| 1. |
- Allström, Andreas, 1978-, et al.
(author)
-
A hybrid approach for short-term traffic state and travel time prediction on highways
- 2016
-
In: TRB 95th annual meeting compendium of papers.
-
Conference paper (peer-reviewed)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.
|
|
| 2. |
- Allström, Andreas, 1978-, et al.
(author)
-
Hybrid Approach for Short-Term Traffic State and Travel Time Prediction on Highways
- 2016
-
In: Transportation Research Record. - Washington, DC, USA : The National Academies of Sciences, Engineering, and Medicine. - 0361-1981 .- 2169-4052. ; 2554, s. 60-68
-
Journal article (peer-reviewed)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
|
|
| 3. |
- Allström, Andreas, et al.
(author)
-
Traffic management for smart cities
- 2016
-
In: Designing, developing, and facilitating smart cities. - Switzerland : Springer. - 9783319449227 - 9783319449241 ; , s. 211-240
-
Book chapter (other academic/artistic)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.
|
|
| 4. |
- Ekström, Joakim, 1980-, et al.
(author)
-
A heuristic method for finding congestion pricing schemes in transportation networks with modal choice
- 2008
-
In: International conference of Hong Kong society for transportation studies,2008. - Hong Kong, China : Hong Kong Society of Transportation Studies Ltd.. - 9789889884734 ; , s. 773-782
-
Conference paper (peer-reviewed)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.
|
|
| 5. |
- Ekström, Joakim, 1980-
(author)
-
A MILP approximation approach for finding optimal toll locations and levels in elastic demand traffic networks
- 2010
-
In: TRANSPORTATION AND URBAN SUSTAINABILITY. - Hong Kong, China : Hong Kong Society for Transportation Studies. - 9789889884789 ; , s. 107-114
-
Conference paper (peer-reviewed)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.
|
|
| 6. |
- Ekström, Joakim, 1980-
(author)
-
Comparison of usage-based congestion pricing schemes
- 2018
-
In: Proceedings Transportation Research Board 97th Annual Meeting. - Washington D.C..
-
Conference paper (peer-reviewed)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.
|
|
| 7. |
|
|
| 8. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Decision support for finding locations and toll levels within a congestion pricing scheme
- 2008
-
In: Transportation Research Board Annual Meeting,2008. - Washington D.C. : TRB.
-
Conference paper (peer-reviewed)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.
|
|
| 9. |
|
|
| 10. |
- Ekström, Joakim, 1980-
(author)
-
Designing Urban Road Congestion Charging Systems : Models and Heuristic Solution Approaches
- 2008
-
Licentiate thesis (other academic/artistic)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.
|
|
| 11. |
|
|
| 12. |
- Ekström, Joakim, 1980-
(author)
-
Finding second-best toll locations and levels by relaxing the set of first-best feasible toll vectors
- 2014
-
In: European Journal of Transport and Infrastructure Research. - : Technische Universiteit Delft. - 1567-7133 .- 1567-7141. ; 14:1, s. 7-29
-
Journal article (peer-reviewed)abstract
- This paper provides a framework for optimizing toll locations and levels in congestion pricing schemes for large urban road networks, with the objective to maximize the social surplus. This optimization problem is referred to as the toll location and level setting problem (TLLP) and is both non-convex, non-smooth and involves binary decision variables, and is therefore considered as a hard problem to solve. In this paper a solution approach is provided which instead of directly solving the TLLP, makes use of the first-best toll level solution, in which no restrictions are imposed on toll locations or levels. A first-best pricing scheme can be obtained by solving a convex program, and it has previously been shown that for the used routes in the network, the first-best toll levels on a route level are unique. By formulating an optimization problem, which instead of maximizing the social surplus, tries to find the link toll levels which minimize the deviation from first-best route tolls, a mixed integer linear program is obtained, and if the toll locations are predetermined the resulting optimization problem is a linear program.The approach of minimizing the deviation from first--best route tolls is applied for two different network models, and results are provided to show the applicability of the approach, as well as to compare with other approaches. Also, it is shown that for the Stockholm network, virtually the first-best level of social surplus can be obtained with a significantly reduced number of located tolls.
