# Leveraging Digital Twin Technology for Sustainable and Efficient Public Transportation
## 3 Challenges and Limitations of Digital Twins
### Interoperability  
Interoperability refers to the connection between the physical element or the infrastructure and its digital counterpart. Successful implementation of DTs requires seamless data exchange and communication among various virtual technologies and their physical counterparts. Development of standardized communication protocols is required to have compatibility as well as efficient data exchange across different DTs.  
One of the primary challenges in achieving interoperability is the need for standardized communication protocols and data formats. The authors of one study pointed out that connecting data from different digital twins can lead to compatibility problems. There is thus a need for standardization to ensure smooth data exchange [75]. Another study mentions that digital twins in logistics require strong IT systems and consistent data man agement to work well together [58]. Without these standards, digital twins cannot fully improve transportation systems to achieve maximum efficiency. One of the key tools identified by the authors of one study is the Asset Administration Shell (AAS), which they used as a common interface that helps different digital twins communicate. The AAS is a standardization of DTs for industrial applications, which allows cross-company interoperability across multiple platforms. Using the AAS, transportation stakeholders can ensure the interoperability of various DTs and their components, making transportation systems more efficient and reliable. This kind of integration is especially important in smart cities, where many digital twins need to work cohesively to manage urban mobility [76; 104].  
Synchronization of data between digital twins and their physical counterparts is also crucial. There is a need to keep DTs up to date with accurate data synchronization to avoid delays in interventions. This synchronization is more complicated when cybersecurity concerns arise. Hence, there is a need for secure and reliable communication channels to ensure the integrity of data exchanged between digital twins and their physical systems [43; 77].  
The architecture of digital twins also plays an important role in their interoperability. Authors discuss a'mobility digital twin' that relies on a clear setup to combine data from different sources and allow these systems to communicate easily [98]. Since different transportation systems use diverse technologies and data formats, the architecture of digital twins needs to handle this variety. For instance, creating digital twins that can work together in bus systems requires a strong tech setup that can manage real-time data-sharing. This includes the use of advanced communication protocols and data models that enable different digital twins to interact seamlessly [44]. Modular software architecture, mentioned in recent studies, also helps digital twins work together better by allowing for quick setup and flexibility for changing needs [99]. This approach reduces the engineering work, making digital twins easier to implement for transportation agencies.  
Furthermore, integration technologies, such as IoT and 5G, can enhance the interoperability of digital twins in transportation. While the authors of one study mainly discuss the IoT with digital twins in power systems, the principles of the IoT and digital twins can similarly be applied to transportation systems, facilitating real-time data exchange and improving responsiveness [60]. This integration is crucial for autonomous vehicles, where low-latency communication is required for decision-making processes [63]. If interoperability challenges are addressed, these technologies can significantly improve the operational efficiency of bus transportation systems.