| 1. |
- Larsson, Torbjörn, 1957-, et al.
(författare)
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A column generation procedure for the side constrained traffic equilibrium problem
- 2004
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Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 38:1, s. 17-38
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Tidskriftsartikel (refereegranskat)abstract
- We present a column generation procedure for the side constrained traffic equilibrium problem. A dual stabilization scheme is introduced to improve the computational performance. Computational experiments for the case of linear side constraints are presented. The test problems are well known traffic equilibrium instances where side constraints of link flow capacity type and general linear side constraints are added. The computational results are promising especially for instances with a relatively small number of side constraints.
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| 2. |
- Mishalani, R. G., et al.
(författare)
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Modeling the spatial behavior of infrastructure condition
- 2002
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Ingår i: Transportation Research Part B. - 0191-2615 .- 1879-2367. ; 36:2, s. 171-194
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Tidskriftsartikel (refereegranskat)abstract
- A new understanding of the spatial behavior of infrastructure condition is presented and a methodology for identifying this behavior is developed. Based on two deterioration mechanisms, causal and interactive, a nonstationary stochastic spatial model with a piecewise constant mean function is proposed. Based on this model, a methodology founded on nonparametric cluster analysis and dynamic programming is developed to identify the optimal spatial regions, referred to as fields, within which behavior is uniform and, consequently, condition can be estimated accurately. Validation using detailed distress data from three roadway facilities, each 15 km long, is presented. The value of the model is also demonstrated by comparing it against existing methods for characterizing infrastructure condition over space.
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| 3. |
- Aurell, Alexander, et al.
(författare)
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Modeling tagged pedestrian motion : A mean-field type game approach
- 2019
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Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 121, s. 168-183
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Tidskriftsartikel (refereegranskat)abstract
- This paper suggests a model for the motion of tagged pedestrians: Pedestrians moving towards a specified targeted destination, which they are forced to reach. It aims to be a decision-making tool for the positioning of fire fighters, security personnel and other services in a pedestrian environment. Taking interaction with the surrounding crowd into account leads to a differential nonzero-sum game model where the tagged pedestrians compete with the surrounding crowd of ordinary pedestrians. When deciding how to act, pedestrians consider crowd distribution-dependent effects, like congestion and crowd aversion. Including such effects in the parameters of the game, makes it a mean-field type game. The equilibrium control is characterized, and special cases are discussed. Behavior in the model is studied by numerical simulations.
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| 4. |
- Bar-Gera, Hillel, et al.
(författare)
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Computational precision of traffic equilibria sensitivities in automatic network design and road pricing
- 2013
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Ingår i: Transportation Research Part B: Methodological. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 57, s. 485-500
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies demonstrate the importance of computational precision of user equilibrium traffic assignment solutions for scenario comparisons. When traffic assignment is hierarchically embedded in a model for network design and/or road pricing, not only the precision of the solution itself becomes more important, but also the precision of its derivatives with respect to the design parameters should be considered. The main purpose of this paper is to present a method for precise computations of equilibrium derivatives. Numerical experiments are used for two evaluations: (1) precision of computed equilibrium derivatives for a medium-size network (Anaheim); and (2) the impact of precise derivatives on capacity-expansion solution quality for a small network (Sioux Falls).
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| 5. |
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| 6. |
- Börjesson, Maria, 1974-, et al.
(författare)
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Valuations of travel time variability in scheduling versus mean-variance models
- 2012
-
Ingår i: Transportation Research Part B. - Stockholm : Statens väg- och transportforskningsinstitut. - 0191-2615 .- 1879-2367. ; 46:7, s. 855-873
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The standard method of estimating the value of travel time variability for use in policy appraisal is to estimate the parameters of a reduced-form utility function, where some measure of travel time variability (such as the standard deviation) is included. A problem with this approach is that the obtained valuation will in general depend on the standardized travel time distribution, and hence cannot be transferred from one context to another. A recently suggested remedy of this problem has been to estimate a scheduling model, which in theory is transferrable, and use the implied reduced-form to derive valuations for use in appraisal. In this paper we estimate both a scheduling model and the implied reduced-form model, using stated choice data. The valuation of travel time variability implied by the scheduling model turns out to be substantially smaller than what is obtained from a reduced-form model estimated on the same sample. The results suggest that the scheduling model does not capture all of the disutility arising from travel time variability. Hence, although it can be shown that scheduling and reduced-form models are “theoretically equivalent”, that hypothesized equivalence is not reflected in the empirical evidence. We speculate that the derivation of reduced-form models from an underlying scheduling model omits two essential features: first, the notion of an exogenously fixed “preferred arrival time” neglects the fact that most activities can be rescheduled given full information about the travel times in advance, and second, disutility may be derived from uncertainty as such, in the form of anxiety, decisions costs or costs for having contingency plans. We also report our estimates of the valuation of travel time variability for public transit trips, for use in applied appraisal.
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| 7. |
- Cats, Oded, et al.
(författare)
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A dynamic stochastic model for evaluating congestion and crowding effects in transit systems
- 2016
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Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 89, s. 43-57
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Tidskriftsartikel (refereegranskat)abstract
- One of the most common motivations for public transport investments is to reduce congestion and increase capacity. Public transport congestion leads to crowding discomfort, denied boardings and lower service reliability. However, transit assignment models and appraisal methodologies usually do not account for the dynamics of public transport congestion and crowding and thus potentially underestimate the related benefits. This study develops a method to capture the benefits of increased capacity by using a dynamic and stochastic transit assignment model. Using an agent-based public transport simulation model, we dynamically model the evolution of network reliability and on-board crowding. The model is embedded in a comprehensive framework for project appraisal.A case study of a metro extension that partially replaces an overloaded bus network in Stockholm demonstrates that congestion effects may account for a substantial share of the expected benefits. A cost-benefit analysis based on a conventional static model will miss more than a third of the benefits. This suggests that failure to represent dynamic congestion effects may substantially underestimate the benefits of projects, especially if they are primarily intended to increase capacity rather than to reduce travel times.
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| 8. |
- Čičić, Mladen, 1991-, et al.
