice-tank tests with broken ice. Ice-tank test campaigns normally do not perform multiple repetitions of tests with the same initial conditions. Therefore, the repeatability of ice-tank tests with broken ice is not well understood. Data from two test campaigns are analysed. The first test campaign studied the interaction between a 4-legged structure with a vertical waterline and several broken and intact level ice conditions. In the second test campaign, a ship hull geometry was tested. We analyse selected test cases from each test campaign. The ice-tank tests are reproduced using a 3-D discrete element method (DEM) model. Each analysed test case is simulated 20 times. The only difference between each simulation is the initial position of the ice floes. The numerical simulation results show that changes in the initial floe positions can cause large changes in the statistical properties of the ice load. Often, a single random interaction event can be identified that is responsible for the change in the results. Such interaction events can cause additional floe accumulation ahead of the structure, thereby influencing the load statistics for a large portion of the interaction length. The observed events occur both in the numerical simulations and in the physical ice-tank tests. This result indicates that ice-tank tests with broken ice have a poor repeatability; a change in an uncontrolled condition, such as the exact initial floe positions, can lead to a large variation in the experimental results. 相似文献
136.
Empirical studies have revealed that travel time variability (TTV) can significantly affect travelers’ behaviors and planners’ cost-benefit assessment of transportation projects. It is therefore important to systematically quantify the value of TTV (VTTV) and its impact. Recently, Fosgerau’s valuation method makes this quantification possible by converting the value of travel time (VTT) and the VTTV into monetary unit. Travel time reliability ratio (TTRR), defined as a ratio of the VTTV to the VTT, is a key parameter in Fosgerau’s valuation method. Calculating TTRR involves an integral of the inverse cumulative distribution function (CDF) of the standardized travel time distribution (STTD), i.e., the mean lateness factor. Using a well-fitted STTD is a straightforward way to calculate TTRR. However, it will encounter the following challenges: (1) determination of a well-fitted STTD; (2) non-existence of an algebraic expression for the CDF and its inverse CDF; and (3) lack of a closed-form expression to efficiently calculate TTRR. To circumvent the above issues, this paper proposes a distribution-fitting-free analytical approach based on the Cornish-Fisher expansion as an alternative way to calculate TTRR without the need to fit the whole CDF. The validity domain is rigorously derived for guaranteeing the accuracy of the proposed method. Realistic travel time datasets that cover 17 links are used to systematically explore the feature and accuracy of the proposed method in estimating TTRR. The comparative results demonstrate that the proposed method can efficiently and effectively estimate TTRR. When travel time datasets satisfy the validity domain, the proposed method outperforms the distribution fitting method in estimating TTRR. 相似文献
137.
In this study, to incorporate realistic discrete stochastic capacity distribution over a large number of sampling days or scenarios (say 30–100 days), we propose a multi-scenario based optimization model with different types of traveler knowledge in an advanced traveler information provision environment. The proposed method categorizes commuters into two classes: (1) those with access to perfect traffic information every day, and (2) those with knowledge of the expected traffic conditions (and related reliability measure) across a large number of different sampling days. Using a gap function framework or describing the mixed user equilibrium under different information availability over a long-term steady state, a nonlinear programming model is formulated to describe the route choice behavior of the perfect information (PI) and expected travel time (ETT) user classes under stochastic day-dependent travel time. Driven by a computationally efficient algorithm suitable for large-scale networks, the model was implemented in a standard optimization solver and an open-source simulation package and further applied to medium-scale networks to examine the effectiveness of dynamic traveler information under realistic stochastic capacity conditions. 相似文献
138.
Because individuals may misperceive travel time distributions, using the implied reduced form of the scheduling model might fall short of capturing all costs of travel time variability. We reformulate a general scheduling model employing rank-dependent utility theory and derive two special cases as econometric specifications to study these uncaptured costs. It is found that reduced-form expected cost functions still have a mean–variance form when misperception is considered, but the value of travel time variability is higher. We estimate these two models with stated-preference data and calculate the empirical cost of misperception. We find that: (i) travelers are mostly pessimistic and thus tend to choose departure times too early to achieve a minimum cost, (ii) scheduling preferences elicited using a stated-choice method can be relatively biased if probability weighting is not considered, and (iii) the extra cost of misperceiving the travel time distribution might be nontrivial when time is valued differently over the time of day and is substantial for some people. 相似文献
139.
为了定量化测度行程时间可变性右偏且长尾的实证特征,考虑实际观测中可能存在的数据样本量不足和离群值干扰问题,提出基于线性矩的L-偏度和L-峰度用于精确表征行程时间可变性。考虑到线性矩是顺序统计量期望的线性组合,给出了避免遍历所有子样本的线性矩估计方法。根据线性矩概念,探究了L-偏度和L-峰度的数学含义和其表征行程时间可变性的有效性,以及样本L-偏度和L-峰度的计算方法。理论研究发现,在表征范围和样本估计质量方面,相较于传统偏度和峰度,L-偏度和L-峰度对行程时间可变性具有更加优越的表征能力。采用深圳市车牌照识别系统的行程时间数据集进行案例分析,从无偏性、鲁棒性和有效性3个维度证明了L-偏度和L-峰度相较于传统偏度和峰度的优越性。分析结果如下：样本L-偏度和L-峰度在样本量不足时仍然是总体近似的无偏估计,而传统偏度和峰度的系统性误差较大;L-偏度和L-峰度对离群值具有鲁棒性,而传统偏度和峰度对离群值过于敏感;样本L-偏度和L-峰度对总体的估计波动小且精度高,具有良好的估计有效性;L-偏度和L-峰度分别与传统偏度和峰度有较高相关性,但又能够辨识出不同时空下行程时间可变性分布的差异。基于L-偏... 相似文献
140.
在分析岩土体在重复荷载作用下永久变形产生和发展的规律,以及对常用重复荷载作用下土体永久变形计算方法的基础上,采用单元强度随机生成的有限元方法对重复荷载下岩土体永久变形规律进行了数值仿真,得出以下主要结论:采用单元强度随机生成的有限元方法模拟方法能够较好的表现土体永久变形的基本规律,路基岩土材料的强度变异性是土体在重复荷载下累积变形表现与其他材料差别的主要因素;红层软岩路堤在不同大小的车辆荷载作用下塑性累积变形逐渐发展;当汽车荷载较小,路基在车辆荷载作用下的变形可以稳定。当荷载较大,则沉降渐进发展而且不能稳定,会出现路基土体移动,路基脱空等病害。 相似文献