## 6 Review of Studies Related to Micromobility in the Context of Multi-Modal Mobility
### Review of Studies  
Despite safety concerns [128], safety hazards [129] and anti-social behavior by riders such as theft, vandalism, carelessly leaving bikes or scooters in inconsiderate locations, obstructing pedestrians/disabled persons, the world has witnessed strong growth in the micromobility market since its inception due to its potential sustainability benefits [130]. According to the reports of [131], the global micromobility market is expected to grow from USD 175 billion in 2022 to USD 360 billion by 2030. The report of [132] projects that the compound annual growth rate (CAGR) is 13.00% during the forecast period (2024-2030) and the report of [133] estimates that the compound annual growth rate (CAGR) is 12.5% during the forecast period (2022-2027). The emerging micromobility transport mode has created several interesting research issues/questions that pose challenges in its application. When a new transport mode appears in the existing transportation system, it may raise several new issues not addressed before. These new issues include the assessment of the impact on other ones caused by the new transport mode, the potential benefits brought by the new transport mode, effective approaches to integrating the new transport mode in a multi-modal network to attain the potential benefits, the determinants of adopting the new transport mode and the development of methods for the optimization of planning/design of the infrastructure in terms of cost, accessibility, efficiency, performance and sustainability, etc. Some of the research questions related to the new issues mentioned above have been studied in recent years. These research questions along with the studies that respond to them are as follows. 1. Question: What are the impacts of bike-sharing on travelers' usage of other transport modes in a multi-modal transportation system? Results: The study [92] focused on developing a spatial agent-based model to assess the impacts of bike-sharing on travelers' usage of other transport modes through simulation. The results showed that providing free bike-sharing to connect the transit system can result in savings of 1.5 million US dollars in transportation damage cost per year, and preventing 22 premature deaths per year due to mode shift to cycling and walking for the city under study. However, the impacts of bike-sharing on the use of motorcycles was limited. The proposed model provides policy makers with a tool to improve the sustainability of a multi-modal transportation system with bike-sharing. 2. Question: How does multi-modal travel improve accessibility of tourist attractions? Results: Due to the assumption of uniform access for each transport mode within the catchment area, applying the two-step floating catchment area (2 SFCA) method results in inaccuracy in measuring the accessibility of tourist attractions. Development of a more effective method to measure the accessibility of tourist attractions accurately is urgent. A multi-modal network incorporating a super-network with the two-step floating catchment area (MMN-2 SFCA) method was proposed in [59] to model transfer behavior, travel mode choice, and travel demand estimation in multi-modal travel by multi-source big data including subway data and bike-sharing data to improve the accuracy in measurement of tourist attraction accessibility. The effectiveness of the proposed method was demonstrated by the results of the case study in Suzhou. 3. Question: How to assess the mode substitution effects of dockless bike-sharing systems and its determinants? Results: An important issue of dock-less bike sharing is to study the mode substitution with respect to other transport modes at the trip level to assess their societal and environmental impact and study the complex effects of built environment factors on the mode substitution patterns of dockless bike sharing by applying machine learning to multiple data sources.