(författare)
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Front-tracking transition system model for traffic state reconstruction, model learning, and control with application to stop-and-go wave dissipation
- 2022
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 166, s. 212-236
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Tidskriftsartikel (refereegranskat)abstract
- Connected and Autonomous Vehicles is a technology that will be disruptive for all layers of traffic control. The Lagrangian, in-the-flow nature of their operation offers untapped new potentials for sensing and actuation, but also presents new fundamental challenges. In order to use these vehicles for traffic state reconstruction and control, we need suitable traffic models, which should be computationally efficient and able to represent complex traffic phenomena. To this end, we propose the Front-tracking Transition System Model, a cell-free modelling approach that can incorporate Lagrangian measurements, and has a structure that yields itself to on-line model learning and control. The model is formulated as a transition system, and based on the front-tracking method for finding entropy solutions to the Lighthill-Whitham-Richards model. We characterize the solution of this model and show that it corresponds to the solution of the underlying PDE traffic model. Algorithms for traffic state reconstruction and model learning are proposed, exploiting the model structure. The model is then used to design a prediction -based control law for stop-and-go wave dissipation using randomly arriving Connected and Autonomous Vehicles. The proposed control framework is able to estimate the traffic state and model, adapt to changes in the traffic dynamics, and achieve a reduction in vehicles' Total Time Spent.
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| 9. |
- Corthout, Ruben, et al.
(författare)
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Non-unique flows in macroscopic first-order intersection models
- 2012
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 46:3, s. 343-359
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Tidskriftsartikel (refereegranskat)abstract
- Currently, most intersection models embedded in macroscopic Dynamic Network Loading (DNL) models are not well suited for urban and regional applications. This is so because so-called internal supply constraints, bounding flows due to crossing and merging conflicts inherent to the intersection itself, are missing. This paper discusses the problems that arise upon introducing such constraints. A general framework for the distribution of (internal) supply is adopted, which is based on the definition of priority parameters that describe the strength of each flow in the competition for a particular supply. Using this representation, it is shown that intersection models - with realistic behavioral assumptions, and in simple configurations - can produce non-unique flow patterns under identical boundary conditions. This solution non-uniqueness is thoroughly discussed and approaches on how it can be dealt with are provided. Also, it is revealed that the undesirable model properties are not solved - but rather enhanced - when diverting from a point-like to a spatial modeling approach.
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| 10. |
- Daly, Andrew, et al.
(författare)
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Calculating errors for measures derived from choice modelling estimates
- 2012
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 46:2, s. 333-341
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of choice models produces a set of parameter estimates and an associated covariance matrix, usually based on maximum likelihood estimation. However, in many cases, the values of interest to analysts are in fact functions of these parameters rather than the parameters themselves. It is thus also crucial to have a measure of variance for these derived quantities and it is preferable that this can be guaranteed to have the maximum likelihood properties, such as minimum variance. While the calculation of standard errors using the Delta method has been described for a number of such measures in the literature, including the ratio of two parameters, these results are often seen to be approximate calculations and do not claim maximum likelihood properties. In this paper, we show that many measures commonly used in transport studies and elsewhere are themselves maximum likelihood estimates and that the standard errors are thus exact, a point we illustrate for a substantial number of commonly used functions. We also discuss less appropriate methods, notably highlighting the issues with using simulation for obtaining the variance of a function of estimates.
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| 11. |
- De Borger, Bruno, et al.
(författare)
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Information provision by regulated public transport companies
- 2012
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 46:4, s. 492-510
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Tidskriftsartikel (refereegranskat)abstract
- We study the interaction between pricing, frequency of service and information provision by public transport firms offering scheduled services, and we do so under various regulatory regimes. The model assumes that users can come to the bus stop or rail station at random or they can plan their trips; the fraction of users who plan their trips is endogenous and depends on the frequency of service and on the quality of information provided. Four institutional regimes are considered, reflecting various degrees of government regulation. A numerical example illustrates the theoretical results. Findings include the following. First, fare regulation induces the firm to provide less frequency and less information than is socially optimal. Second, if information and frequency did not affect the number of planning users a higher fare always induces the firm to raise both frequency and the quality of information. With endogenous planning, however, this need not be the case, as the effect of higher fares strongly depends on how frequency and information quality affect the number of planners. Third, a profit-maximizing firm offers more information than a fare-regulated firm. Fourth, if the agency regulates both the fare and the quality of information then more stringent information requirements induce the firm to reduce frequency; this strongly limits the welfare improvement of information regulation. Finally, of all institutional structures considered, socially optimal fares, frequency and quality of information stimulate passengers least to plan their trips, because the high frequency offered reduces the benefits of trip planning.
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| 12. |
- Ding-Mastera, Jing, et al.
(författare)
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A latent-class adaptive routing choice model in stochastic time-dependent networks
- 2019
-
Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 124, s. 1-17
-
Tidskriftsartikel (refereegranskat)abstract
- Transportation networks are inherently uncertain due to random disruptions; meanwhile, real-time information potentially helps travelers adapt to realized traffic conditions and make better route choices under such disruptions. Modeling adaptive route choice behavior is essential in evaluating real-time traveler information systems and related policies. This research contributes to the state of the art by developing a latent-class routing policy choice model in a stochastic time-dependent network with revealed preference data. A routing policy is defined as a decision rule applied at each link that maps possible realized traffic conditions to decisions on the link to take next. It represents a traveler's ability to look ahead in order to incorporate real-time information not yet available at the time of decision. A case study is conducted in Stockholm, Sweden and data for the stochastic time-dependent network are generated from hired taxi Global Positioning System (GPS) readings. A latent-class Policy Size Logit model is specified, with routing policy users who follow routing policies and path users who follow fixed paths. Two additional layers of latency in the measurement equation are accounted for: 1) the choice of a routing policy is latent and only its realized path on a given day can be observed; and 2) when GPS readings have relatively long gaps, the realized path cannot be uniquely identified, and the likelihood of observing vehicle traces with non-consecutive links is instead maximized. Routing policy choice set generation is based on the generalization of path choice set generation methods. The generated choice sets achieve 95% coverage for 100% overlap threshold after correcting GPS mistakes and breaking up trips with intermediate stops, and further achieve 100% coverage for 90% overlap threshold. Estimation results show that the routing policy user class probability increases with trip length, and the latent-class routing policy choice model fits the data better than a single-class path choice or routing policy choice model. This suggests that travelers are heterogeneous in terms of their ability and/or willingness to plan ahead and utilize real-time information, and an appropriate route choice model for uncertain networks should take into account the underlying stochastic travel times and structured traveler heterogeneity in terms of real-time information utilization.
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| 13. |
- Ekström, Joakim, et al.
