# Designing for Trust: Enhancing Passenger Confidence in Shared Autonomous Vehicles
## 1 Introduction  
With advancements in fully autonomous technology (Level 5), it is anticipated that SAVs could potentially become a reality when this autonomous driving technology is combined with on-demand shared mobility services (e.g., Uber, Didi) [1]. SAVs have been trialled in a number of cities around the world but are only provided on a commercial basis in certain areas, such as Waymo One (Waymo LLC, Mountain View, CA, USA) and EZ10 (EasyMile, Toulouse, France) [2].  
SAVs integrate autonomous vehicles (AVs) and shared mobility, offering benefits such as reduced pollution, improved safety, and cost efficiency [1, 3]. However, they may also increase vehicle numbers and service wait times [4]. Given their limited real-world deployment, their full impact remains uncertain. To maximize benefits, SAVs need to be shared simultaneously between strangers.  
Although AV technology and ride-sharing schemes are increasingly implemented, little is known about whether passengers prefer to ride alone or share space with strangers. SAVs offer potential advantages, such as carpooling, that already exist but are not widelyadopted. While many technical challenges have been addressed, broader adoption is still limited due to social barriers, particularly issues of trust.  
Studies have shown that distrust in automated systems and discomfort with unfamiliar co-riders, especially in the absence of an authority figure, are significant obstacles to SAV implementation [5; 6; 7]. A strong correlation was found between trust in the vehicle and trust in strangers, as the passengers' trust level in strangers may be affected by the low trust in a vehicle without a human driver [8; 9].  
Discussions about designing trustworthy SAVs often emphasise driving technology and human-machine interaction (HMI), particularly in the automation literature [10]. However, these discussions frequently prioritise technological aspects or are constrained by commercial confidentiality. In addition to technology, vehicle design features also significantly influence users' trust. Yet, limited research has examined how industrial design can address trust issues, both in relation to the vehicle itself and among co-passengers.  
This study assumes a future scenario in which SAVs are technically capable of ensuring safety for both co-passengers and pedestrians, in line with the development of fully autonomous Level 5 vehicles. Therefore, the focus of this research is not on the technical implementation of safety systems, but on how industrial design, including form, space, interface, and app features, can enhance users' perception of trust when using SAVs. Specific technological and ethical considerations, such as the prioritisation between pedestrian and passenger safety, are considered to be beyond the scope of this study.  
To avoid an overly broad scope, the context of SAVs in this study represents the envisioned end state of SAVs as currently perceived. The focus is on design challenges related to passengers' trust issues within a hypothetical future scenario where multiple strangers share space during the use phase in an SAV. The design work is guided by a set of key assumptions:  
1. SAVs are defined as fully autonomous vehicles (Level 5) with no onboard operator.
2. From a technological perspective, SAVs are assumed to ensure safety for both passengers and pedestrians.  
Given the significance of trust in the adoption of SAVs, this study addresses how to enhance passengers' trust through design practice. It focuses on two primary dimensions: trust in the vehicle and trust in fellow passengers. The research responds to a gap in the design literature by investigating how industrial design can mitigate trust-related challenges in SAVs. To achieve this aim, the following objectives are intended to be fulfilled:  
1. To discover the potential challenges and opportunities of trust design for future SAVs.
2. To develop a conceptual design solution for future SAVs through design practice that could engender trust between the vehicle and fellow passengers.