# Towards Understanding Driver Acceptance of C-ITS Services--A Multi-Use Case Field Study Approach
## 4 Discussion
### Usefulness  
The _usefulness_ of C-ITS-based information correlates with drivers' concerns, which are primarily related to safety-critical and unexpected road situations. In ESRIUM, 62% of respondents reported concerns about poor road surface conditions. Similar findings were observed in the ASFINAG study, where a minimum of 60% and a maximum of 72% of participants expressed concerns about potential driving hazards (see Figure 15). These concerns mainly revolve around exceeding the speed limit and encountering unexpected events such as traffic congestion or road construction. A majority of respondents believe that C-ITS information can help mitigate these concerns. The ESRIUM questionnaire examined the use of C-ITS services for bad surface information, with 85% of respondents indicating that they would like to receive such updates. In the ASFINAG study, 50% of online questionnaire respondents and a minimum of 75% and a maximum of 87.5% of interview participants agreed that having in-vehicle C-ITS information is beneficial. The approval rate primarily depends on the perceived safety benefits. In ESRIUM, 92% of respondents agreed that bad surface information would improve safety. Similarly, in the ASFINAG study, respondents believed that in-vehicle information enhances both road safety (78% approval) and personal safety (56% approval). Second, the likelihood of adoption increases if the C-ITS service is easy to use and understand. In the ESRIUM project, 10 truck drivers were asked to rate the following statement after their test drive: \"The bad surface information provided is clear and easy to understand.\" All drivers responded with \"I fully agree.\" Similarly, in the ASFINAG study, all eight car drivers unanimously agreed that the provided C-ITS services were clear and easy to understand, highlighting the high expected ease of use of these services. Testing of IVIS revealed a significant difference in the effectiveness of information delivery to users. Experimental results indicated that fewer errors occurred in response to hazard warnings when the system provided both aural and visual feedback. Notably, the accuracy of correct turns improved under complex driving conditions, with this effect being particularly pronounced among older drivers, who benefited to a greater extent. The findings suggest that adopting a multimodal approach that integrates visual and aural feedback may enhance response times and overall driving performance [38]. Also, trust in IVIS depends on the intuitive design of alerts; auditory signs that match real-world driving contexts are more effective in gaining user trust [39]. The exclusive use of visual information presentation may not be optimal, as research indicates that an increased visual load can negatively impact both hazard detection and lane-keeping performance. Therefore, interfaces that enable drivers to maintain their focus on the road, such as those integrating visual and auditory feedback, are considered more suitable from a safety perspective [39]. A study also showed that in order to increase the drivers' perceived urgency, faster auditory signals are needed and high fundamental frequencies [31]. A study with a similar design, featuring warning signals composed of symbols on a mobile phone accompanied by an acoustic signal, found that urgent IVIS warnings such as EEBL (Emergency Electronic Brake Light) and EVW (Emergency Vehicle Warning) had a positive impact on driving behaviour. Additionally, drivers' reaction times decreased by an average of 2.8 s when a leading vehicle was visible and by 3.5 s in low-visibility conditions. Furthermore, the average driving speed decreased after the EEBL warning was issued. These improvements suggest that IVIS warnings significantly enhance drivers' situational awareness [35]. Less urgent warnings, such as RWW (Road Work Warning) and TCW (Traffic Congestion Warning), did not significantly influence driving speed, as road signs already provided sufficient information about these situations.