(författare)
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Optimizing Toll Locations and Levels Using a Mixed Integer Linear Approximation Approach
- 2012
-
Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 46:7, s. 834-854
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the toll design problem of finding the toll locations and levels in a congestion pricing scheme, which minimize the total travel time and the toll-point cost (set-up and operational costs of the toll collecting facilities). Road users in the network are assumed to be distributed according to the principle of user equilibrium, with the demand assumed to be fixed and given a priori. The toll design problem is commonly formulated as a nonlinear program, which in general is non-convex and non-smooth, and thus difficult to solve for a global optimum. In this paper, the toll design problem is approximated by a mixed integer linear program (MILP), which can be solved to its globally optimal solution. The MILP also gives a lower bound estimation of the original non-linear problem, and the accuracy of the approximation is improved by iteratively updating the MILP. To demonstrate the approach, we apply the algorithm to two networks: a smaller network with 18 links and 4 OD-pairs to illustrate the properties of the approach, and the Sioux Falls network with 87 links and 30 OD-pairs to demonstrate the applicability of the approach.
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| 14. |
- Eliasson, Jonas, et al.
(författare)
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Cost overruns and demand shortfalls - Deception or selection?
- 2013
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 57, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- A number of highly cited papers by Flyvbjerg and associates have shown that ex ante infrastructure appraisals tend to be overly optimistic. Ex post evaluations indicate a bias where investment costs are higher and benefits lower on average than predicted ex ante. These authors argue that the bias must be attributed to intentional misrepresentation by project developers. This paper shows that the bias may arise simply as a selection bias, without there being any bias at all in predictions ex ante, and that such a bias is bound to arise whenever ex ante predictions are related to the decisions whether to implement projects. Using a database of projects we present examples indicating that the selection bias may be substantial. The examples also indicate that benefit-cost ratios remain a useful selection criterion even when cost and benefits are highly uncertain, gainsaying the argument that such uncertainties render cost-benefit analyses useless.
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| 15. |
- Eliasson, Jonas, et al.
(författare)
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Costs and benefits of parking charges in residential areas
- 2022
-
Ingår i: Transportation Research Part B. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0191-2615 .- 1879-2367. ; 166, s. 95-109
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Tidskriftsartikel (refereegranskat)abstract
- We develop a model for empirical evaluation of the social costs and benefits of street parking charges. From the model, we derive an expression for optimal parking charges and occupancy levels: in optimum, parking search costs are balanced against the loss of consumer surplus from unused parking spaces. Contrary to rules-of-thumb common in practice, optimal occupancy levels are not constant but depend on parking turnover rates and parking search costs. We demonstrate the model's applicability in a case study from Stockholm, where parking charges were recently introduced in suburban residential areas. The charges had considerable effects on parking de-mand, but our analysis shows that the overall welfare effect was a substantial welfare loss. Using parameters and demand functions estimated from the case study, we calculate optimal parking charges and occupancy levels, and show that the welfare loss arises because the introduced charges were considerably higher than the optimal ones.
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| 16. |
- Engelson, Leonid, et al.
(författare)
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Additive measures of travel time variability
- 2011
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:10, s. 1560-1571
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Tidskriftsartikel (refereegranskat)abstract
- This paper derives a measure of travel time variability for travellers equipped with scheduling preferences defined in terms of time-varying utility rates, and who choose departure time optimally. The corresponding value of travel time variability is a constant that depends only on preference parameters. The measure is unique in being additive with respect to independent parts of a trip. It has the variance of travel time as a special case. Extension is provided to the case of travellers who use a scheduled service with fixed headway.
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| 17. |
- Engelson, Leonid, et al.
(författare)
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Scheduling preferences and the value of travel time information
- 2020
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Ingår i: Transportation Research Part B. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0191-2615 .- 1879-2367. ; 134, s. 256-265
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we derive the value of a signal obtained by a traveller prior to the choice of departure time. The signal does not have to be a perfect prediction of the travel time. It is sufficient that it carries information about the travel time. The traveller may then consider the distribution of travel time conditional on the signal to increase her expected utility by making a better informed choice of departure time. We show that a signal always increases the expected utility compared to the situation without any signal. For a broad class of signals, the expected utility is monotone with respect to signal strength. Furthermore, we demonstrate that even perfect travel time information does not necessarily eliminate the cost of travel time variability and we establish necessary and sufficient conditions for when it does. We find that the predictable part of travel time variability may or may not be costly, depending on the shape of the traveller's scheduling utility at the origin of the trip. Using estimates of scheduling preferences from the literature, we show that the cost of predictable travel time variability may constitute a substantial part of the total cost of travel time variability. In a particular case of scheduling preferences, travel time distribution and noise distribution, we establish an analytic relationship between the strength of the signal and the expected utility of the trip and evaluate the marginal cost of signal weakness. This knowledge may facilitate design and cost-benefit analysis of traveller information systems and policies decreasing travel time variability. (C) 2020 Elsevier Ltd. All rights reserved.
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| 18. |
- Engelson, Leonid, et al.
(författare)
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The cost of travel time variability : Three measures with properties
- 2016
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Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 91, s. 555-564
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the relationships between three types of measures of the cost of travel time variability: measures based on scheduling preferences and implicit departure time choice, Bernoulli type measures based on a univariate function of travel time, and mean-dispersion measures. We characterise measures that are both scheduling measures and mean-dispersion measures and measures that are both Bernoulli and mean-dispersion. There are no measures that are both scheduling and Bernoulli. We consider the impact of requiring that measures are additive or homogeneous, proving also a new strong result on the utility rates in an additive scheduling measure. These insights are useful for selecting cost measures to use in applications.
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| 19. |
- Farhad, Farokhi, et al.
(författare)
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A piecewise-constant congestion taxing policy for repeated routing games
- 2015
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 78, s. 123-143
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider repeated routing games with piecewise-constant congestion taxing in which a central planner sets and announces the congestion taxes for fixed windows of time in advance. Specifically, congestion taxes are calculated using marginal congestion pricing based on the flow of the vehicles on each road prior to the beginning of the taxing window (and, hence, there is a time-varying delay in setting the congestion taxes). We motivate the piecewise-constant taxing policy by that users or drivers may dislike fast-changing prices and that they also prefer prior knowledge of the prices. We prove for this model that the multiplicative update rule and the discretized replicator dynamics converge to a socially optimal flow when using vanishing step sizes. Considering that the algorithm cannot adapt itself to a changing environment when using vanishing step sizes, we propose adopting constant step sizes in this case. Then, however, we can only prove the convergence of the dynamics to a neighborhood of the socially optimal flow (with the size of the neighbourhood being of the order of the selected step size). The results are illustrated on a nonlinear version of Pigou's famous routing game.
