Sidewalk, A Wayfinding Message Syntax for People with a Visual Impairment
Joey van der Bie, Christina Jaschinski, Somaya Ben Allouch · 2019 · Proceedings of the 21st International ACM SIGACCESS Conference on Computers and Accessibility (ASSETS 2019) · doi:10.1145/3308561.3354625
Summary
This poster paper introduces Sidewalk, a structured wayfinding message syntax designed to improve navigation instructions for people with visual impairments (PVI) using mobile applications. The authors argue that traditional turn-by-turn navigation apps fail PVI because they lack sufficient detail about the surrounding environment, hazards, and orientation cues needed for safe and confident pedestrian navigation. Sidewalk addresses this by defining a consistent message structure with both obligatory and optional elements. The syntax follows a logical sequence: attention indicators and warnings come first, followed by current orientation confirmation, distance information, the action to perform, action indicators (landmarks), destination name, and finally orientation details about what the user will pass. This ordering is deliberate — critical safety information appears at the start so users can act immediately without listening to the entire message, reducing cognitive load. The syntax supports three levels of detail: attention alerts for hazards, short instructions for simple navigation points, and detailed messages for complex situations. Users can customize message length by including or excluding optional elements. The system was implemented using the EyeBeacons wayfinding app with Bluetooth beacons for precise location-triggered message delivery, and participants used bone-conducting headsets to keep their ears open to environmental sounds.
Key findings
Testing with six PVI (ages 44-69, varying visual acuity levels) on a route through urban Amsterdam yielded strong results. The System Usability Scale (SUS) averaged 84.2 (SD=10.4), well above the acceptability threshold of 68, with individual scores ranging from 82.5 to 95. The NASA Task Load Index (RTLX) averaged just 17.3 out of 90, indicating low cognitive and physical demand. All participants found Sidewalk superior to traditional turn-by-turn instructions, primarily valuing the environmental context and orientation information. However, two participants who were generally less confident navigators reported higher mental and physical demand, suggesting that navigation confidence is an important variable to account for. Complex crossings proved most challenging, with participants requesting less information at those locations — an interesting finding that more detail is not always better. All participants appreciated the tiered message types and recommended integration into existing navigation apps. The syntax design choices around distance were notable: absolute meters rather than step counts (which vary by person and cause users to count rather than attend to their environment), and a combination of absolute and relative distance using landmarks.
Relevance
This research offers practical, implementable guidance for developers building navigation applications for blind and low-vision users. The Sidewalk syntax provides a concrete template that could be adopted by any wayfinding app, moving beyond vague recommendations to a specific message structure. The finding that information ordering matters — safety first, details after — is directly applicable to any spoken interface design. The tension between providing enough environmental detail for orientation while avoiding information overload at complex intersections reflects a real design challenge in accessible navigation. The small sample size (six participants) limits generalizability, and the use of Bluetooth beacons for location precision means the approach depends on infrastructure that is not widely deployed. Nevertheless, the syntax itself is technology-agnostic and could work with GPS or other positioning systems. For practitioners, the key takeaway is that accessible navigation is not just about routing accuracy — it requires structured, context-rich communication that accounts for varying user confidence levels and environmental complexity.
Tags: visual impairment · wayfinding · navigation · natural language · mobile accessibility · spoken messages · urban navigation
Standards referenced: Wayfindr Open Standard