• Redundancy increases noticeability: Presenting the same instruction via multiple channels (visual signs, audio announcements, haptic cues, and staff presence) raises the chance passengers perceive it despite distractions, noise, or sensory limitations. (Signal detection theory; see Wickens 2002.)

• Reduces ambiguity and cognitive load: Complementary modes can present the same instruction in different forms (text + icon + spoken phrase), making meaning clearer and faster to process, so passengers comply more quickly. (Dual-coding theory; Paivio 1971.)

• Compensates for individual differences and situational limits: Different passengers have different sensory abilities, languages, or attention states; multiple channels ensure at least one channel is effective for each person, increasing overall compliance.

• Reinforces urgency and authority: Repeated, concordant messages across modes convey importance and legitimacy, prompting faster and more consistent action (social proof and authority effects).

• Limits bottlenecks and errors, improving throughput: Faster, more uniform compliance reduces hesitation, misrouting, and the need for corrective interventions by staff, thereby increasing flow rate and reducing dwell time.

Practical implications: Use concise, redundant cues timed and prioritized (e.g., synchronous audio + visual + staff prompts at decision points), avoid contradictory signals, and adapt channel mix to context (noisy environments → stronger visual/haptic cues).

Key references: Paivio, A. (1971) Mental Imagery in Associative Learning; Wickens, C.D. (2002) Multiple resources and performance prediction; Norman, D. (2013) The Design of Everyday Things (for affordances and clarity).