By John Shutko
As AVs (automated vehicles) move closer to proliferating on the roads, new challenges emerge — especially in how these vehicles interact with the people around them. ISO/PAS 23735:2025 is a publicly-available specification developed by the International Organization for Standardization, which offers design guidance for how fully automated vehicles should use visual signals to communicate with other road users. Its aim is to support safety and promote trust as machines replace human drivers.
This document focuses on Level-4 and -5 AVs, and how these vehicles should visually communicate to other road users. On highways, in cities, and in rural areas, these vehicles will need to engage with other road users: pedestrians, cyclists, human-driven vehicles, and all other traffic participants and interactors. Because traditional human communication modes like eye contact or hand waves won’t be possible, AVs must fill that gap in a universally intuitive, consistent manner.
ISO/PAS 23735 outlines a communication framework that categorizes road interactions into three types: encounters (simple proximity), interactions (requiring behavioural responses), and conflicts (users compete for the same space). It recommends combining implicit signals, like how a vehicle moves or slows down, with explicit ones, such as lights or visual displays that clearly indicate the vehicle’s intent. The goal is redundancy and clarity: to reinforce intent through multiple channels and reduce uncertainty for nearby road users.
To be effective, these signals need to be designed well. Factors like brightness, vehicle location, and colour influence whether a message is seen and understood. Signals should be immediately, unambiguously recognizable without demanding too much mental effort or causing distraction. They should integrate seamlessly with the vehicle’s actual motion, to avoid mixed messages which could create confusion or even danger.
The specification also emphasizes that AVs will interact with children, older adults, and people with disabilities, all of whom experience and interpret visual information differently, and these differences must be considered in design. Cultural and regional differences also matter; a visual signal that’s obvious in one country may be misunderstood in another. The document encourages universally intuitive designs while acknowledging that education and repeated exposure will likely be needed for wide-scale understanding.
Beyond design, the standard speaks to the human psychology of adoption. Acceptance of AVs isn’t just about technology; it’s about trust. Clear, consistent, and human-centred signals can help build that trust, while poor or misleading communication can do the opposite, potentially setting back public confidence in AVs.
The document includes a comprehensive set of real-world use cases — scenarios like pedestrian crossings, traffic merges, and intersections — along with guidance on which signals work best in each case. It touches on safety standards and how these new systems might integrate with existing traffic infrastructure.
