Antonino Vitetta

Heuristics for urban road network design: Lane layout and signal settings

This paper concerns the urban road network design problem. In urban areas supply has usually been unable to keep pace with increasing demand: the only possibility is often to reorganise the current supply configuration in order to use existing resources efficiently. Thus, in urban areas signal settings and network topology (in particular lane layout) are the two major factors that can be handled by design models. Methods for the combined design of signal settings and topology are proposed in this paper. All the methods proceed in two stages: the first deals with integer variables (topology), while the second deals with continuous variables (signal settings). Some metaheuristics (Hill Climbing, Simulated Annealing, Tabu Search, Genetic Algorithms and Path Relinking) are specified for the topology design stage, and they are used singularly or jointly. The continuous part of the solution, with fixed topology is optimized through an algorithm for asymmetrical deterministic equilibrium assignment. This paper focuses on evaluating performances obtained by all the different algorithms proposed for the topology design stage. The algorithms are compared by applications to real networks, and some conclusions are drawn about their efficiency.

AN ASSIGNMENT MODEL WITH MODIFIED LOGIT, WHICH OBVIATES ENUMERATION AND OVERLAPPING PROBLEMS

One of the main components of stochastic assignment models is the route choice model solved with implicit or explicit path enumeration algorithms. Such models are used both for congested networks within equilibrium or dynamic models and for non-congested networks within static or pseudo-dynamic network loading models. This paper proposes a C-Logit model specification within a Dial algorithm structure for the implicit assignment of network flows. The model and its solution algorithm, called D-C-Logit, combine several positive features found in the literature for choice set generation and choices from a given choice set:• generation of a set of alternatives with a selective approach;• calculation of the path choice probability in a closed form;• simulation of the overlapping effect among alternative paths;• computation of just one tree for each origin avoiding explicit path enumeration.This paper has two main objectives: the proposition of a Dial-like algorithm to solve a C-Logit assignment model and application of the algorithm to different networks in order to demonstrate certain properties.

Risk Evaluation In A Transportation System

METHODS for planning and managing a transportation system in an urban area, when exogenous events occur and/or in emergency conditions, have received little attention from transportation system researchers, research institutions and journals. Models and algorithms specified and calibrated for ordinary conditions cannot be directly applied in emergency conditions. In this paper, the main problems developed concern: formalization of the risk problem in a transportation system with an improvement over consolidated quantitative risk analysis models; specification of a system of models for evacuation design and simulation, and in the particular case of path design in emergency conditions; the application of the model to simulate a real system for exposure reduction. The application was developed for an Italian town of about 9,000 inhabitants which was chosen as it has a similar number of potential evacuees to the majority of cases in real events when entire small towns, parts of a city or big buildings had to be evacuated. The curve between vulnerability and exposure is quantitatively represented. Keywords evacuation, network design, risk analysis, simulation. Language: en

Reverse assignment: calibrating link cost functions and updating demand from traffic counts and time measurements

In the literature, various models and procedures have been proposed for calibrating parameters of demand models or updating the demand values from traffic counts. Different models in terms of theoretical approaches have been used for congested and uncongested networks. Also for supply, models have been proposed for calibrating parameters of link cost functions. Link cost functions are calibrated separately from the demand. Congruence between the two calibrations is not guaranteed. This article proposes a unified formulation to obtain at the same time the parameters of link performance functions and the demand values (and/or the values of demand model parameters) of a static traffic assignment model. Model input consists of the a priori demand values, travel times measured on different links on the network, the link cost functions for each link category and the simulation model for user behaviour in path choice. Model output consists of the optimal demand, the parameters calibrated on link cost functions and the congruent flow on the links. The proposed model is thus called reverse assignment because the input is the output of a classical traffic assignment and the output is the input. The model is formulated as an optimization model for which the minimization of the distances between the a priori and optimal demand and modelled flows, measured and modelled travel times is sought. A heuristic optimization procedure for solving the model is proposed. The procedure considers the network that is congested and in each iteration of the optimization procedure a deterministic or a stochastic user equilibrium is solved. The problem of the existence of different local minimum points is discussed. There are major practical implications deriving from the solution of this problem. It allows transport models to be calibrated to simulate present and hypothetical scenario configurations prior to scenario implementation or within before–after planning procedures. The model and procedure are applied in a test and in a real system for different sets of parameters. The results confirm that if the unified formulation proposed is applied, the optimal demand and cost are better reproduced with respect to the traditional procedure where only demand or cost parameters are updated and the optimal point is strongly influenced by the a priori errors in the demand and link cost parameters.

STOCHASTIC USER EQUILIBRIUM ASSIGNMENT WITH EXPLICIT PATH ENUMERATION: COMPARISON OF MODELS AND ALGORITHMS

Abstract In this paper a preliminary analysis of alternative models for “feasible” path generation and choice is presented. In particular a k-shortest path multi-criteria model for path enumeration is explored and different choice models (Logit, recently proposed C-Logit and Probit) are tested by comparing SUE assignment link flows with counts on an urban road network. Flows are also compared for more traditional DUE and SUE Probit implicit path enumeration models. The results obtained show that a limited number (4-7) of paths generated with rather “simple” criteria give satisfactory results, SUE with explicit path enumeration is largely comparable with, and in some cases superior to, traditional implicit SUE and DUE models. Explicit path enumeration allow also the specification of more sophisticated non additive attributes in the utility function of route choice models. From the computational point of view the explicit path C-Logit and Probit SUE algorithms are from three to twenty times superior to the implicit Probit SUE assignment.

