  External Human-Machine Interfaces (eHMI) are widely used on robots and
autonomous vehicles to convey the machine's intent to humans. Delivery robots
are getting common, and they share the sidewalk along with the pedestrians.
Current research has explored the design of eHMI and its effectiveness for
social robots and autonomous vehicles, but the use of eHMIs on delivery robots
still remains unexplored. There is a knowledge gap on the effective use of
eHMIs on delivery robots for indicating the robot's navigational intent to the
pedestrians. An online survey with 152 participants was conducted to
investigate the comprehensibility of the display and light-based eHMIs that
convey the delivery robot's navigational intent under common navigation
scenarios. Results show that display is preferred over lights in conveying the
intent. The preferred type of content to be displayed varies according to the
scenarios. Additionally, light is preferred as an auxiliary eHMI to present
redundant information. The findings of this study can contribute to the
development of future designs of eHMI on delivery robots.