|
|
| 13. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Heuristic algorithms for a second-best congestion pricing problem
- 2009
-
In: Netnomics. - : Springer Science and Business Media LLC. - 1385-9587 .- 1573-7071. ; 10:1, s. 85-102
-
Journal article (peer-reviewed)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 findingthe number of toll links, the link toll locations and their corresponding toll level and schedule.In this paper, we develop and evaluate methods for finding the most efficient design for a congestion pricing scheme in a road network model 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 operational costs) of the congestion pricing system. The problem of finding such a scheme is stated as a combinatorial bi-level optimization problem. At the upper level, we maximize the net social surplus and at 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 toll facilities as well. A new heuristic procedure, based on repeated solutions of a continuous approximation of the combinatorial problem is also presented. Numerical results for two small test networks are presented. Both methods perform satisfactorily on the two networks. Comparing the two methods, we find that the continuous approximation procedure is the one which shows the best results.
|
|
| 14. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Metodik för beräkning av emissioner baserat på trafikdata från dynamiska trafikmodeller och trafikmätningar
- 2021
-
Reports (other academic/artistic)abstract
- Dynamiska trafikmodeller förväntas i större utsträckning komplettera och på sikt helt eller delvis ersätta statiska trafikmodeller. Samtidigt blir trafikmätningar mer och mer tillgängliga, och utifrån dessa kan tidsvarierade estimeringar av flöden och hastighet över större områden tas fram. I Sverige används idag HBEFA för estimering av emissioner. HBEFA är en EU-gemensam modell som används i flera europeiska länder för beräkning av luftföroreningar och bränsleförbrukning. Detta projekt syftar till att ta fram en metod för tillämpning av HBEFA på trafikdata från mätningar och dynamiska trafikmodeller på ett sätt som är konsistent med den tillämpning av HBEFA som idag sker med statisk trafikdata. Projektet fokuserar främst på tillämpningar där lokala emissioner från vägtrafik är av intresse. Exempel på sådana tillämpningar är uppföljning, estimering och prediktering av luftkvalitet. Men även analys av förändring av utsläpp från vägtrafiken över tid, samt före/efter studier vid förändringar av trafikinfrastrukturen. Detta kräver att den tillämpade beräkningsmetodiken för utsläpp anpassas för att kunna dra nytta av den rikare information som dynamisk trafikdata innehåller.I HBEFA är skattning av trafiktillstånd centralt för estimering av emissioner. I denna studie har vi studerat och jämfört tre olika sätt att definiera trafiktillståndet i HBEFAstrafiksituationer nämligen baserat på: flöde (det som används i nuläget), hastighet och densitet. Flödesbaserade definitioner har en inbyggd begränsning i att de inte entydigt kan beskriva trafiksituationen, då lågt flöde kan innebära både låg trängsel och hög trängsel, beroende på hastighet. Detta är inget problem i nuvarande tillämpning av HBEFA med statisk trafikdata, då en förenklad beskrivning av det överbelastade fallet görs, som tillåter flöden över kapaciteten, men som då representerar en efterfrågan snarare än flöde. Undersökningarna i denna studieindikerar att en hastighetsbaserad definition av trafiktillstånd inte är att föredra då hastigheten kan variera relativt mycket mellan olika fordon och över en sträcka vid liknande flödes- och densitetsförhållanden. Hastighetsbaserade gränser mellan trafiktillstånd blir främst problematiskt vid tillämpning på mätdata. Vid hastighetsbaserade gränser blir varje fordonspassage med låg hastighet automatiskt klassade i ett trafiktillstånd som innebär trängsel. Densitet är ett mer stabilt mått vid liknande trafikförhållanden och kan sägas bättre definiera graden av trängsel i trafikteoretisk mening. En densitetsbaserad definition kan entydigt bestämma samtliga trafiktillstånd, till skillnad från en flödesbaserad definition som endast kan bestämma icke överbelastade trafiktillstånd entydigt. För de icke överbelastade trafiktillstånden (dvs. 1 och 2) har vi också kunnat visa att en densitetsbaserad definition ger ungefär samma fördelning av trafikarbete mellan trafiktillstånden.För totala emissioner är skillnaden mellan skattade emissioner med nuvarande flödesbaserade definitioner av trafiktillstånd och utvärderad densitetsbaserade definitioner av trafiktillstånd oftast liten. Dock är den densitetsbaserade versionen bättre på att fånga hur emissionerna varierar i tid och rum.
