Product design question
Design an elevator for a 100 story building.
- Product design
- Medium
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What this question tests
Tests structured product design applied to a physical system: defining users, constraints, and prioritized features for a critical infrastructure product.
How to approach it
- Identify users: daily commuting residents or office workers, visitors, maintenance staff, and emergency responders, each with different needs.
- Identify constraints: throughput at peak hours (morning rush), safety, accessibility, and building code and emergency requirements.
- Prioritize the core problem: minimizing wait and travel time at peak hours while guaranteeing safety and accessibility at all times.
- Propose the solution: a smart destination-dispatch system where users select their floor before boarding, so the system groups riders efficiently, rather than simple up and down buttons.
- Address edge cases: a dedicated accessible car, an emergency override mode, and a fireman's service protocol as required by code.
- Define success: average wait time and travel time at peak hours, plus safety incident rate as a hard guardrail.
What a strong answer includes
- Frames the elevator as a system optimization problem (peak-hour throughput) rather than a single-cab design exercise.
- Proposes destination dispatch, a known real-world technique used in modern high-rises, showing awareness of actual elevator system design.
- Explicitly addresses accessibility and emergency requirements as non-negotiable constraints, not optional features.
- Defines success with a measurable operational metric, average wait and travel time at peak, tied to the actual user pain point.
Common mistakes
- Designing only for a single elevator car in isolation instead of the building's overall vertical transport system.
- Ignoring safety, accessibility, and code requirements as core constraints rather than afterthoughts.
Likely follow-up questions
- How would you handle elevator allocation differently during a fire alarm versus normal peak hours?
- How would you reduce perceived wait time even if actual wait time cannot be reduced further?
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Learn the skill behind it
Chapters of the AI PM course that teach what this question tests.
- Chapter 4: Discovery and strategy for AI products
- Chapter 7: AI UX and human oversight: design for a system that is wrong sometimes
- Chapter 14: Get the job: the AI PM interview loop