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Route Choice (route + choice)
Selected AbstractsDesign and Management Strategies for Mixed Public Private Transportation Networks: A Meta-Heuristic ApproachCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2009Avinash Unnikrishnan In this study, private companies are assumed to have a degree of control over highway sections on which they perform maintenance and rehabilitation and capacity expansion activities. The private investors recover the cost of construction by levying tolls. The public agency is assumed to maintain the rest of the network with the objective of minimizing total system generalized cost. The bi-directional impact of roadway utilization on deterioration and deterioration on utilization is modeled in this study. The model accounts for route choice of users and all users are assumed to choose routes that have equal and minimal experienced generalized cost. The nonconvex and discontinuous multi-objective mathematical program is solved using nondominant sorting genetic algorithm-II and the pareto-optimal trade-off surface between the profit of the private company and the total system cost is generated. Computational runs are conducted to demonstrate the suitability and flexibility of the developed framework in modeling various policy decisions such as the presence of noncompete clauses. [source] Bi-level Programming Formulation and Heuristic Solution Approach for Dynamic Traffic Signal OptimizationCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2006Dazhi Sun Conventional methods of signal timing optimization assume given traffic flow pattern, whereas traffic assignment is performed with the assumption of fixed signal timing. This study develops a bi-level programming formulation and heuristic solution approach (HSA) for dynamic traffic signal optimization in networks with time-dependent demand and stochastic route choice. In the bi-level programming model, the upper level problem represents the decision-making behavior (signal control) of the system manager, while the user travel behavior is represented at the lower level. The HSA consists of a Genetic Algorithm (GA) and a Cell Transmission Simulation (CTS) based Incremental Logit Assignment (ILA) procedure. GA is used to seek the upper level signal control variables. ILA is developed to find user optimal flow pattern at the lower level, and CTS is implemented to propagate traffic and collect real-time traffic information. The performance of the HSA is investigated in numerical applications in a sample network. These applications compare the efficiency and quality of the global optima achieved by Elitist GA and Micro GA. Furthermore, the impact of different frequencies of updating information and different population sizes of GA on system performance is analyzed. [source] Loop migration in adult marsh harriers Circus aeruginosus, as revealed by satellite telemetryJOURNAL OF AVIAN BIOLOGY, Issue 2 2010Raymond H. G. Klaassen Loop migration among birds is characterized by the spring route lying consistently west or east of the autumn route. The existence of loops has been explained by general wind conditions or seasonal differences in habitat distribution. Loop migration has predominantly been studied at the population level, for example by analysing ring recoveries. Here we study loop migration of individual marsh harriers Circus aeruginosus tracked by satellite telemetry. We show that despite a generally narrow migration corridor the harriers travelled in a distinct clockwise loop through Africa and southern Europe, following more westerly routes in spring than in autumn. We used the Normalized Difference Vegetation Index (NDVI) to identify potential feeding habitat in Africa. Suitable habitat seemed always more abundant along the western route, both in spring and autumn, and no important stopover site was found along the eastern route. Observed routes did thus not coincide with seasonal variation in habitat availability. However, favourable habitat might be more important during spring migration, when the crossing of the Sahara seems more challenging, and thus habitat availability might play an indirect role in the harriers' route choice. Grid-based wind data were used to reconstruct general wind patterns, and in qualitative agreement with the observed loop marsh harriers predominantly encountered westerly winds in Europe and easterly winds in Africa, both in autumn and in spring. By correlating tail- and crosswinds with forward and perpendicular movement rates, respectively, we show that marsh harriers are partially drifted by wind. Thus, we tentatively conclude that wind rather than habitat seems to have an overriding effect on the shape of the migration routes of marsh harriers. General wind conditions seem to play an important role also in the evolution of narrow migratory loops as demonstrated for individual marsh harriers. [source] Simulating the East African wildebeest migration patterns using GIS and remote sensingAFRICAN JOURNAL OF ECOLOGY, Issue 4 2004Douglas E. Musiega Abstract The Serengeti,Mara ecosystem in East Africa is a spectacular natural heritage endowed with diverse fauna and flora. The presence of the seasonally migrating wildebeest (Connochaetes taurinus) is a major boost for tourism. This migration however has enormous impacts to the ecosystem. Consequently efforts at monitoring the herd's migration trends and patterns remain a challenge to wildlife managers and ecologists in the region. In this paper, the relative influence of vegetation (normalized difference vegetation index), landscape and relief on herds migration routes are investigated and the migration routes simulated using GIS and remote sensing techniques. The results are compared with the annual mean route taken by the herds, as determined by radio tracking over the 1995,1997 period. Green vegetation availability is shown to be the major criterion in route choice. It is also shown that during the dry season phases of the migration (western trek, western corridor), the herd endures complex relief (complexity quantified based on slope and inter-visibility) in the search for greener grass. During the season of abundance (southern trek), relief becomes critical in making route choices, with herds avoiding difficult terrain, notwithstanding their relatively more abundant vegetation. The method proposed in this paper is viable for rapid