A Simulation-Based Accessibility Modeling Approach to Evaluate Performance of Transportation Networks by using Directness Concept and GIS

Abstract

Ranging from simple to sophisticated, numerous types of accessibility measures are found in the accessibility modeling literature which helps to understand accessibility of people, place and transportation networks. Transportation network directness (reciprocal is circuity), which is defined as the ratio of the shortest Euclidean distance over network distance between demand (origin) and destination (supply) points, could be considered as an important type of measure for understanding accessibility for a variety of context. Although there are several research and literature on transportation network directness and accessibility modeling, the research that integrates transportation network directness concept into accessibility modeling process in such a way to provide understanding of the overall accessibility performance of the transportation networks without losing the local interactions is quite limited. Based on this idea, the basic aim of this research is to propose a new transportation network directness-based accessibility modeling methodology that could be used to test both the local and the overall accessibility performance of transportation networks in a simple and comparable manner by using GIS. By considering regularly produced virtual origins and destinations on the transportation network in a simulation manner, the proposed methodology could produce travel time/distance based accessibility measures that could operate without a need for real time supply/demand or origin/destination data. The advantage of using a virtual regular data set instead of real time data is that; it is more simple, easy to operate and most importantly, more realistic to understand performance of transportation networks as most of the possible origin/destination scenarios could be represented in the proposed model. The outputs of the model could be widely used by the decision-makers who are supposed to deal with accessibility, location/allocation, and service/catchment area related issues by several aims such as; to test the overall/partial performance of the transportation networks, to understand the weakly connected parts of the transportation network and/or to compare the accessibility performance of different networks with each other. The proposed methodology is applied in 3 cities with different types of transportation network which are Paris, FRANCE (radial network); San Francisco, USA (grid network) and Ankara, TURKEY (mixed network) in order to able to demonstrate the performance and efficiency of the proposed model. The main focus of the case study is not to evaluate specific accessibility conditions or transportation network performance in a detailed manner but to provide a methodological discussion about the proposed directness based accessibility modeling process.