| 1. |
- Allström, Andreas, 1978-, et al.
(författare)
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A hybrid approach for short-term traffic state and travel time prediction on highways
- 2016
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Ingår i: TRB 95th annual meeting compendium of papers.
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Konferensbidrag (refereegranskat)abstract
- Traffic management and traffic information are essential in urban areas, and require a good knowledge about both the current and the future traffic state. Both parametric and non-parametric traffic state prediction techniques have previously been developed, with different advantages and shortcomings. While non-parametric prediction has shown good results for predicting the traffic state during recurrent traffic conditions, parametric traffic state prediction can be used during non-recurring traffic conditions such as incidents and events. Hybrid approaches, combining the two prediction paradigms have previously been proposed by using non-parametric methods for predicting boundary conditions used in a parametric method. In this paper we instead combine parametric and non-parametric traffic state prediction techniques through assimilation in an Ensemble Kalman filter. As non-parametric prediction method a neural network method is adopted, and the parametric prediction is carried out using a cell transmission model with velocity as state. The results show that our hybrid approach can improve travel time prediction of journeys planned to commence 15 to 30 minutes into the future, using a prediction horizon of up to 50 minutes ahead in time to allow the journey to be completed.
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| 2. |
- Allström, Andreas, 1978-, et al.
(författare)
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Hybrid Approach for Short-Term Traffic State and Travel Time Prediction on Highways
- 2016
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Ingår i: Transportation Research Record. - Washington, DC, USA : The National Academies of Sciences, Engineering, and Medicine. - 0361-1981 .- 2169-4052. ; 2554, s. 60-68
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Tidskriftsartikel (refereegranskat)abstract
- Traffic management and traffic information are essential in urban areas and require reliable knowledge about the current and future traffic state. Parametric and nonparametric traffic state prediction techniques have previously been developed with different advantages and shortcomings. While nonparametric prediction has shown good results for predicting the traffic state during recurrent traffic conditions, parametric traffic state prediction can be used during nonrecurring traffic conditions, such as incidents and events. Hybrid approaches have previously been proposed; these approaches combine the two prediction paradigms by using nonparametric methods for predicting boundary conditions used in a parametric method. In this paper, parametric and nonparametric traffic state prediction techniques are instead combined through assimilation in an ensemble Kalman filter. For nonparametric prediction, a neural network method is adopted; the parametric prediction is carried out with a cell transmission model with velocity as state. The results show that the hybrid approach can improve travel time prediction of journeys planned to commence 15 to 30 min into the future, with a prediction horizon of up to 50 min ahead in time to allow the journey to be completed
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| 3. |
- Allström, Andreas, et al.
(författare)
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Traffic management for smart cities
- 2016
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Ingår i: Designing, developing, and facilitating smart cities. - Switzerland : Springer. - 9783319449227 - 9783319449241 ; , s. 211-240
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Smart cities, participatory sensing as well as location data available in communication systems and social networks generates a vast amount of heterogeneous mobility data that can be used for traffic management. This chapter gives an overview of the different data sources and their characteristics and describes a framework for utilizing the various sources efficiently in the context of traffic management. Furthermore, different types of traffic models and algorithms are related to both the different data sources as well as some key functionalities of active traffic management, for example short-term prediction and control.
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| 4. |
- Ekström, Joakim, 1980-, et al.
(författare)
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A heuristic method for finding congestion pricing schemes in transportation networks with modal choice
- 2008
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Ingår i: International conference of Hong Kong society for transportation studies,2008. - Hong Kong, China : Hong Kong Society of Transportation Studies Ltd.. - 9789889884734 ; , s. 773-782
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Konferensbidrag (refereegranskat)abstract
- In this paper we extend a previously developed heuristic procedure, with a modal choice model, to solve the congestion pricing problem of simultaneously finding the optimal number of toll facilities, their corresponding location and toll levels. When considering a congestion pricing scheme the cost of collecting the tolls can not be disregarded. The objective is where-fore to maximize the net social surplus, which is the social surplus minus the cost of collect-ing the tolls. The heuristic method is an iterative solution procedure, in which the integer part of the objec-tive function is approximated by a continuous function. A version of the Sioux Falls network (76 links) is used to demonstrate the solution procedure. The solution is a congestion pricing scheme which divide the network into four zones, by locating tolls on 27 links. This solution yields a social surplus which is only 13.5% lower than the marginal social cost pricing solu-tion.