|
|
| 15. |
- Ekström, Joakim, 1980-
(author)
-
Optimization Approaches for Design of Congestion Pricing Schemes
- 2012
-
Doctoral thesis (other academic/artistic)abstract
- In recent years, there has been a growing interest in congestion pricing as a tool for solving traffic congestion problems in urban areas. However, the transportation system is complex and to design a congestion pricing scheme, i.e. to decide where and how much to charge the road users, is not trivial. This thesis considers congestion pricing schemes based on road tolls, and the efficiency of a pricing scheme is evaluated by a social welfare measure. To assist in the process of designing congestion pricing schemes, the toll design problem (TDP) is formulated as an optimization problem with the objective function describing the change in social welfare. In the TDP, the road users are assumed to be distributed in the traffic network according to a Wardrop equilibrium. The TDP is a non-convex optimization problem, and its objective function is non-smooth. Thus, the TDP is considered as a hard optimization problem to solve.This thesis aims to develop methods capable of optimizing both toll locations and their corresponding toll levels for real world traffic networks; methods which can be used in a decision support framework when designing new congestion pricing schemes or tuning already implemented ones. Also, this thesis addresses the global optimality of the TDP. 'In this thesis, a smoothening technique is applied which approximates the discrete toll location variables by continuous functions (Paper I). This allows for simultaneous optimization of both toll locations and their corresponding toll levels, using a sensitivity analysis based ascent algorithm. The smoothening technique is applied in a Stockholm case study (Paper II), which shows the potential of using optimization when designing congestion pricing schemes.Global optimality of the TDP is addressed by piecewise linear approximations of the non-linear functions in the TDP (Papers III and IV), resulting in a mixed integer linear program (MILP). The MILP can be solved to global optimality by branch and bound/cut methods which are implemented in commercially available software.
|
|
| 16. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Optimizing toll levels using linear approximation approach
- 2009
-
In: 4th Kuhmo Nectar Conference.
-
Conference paper (peer-reviewed)abstract
- This paper proposes a heuristic solution algorithm for solving the non-convex toll level problem for fixed demand networks in which the road users are distributed according to a user equilibrium. In the toll level problem we search for continuous toll levels, given a fixed set of tollable links, to minimize the total travel time in the traffic network. The toll level problem is converted by a linearization scheme to approximate the objective function and constraints in the original problem. This approximation gives a mixed integer linear program (MILP) which has the property of global optimum, and gives a lower bound estimation of the original non-linear problem. The user equilibrium condition is represented by the variational inequality (VI) constraints, and the MILP approximation is solved by applying a cutting constraint algorithm (to deal with the VI-constraints) together with a commercial MILP-solver. Numerical results are presented for a small network, and the results are encouraging.
|
|
| 17. |
- Ekström, Joakim, 1980-
(author)
-
Optimizing toll locations and levels in a road congestion pricing schemes by minimizing the deviation from marginal social cost pricing tolls
- 2012
-
In: Transportation & Logistics Management. - Hong Kong : Hong Kong Society for Transportation Studies (HKSTS). - 9789881581419
-
Conference paper (other academic/artistic)abstract
- To find second-best optimal toll locations and toll levels in a road traffic network, which maximize the social surplus, can be formulated as a bi-level optimization program. The bi-level program is both non-convex and non-smooth and therefore considered as a demanding optimization problem to solve. First-best optimal tolls can, however, easily be computed by solving a convex program, and this paper examines the possibility to make use of these first-best tolls when searching for second-best solutions. By formulating an optimization problem, which instead of maximizing the social surplus, search for the toll locations and toll levels which minimize the deviation from first-best tolls on a route-level, a mixed integer linear program is formulated. The approach of minimizing the deviation from first-best route tolls is applied to a Stockholm network model, and results are provided to evaluate the applicability of the approach.
