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 accessibilitymeasures are found in the accessibility modeling literature which helpsto understand accessibility of people, place and transportationnetworks. Transportation network directness (reciprocal is “circuity”),which is defined as the ratio of the shortest Euclidean distance overnetwork distance between demand (origin) and destination (supply)points, could be considered as an important type of measure forunderstanding accessibility for a variety of context. Although there are several research and literature on transportationnetwork directness and accessibility modeling, the research thatintegrates transportation network directness concept into accessibilitymodeling process in such a way to provide understanding of the overallaccessibility performance of the transportation networks without losingthe local interactions is quite limited.Based on this idea, the basic aim of this research is to propose a newtransportation network directness-based accessibility modelingmethodology that could be used to test both the local and the overallaccessibility performance of transportation networks in a simple andcomparable manner by using GIS. By considering regularly producedvirtual origins and destinations on the transportation network in a“simulation” manner, the proposed methodology could produce “traveltime/distance” based accessibility measures that could operate withouta need for real time supply/demand or origin/destination data.The advantage of using a virtual regular data set instead of real time datais that; it is more simple, easy to operate and most importantly, morerealistic to understand performance of transportation networks as mostof the possible origin/destination scenarios could be represented in theproposed model. The outputs of the model could be widely used by thedecision-makers who are supposed to deal with accessibility,location/allocation, and service/catchment area related issues byseveral aims such as; to test the overall/partial performance of thetransportation networks, to understand the weakly connected parts ofthe transportation network and/or to compare the accessibilityperformance of different networks with each other.The proposed methodology is applied in 3 cities with different types oftransportation network which are Paris, FRANCE (radial network); SanFrancisco, USA (grid network) and Ankara, TURKEY (mixed network) inorder to able to demonstrate the performance and efficiency of theproposed model. The main focus of the case study is not to evaluatespecific accessibility conditions or transportation network performancein a detailed manner but to provide a methodological discussion aboutthe proposed directness based accessibility modeling process.