A MIP model for locating slow-charging stations for electric vehicles in urban areas accounting for driver tours

In this paper we propose an improved mathematical model for locating EV charging stations. We consider the successive activities of the travelers, i.e., a person with two main stops during the day should charge the vehicle in just one of the parking spots, hence avoiding double counting the demand. The model is tested for the city of Coimbra (Portugal), where there is a network of nine stations. We conclude that our solution is better than the one that was implemented in reality, moreover we are able to conclude that demand transference has a rather significant impact on the solutions.     

A diagrammatic analysis of the market for cruising taxis

A diagrammatic approach is used to study the characteristics of the cruising taxi market. For cost modeling, both taxi operator and passenger are taken as service producers. The former provides his vehicle operation and the latter, his waiting and travel time. Market demand is defined as a function of generalized price. It is shown that under short and long run conditions a unique equilibrium exists for a deregulated industry and it corresponds to a monopolistic competition. The relations among the free market equilibrium, social optimum and second best solution are analyzed. Regulations are studied in order to find their social convenience.     

TRIBUTE: Trip-based urban transportation emissions model for municipalities

This research aims at developing modeling and scenario-comparison tools to explore the impacts of various transportation and land use planning policies on changing travel behavior and eventually greenhouse gas (GHG) emissions. A Trip-Based Urban Transportation Emissions (TRIBUTE) model is developed. Data required for TRIBUTE comes from household travel surveys and emissions inventories, which is a major advantage in cases where a detailed transportation network model is unavailable. TRIBUTE is composed of two main parts: a mode choice model and an emissions forecasting model. The mode choice model is responsible for estimating modal shares of alternative modes of travel in response to changes in personal, modal, and land use attributes. The emissions forecasting model translates the modal shares into vehicle kilometers traveled, and subsequently GHG emissions. TRIBUTE is a macroscopic model intended to assist municipalities evaluate alternative transportation and land use policy scenarios and eventually select the one(s) that help them meet their future GHG emission targets. This paper reports on the conceptual framework of the developed model and presents a case study.     

Airports in their urban settings: towards a conceptual model of interfaces in the Australian context

In Australia, airports have emerged as important sub-regional activity centres and now pose challenges for both airport operation and planning in the surrounding urban and regional environment. The changing nature of airports in their metropolitan context and the emergence of new pressures and problems require the introduction of a fresh conceptual framework to assist the better understanding of these complex roles and spatial interactions. The approach draws upon the meta-concept of interfaces of an ‘airport metropolis’ as an organising device consisting of four main domains: economic development, land use, infrastructure, and governance. The paper uses the framework to further discuss airport and regional interactions and highlights the use of sustainability criteria to operationalise the model. The approach aims to move research and practice beyond the traditionally compartmentalised analysis of airport issues and policy-making by highlighting interdependencies between airports and regions.     

A traffic engineering model for air taxi services

We propose a single-provider model for on-demand air taxi services. Data from a discrete-event model support a “flow model,” which describes the aggregate flow of passengers and aircraft for an air taxi service provider without specifying event-level operation. Using a set of hypothetical scenarios for air taxi network operation, we evaluate the accuracy of the flow model against the outputs of the discrete-event model. Finally, we illustrate how the flow model can be applied towards the optimal pricing of passenger fares for a single air taxi service provider.     

A non-additive model for evaluating airline service quality

This study develops a non-additive model for evaluating and improving the service quality of airlines and compares its results with the conventional additive method. Service quality is a composite of various attributes and many in a system have inter-dependent characteristics that may not be correctly evaluated using conventional additive measures. A fuzzy integral is thus proposed. Factor analysis is initially used to extract some independent common-factors and fuzzy integral used to integrate the performance ratings of inter-dependent attributes in each common-factor. For the analytic hierarchy process a pair-wise comparative approach is adopted to determine the relative weights linking each independent common-factor. Finally, Grey relation analysis and simple additive weight method are used to find airline service quality. A study of international airlines is conducted for verification. Safety and reliability emerge as the critical factors of service quality.     

A location-inventory model for large three-level supply chains

We study the location-inventory problem in three-level supply networks. Our model integrates three decisions: the distribution centers location, flows allocation, and shipment sizes. We propose a nonlinear continuous formulation, including transportation, fixed, handling and holding costs, which decomposes into a closed-form equation and a linear program when the DC flows are fixed. We thus develop an iterative heuristic that estimates the DC flows a priori, solves the linear program, and then improves the DC flow estimations. Extensive numerical experiments show that the approach can design large supply networks both effectively and efficiently, and a case study is discussed.     