|
|
| 18. |
- Ekström, Joakim, 1980-
(author)
-
Optimizing toll locations and levels in a road congestion pricing schemes by minimizing the deviation from marginal social cost pricing tolls
- 2012
-
Conference paper (other academic/artistic)abstract
- The problem of designing a congestion pricing system, assuming that the road users are distributed according to a static user equilibrium, is commonly formulated as a bi-level program, with the toll locations and toll levels being the decision variables. The upper level objective is to maximize the social surplus, and on the lower level a convex program is solved to obtain the road users response to the toll level solution. This optimization problem is both non-convex and non-smooth and therefore difficult to solve for a global optimum. For one special case, when all links are tollable and when there are no restrictions on the toll levels, the bi-level program can be formulated as a convex program which can easily be solved, with one optimal solution, among possibly several ones, equal to marginal cost pricing tolls (MSCP). With MSCP tolls, the road users are charged a toll on each congested road segment equal to the marginal increase in total travel cost incurred by one additional road user on the road segment. Any solution which maximizes the social surplus functions is referred to as a first-best toll level solution (as opposed to second-best when there are restrictions on toll locations and/or toll levels) with system optimal link flows and demands. While there may exist several first-best toll level solutions, they all satisfy the principle of MSCP on a route level, if the demand in the traffic network is elastic. This result has previously in the literature been used to devise a set of feasible toll vectors which all result in system optimal flows and demands. In this paper the set of feasible first-best toll vectors is relaxed to allow second-best solutions. The relaxation is performed on a route level, and the deviation from first-best route tolls is penalized. The objective then becomes to minimize the penalty, weighted by some factor to reflect each routes importance. The optimization problem either takes the form of a linear program (LP), if the toll locations are fixed, or a mixed integer linear program (MILP), if the toll locations are variable. For solutions with optimal objective function value close to zero, the toll level solution will be close to the global maximizer of the social surplus function. As the number of tollable links is reduced, the true equilibrium demands and link flows may differ from the system optimal ones. Thus, the performance of the approach can be assumed to be dependent of the number of tollable links. Numerical results show that the approach can give valuable information on close to optimal toll locations and toll levels, even when a small subset of the links are tollable.
|
|
| 19. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Simulation based optimisation of toll levels in urban road traffic networks
- 2014
-
Conference paper (other academic/artistic)abstract
- There has recently been a growing interest in analysing road pricing schemes in urban areas using dynamic traffic assignment (DTA) tools. The motivation behind this development is the problem for static transportation models to accurately predict travel time savings, from introducing road pricing, in networks with severe congestion. Finding optimal toll levels and locations in urban road traffic networks has so far mainly been studied using either derivative-free heuristics (e.g. genetic algorithms and simulated annealing) or ascent methods. Both approaches rely on fast computations of the road users response (traffic flows, travel times and demands), given the road pricing scheme, and for the case of ascent methods, the methods also rely on fast computations (or rather approximation) of derivatives. Using DTA tools for evaluating the road users’ response to a pricing scheme is, however, very computationally expensive. Previously developed methods are therefore not suitable to use together with DTA.Surrogate models, e.g. in terms of response surfaces, are commonly used for optimisation problems with expensive-to-evaluate objective functions. The surrogate model is used for approximating the expensive-to-evaluate objective function, and the optimisation is then done on the surrogate model instead. The performances of optimisation methods based on surrogate models are, however, dependent on experimental design, infill strategy and choice of surrogate model itself. The experimental design will give the initial set of toll levels, for which the DTA needs to be evaluated, the infill strategy determined additional toll levels to be evaluated by the DTA, and the choice of surrogate model will give the functional form to be fitted to the sampled toll levels.We apply a surrogate model framework for optimising toll levels in a multiple cordon pricing scheme. In the first stage we evaluate the experimental design, infill strategy and choice of surrogate model, using a static macroscopic traffic model. This allows a large number of experiments to be carried out, which would not be possible with a DTA tool. It also allows us to compare the performance of the surrogate modelling approach with other global optimisation methods. In the second stage, the insight which has been gained from the experiments with the static model is used when applying the surrogate modelling approach to a DTA model of Stockholm.Computational results are presented for a Stockholm network with three cordons, each with differentiated toll level in both directions, resulting in a total of six toll level variables. Surrogate models in the form of Radial Basis Functions and Kriging models are evaluated with a static model of Stockholm, for different initial experimental designs, infill strategies and choice of surrogate models. In comparison with previously developed derivative based methods for static models, our results show that the surrogate based optimisation approach performs better, since it allows for metaheuristic methods to search for global optimal solutions efficiently.
