Trust-Building in Level 4 Automation by Intent Communication: In-Vehicle HMI Design, Passenger Trust, and Visual Attention

Details

• Creators:
  Pradhan, Anuj K. ; Hungund, Apoorva P. ; Onyeukwu, Stephen G.
• Corporate Creators:
  New England University Transportation Center (NEUTC) Region 1 University Transportation Center (UTC) ; University of Massachusetts at Amherst
• Corporate Contributors:
  United States. Department of Transportation. University Transportation Centers (UTC) Program ; United States. Department of Transportation. Office of the Assistant Secretary for Research and Technology
• Subject/TRT Terms:
  • Automated vehicle control
  • Human machine systems
  • Passengers
  • Eye tracking
  • Driving simulators
  • Databases
  • Psychological trust
  • Level 4 driving automation
  • Autonomous vehicles
  • Vehicle Automation
  More +
• Publication/ Report Number:
  01938993
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States
• Edition:
  Final Report: February 1, 2025 - January 31, 2026
• Corporate Publisher:
  New England University Transportation Center
• Abstract:
  At SAE Level 4 automation the vehicle occupant becomes a passenger with no driving role, no fallback obligation, and no expectation of takeover. The passenger cannot intervene with the driving and thus must rely on trust. Here, it is the in-vehicle human-machine interface (HMI) that is the primary channel through which the vehicle can make its perception and intent legible. Passenger-facing HMI is sparsely researched relative to external interfaces and to drivers at lower automation levels. This project addressed that gap in three tasks. A systematic review following PRISMA searched seven databases, screened 3,364 records, and synthesized 37 studies on how in-vehicle HMI modality, content, and quality shape passenger trust. Guided by that synthesis, three in-vehicle HMI conditions (auditory, visual, and multimodal) were built in Unity and integrated with a high-fidelity driving simulator, that communicated the vehicle's perception and intent five seconds before every maneuver. This was experimentally evaluated with thirty-six participants who rode as rear-seat passengers through a seven-minute Level 4 drive containing eight scenarios, with survey and head-mounted eye-tracking measures. Reported trust increased significantly from pre-drive to post-drive in all three conditions. The multimodal interface produced significantly higher trust and perceived system transparency than the visual interface, with no penalty in workload or usability. HMI modality shifted visual attention only toward the in-vehicle display, and trust was negatively correlated with time spent monitoring that display. Passenger scanning remained anchored on the forward roadway and varied with the driving scenario rather than with the interface. Communicating intent builds passenger trust irrespective of channel, and redundant multimodal delivery builds the most trust.
• Format:
  PDF
• Funding:
  69A35523483
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/93332/dot_93332_DS1.pdf
• File Type:
  [PDF - 548.58 KB]
• Collection(s):
  Autonomous Vehicles ; University Transportation Centers
• Main Document Checksum:
  urn:sha-512:d0ff0b636ab9d607b5ba0ec90e93991e11981d0e86fc2eb925979761f83befa7d9fc4f024f5be979fd80c029483238a74bc3d4656c70bbc4bc91661c1e88d647