Safety of Users in Road Evacuation: Supply ad Demand-Supply Interaction Models for Users

This paper presents the results that were obtained in the SICURO research project that was carried out by the Laboratory for Transport Systems Analysis (LAST) of Mediterranea University of Reggio Calabria (Italy). Microscopic models able to simulate supply and demand-supply interaction of a road transportation system in emergency conditions are described. A microscopic link model (car-following) is specified and calibrated. Parameters are calibrated from data observed during a real simulation of evacuation executed in the test site of Melito Porto Salvo (Italy). A computer application is performed in order to reproduce the evacuation phases observed. Some indicators for testing the performance of a road transportation network in emergency conditions are defined and estimated.

Safety of Users in Road Evacuation: Calibration of Cost Functions And Simulation

This paper on the calibration of cost functions and simulation is from the proceedings of 14th international Conference on Urban Transport and the Environment in the 21st Century, which was held in Malta in 2008. This paper is one of five papers that focus on the safety of users in road evacuation. In this paper, the authors present advancements in Dynamic Traffic Assignment (DTA) microscopic models that are used for the simulation of supply and demand-supply interaction of a road transportation system in emergency conditions. These microscopic models are related to link and node models specified in the research project SICURO, carried out by the Laboratory for Transport Systems Analysis (LAST) of the Mediterranea University of Reggio Calabria in Italy. The models include microscopic link (car-following) and gap-acceptance (rejection) models for non-signalized intersections; the models are calibrated from data observed during a simulation of an evacuation conducted at Melito Porto Salvo, Italy.

Safety of Users in Road Evacuation: Design of Path Choice Models for Emergency Vehicles

Within the framework of the SICURO research project, the main objective of this paper is to define the procedures that were planned and activated in emergencies in order to allow the evacuation of weak users (disabled, old persons, etc.) from the area affected by a disaster and design the optimal path for emergency vehicles to reduce evacuation times. Specification, calibration and validation of a path choice generation model in order to simulate the behavior of emergency vehicle drivers at an urban level during an evacuation is proposed. The authors specify the factors that affect path choice behavior and the two main approaches: one to one and many to one. The first regards the minimization of generalized cost of a path that connects an origin to a destination; the second instead considers the connection of one origin to many destinations. The authors report some experimental results, obtained in the context of the SICURO Project, by applying the proposed model to a real road transport network at urban scale during a simulation of an evacuation.

Safety of Users in Road Evacuation: Algorithms for Path Design of Emergency Vehicles

This paper on the path design of emergency vehicles is from the proceedings of 14th international Conference on Urban Transport and the Environment in the 21st Century, which was held in Malta in 2008. This paper is one of five papers that focus on the safety of users in road evacuation. In this paper, the authors propose an advancement relating to the design of path choice models for emergency vehicles is proposed. They focus on how the procedures to be planned and activated in emergency conditions were defined in order to allow the evacuation of weak users (the disabled, senior citizens, etc.) from the area affected by a disaster. In addition, some advanced instruments and scenarios for designing the optimal path for emergency vehicles to reduce evacuation times are introduced. The authors use the SICURO research project data, carried out by the Laboratory for Transport Systems Analysis (LAST) of the Mediterranea University of Reggio Calabria in Italy. The problem of an emergency vehicle that has to pick up some users at fixed points of the network and to take them to the refuge area is schematized (as in a previous work) with two different approaches: as a shortest-path problem (one to one) and as a vehicle routing problem (many to one). The authors describe two different algorithms: the k shortest paths algorithm is applied to obtain the best k paths that satisfy specific choice criteria; and a metaheuristic procedure (genetic algorithm) which allows route optimization of a fleet of emergency vehicles.

Safety of Users in Road Evacuation: Modelling and DSS for Transport Supply and Supply-Demand Interaction

This paper describes how several Decision Support Systems (DSS) implementing transport modeling have been developed in last two decades to support transport planning in ordinary conditions. However, especially since 9/11, great efforts have been made to adapt the existing DSS, on the one hand, and develop dedicated DSS, on the other, to simulate transportation systems in emergency conditions in order to support evacuation planning and/or operative stages. Nowadays, several DSS are available on the market, or have been developed as research prototypes, for the above purpose. In this paper, based upon a comprehensive literature review, a selection of DSS are analyzed and compared according to their ability to support evacuation planning activities. An application is set up to test transport system simulation through a DSS implementing a microscopic Dynamic Traffic Assignment (DTA) model in order to support evacuation planning. The objective is to test the response capabilities of a DSS in supporting the validation of procedures to be undertaken in the event of emergency evacuation. The aim of the work is to provide planners, technicians and agencies with detailed understanding of the potential and shortcomings of modeling and DSS currently available both on the market and in research.