|
|
| 20. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Surrogatbaserad optimering av avgiftsnivåer i trängselavgiftssystem
- 2015
-
Reports (other academic/artistic)abstract
- Trängselskatt finns idag i både Stockholm och Göteborg, och det är troligt att utformningen av dessa trängselskattesystem kommer att justeras framöver med avseende på avgiftsnivå, placering och tidpunkt. För Stockholm finns beslut om ändring från januari 2016 och i Göteborg ändrades avgiftsnivåerna i januari 2015. I detta projekt utvecklas metoder som ska kunna ge stöd vid justering av avigiftsnivåer, så att en så stor samhällsekonomisk nytta som är möjligt uppnås med trängselskattesystemet.För storstadsområden, där det under rusningstrafik är trängsel i delar av nätverket, är trängselskatt främst intressant att analysera med dynamiska transportmodeller. Tidigare utveckling av metoder för optimal avgiftssättning har dock främst fokuserat på statiska modeller, exempelvis Emme, som har kända problem med att korrekt uppskatta förändring i restider när det är trängsel i delar av trafiknätverket. I detta projekt har vi därför tillämpat surrogat-baserad optimering, som är en metodansats som ställer få krav på vilken transportmodell som används. Den dynamiska transportmodellen Regent/VisumDUE finns sedan tidigare implementerad för Stockholmsregionen, och har därför även använts i detta projekt. VisumDUE är en makroskopisk nätutläggningsmodell med dynamiskt ruttval, och Regent är en efterfrågemodell som innehåller resgenerering, färdmedelsval och destinationsval för arbetsresor[1].Surrogat-baserad optimering erbjuder ett ramverk för optimering av problem med beräkningsmässigt kostsamma målfunktioner. Genom att approximera en funktionsyta till samplade punkter från den kostsamma målfunktionen, kan optimeringen istället göras över den approximerade funktionsytan. För Regent/VisumDUE tar utvärderingen av ett givet trängselskattescenario ca tio timmar, och det är denna beräkningstid som gör målfunktionen kostsam. Givet ett antal samplade punkter, görs ytterligare sampling utifrån en given strategi för att förbättra approximationen, så kallad iterativ sampling. Inom ramverket finns dock en mängd möjligheter för hur de olika komponenterna designas. Därför är det svårt att utvärdera surrogat-baserad optimering med endast Regent/VisumDUE. En statisk transportmodell har därför använts för att utvärdera ett antal kombinationer av samplingsstrategi och funktionsyta. Den mest lovande kombinationen har sedan även utvärderats med Regent/VisumDUE. För att vara praktiskt tillämpbart i framtiden har fokus i projektet varit att utvärdera hur metodansatsen fungerar när antalet möjliga tulluppsättningar är kraftigt begränsat (20-40 stycken).Det scenario som har använts som grund i projektet är trängselskatt i Stockholm på nuvarande tullring, på Essingeleden samt på innerstadsbroarna. Skatten är differentierad med avseende på riktning, vilket ger sex olika skattenivåer att optimera. Optimeringen har gjorts för trängselskattenivå under maxtimmen. I det dynamiska fallet har trängselskattens nivå utanför maxtimme funnits med som indata, men samma tidsprofil som på nuvarande tullring har antagits i alla scenarier (avgiftstrappa 50%, 75%, 100%, 75%, 50%). Utvärderingen med den statiska transportmodellen visar att lösningar nära globalt optimum kan uppnås med endast 40 utvärderade trängselskattenivåer, och en tydlig förbättring av den samhällsekonomiska nyttan uppnås redan vid 20 utvärderade trängselskattenivåer.Även med ett kraftigt begränsat antal utvärderingar av den kostsamma målfunktionen i Regent/VisumDUE, har vi visat att det är möjligt att använda metodansatsen. En tydlig förbättring av den samhällsekonomiska nyttan uppnås med endast 22 utvärderade trängselskattenivåer. Ytterligare experiment skulle dock behövas för att undersöka hur stor denna förbättring är i förhållande till vad som skulle kunna uppnås.
