Safety for Automated Vehicles in Mixed Traffic as a Partial Result of the Consortium Project SALSA

April 16,  2025 – Reading time: 8 minutes

The SALSA project is revolutionizing road safety by addressing the integration of automated vehicles into mixed traffic. Focusing on safety, user trust, and adaptive communication systems, SALSA develops standardized eHMI solutions and legal frameworks to ensure smooth and secure interactions between all road users. Supported by the German Federal Ministry for Economic Affairs and Climate Protection, the project paves the way for the future of mobility.

The integration of automated and autonomous vehicles into mixed traffic presents high demands for communication and technology. The consortium project SALSA (“Smart, Adaptive, and Learnable Systems for All”) develops innovative approaches to improve the safety and acceptance of these vehicles. SALSA focuses on three key challenges:

1. Safety: Preventing accidents and minimizing risks to ensure smooth interaction between autonomous and non-autonomous road users.
2. Trustworthy User Experience: The societal acceptance of autonomous vehicles largely depends on transparent and intuitive interactions.
3. Adaptive Interaction Systems: Systems must be flexible enough to respond to different driving situations and individual preferences.

A central research focus is the optimization of external human-machine interfaces (eHMI). INVENSITY analyzed the safety-critical requirements for eHMI, considering relevant standards and regulations. Since traditional non-verbal communication forms, such as eye contact or hand signals, are not applicable to autonomous vehicles, eHMI systems must provide clear, intuitive, and easily understandable signals. This will help avoid misunderstandings, increase road safety, and build trust in this technology.

We analyzed communication mechanisms between automated vehicles and other road users, taking into account established safety standards:

• ISO 26262 (Functional Safety)
• ISO 21448 (SOTIF) (Safety of the Intended Functionality)
• ISO/TR 4804 (Safety and Cybersecurity for Automated Driving)

Based on these investigations, we derived concrete safety requirements and design recommendations. Additionally, we developed proposals for adapting traffic regulations (StVO) to further advance the legal framework for eHMI.

Another central research goal is to identify requirements that would allow for the standardization of eHMI. We analyzed existing standards and scientific findings on human-machine interfaces. Although there are currently few specific and well-applicable standards for eHMI, we were able to extract, refine, and compile a variety of safety-relevant principles from various sources. These can serve as a basis for manufacturers and suppliers in the development of safe and standardized eHMI systems in the future.

Another important aspect is the adaptation of the legal framework. We investigated what modifications to the traffic regulations (StVO) would be required to efficiently regulate the interaction of autonomous vehicles in mixed traffic. To do this, we identified relevant traffic scenarios and compared them with existing StVO guidelines. The resulting insights allowed us to formulate targeted proposals for adapting the legislation to support the safe and seamless integration of autonomous vehicles into road traffic.

We analyzed how eHMI influences the HIRE process (= “Hazard Identification and Risk Evaluation”) according to ISO 21448 (SOTIF) in critical traffic situations. Our study shows that effective communication strategies can significantly reduce risks and increase the safety of autonomous systems.

In addition to traffic safety, we also considered factors such as traffic flow and energy efficiency, ensuring the optimal integration of autonomous vehicles into mixed traffic while reducing resource consumption through efficiency gains.

The SALSA project makes a significant contribution to the safe, efficient, and accepted integration of automated vehicles. Standardized communication mechanisms and clear legal frameworks strengthen the trust of all road users in this technology and are a crucial step toward making autonomous driving a reality.

Through interdisciplinary collaboration between technology, psychology, law, and society, SALSA ensures that the integration of autonomous systems is not only technically feasible but also safe and socially accepted. By focusing on the research and development of eHMI, safety standards, and regulatory adjustments, the project actively shapes the future of mobility – safe, efficient, and comfortable.

The SALSA research project is supported by the German Federal Ministry for Economic Affairs and Climate Protection.

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