A passenger demand model for air transportation in a hub-and-spoke network

This paper develops an air passenger model that deals with city-pair demand generation and demand assignment in a single framework. Using publicly available and regularly collected panel data, the model captures both time series and cross-sectional variation of air travel demand. The empirical analysis finds that pattern of correlations among alternatives can be described by a three-level nested logit model. Fare, frequency, flight time, direct routing, on-time performance, income, and market distance have significantly effects on air demand. Correcting for the problem of endogenous air fares using instrumental variables yields more plausible estimates of price sensitivity and value of time.     

An optimization model for gate reassignment in response to flight delays

In this paper, a binary integer program is formulated for the optimal reassignment of planes to gates in response to day-of flight delays. This program minimizes the total walking distance of those passengers either connecting or originating at an airport whose boarding passes for affected flights were issued prior to the reassignment of gates. A numerical illustration using operations of Continental Airlines at the George W. Bush Intercontinental Airport in Houston, Texas demonstrates the speed and efficiency of this program in both a real world and real time setting.     

A three-stage stochastic facility routing model for disaster response planning

This paper presents a three-stage mixed-integer stochastic programming model for disaster response planning, considering the opening of local distribution facilities, initial allocation of supplies, and last mile distribution of aid. The vehicles available for transportation, the state of the infrastructure and the demand of the potential beneficiaries are considered as stochastic elements. Extensive computational testing performed on realistic instances shows that the solutions produced by the stochastic programming model are significantly better than those produced by a deterministic expected value approach.     

A model for taxi pooling with stochastic vehicle travel times

Taxi pooling means the sharing of a taxi by more than one passenger with at least a semi-common route. Currently, a trial-and-error process is adopted, taking into account expected travel times, for taxi pooling, a method which is neither effective nor efficient. This is because stochastic disturbances arising from variations in the taxi travel times that occur in actual traveling are neglected. In the worst case scenario, where vehicle travel times fluctuate wildly during operations, the planned schedule can be disturbed enough to lose its optimality. Therefore, in this study, a network flow technique is used to construct a stochastic taxi pooling model incorporating stochastic vehicle travel times. A solution algorithm is also proposed to efficiently solve the problem. The performance of the proposed models and the use of the solution method in practice are evaluated by executing numerical tests using real data with suitable assumptions. The test results show that the stochastic model and the solution method could be useful references for practice.     

A model for projecting flight delays during irregular operation conditions

On-time performance of airlines schedule is key factor in maintaining current customer satisfaction and attracting new ones. This requires management of the different operation resources (crew/aircraft) to ensure their on-time readiness for each flight in the planned schedule. However, flight schedules are often subjected to irregularity. In particular, weather accounts for nearly 75% of system delays. Due to the tight connection among airlines resources, these delays could dramatically propagate over time and space unless the proper recovery actions are taken. This paper presents a model which projects flight delays and alerts for possible future breaks during irregular operation conditions. The results of applying the model at the operation control center of a major airlines company in the US are presented.     

A generalized algebraic model for optimizing inventory decisions in a multi-stage complex supply chain

In this paper, we deal with more generalized inventory coordination mechanism in an n-stage, multi-customer, non-serial supply chain, where we extend and generalize pervious works that use algebraic methods to optimize this coordinated supply chain. We establish the recursive expressions for this multi-variable optimization problem. These expressions are used for the derivation of the optimal replenishment policy and the development of the solution algorithm. Further, we describe a simple procedure that can help in sharing the coordination cost benefits to induce all stages to adopt the inventory coordination mechanism. We provide a numerical example for illustrative purposes.     

Transit-oriented development,integration of land use and transport,and pedestrian accessibility: Combining node-place model with pedestrian shed ratio to evaluate and classify station areas in Lisbon

Transit-oriented development is being actively promoted as an urban design model for areas around transit stations. In addition, planning for accessibility is being promoted, which requires integrating land use with transportation planning, and to match the transportation features with the intensity and diversity of land use of the station areas. Nevertheless, and despite the evident similarities between the two approaches, an integrated evaluation tool of a station area in terms of its transportation, land use, and urban design features is missing. In this paper, we bring into the literature on integration of land use and transport a key feature of the transit-oriented development literature: the urban design features of the station areas, in particular their pedestrian friendliness. By complementing the node-place model with an evaluation of the pedestrian connectivity of station areas of Lisbon, we combine these two perspectives in order to evaluate and classify station areas in three different aspects: land use, transportation, and walkability conditions. Our results show that a balanced node-place is not necessarily a transit-oriented development, and vice versa, and so a complementary analysis of both is useful to identify and classify a station area. Therefore, we suggest a typology of station areas based on the three components, which might be used as a planning tool for the development of the station areas into balanced transit-oriented development areas.     

