The location of two ring roads and the control of traffic speed which together minimises radial travel in a town

In a simple theoretical model, we seek the location of two ring roads which minimises the total radial travel in a circular town of unit radius. We assume that drivers choose least time paths and that the speed of vehicles is controlled so as to minimise radial travel. We show that, whatever the distribution of origins and destinations, if an internal ring road minimises the total radial travel then the radial traffic flow just inside the ring equals the radial traffic flow just outside the ring. We show that if origins and destinations are uniformly and independently distributed over that part of the radials within the town, and a circumferential ring road already exists, then the optimum radius of a single inner ring road is √2 − 1.     

System optimal dynamic traffic assignment: Properties and solution procedures in the case of a many-to-one network

Thanks to its high dimensionality and a usually non-convex constraint set, system optimal dynamic traffic assignment remains one of the most challenging problems in transportation research. This paper identifies two fundamental properties of the problem and uses them to design an efficient solution procedure. We first show that the non-convexity of the problem can be circumvented by first solving a relaxed problem and then applying a traffic holding elimination procedure to obtain the solution(s) of the original problem. To efficiently solve the relaxed problem, we explore the relationship between the relaxed problems based on different traffic flow models (PQ, SQ, CTM) and a minimal cost flow (MCF) problem for a special space-expansion network. It is shown that all the four problem formulations produce the same minimal system cost and share one common solution which does not involve inside queues in the network. Efficient solution algorithms such as the network simplex method can be applied to solve the MCF problem and identify such an optimal traffic pattern. Numerical examples are also presented to demonstrate the efficiency of the proposed solution procedure.     

Mathematical characterization of spatiotemporal congested traffic patterns: mixed speed data analysis in the greater Toronto and Hamilton area,Canada

This paper formulates a comprehensive methodology for analyzing, quantifying and identifying congestion characteristics based on speed distribution. Utilizing vehicle speed data, a mathematical approach is applied, in order to characterize roadway segments, in terms of travel reliability, congestion severity and duration. We argue that the Gaussian mixture model (GMM) and its parameter combination is the appropriate tool if we are to obtain quantitative congestion measures and rank roadway performance. A significant contribution of our approach is that it is based on assumptions regarding mixed components as well as speed distribution and can be applied to large databases. We test our framework on the greater Toronto and Hamilton area in Ontario, Canada, and conclude that congestion quantification through the application of the GMM can be successfully accomplished. Results indicate that speed patterns differ significantly between counties as well as days of the week.     

Modelling and real-time control of traffic flow on the southern part of Boulevard Peripherique in Paris: Part I: Modelling

A microscopic mathematical model of freeway traffic flow is applied to a 6 km stretch of the Boulevard Périphérique in Paris including several on-ramps and off-ramps. The model is validated on the basis of real traffic flow measurements selected under a broad spectrum of traffic conditions. The mathematical model is capable of describing complicated traffic phenomena with considerable accuracy. A simulation program which is developed on the basis of the modelling equations may be used as a tool for testing of control strategies. Development and testing of control strategies is the strategies is the subject of a subsequent paper.     

四川崇州某水电站引水隧洞混凝土腐蚀原因分析及防治建议

文章对四川某水电站引水隧洞衬砌混凝土产生腐蚀变质的原因进行了分析,指出环境水对混凝土的硫酸盐及碳酸水侵蚀是最根本和直接的因素.由于在水电站勘察设计阶段未对地质环境,尤其是水文地质及地下水化学性质进行评价,故而在工程设计方案中对混凝土的主要原材料--水泥的标号及成份的要求中未考虑环境水对混凝土的侵蚀问题,因此文章对此提出了相应的防治建议.