## 4 Review of Studies Related to Sustainability in the Context of Multi-Modal Mobility
### Review of Studies
(6) Question: What are the types, variants, characteristics of shared mobility problems, the related solution approaches, the current trends and future research directions? Results: The emerging shared mobility services not only receive widespread adoption by cities to achieve the sustainability goals and high utilization by users to benefit from low cost and accessible journey in daily life but also attract the attention of numerous researchers, practitioners and related stakeholders. This leads to a large number of studies and papers on shared mobility problems. A systematic review of shared mobility problems is required to provide insights into the current trends and future research directions. A systematic review of the literature on shared mobility problems according to problem types, variants, characteristics, and solution methods is provided in the paper [104]. The findings are that the main issue in the shared mobility literature is the total cost minimization for static and dynamic cases. Shared mobility problems considering time window and multi-objective characteristics are popular among the research community. The most widely adopted solution approaches to shared mobility problems are heuristic and metaheuristic approaches. (7) Question: How to develop a decision model for travelers to choose routes and decide travel modes to minimize travelers' generalized travel cost in a multi-modal transportation system with ridesharing and public transit? Results: In a multi-modal transportation system with ridesharing and public transit, travelers must choose routes and decide travel modes. A traveler may play the role of a solo driver, ridesharing driver, ridesharing passenger, or transit passenger. A decision model must be developed for this problem. In [76], a multi-modal route choice model with ridesharing and public transit was developed based on single-origin-destination (OD) pair network and was expressed as an equivalent complementarity problem. The results in equilibrium indicate that the travelers' route and mode choice behavior is significantly influenced by rewards of passengers' and toll charge of solo drivers. The results also show that increasing passengers' rewards can attract more travelers to adopt environmentally friendly transport modes. (8) Question: How to simulate and optimize multi-modal transport systems with P2P ridesharing, transit, city bike-sharing and walking? Results: Although P2P ridesharing, transit, city bike-sharing and walking have been implemented separately in cities, there lacks a study on the integration of these heterogeneous transport modes and effectiveness of the resulting integrated system. A study based on simulation of multi-modal transport systems with P2P ridesharing, transit, city bike-sharing and walking is needed. In [77], a scheme to offer travel alternatives across multiple transport modes, including P2P ridesharing, transit, city bike-sharing and walking, were developed. By applying the proposed method to the case of the multi-modal system of Los Angeles, a simulation enhanced with optimization was conducted. The study found that properly designed ride ridesharing and bike-sharing, when integrated into the transit system, can form a multi-modal network that expands the coverage of public transit. (9) Questions: Can ridesharing help reduce traffic congestion in a multi-modal transport system? If ridesharing cannot necessarily reduce traffic congestion, is it possible to reduce traffic congestion by implementing pricing strategies along with ridesharing?Results: For a multi-modal transport system with ridesharing, an interesting research issue is to study whether ridesharing can help reduce traffic congestion. If ridesharing cannot necessarily reduce traffic congestion, is it possible to reduce traffic congestion by implementing pricing strategies along with ridesharing? In [78], different pricing strategies were proposed and compared for a multi-modal network with ridesharing services.