How to ensure trust and societal acceptance of automated vehicles (AVs) is a widely-discussed topic today. While trust and acceptance could be influenced by a range of factors, one thing is sure: the ability of AVs to safely and smoothly interact with other road users will play a key role. Based on our experiences from a series of studies, this paper elaborates on issues that AVs may face in interactions with other road users and whether external vehicle interfaces could support these interactions. Our overall conclusion is that such interfaces may be beneficial in situations where negotiation is needed. However, these benefits, and potential drawbacks, need to be further explored to create a common language, or standard, for how AVs should communicate with other road users.