## 3 Review of Studies Related to MaaS in the Context of Multi-
### Potential Future Research Directions
(iii) Strategies to facilitate the implementation of multi-modal shared mobility  
Although MaaS may enable cities to achieve more sustainable future, an important issue is how to implement multi-modal shared mobility through policy implementation. The study [98] called for the government policy makers to innovatively promote shared MaaS. Establishment and operation of shared MaaS requires the development of Merit-based business models, organizational promotions, provision of infrastructure, and smart operation systems. The paper [99] reported the planning process for integrating the services of several transport operators, including public transport operators, a micromobility service provider and a taxi operator, into the MaaS demo site of Athens' in Greece. One future research direction is to use surveys to focus on desired app features. Developing a mobility platform to facilitate combination of transport modes and the business models to promote such combination and guiding the interested stakeholders to create sustainable MaaS schemes are also potential future research directions. The work [97] analyzed the requirements of MaaS and the development of a sustainable business model describing connectivity between transport operators for MaaS considering risk reallocation and data sharing. A future research direction suggested in [97] is to standardize interfaces with operators to extend the proposed MaaS Lite model to achieve operational integration. 4. Advanced frameworks/models to simulate/optimize the performance of MaaS  
The work [67] focuses on design of a mobility hub through combining many transport options for transferring of passengers and reducing vehicle miles in the city to achieve sustainability, high performance and efficiency. There are two future research directions following the study [67]: (1) extending the proposed method by integrating interval-valued Fermatean fuzzy sets to improve robustness and reliability of the proposed framework and (2) studying the influence of the number of decision making on the outcomes. In the work [65], [PERSON] et al. studied how to develop a general modelling framework for MaaS based on analysis and consideration of main actors and factors. The model proposed in [65] considers the first generation of MaaS. Further study on integrating non-transport features into the model for the second generation of MaaS is required. Development of microsimulation models based on agents is an important future research direction. The development of multi-actor models for MaaS service providers, MaaS Broker and the government to adapt to the specific area is another interesting research direction. To evaluate a variety of performance measures and inter-modal interactions, the study [66] focused on the issue to simulate multi-modal operations of MaaS in low-density cities. The study outlined strategies to reduce travel time, waiting time, and overall network delay based on optimization ofidesourcing-transit integration. The study [66] pointed out that further study on optimization ofidesourcing-transit integration is required. The problem to determine the route choices of different transport modes for transporting the user from origin to destination in MaaS was addressed in the study [68]. Assessment of the prediction performances and comparison with other models based on the stated preference surveys and smart phone data is an important future research direction following the study [68]. Studies on matching the trajectory data to the multi-modal network and the generation of choice set for combined routes are also important future research directions. 5. Effective approaches to dealing with threats while protecting privacy and allowing data sharing in MaaS  
The study of [100] focused on security and privacy issues and proposed an overlay networking architecture to constrain the data obtainable at the data sharing and processing level while optimizing the users' requests.