|
|
| 21. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Surrogate-based optimisation of toll levels in congestion pricing schemes
- 2014
-
In: Transportation Infrastructure. - Hong Kong : Hong Kong Society of Transportation Studies Limited. - 9789881581433 ; , s. 209-216
-
Conference paper (peer-reviewed)abstract
- There has recently been a growing interest in analysing road pricing schemes in urban areas using dynamic traffic assignment (DTA) tools. Finding optimal toll levels in cordon based road pricing schemes has so far mainly been studied using either derivative-free heuristics or ascent methods. For future use of DTA tools such methods are not suitable and in this paper we investigate how a surrogate modelling framework can be used instead. We focus on cases when the number of costly objective function evaluations is limited to between 20 and 40. In order to allow a large number of different configurations of the surrogate modelling framework to be evaluated, a static user equilibrium model is used for simulating the road users’ response to a given pricing scheme. The results show that for a realistic scenario, valuable information on close to optimal toll levels can be achieved with only 20 costly function evaluations.
|
|
| 22. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Towards optimal locations and toll levels in congestion pricing schemes
- 2009
-
In: 16th ITS World Congress. - : World Congress on Intelligent Transport Systems (ITS).
-
Conference paper (peer-reviewed)abstract
- This paper addresses the problem of designing a road congestion pricing scheme with link tolls. The problem involves decisions on where to locate the toll collecting facilities and what tolls to charge the road users. We formulate this problem as a bi-level program, with the objective to maximize the net social surplus, which include the cost of setting up and operate the toll collection system. A previously developed heuristic method is applied to find close to optimal toll locations and charges for a traffic network representing the Stockholm region. The result is compared with the current congestion pricing scheme in Stockholm.
|
|
| 23. |
- Ekström, Joakim, 1980-, et al.
(author)
-
Why modeling of heavy goods vehicles matters when designing congestion pricing schemes
- 2013
-
Conference paper (other academic/artistic)abstract
- Differentiated tolls for cars and heavy goods vehicles (HGVs) may improve the efficiency of congestion pricing schemes. Not only do private trips by car and commercial activities by HGV differ in how the time is valued by the user/operator, in general, one additional truck will also contribute to the congestion more than one additional car. In this paper we show how different modeling approaches for HGV route choice and demand may affect the evaluation of road pricing schemes. Also, we provide a small example to illustrate potential problems, and present results for a larger model of the German city Stuttgart.
|
|
| 24. |
- Grumert, Ellen, 1983-, et al.
(author)
-
Effects of incidents on motorways : a proposed methodology for estimating and predicting demand, duration and capacity for incident management
- 2021
-
Reports (other academic/artistic)abstract
- Effective traffic incident management is important to minimize negative impacts of congestion caused by incidents. Predictions of the traffic state at the incident site and its surrounding road network, together with an estimate of incident duration, can be used to get increased knowledge about current and future incident characteristics. The aim is to propose methods for estimating capacity, duration and demand profiles in case of an incident, and to explore how the level of detail and the possibility to identify explanatory variables for incidents with similar characteristics given currently available data sources affects the proposed methods. The knowledge obtained within the project is intended to be used for incident management. The report presents a methodology for predicting capacity, traffic demand, and incident duration, when none of the parameters are known. The proposed methods can be used as input to traffic models, when the purpose is to perform scenario-based analysis and real-time predictions to be used in the decision-making processes for traffic management/control, but also for predicting travel times which can be communicated to road users.A motorway use-case study area south of Stockholm is used to propose methods for predicting incident duration, capacity and demand profiles based on the availability of data. The methodology is evaluated by using the predicted variables as input in a scenario-based analysis with two queue models.
|
|
| 25. |
|
|
