  In the governance of the shared mobility market of a city or of a
metropolitan area, there are two conflicting principles: 1) the healthy
competition between multiple platforms, such as between Uber and Lyft in the
United States, and 2) economies of network scale, which leads to higher chances
for trips to be matched, and thus higher operation efficiency, but which also
implies monopoly. The current shared mobility markets, as observed in different
cities in the world, are either monopolistic, or largely segmented by multiple
platforms, the latter with significant efficiency loss. How to keep the
competition between platforms, but to reduce the efficiency loss due to
segmentation with new market designs is the focus of this paper. We first
propose a theoretical framework of shared mobility market segmentation and then
propose four market structure designs thereupon. The framework and four designs
are first discussed as an abstract model, without losing generality, thus not
constrained to any specific city. High-level perspectives and detailed
mechanisms for each proposed market structure are both examined. Then, to
assess the real-world performance of these market structure designs, we used a
ride-sharing simulator with real-world ride-hailing trip data from New York
City to simulate. The proposed market designs can reduce the total
vehicle-miles traveled (VMT) by 6\% while serving more customers with 8.4\%
fewer total number of trips. In the meantime, customers receive better services
with on-average 5.4\% shorter waiting time. At the end of the paper, the
feasibility of implementation for each proposed market structure is discussed.