prediction of approximate routes for the migrating wildebeest in different climatic conditions. Résumé L'écosystème Serengeti,Mara en Afrique Occidental est un patrimoine naturel spectaculaire, doté des divers variétés de flore et de faune. La présence du gnou migrateur (Connochaetes taurinus) représente un atout majeur pour le tourisme. Néanmoins, cette migration a un impact énorme sur l'écosystème. Par conséquence, la surveillance des tendances migratoires du troupeau est un défi constant pour les gérants et les écologistes dans la région. Dans cette enquête, l'influence relative de la végétation (NDVI), le paysage et le relief, sur les routes du migration prises par le troupeau ont étéétudiés, et simulés utilisant le Système d'Information Géographique (SIG) et des techniques de perception à distance. Les résultats sont comparés à la moyenne annuelle des routes prises par les troupeaux, déterminée par le repérage radio pendant la période allant de 1995 a 1997. Le disponibilité de végétation verte s'avère le déterminant majeur dans le choix du chemin. Il est aussi démontré que pendant les phases du migration en saison sèche (périple vers l'ouest, couloir vers l'ouest) le troupeau subit des reliefs complexes (complexité calculée sur la pente et inter visibilité) à la recherche de l'herbe la plus verte. Pendant la saison d'abondance (périple vers le sud), l'impact du relief sur le choix des routes devient critique, les troupeaux évitant le terrain difficile, malgré sa végétation relativement abondante. La méthode présentée dans cette étude permet de prédire de façon rapide et valable la route approximative des gnous en cours de migration dans des conditions climatiques diverses. [source] A risk-averse user equilibrium model for route choice problem in signal-controlled networksJOURNAL OF ADVANCED TRANSPORTATION, Issue 4 2010William H.K. Lam Abstract This paper proposes a new risk-averse user equilibrium (RAUE) model to estimate the distribution of traffic flows over road networks with taking account the effects of accident risks due to the conflicting traffic flows (left- and right-turning and through traffic flows) at signalized intersections. It is assumed in the proposed model that drivers consider simultaneously both the travel time and accident risk in their route choices. The accident risk of a route is measured by the potential accident rate on that route. The RAUE conditions are formulated as an equivalent path-based variational inequality problem which can be solved by a path-based solution algorithm. It is shown that the traditional user equilibrium (UE) model is in fact a special case of the proposed model. A numerical example on a grid network is used to illustrate the application of the proposed model and to compare the results with the conventional UE traffic assignment. Numerical results show that the traditional UE model may underestimate the total system travel time and overestimate the system accident rate. Sensitivity tests are also carried out to assess the effects of drivers' preferences, signal control parameters (i.e., green time proportions), and various network demand levels on the route choice problem. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simulating the East African wildebeest migration patterns using GIS and remote sensingAFRICAN JOURNAL OF ECOLOGY, Issue 4 2004Douglas E. Musiega Abstract The Serengeti,Mara ecosystem in East Africa is a spectacular natural heritage endowed with diverse fauna and flora. The presence of the seasonally migrating wildebeest (Connochaetes taurinus) is a major boost for tourism. This migration however has enormous impacts to the ecosystem. Consequently efforts at monitoring the herd's migration trends and patterns remain a challenge to wildlife managers and ecologists in the region. In this paper, the relative influence of vegetation (normalized difference vegetation index), landscape and relief on herds migration routes are investigated and the migration routes simulated using GIS and remote sensing techniques. The results are compared with the annual mean route taken by the herds, as determined by radio tracking over the 1995,1997 period. Green vegetation availability is shown to be the major criterion in route choice. It is also shown that during the dry season phases of the migration (western trek, western corridor), the herd endures complex relief (complexity quantified based on slope and inter-visibility) in the search for greener grass. During the season of abundance (southern trek), relief becomes critical in making route choices, with herds avoiding difficult terrain, notwithstanding their relatively more abundant vegetation. The method proposed in this paper is viable for rapid prediction of approximate routes for the migrating wildebeest in different climatic conditions. Résumé L'écosystème Serengeti,Mara en Afrique Occidental est un patrimoine naturel spectaculaire, doté des divers variétés de flore et de faune. La présence du gnou migrateur (Connochaetes taurinus) représente un atout majeur pour le tourisme. Néanmoins, cette migration a un impact énorme sur l'écosystème. Par conséquence, la surveillance des tendances migratoires du troupeau est un défi constant pour les gérants et les écologistes dans la région. Dans cette enquête, l'influence relative de la végétation (NDVI), le paysage et le relief, sur les routes du migration prises par le troupeau ont étéétudiés, et simulés utilisant le Système d'Information Géographique (SIG) et des techniques de perception à distance. Les résultats sont comparés à la moyenne annuelle des routes prises par les troupeaux, déterminée par le repérage radio pendant la période allant de 1995 a 1997. Le disponibilité de végétation verte s'avère le déterminant majeur dans le choix du chemin. Il est aussi démontré que pendant les phases du migration en saison sèche (périple vers l'ouest, couloir vers l'ouest) le troupeau subit des reliefs complexes (complexité calculée sur la pente et inter visibilité) à la recherche de l'herbe la plus verte. Pendant la saison d'abondance (périple vers le sud), l'impact du relief sur le choix des routes devient critique, les troupeaux évitant le terrain difficile, malgré sa végétation relativement abondante. La méthode présentée dans cette étude permet de prédire de façon rapide et valable la route approximative des gnous en cours de migration dans des conditions climatiques diverses. [source] |