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Assigning user class link flows uniquely

机译：唯一地分配用户类链接流

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Static user-equilibrium traffic assignment, the standard method for predicting traffic flows on urban road networks, is based on the principle that drivers choose their own least cost routes from their origins to their destinations. This principle may be formally described by user-equilibrium conditions, which correspond to the optimal solution to a nonlinear minimization problem. Although the total flows on links of the road network are uniquely determined by this formulation, multiple user-class link flows, as well as route flows, are not. Nevertheless, professionals frequently use class link flows output by their software for project evaluation, and class route flows to perform select link analyses. These applications may result in misleading findings, for example, in scenario analyses. An additional assumption may be imposed to determine these user class link flows and route flows uniquely. A possible assumption is the condition of proportionality, namely that the proportion of vehicles on each of two alternative, equal-cost segments (sequences of links) should be the same regardless of their user class, origin or destination. This paper compares two assignments in which the order of the car and truck trip matrices was specified as car followed by truck, and truck followed by car. Although the total link flows for the two assignments are effectively equal, substantial differences exist between the user class link flows determined by the different orderings of the matrices. Post-processing to impose the condition of proportionality on the class 0-D flows removes about 90% of these differences. Analyses of class link flows of cars and trucks before and after imposing the condition of proportionality for one of these assignments reveal that about half of all links experience differences in user class flows, ranging up to ±300 vph. These findings offer insights into the magnitude of the differences arising from the non-uniqueness of class link flows, and identify which links are subject to differences. Imposing the condition of proportionality in multi-class traffic assignments is recommended in travel forecasting practice.
机译：静态用户平衡交通分配是预测城市道路网络交通流量的标准方法，其依据是驾驶员选择从起点到目的地的成本最低的路线。可以通过用户平衡条件来正式描述该原理，该条件与非线性最小化问题的最优解相对应。尽管通过此公式唯一确定了道路网络链路上的总流量，但是并没有多个用户类的链路流量以及路线流量。但是，专业人员经常使用其软件输出的类链接流进行项目评估，并使用类路线流执行选择链接分析。这些应用程序可能会导致误导性的发现，例如在场景分析中。可以施加一个附加的假设来唯一地确定这些用户类链路流和路由流。一个可能的假设是成比例的条件，即，在两个替代的等价段（链接的序列）中的每一个上，车辆的比例应相同，而不论其用户类别，来源或目的地。本文比较了两个分配，其中将轿厢和卡车行驶矩阵的顺序指定为轿厢后跟卡车，以及卡车后跟轿厢。尽管两个分配的总链接流实际上相等，但是由矩阵的不同顺序确定的用户类链接流之间存在实质性差异。对0-D类流施加比例条件的后处理可消除大约90％的这些差异。对这些分配之一施加比例条件之前和之后的汽车和卡车的类别链接流的分析表明，所有链接中约有一半经历了用户类别流的差异，差异最大为±300 vph。这些发现提供了对由类链接流的非唯一性引起的差异的大小的见解，并确定了哪些链接存在差异。在旅行预测实践中建议在多类交通分配中施加比例条件。

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