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| 20. |
- Farooq, Bilal, et al.
(författare)
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Simulation based population synthesis
- 2013
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 58:SI, s. 243-263
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Tidskriftsartikel (refereegranskat)abstract
- Microsimulation of urban systems evolution requires synthetic population as a key input. Currently, the focus is on treating synthesis as a fitting problem and thus various techniques have been developed, including Iterative Proportional Fitting (IPF) and Combinatorial Optimization based techniques. The key shortcomings of these procedures include: (a) fitting of one contingency table, while there may be other solutions matching the available data (b) due to cloning rather than true synthesis of the population, losing the heterogeneity that may not have been captured in the microdata (c) over reliance on the accuracy of the data to determine the cloning weights (d) poor scalability with respect to the increase in number of attributes of the synthesized agents. In order to overcome these shortcomings, we propose a Markov Chain Monte Carlo (MCMC) simulation based approach. Partial views of the joint distribution of agent's attributes that are available from various data sources can be used to simulate draws from the original distribution. The real population from Swiss census is used to compare the performance of simulation based synthesis with the standard IPF. The standard root mean square error statistics indicated that even the worst case simulation based synthesis (SRMSE = 0.35) outperformed the best case IPF synthesis (SRMSE = 0.64). We also used this methodology to generate the synthetic population for Brussels, Belgium where the data availability was highly limited.
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| 21. |
- Flötteröd, Gunnar, et al.
(författare)
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Bidirectional pedestrian fundamental diagram
- 2015
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 71, s. 194-212
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a new model of stationary bidirectional pedestrian flow. Starting out from microscopic first principles, a bidirectional fundamental diagram (FD) is derived that defines direction-specific flow rates as functions of direction-specific densities. The FD yields non-negative and bounded flows and guarantees that the instantaneous density changes that would result from these flows stay bounded between zero and jam density. In its minimal configuration, it uses just as many parameters as a unidirectional triangular FD: maximum walking speed, jam density, a collision avoidance parameter (from which the backward wave speed can be derived). A one-on-one mapping between the parameters guiding uni- and bidirectional pedestrian flows is proposed and both conceptually and empirically justified. Generalizations of the FD that maintain its desirable properties turn out to be straightforward by making its parameters density-dependent. The FD performs very well in comparisons against simulated and real data.
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| 22. |
- Flötteröd, Gunnar, et al.
(författare)
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Metropolis-Hastings sampling of paths
- 2013
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 48, s. 53-66
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Tidskriftsartikel (refereegranskat)abstract
- We consider the previously unsolved problem of sampling paths according to a given distribution from a general network. The problem is difficult because of the combinatorial number of alternatives, which prohibits a complete enumeration of all paths and hence also forbids to compute the normalizing constant of the sampling distribution. The problem is important because the ability to sample from a known distribution introduces mathematical rigor into many applications, including the estimation of choice models with sampling of alternatives that can be formalized as paths in a decision network (most obviously route choice), probabilistic map matching, dynamic traffic assignment, and route guidance.
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| 23. |
- Flötteröd, Gunnar, et al.
(författare)
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Operational macroscopic modeling of complex urban road intersections
- 2011
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:6, s. 903-922
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Tidskriftsartikel (refereegranskat)abstract
- This article describes a new approach to the macroscopic first order modeling and simulation of traffic flow in complex urban road intersections. The framework is theoretically sound, operational, and comprises a large body of models presented so far in the literature. Working within the generic node model class of Tampere et al. (2011), the approach is developed in two steps. First, building on the incremental transfer principle of Daganzo et al. (1997), an incremental node model for general road intersections is developed. A limitation of this model (as of the original incremental transfer principle) is that it does not capture situations where the increase of one flow decreases another flow, e.g., due to conflicts. In a second step, the new model is therefore supplemented with the capability to describe such situations. A fixed-point formulation of the enhanced model is given, solution existence and uniqueness are investigated, and two solution algorithms are developed. The feasibility and realism of the new approach is demonstrated through a synthetic and a real case study.
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| 24. |
- Flötteröd, Gunnar, et al.
(författare)
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Stochastic network link transmission model
- 2017
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Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 102, s. 180-209
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Tidskriftsartikel (refereegranskat)abstract
- This article considers the stochastic modeling of vehicular network flows, including the analytical approximation of joint queue-length distributions. The article presents two main methodological contributions. First, it proposes a tractable network model for finite space capacity Markovian queueing networks. This methodology decomposes a general topology queueing network into a set of overlapping subnetworks and approximates the transient joint queue-length distribution of each subnetwork. The subnetwork overlap allows to approximate stochastic dependencies across multiple subnetworks with a complexity that is linear in the number of subnetworks. Additionally, the network model maintains mutually consistent overlapping subnetwork distributions. Second, a stochastic network link transmission model (SLTM) is formulated that builds on the proposed queueing network decomposition and on the stochastic single-link model of Osorio and Flötteröd (2015). The SLTM represents each direction of a road and each road intersection as one queueing subnetwork. Three experiments are presented. First, the analytical approximations of the queueing-theoretical model are validated against simulation-based estimates. An experiment with intricate traffic dynamics and multi-modal joint distributions is studied. The analytical model captures most dependency structure and approximates well the simulated network dynamics and joint distributions. Even for the considered simple network, which consists of only eight links, the proposed subnetwork decomposition yields significant gains in computational efficiency: It uses less than 0.0025% of the memory that is required by the use of a full network model. Second and third, the proposed SLTM is illustrated with a linear test network adopted from the literature and a more general topology network containing a diverge node and a merge node. Time-dependent probabilistic performance measures (occupancy uncertainty bands, spillback probabilities) are presented and discussed.
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| 25. |
- Fosgerau, Mogens, et al.
(författare)
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A link based network route choice model with unrestricted choice set
- 2013
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 56, s. 70-80
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers the path choice problem, formulating and discussing an econometric random utility model for the choice of path in a network with no restriction on the choice set. Starting from a dynamic specification of link choices we show that it is equivalent to a static model of the multinomial logit form but with infinitely many alternatives. The model can be consistently estimated and used for prediction in a computationally efficient way. Similarly to the path size logit model, we propose an attribute called link size that corrects utilities of overlapping paths but that is link additive. The model is applied to data recording path choices in a network with more than 3000 nodes and 7000 links.