A Cournot model for analysing the effects of an open skies agreement

In the last decades there has been a gradual liberalisation of international air transport markets through the implementation of open skies agreements which seek the deregulation of the air transport industry and consequently the functioning of the market in a freer way. The objective of this work is to study the effects of an open skies agreement in order to understand if the airlines and the consumers will benefit after the market deregulation. With this purpose, we develop a Cournot model to compare the initial situation (without agreement) and the situation after the implementation of the open skies agreement.Based on the model developed we conclude that after market liberalisation the prices on international market segments where competition increases should decline, thus benefiting consumers. Regarding the incumbent airlines in the market, an open skies agreement should jeopardize the airlines that fail to operate new routes, leading to decreased profits.     

A stochastic programming winner determination model for truckload procurement under shipment uncertainty

We propose a two-stage stochastic integer programming model for the winner determination problem (WDP) in combinatorial auctions to hedge the shipper’s risk under shipment uncertainty. The shipper allows bids on combinations of lanes and solves the WDP to determine which carriers are to be awarded lanes. In addition, many other important comprehensive business side constraints are included in the model. We demonstrate the value of the stochastic solution over one obtained by a deterministic model based on using average shipment volumes. Computational results are given that indicate that moderately sized realistic instances can be solved by commercial branch and bound solvers in reasonable time.     

A generalized algebraic model for optimizing inventory decisions in a centralized or decentralized multi-stage multi-firm supply chain

First of all, a number of integrated models with/without lot streaming under the integer multiplier coordination mechanism is generalized by allowing lot streaming and three types of inspection for some/all upstream firms. Secondly, the optimal solutions to the three- and four-stage models are individually derived, both using the perfect squares method, which is a simple algebraic approach so that ordinary readers unfamiliar with differential calculus can easily understand how to obtain the optimal solution procedures. Thirdly, optimal expressions for some well-known models are deduced. Fourthly, expressions for sharing the coordination benefits based on Goyal’s (1976) scheme are derived, and a further sharing scheme is introduced. Fifthly, two numerical examples for illustrative purposes are presented. Finally, some future research works involving extension or modification of the generalized model are suggested.     

A supply chain generalized network oligopoly model for pharmaceuticals under brand differentiation and perishability

In this paper, we construct a generalized network oligopoly model with arc multipliers for supply chains of pharmaceutical products using variational inequality theory. The model captures the Cournot competition among the manufacturers who seek to determine their profit-maximizing product flows, which can be perishable, with the consumers differentiating among the products of the firms, whether branded or generic, and the firms taking into consideration the discarding costs. The numerical examples demonstrate that a brand pharmaceutical product may lose its dominant market share as a consequence of patent rights expiration and because of generic competition.     

A freight transport optimization model for integrated network,service, and policy design

This paper presents a freight transport optimization model that simultaneously incorporates multimodal infrastructure, hub-based service network structures, and the various design objectives of multiple actors. The model has been calibrated and validated using real-life data from the case study of hinterland container transport of the Netherlands, where CO₂ pricing, terminal network configuration, and hub-service networks are chosen as the design measures. Policy packages combining multiple types of policies show better network performance as compared with the optimal performance resulting from a single policy type. This illustrates the value of incorporating multiple types of policies simultaneously in freight transport optimization.     

Errors in variables in multinomial choice modeling: A simulation study applied to a multinomial logit model of travel mode choice

Modeling travel demand is a vital part of transportation planning and management. Level of service (LOS) attributes representing the performance of transportation system and characteristics of travelers including their households are major factors determining the travel demand. Information on actual choice and characteristics of travelers is obtained from a travel survey at an individual level. Since accurate measurement of LOS attributes such as travel time and cost components for different travel modes at an individual level is critical, they are normally obtained from network models. The network-based LOS attributes introduce measurement errors to individual trips thereby causing errors in variables problem in a disaggregate model of travel demand. This paper investigates the possible structure and magnitude of biases introduced to the coefficients of a multinomial logit model of travel mode choice due to random measurement errors in two variables, namely, access/egress time for public transport and walking and cycling distance to work. A model was set up that satisfies the standard assumptions of a multinomial logit model. This model was estimated on a data set from a travel survey on the assumption of correctly measured variables. Subsequently random measurement errors were introduced and the mean values of the parameters from 200 estimations were presented and compared with the original estimates. The key finding in this paper is that errors in variables result in biased parameter estimates of a multinomial logit model and consequently leading to poor policy decisions if the models having biased parameters are applied in policy and planning purposes. In addition, the paper discusses some potential remedial measures and identifies research topics that deserve a detailed investigation to overcome the problem. The paper therefore significantly contributes to bridge the gap between theory and practice in transport.