# Towards Understanding Driver Acceptance of C-ITS Services--A Multi-Use Case Field Study Approach
## 4 Discussion
### Compliance  
Both studies investigated _compliance_ with the provided information. The key finding is that compliance rates for \"reduce speed\" or \"change lane/lane offset\" instructions are highest when the information is safety-related (see Figure 14). In ESRIUM, truck drivers showed a 92% compliance rate for safety-related lane change recommendations, compared to only 37% for non-safety-related ones. A similar trend is observed for lane-offset manoeuvres: 70% of truck drivers comply with safety-related recommendations, whereas only 26% follow non-safety-related ones. In the ASFINAG study, compliance with safety-related warnings was also high. On average, 89% of respondents said they would reduce their speed in response to road works warnings (RWW) and hazardous location notifications (HLN). Research has shown that new features such as EVW (Emergency Vehicle Warning) and EEBL (Emergency Electronic Brake Light) have the highest urgency for implementation and could enhance safety. IVIS has the potential to improve drivers' situational awareness and help them anticipate hazardous situations of varying urgency and criticality at an early stage [31]. A study also demonstrated that drivers were more likely to comply with in-vehicle information when it was synchronized with external visual cues, such as overhead gantries. For instance, the earlier the in-vehicle information was displayed, the slower the drivers' speeds were when speed limits were reduced [32]. Additionally, compliance rates increase with trust in the information provider. In ESRIUM, truck drivers were asked about their trust in road operators regarding bad surface information and whether they would use it. The results are clear: roughly 90% rated road operators as highly or very highly trustworthy, and 92% would use the information. Similarly, in the ASFINAG study, all car drivers agreed that safety-related information (RWW and HLN) from a road operator is trustworthy. This trust is reflected in statements from the online questionnaire, such as: \"Trust in the road operator is higher than in the navigation device,\" and \"The road operator has more information about road conditions than I do, especially for unfamiliar routes.\"  
Finally, the accuracy of the provided information plays a crucial role in compliance. Some respondents emphasized this in the online questionnaire, stating: \"It depends on the accuracy and implementation of the supplier,\" and \"Sometimes I don't find the suggestions from operators reliable.\"  
These findings align with the driving simulator study by Payre and Diels, which suggests that in-vehicle speed limit warnings can enhance drivers' situational awareness and promote more stable speed control [32]. However, while participants accepted the use of digital speed limit warnings via a mobile app, they remained hesitant to fully replace traditional road signs, highlighting the continued trust in established traffic control measures [32]. User acceptance of in-vehicle technology is crucial, as it ensures that the systems are utilized, thereby meeting fundamental design goals such as safety and driving efficiency [35]. Furthermore, it was found that to instill, build, and maintain trust in the user of in-vehicle information, the information must be accurate [36], delivered precisely [37] and clearly [37], and relevant, meaning both accurate and context-aware [37]. Otherwise, the credibility and trust in, for example, an in-vehicle information system, are negatively affected [36]. Results of a study investigating the level of accuracy necessary in IVIS to elicit positive behavioural and attitudinal responses from drivers indicate that a decrease in system accuracy leads to a decline in both driving performance and trust and liking of the IVIS. Females appear to be slightly more tolerant of inaccuracies compared to males [36].