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| 26. |
- Fosgerau, Mogens
(författare)
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How a fast lane may replace a congestion tollle
- 2011
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Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:6, s. 845-851
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers a congested bottleneck. A fast lane reserves a more than proportional share of capacity to a designated group of travelers. Travelers are otherwise identical and other travelers can use the reserved capacity when it would otherwise be idle. The paper shows that such a fast lane is always Pareto improving under Nash equilibrium in arrival times at the bottleneck and inelastic demand. It can replicate the arrival schedule and queueing outcomes of a toll that optimally charges a constant toll during part of the demand peak. Within some bounds, the fast lane scheme is still welfare improving when demand is elastic.
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| 27. |
- Fosgerau, Mogens, et al.
(författare)
-
The value of reliability
- 2010
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 44:1, s. 38-49
-
Tidskriftsartikel (refereegranskat)abstract
- We derive the value of reliability in the scheduling of an activity of random duration, such as travel under congested conditions. Using a simple formulation of scheduling utility, we show that the maximal expected utility is linear in the mean and standard deviation of trip duration, regardless of the form of the standardised distribution of trip durations. This insight provides a unification of the scheduling model and models that include the standard deviation of trip duration directly as an argument in the cost or utility function. The results generalise approximately to the case where the mean and standard deviation of trip duration depend on the starting time. An empirical illustration is provided.
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| 28. |
- Fosgerau, Mogens, et al.
(författare)
-
The value of travel time variance
- 2011
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:1, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers the value of travel time variability under scheduling preferences that are defined in terms of linearly time varying utility rates associated with being at the origin and at the destination. The main result is a simple expression for the value of travel time variability that does not depend on the shape of the travel time distribution. The related measure of travel time variability is the variance of travel time. These conclusions apply equally to travellers who can freely choose departure time and to travellers who use a scheduled service with fixed headway. Depending on parameters, travellers may be risk averse or risk seeking and the value of travel time may increase or decrease in the mean travel time.
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| 29. |
- Frejinger, Emma, 1979-, et al.
(författare)
-
Capturing correlation with subnetworks in route choice models
- 2007
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 41:3, s. 363-378
-
Tidskriftsartikel (refereegranskat)abstract
- When using random utility models for a route choice problem, a critical issue is the significant correlation among alternatives. There are basically two types of models proposed in the literature to address it: (i) a deterministic correction of the path utilities in a Multinomial Logit model (Such as the Path Size Logit or the C-Logit models) and (ii) an explicit modeling of the correlation through assumptions about the error terms, and the use of advanced discrete choice models such as the Cross-Nested Logit or the Error Component models. The first is simple, easy to handle and often used in practice. Unfortunately, it does not correctly capture the correlation structure, as we discuss in details in the paper. The second is more consistent with the modeling objectives, but very complicated to specify and estimate. The modeling framework proposed in this paper allows the analyst to control the trade-off between the simplicity of the model and the level of realism. Within this framework, the key concept capturing the correlation structure is called subnetwork. A subnetwork is a simplification of the road network only containing easy identifiable and behaviorally relevant roads. In practice, the subnetwork can easily be defined based oil the route network hierarchy. The importance and the originality of our approach lie in the possibility to capture the most important correlation without considerably increasing the model complexity. This makes it suitable for a wide spectrum of application,.;, namely involving realistic large-scale networks. As an illustration, we present estimation results of a factor analytic specification of a mixture of Multinomial Logit model, where the correlation among paths is captured by error components. The estimation is based on a GPS dataset collected in the Swedish city of Borlange. The results show a significant increase in model fit and forecasting performance for the Error Component model compared to a Path Size Logit model. Moreover, the correlation parameters are significant.
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| 30. |
- Frejinger, Emma, et al.
(författare)
-
Sampling of alternatives for route choice modeling
- 2009
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 43:10, s. 984-994
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new paradigm for choice set generation in the context of route choice model estimation. We assume that the choice sets contain all paths connecting each origin-destination pair. Although this is behaviorally questionable, we make this assumption in order to avoid bias in the econometric model. These sets are in general impossible to generate explicitly. Therefore, we propose an importance sampling approach to generate subsets of paths suitable for model estimation. Using only a subset of alternatives requires the path utilities to be corrected according to the sampling protocol in order to obtain unbiased parameter estimates. We derive such a sampling correction for the proposed algorithm. Estimating models based on samples of alternatives is straightforward for some types of models, in particular the multinomial logit (MNL) model. In order to apply MNL for route choice, the utilities should also be corrected to account for the correlation using, for instance, a path size (PS) formulation. We argue that the PS attribute should be computed based on the full choice set. Again, this is not feasible in general, and we propose a new version of the PS attribute derived from the sampling protocol, called Expanded PS. Numerical results based on synthetic data show that models including a sampling correction are remarkably better than the ones that do not. Moreover, the Expanded PS shows good results and outperforms models with the original PS formulation.
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| 31. |
- Hjorth, Katrine, et al.
(författare)
-
Estimating exponential scheduling preferences
- 2015
-
Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 81:1, s. 230-251
-
Tidskriftsartikel (refereegranskat)abstract
- Different assumptions about travelers' scheduling preferences yield different measures of the cost of travel time variability. Only few forms of scheduling preferences provide non-trivial measures which are additive over links in transport networks where link travel times are arbitrarily distributed independent random variables. Assuming smooth preferences, this holds only for specifications with a constant marginal utility of time at the origin and an exponential or affine marginal utility of time at the destination. We apply a generalized version of this model to stated preference data of car drivers' route and mode choice under uncertain travel times. Our analysis exposes some important methodological issues related to complex non-linear scheduling models. One issue is identifying the point in time where the marginal utility of being at the destination becomes larger than the marginal utility of being at the origin. Another issue is that models with the exponential marginal utility formulation suffer from empirical identification problems. Though our results are not decisive, they partly support the constant-affine specification, in which the value of travel time variability is proportional to the variance of travel time.
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| 32. |
- Hjorth, Katrine, et al.
