Abstract
This paper extends the discussion about the bus network design in face of the mobility patterns associated with different degrees of urban dispersion. Based on an analytical approach, a comparison of total costs among different network structures is made for a ring-radial city, which is the other most common regular city layout. The results clarify what structure is the best solution for different scenarios of dispersion and city and transport characteristics. Simultaneously, the effect of the street pattern on the applicability of each structure is evaluated comparing these results to a previous research for a grid city. Three basic structures are analyzed: a radial scheme, a direct-trip-based network, and a hybrid structure as a transfer-based alternative. Each structure is dominant for a specific range of dispersion: radial networks for scenarios of high concentration, direct-trip-based systems for intermediate degrees of dispersion, and transfer-based structures when the activities are decentralized. However, constraints on stop capacity modify these ranges. Each structure presents a different distribution of travel time in the transit chain and agency costs that determine the most competitive alternative. In addition, the behavior of the structures and the evolution of costs regarding urban decentralization are practically the same for both street patterns: system costs grow with increasing mobility dispersion, the range of applicability for each structure is the same, and changes in their applicability when main input parameters vary are very similar. Therefore, these results make it possible to generalize about the conclusions obtained independently of the street layout.
Highlights
A transit system is the key transport mode for urban mobility when faced with congestion, pollution, space degradation, or inefficient energy consumption derived from the excessive use of automobiles
Three basic structures found in the literature (Vuchic 2005) are compared in this study: a radial network, a direct-trip-based one, and a transfer-based system represented by the hybrid scheme
If we focus on the unconstrained headway case, the transition is the same as in the case of the grid street pattern: a radial scheme for concentrated demands, direct trips in intermediate scenarios, and a hybrid structure when the decentralization is higher
Summary
A transit system is the key transport mode for urban mobility when faced with congestion, pollution, space degradation, or inefficient energy consumption derived from the excessive use of automobiles. Authors like Thompson (1977) and Newell (1979) compared alternative design approaches in extreme scenarios of complete dispersion or high concentration The former defended transfer-based structures due to the increasing urban sprawl, while the latter considered that the most suitable solution was still a network focused on the traditional center since that center remained as the main focus of demand. In order to make this alternative comparison, we adapt the pre-existing models to describe the operation of the different structures on that ring-radial street pattern: radial, direct-trip-based and transfer-based structures For this last network, the starting model is the ring-radial hybrid model presented in Badia et al (2014), the original model is modified to represent different scenarios of demand dispersion.
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