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| 5. |
- Ekström, Joakim, 1980-
(författare)
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A MILP approximation approach for finding optimal toll locations and levels in elastic demand traffic networks
- 2010
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Ingår i: TRANSPORTATION AND URBAN SUSTAINABILITY. - Hong Kong, China : Hong Kong Society for Transportation Studies. - 9789889884789 ; , s. 107-114
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Konferensbidrag (refereegranskat)abstract
- The toll design problem (TDP) is to find optimal toll locations and corresponding toll levels in a congestion pricing scheme. The TDP can be formulated as a non-convex mathematical program, in which the road users are assumed to be distributed according to a user-equilibrium with elastic demand. This program is hard to solve due to non-convexity and non-smoothness. In this paper, the TDP is approximated by a mixed integer linear program (MILP), in which the non-linear functions of the TDP are approximated by piecewise linear ones. The MILP can be solved to its global optimal solution by known methods, and its optimal solution will give a lower bound on the optimal solution to the TDP. By iteratively updating the MILP approximation, the error introduced by the approximation is reduced, and for a test network with nine nodes and 18 links, the global optimal solution is obtained.
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| 6. |
- Ekström, Joakim, 1980-
(författare)
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Comparison of usage-based congestion pricing schemes
- 2018
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Ingår i: Proceedings Transportation Research Board 97th Annual Meeting. - Washington D.C..
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Konferensbidrag (refereegranskat)abstract
- This paper investigates how usage-based pricing can be applied in order to improve the efficiency of the transportation system. Distance-based, travel time-based and delayed-based pricing schemes are investigated, both from a one-link and network perspective. A static modeling framework is adopted, based on user-equilibrium, and a simplified emission model based on the HBEFA emission model is used. Optimal usage-based fees are calculated using a surrogate-based optimization framework, and determination of zone layout is done using k-means clustering. The results for a Stockholm region network show that already with network wide pricing a large proportion of the maximum improvement of social surplus achievable with first-best pricing, can be reached. Delay-based pricing, in which the users are charged based on the excess travel time in comparison to free flow travel times, achieves 99% of the maximum improvement, already with one single fee across the whole network. With clustering of links based on their first-best optimal fees, the benefits of both distance and travel time-based fees can significantly be improved.
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| 7. |
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| 8. |
- Ekström, Joakim, 1980-, et al.
(författare)
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Decision support for finding locations and toll levels within a congestion pricing scheme
- 2008
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Ingår i: Transportation Research Board Annual Meeting,2008. - Washington D.C. : TRB.
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Konferensbidrag (refereegranskat)abstract
- Designing a congestion pricing scheme involves a number of complex decisions. Focusing on the quantitative parts of a congestion pricing system with link tolls, the problem involves finding the number of tolled links, the link toll locations and their corresponding toll level and schedule. In this paper, we develop and evaluate methods for finding a most efficient design of a congestion pricing scheme in a road network with elastic demand. The design efficiency is measured by the net social surplus, which is computed as the difference between the social surplus and the collection costs (i.e. setup and operation cost) of the congestion pricing system. The problem of finding such a scheme is stated as a combinatorial bi-level optimization problem. On the upper level we maximize the net social surplus and on the lower level we solve a user equilibrium problem with elastic demand, given the toll locations and toll levels, to simulate the user response. We modify a known heuristic procedure for finding the optimal locations and toll levels given a fixed number of tolls to locate, to find the optimal number of tolls to locate as well. A new heuristic procedure is also presented which is based on repeated solutions of a continuous approximation of the combinatorial problem. Numerical results for two small scale test networks are presented. Both methods perform satisfactory on the two networks. Comparing the two methods, the iterative approximation procedure is the one which shows the best results. The results are compared to solutions obtained by an exhaustive search.
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| 9. |
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| 10. |
- Ekström, Joakim, 1980-
(författare)
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Designing Urban Road Congestion Charging Systems : Models and Heuristic Solution Approaches
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The question of how to design a congestion pricing scheme is difficult to answer and involves a number of complex decisions. This thesis is devoted to the quantitative parts of designing a congestion pricing scheme with link tolls in an urban car traffic network. The problem involves finding the number of tolled links, the link toll locations and their corresponding toll level. The road users are modeled in a static framework, with elastic travel demand.Assuming the toll locations to be fixed, we recognize a level setting problem as to find toll levels which maximize the social surplus. A heuristic procedure based on sensitivity analysis is developed to solve this optimization problem. In the numerical examples the heuristic is shown to converge towards the optimum for cases when all links are tollable, and when only some links are tollable.We formulate a combined toll location and level setting problem as to find both toll locations and toll levels which maximize the net social surplus, which is the social surplus minus the cost of collecting the tolls. The collection cost is assumed to be given for each possible toll location, and to be independent of toll level and traffic flow. We develop a new heuristic method which is based on repeated solutions of an approximation to the combined toll location and level setting problem. Also, a known heuristic method for locating a fixed number of toll facilities is extended, to find the optimal number of facilities to locate. Both heuristics are evaluated on two small networks, where our approximation procedure shows the best results.Our approximation procedure is also employed on the Sioux Falls network. The result is compared with different judgmental closed cordon structures, and the solution suggested by our method clearly improves the net social surplus more than any of the judgmental cordons.
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