(författare)
-
Using prospect theory to investigate the low marginal value of travel time for small time changes
- 2012
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 46:8, s. 917-932
-
Tidskriftsartikel (refereegranskat)abstract
- A common finding in stated preference studies that measure the value of travel time (VTT) is that the measured VTT increases with the size of the time change considered, in conflict with standard neoclassical economic theory. We present a new test of a possible explanation for the phenomenon that builds on the diminishing or constant sensitivity of the value functions in prospect theory. We use stated preference data with trade-offs between travel time and money that provide separate identification of the degrees of diminishing sensitivity for time and money gains and losses. This enables us to test and potentially falsify the prospect theory explanation. We conclude that prospect theory remains a potential explanation of the phenomenon.
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| 33. |
- Högdahl, Johan, 1989-, et al.
(författare)
-
A combined simulation-optimization approach for minimizing travel time and delays in railway timetables
- 2019
-
Ingår i: Transportation Research Part B. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0191-2615 .- 1879-2367. ; 126, s. 192-212
-
Tidskriftsartikel (refereegranskat)abstract
- Minimal travel time and maximal reliability are two of the most important properties of a railway transportation service. This paper considers the problem of finding a timetable for a given set of departures that minimizes the weighted sum of scheduled travel time and expected delay, thereby capturing these two important socio-economic properties of a timetable. To accurately represent the complex secondary delays in operational railway traffic, an approach combining microscopic simulation and macroscopic timetable optimization is proposed. To predict the expected delay in the macroscopic timetable, a surrogate function is formulated, as well as a subproblem to calibrate the parameters in the model. In a set of computational experiments, the approach increased the socio-economic benefit by 2-5% and improved the punctuality by 8-25%.
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| 34. |
- Jenelius, Erik, et al.
(författare)
-
Probe vehicle data sampled by time or space : Consistent travel time allocation and estimation
- 2015
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 71, s. 120-137
-
Tidskriftsartikel (refereegranskat)abstract
- A characteristic of low frequency probe vehicle data is that vehicles traverse multiple network components (e.g., links) between consecutive position samplings, creating challenges for (i) the allocation of the measured travel time to the traversed components, and (ii) the consistent estimation of component travel time distribution parameters. This paper shows that the solution to these problems depends on whether sampling is based on time (e.g., one report every minute) or space (e.g., one every 500 m). For the special case of segments with uniform space-mean speeds, explicit formulae are derived under both sampling principles for the likelihood of the measurements and the allocation of travel time. It is shown that time-based sampling is biased towards measurements where a disproportionally long time is spent on the last segment. Numerical experiments show that an incorrect likelihood formulation can lead to significantly biased parameter estimates depending on the shapes of the travel time distributions. The analysis reveals that the sampling protocol needs to be considered in travel time estimation using probe vehicle data.
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| 35. |
- Jenelius, Erik
(författare)
-
The value of travel time variability with trip chains, flexible scheduling and correlated travel times
- 2012
-
Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 46:6, s. 762-780
-
Tidskriftsartikel (refereegranskat)abstract
- This paper extends the analysis of the value of mean travel time (VMTT) and day-to-day travel time variability (VTTV) from single, isolated trips to daily trip chains, considering the effects of flexibility in activity scheduling and within-day correlation of travel times. Using a multi-stage stochastic programming approach, we show that the VMTT and VTTV on a trip is conditional on the realized travel times on preceding trips, first through the arrival time to the preceding activity and second through the information provided about subsequent travel times. Analytical formulas for the VMTT and VTTV are obtained for two special cases with piecewise constant and linear marginal cost functions, respectively. With flexible scheduling, there is typically a cost associated with a positive correlation of travel times, arising from persistent deviations from typical travel demand or supply on a given day. However, there is also a strict benefit in the dependence since it allows for a more efficient scheduling of later trips.
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| 36. |
- Jenelius, Erik, et al.
(författare)
-
Travel time estimation for urban road networks using low frequency probe vehicle data
- 2013
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 53, s. 64-81
-
Tidskriftsartikel (refereegranskat)abstract
- The paper presents a statistical model for urban road network travel time estimation using vehicle trajectories obtained from low frequency GPS probes as observations, where the vehicles typically cover multiple network links between reports. The network model separates trip travel times into link travel times and intersection delays and allows correlation between travel times on different network links based on a spatial moving average (SMA) structure. The observation model presents a way to estimate the parameters of the network model, including the correlation structure, through low frequency sampling of vehicle traces. Link-specific effects are combined with link attributes (speed limit, functional class, etc.) and trip conditions (day of week, season, weather, etc.) as explanatory variables. The approach captures the underlying factors behind spatial and temporal variations in speeds, which is useful for traffic management, planning and forecasting. The model is estimated using maximum likelihood. The model is applied in a case study for the network of Stockholm, Sweden. Link attributes and trip conditions (including recent snowfall) have significant effects on travel times and there is significant positive correlation between segments. The case study highlights the potential of using sparse probe vehicle data for monitoring the performance of the urban transport system.
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| 37. |
- Jenelius, Erik, et al.
(författare)
-
Traveler delay costs and value of time with trip chains, flexible activity scheduling and information
- 2011
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:5, s. 789-807
-
Tidskriftsartikel (refereegranskat)abstract
- The delay costs of traffic disruptions and congestion and the value of travel time reliability are typically evaluated using single trip scheduling models, which treat the trip in isolation of previous and subsequent trips and activities. In practice, however, when activity scheduling to some extent is flexible, the impact of delay on one trip will depend on the actual and predicted travel time on itself as well as other trips, which is important to consider for long-lasting disturbances and when assessing the value of travel information. In this paper we extend the single trip approach into a two trips chain and activity scheduling model. Preferences are represented as marginal activity utility functions that take scheduling flexibility into account. We analytically derive trip timing optimality conditions, the value of travel time and schedule adjustments in response to travel time increases. We show how the single trip models are special cases of the present model and can be generalized to a setting with trip chains and flexible scheduling. We investigate numerically how the delay cost depends on the delay duration and its distribution on different trips during the day, the accuracy of delay prediction and travel information, and the scheduling flexibility of work hours. The extension of the model framework to more complex schedules is discussed.
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| 38. |
|
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| 39. |
|
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| 40. |
- Koutsopoulos, Haris N., et al.
