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Google·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Apr 2026

Summary

Google interview with a single system design question about autonomous vehicles. Pretty niche and I wasn't expecting it to go in that direction, but it was actually one of the more interesting problems I've had to think through.

Questions Asked (1)

Q1

Design a post-accident algorithm for a self-driving car.

System DesignTechnical Trade-offsAdaptability & Ambiguity
Author's notes

I spent the first minute or two just trying to figure out what 'post-accident' even meant in this context.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the scope and requirements of the post-accident algorithm, such as the definition of an accident, the car's capabilities, and regulatory constraints. Then, outline a high-level system design that prioritizes safety, communication, and data collection, and discuss trade-offs between different approaches. Finally, dive into specific components like detection, response, and post-incident analysis, ensuring to address edge cases and ethical considerations.

Pro tip: Emphasize a safety-first mindset by discussing fail-safes and redundancy, and show awareness of real-world constraints like sensor limitations and legal liability. This demonstrates maturity and a holistic understanding beyond just coding.

1. Clarify Requirements and Scope

Ask questions to understand what constitutes an 'accident', the car's autonomy level, available sensors, and regulatory environment. Define the goals: minimize harm, ensure passenger safety, alert authorities, and collect data.

2. High-Level System Design

Outline the main phases: detection (using sensor fusion), immediate response (safe stop, hazard lights), communication (emergency services, manufacturer), and data logging. Consider redundancy and fail-safes.

3. Detailed Component Design

Dive into each component: how to detect an accident (e.g., sudden deceleration, airbag deployment), how to respond (e.g., pull over, unlock doors), and how to communicate (e.g., via cellular, satellite). Discuss trade-offs like latency vs. reliability.

4. Address Edge Cases and Ethics

Consider scenarios like multi-car accidents, sensor failure, or communication blackouts. Discuss ethical dilemmas (e.g., who to prioritize) and how to handle them within legal and ethical frameworks.

5. Testing and Validation

Explain how to test the algorithm using simulations, closed-course tests, and real-world data. Mention the importance of continuous improvement and over-the-air updates.

Key Points to Mention

  • Sensor fusion for reliable accident detection (e.g., combining lidar, radar, cameras, IMU).
  • Immediate safety responses: safe stop, hazard lights, unlocking doors, and disabling autonomous mode.
  • Communication protocols: alerting emergency services, sharing location and sensor data, and notifying the manufacturer.
  • Data logging and black box for post-incident analysis, ensuring data integrity and privacy.
  • Redundancy and fail-safes: backup power, communication channels, and fallback to manual control if possible.
  • Regulatory and ethical considerations: compliance with laws, liability, and ethical decision-making frameworks.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.