Chapter 16: Modeling Accessibility in Urban Transportation Networks: A Graph-Based Hierarchical Approach

Transportation systems are composed of a complex set of relationships between supply, (mainly the operational capacity of the network), demand, and the networks that support movements. The planning and design of urban transportation systems have been primarily based on engineering principles that address optimization of certain operational and safety indicators with little or no focus on the accessibility and mobility of system users at different parts of the network.

Accessibility is considered a combination of both impedance factors (time or cost of reaching a destination) and an attractiveness factor (the qualities of the potential destinations and the availability of desired services and activities). Hansen (1959) defined accessibility as the “potential for interaction”. In the context of transportation planning, accessibility can be thought of as the ease with which desired destinations could be reached (Niemeier, 1997). Mobility, on the other hand, has been defined as the potential for movement, the ability to get from one place to another, and the ability to move around (Hansen 1959) and (Handy and Niemeier 1997). Mobility, with this definition, is related to the impendence components of accessibility. Decision makers need evaluation tools that allow them to determine how a particular decision or activity affects the network accessibility. Traditional level-of-service (LOS) measures in different transportation facilities have been used as measures of mobility. Accessibility, however, needs to be evaluated by examining factors that measure both the availability and quality of transportation services. Examples of such factors are presented in (BTS 1997), Litman (2003) and (Neimeier 1997).