(författare)
-
Latent Class Model for Car Following Behavior
- 2012
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 46:5, s. 563-578
-
Tidskriftsartikel (refereegranskat)abstract
- Car-following behavior, which describes the behavior of a vehicle while following the vehicle in front of it, has a significant impact on traffic performance, safety, and air pollution. In addition, car-following is an essential component of micro-simulation models. Over the last decade the use of microscopic simulation models as a tool for investigating traffic systems, ITS applications, and emission impacts, is becoming increasingly popular. The paper presents a flexible framework for modeling car-following behavior that relaxes some limitations and assumptions of the most commonly used car following models. The proposed approach recognizes different regimes in driving such as car-following, free-flow, emergency stopping, and incorporates different decisions in each regime, such as acceleration, deceleration, and do-nothing depending on the situation. A case study using NGSIM vehicle trajectory data is used to illustrate the proposed model structure. Statistical tests suggest that the model performs better than previous models.
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| 41. |
- Lorenzo Varela, Juan Manuel, 1987-, et al.
(författare)
-
Quantifying errors in travel time and cost by latent variables
- 2018
-
Ingår i: Transportation Research Part B. - : Elsevier. - 0191-2615 .- 1879-2367. ; 117, s. 520-541
-
Tidskriftsartikel (refereegranskat)abstract
- Travel time and travel cost are key variables for explaining travel behaviour and deriving the value of time. However, a general problem in transport modelling is that these variables are subject to measurement errors in transport network models. In this paper we show how to assess the magnitude of the measurement errors in travel time and travel cost by latent variables, in a large-scale travel demand model. The case study for Stockholm commuters shows that assuming multiplicative measurement errors for travel time and cost result in a better fit than additive ones, and that parameter estimates of the choice model are impacted by some of the key modelling assumptions. Moreover, our results suggest that measurement errors in our dataset are larger for the travel cost than for the travel time, and that measurement errors are larger in self-reported travel time than software-calculated travel time for car-driver and car-passenger, and of similar magnitude for public transport. Among self-reported travel times, car-passenger has the largest errors, followed by car-driver and public transport, and for the software-calculated times, public transport exhibits larger errors than car. These errors, if not corrected, lead to biases in measures derived from the models, such as elasticities and values of travel time.
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| 42. |
- Lundgren, Jan, et al.
(författare)
-
A Heuristic for the Bilevel Origin–Destination Matrix Estimation Problem
- 2008
-
Ingår i: Transportation Research Part B. - : Institutionen för teknik och naturvetenskap. - 0191-2615 .- 1879-2367. ; 42:4, s. 339-354
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider the estimation of an origin–destination (OD) matrix, given a target OD-matrix and traffic counts on a subset of the links in the network. We use a general nonlinear bilevel minimization formulation of the problem, where the lower level problem is to assign a given OD-matrix onto the network according to the user equilibrium principle. After reformulating the problem to a single level problem, the objective function includes implicitly given link flow variables, corresponding to the given OD-matrix. We propose a descent heuristic to solve the problem, which is an adaptation of the wellknown projected gradient method. In order to compute a search direction we have to approximate the Jacobian matrix representing the derivatives of the link flows with respect to a change in the OD-flows, and we propose to do this by solving a set of quadratic programs with linear constraints only. If the objective function is differentiable at the current point, the Jacobian is exact and we obtain a gradient. Numerical experiments are presented which indicate that the solution approach can be applied in practice to medium to large size networks.
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| 43. |
- Mai, T., et al.
(författare)
-
A nested recursive logit model for route choice analysis
- 2015
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 75, s. 100-112
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a route choice model that relaxes the independence from irrelevant alternatives property of the logit model by allowing scale parameters to be link specific. Similar to the recursive logit (RL) model proposed by Fosgerau et al. (2013), the choice of path is modeled as a sequence of link choices and the model does not require any sampling of choice sets. Furthermore, the model can be consistently estimated and efficiently used for prediction.A key challenge lies in the computation of the value functions, i.e. the expected maximum utility from any position in the network to a destination. The value functions are the solution to a system of non-linear equations. We propose an iterative method with dynamic accuracy that allows to efficiently solve these systems.We report estimation results and a cross-validation study for a real network. The results show that the NRL model yields sensible parameter estimates and the fit is significantly better than the RL model. Moreover, the NRL model outperforms the RL model in terms of prediction.
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| 44. |
- Mattsson, Lars-Göran, et al.
(författare)
-
Extreme values, invariance and choice probabilities
- 2014
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 59, s. 81-95
-
Tidskriftsartikel (refereegranskat)abstract
- Since the pioneering work of McFadden (1974), discrete choice random-utility models have become work horses in many areas in transportation analysis and economics. In these models, the random variables enter additively or multiplicatively and the noise distributions take a particular parametric form. We show that the same qualitative results, with closed-form choice probabilities, can be obtained for a wide class of distributions without such specifications. This class generalizes the statistically independent distributions where any two c.d.f.:s are powers of each others to a class that allows for statistical dependence, in a way analogous to how the independent distributions in the MNL models were generalized into the subclass of MEV distributions that generates the GEV choice models. We show that this generalization is sufficient, and under statistical independence also necessary, for the following invariance property: all conditional random variables, when conditioning upon a certain alternative having been chosen, are identically distributed. While some of these results have been published earlier, we place them in a general unified framework that allows us to extend several of the results and to provide proofs that are simpler, more direct and transparent. Well-known results are obtained as special cases, and we characterize the Gumbel, Frechet and Weibull distributions.
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| 45. |
- Moustaid, Elhabib, et al.
(författare)
-
Macroscopic model of multidirectional pedestrian network flows
- 2021
-
Ingår i: Transportation Research Part B. - : Pergamon-Elsevier Science Ltd. - 0191-2615 .- 1879-2367. ; 145
-
Tidskriftsartikel (refereegranskat)abstract
- Pedestrian flow models are useful for the design and operation of pedestrian spaces. This article describes a macroscopic model of pedestrian flows through networks composed of bidirectional corridors that are connected by multidirectional intersections. The proposed model builds on an existing pedestrian bidirectional fundamental diagram to define bidirectional sending and receiving flows, and it relies on the incremental transfer principle to model bidirectional flows across nodes with an arbitrary number of adjacent links. The model is solved in a cell-transmission formulation that is in all of its unidirectional properties consistent with the kinematic wave model. (C) 2021 The Authors. Published by Elsevier Ltd.
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| 46. |
- Osorio, Carolina, et al.
(författare)
-
Dynamic network loading: A stochastic differentiable model that derives link state distributions
- 2011
-
Ingår i: Transportation Research Part B. - : Elsevier BV. - 0191-2615 .- 1879-2367. ; 45:9, s. 1410-1423
-
Tidskriftsartikel (refereegranskat)abstract
- We present a dynamic network loading model that yields queue length distributions, accounts for spillbacks, and maintains a differentiable mapping from the dynamic demand on the dynamic queue lengths. The model also captures the spatial correlation of all queues adjacent to a node, and derives their joint distribution. The approach builds upon an existing stationary queueing network model that is based on finite capacity queueing theory. The original model is specified in terms of a set of differentiable equations, which in the new model are carried over to a set of equally smooth difference equations. The physical correctness of the new model is experimentally confirmed in several congestion regimes. A comparison with results predicted by the kinematic wave model (KWM) shows that the new model correctly represents the dynamic build-up, spillback and dissipation of queues. It goes beyond the KWM in that it captures queue lengths and spillbacks probabilistically, which allows for a richer analysis than the deterministic predictions of the KWM. The new model also generates a plausible fundamental diagram, which demonstrates that it captures well the stationary flow/density relationships in both congested and uncongested conditions.
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| 47. |
- Zhang, Chao, et al.
(författare)
-
Efficient calibration techniques for large-scale traffic simulators
- 2017
-
Ingår i: Transportation Research Part B. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0191-2615 .- 1879-2367. ; 97, s. 214-239
-
Tidskriftsartikel (refereegranskat)abstract
- Road transportation simulators are increasingly used by transportation stakeholders around the world for the analysis of intricate transportation systems. Model calibration is a crucial prerequisite for transportation simulators to reliably reproduce and predict traffic conditions. This paper considers the calibration of transportation simulators. The methodology is suitable for a broad family of simulators. Its use is illustrated with stochastic and computationally costly simulators. The calibration problem is formulated as a simulation based optimization (SO) problem. We propose a metamodel approach. The analytical meta model combines information from the simulator with information from an analytical differentiable and tractable network model that relates the calibration parameters to the simulation-based objective function. The proposed algorithm is validated by considering synthetic experiments on a toy network. It is then used to address a calibration problem with real data for a large-scale network: the Berlin metropolitan network with over 24300 links and 11300 nodes. The performance of the proposed approach is compared to a traditional benchmark method. The proposed approach significantly improves the computational efficiency of the calibration algorithm with an average reduction in simulation runtime until convergence of more than 80%. The results illustrate the scalability of the approach and its suitability for the calibration of large-scale computationally inefficient network simulators. (C) 2016 Elsevier Ltd. All rights reserved.
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| 48. |
- Basso, Rafael, 1979, et al.
(författare)
-
Electric Vehicle Routing Problem with Machine Learning for Energy Prediction
- 2021
-
Ingår i: Transportation Research Part B: Methodological. - : Elsevier BV. - 0191-2615. ; 145, s. 24-55
-
Tidskriftsartikel (refereegranskat)abstract
- Routing electric commercial vehicles requires taking into account their limited driving range, which is affected by several uncertain factors such as traffic conditions. This paper presents the time-dependent Electric Vehicle Routing Problem with Chance- Constraints (EVRP-CC) and partial recharging. The routing method is divided into two stages, where the first finds the best paths and the second optimizes the routes. A probabilistic Bayesian machine learning approach is proposed for predicting the expected energy consumption and variance for the road links, paths and routes. Hence it is possible to consider the uncertainty in energy demand by planning charging within a confidence interval. The energy estimation is validated with data from electric buses driving a public transport route in Gothenburg-Sweden as well as with realistic simulations for 24 hours traffic in the city of Luxembourg connected to a high fidelity vehicle model. Routing solutions are compared with a deterministic formulation of the problem similar to the ones found in the literature. The results indicate high accuracy for the energy prediction as well as energy savings and more reliability for the routes.
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| 49. |
- Como, Giacomo, et al.
(författare)
-
Convexity and robustness of dynamic traffic assignment and freeway network control
- 2016
-
Ingår i: Transportation Research. Part B: Methodological. - : Elsevier BV. - 0191-2615. ; 91, s. 446-465
-
Tidskriftsartikel (refereegranskat)abstract
- We study the use of the System Optimum (SO) Dynamic Traffic Assignment (DTA) problem to design optimal traffic flow controls for freeway networks as modeled by the Cell Transmission Model, using variable speed limit, ramp metering, and routing. We consider two optimal control problems: the DTA problem, where turning ratios are part of the control inputs, and the Freeway Network Control (FNC), where turning ratios are instead assigned exogenous parameters. It is known that relaxation of the supply and demand constraints in the cell-based formulations of the DTA problem results in a linear program. However, solutions to the relaxed problem can be infeasible with respect to traffic dynamics. Previous work has shown that such solutions can be made feasible by proper choice of ramp metering and variable speed limit control for specific traffic networks. We extend this procedure to arbitrary networks and provide insight into the structure and robustness of the proposed optimal controllers. For a network consisting only of ordinary, merge, and diverge junctions, where the cells have linear demand functions and affine supply functions with identical slopes, and the cost is the total traffic volume, we show, using the Pontryagin maximum principle, that variable speed limits are not needed in order to achieve optimality in the FNC problem, and ramp metering is sufficient. We also prove bounds on perturbation of the controlled system trajectory in terms of perturbations in initial traffic volume and exogenous inflows. These bounds, which leverage monotonicity properties of the controlled trajectory, are shown to be in close agreement with numerical simulation results.
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| 50. |
- Como, Giacomo, et al.
(författare)
-
On the well-posedness of deterministic queuing networks with feedback control
- 2021
-
Ingår i: Transportation Research. Part B: Methodological. - : Elsevier BV. - 0191-2615. ; 150, s. 323-335
-
Tidskriftsartikel (refereegranskat)abstract
- We study the well-posedness of a class of dynamical flow network systems describing the dynamical mass balance among a finite number of cells exchanging flow of traffic between themselves and with the external environment. Dynamical systems in the considered class are described as differential inclusions whereby the routing matrix is constant and the outflow from each cell in the network is limited by a control that is a Lipschitz continuous function of the state of the network. This framework finds application in particular within traffic signal control, whereby it is common that an empty queue can be allowed to have more outflow than vehicles in the queue. While models for this scenario have previously been presented for open-loop outflow controls, our result ensures the existence and uniqueness of solutions for the network flow dynamics in the case Lipschitz continuous feedback controllers.
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