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Waymo Common Problems

Parking Lot / Ride-Hailing System Design

System DesigneasyLast reported September 2025
By AceOffer · Updated September 2025 · Reported 1× across 190+ candidate reports

Understanding the Problem

Design a hybrid parking management and on-demand ride system (similar to an autonomous vehicle fleet operation). Key constraints and behaviors: (1) Customers summon vehicles at parking lot exits and wait for pickup. (2) Vehicles cycle through multiple spot types in the lot — e.g., they move from charging spots (replenishing power) to maintenance spots (inspection/repair) and finally to regular (non-charging) waiting spots before being dispatched to a customer. (3) The system must manage the full vehicle lifecycle across these spot categories and orchestrate efficient dispatch. As a follow-up, discuss which performance metrics you would design and monitor for such a system.

Functional Requirements

Structured requirements coming soon. For now, see the full problem statement above and the deep-dive prompts below.

Non-Functional Requirements

Latency, throughput, availability, consistency targets — being authored.

The Set Up

Defining the Core Entities

Core entities (Request, Batch, Worker, Cache, etc.) — being authored.

The API

POST /endpoint → describe request shape GET /endpoint → describe response shape (API spec being authored)

High-Level Design

Component diagram + walkthrough mapping each functional requirement to a system flow — being authored.

Potential Deep Dives

These are the directions the interviewer is likely to push you. Each one has multiple valid solutions at different quality tiers.

1)What performance metrics would you instrument and monitor for this system? (when: After core design is laid out)

Bad
Naive approach with serious trade-off — being authored.
Good
Solid baseline with reasonable trade-offs — being authored.
Great
Production-grade approach with explicit trade-off rationale — being authored.

2)How does a vehicle move between spot types — who controls that flow, and how do you prevent a spot from being double-assigned? (when: If candidate only covers the ride-hailing side)

Bad
Naive approach with serious trade-off — being authored.
Good
Solid baseline with reasonable trade-offs — being authored.
Great
Production-grade approach with explicit trade-off rationale — being authored.

What is Expected at Each Level?

L4 / Mid-level
Cover happy path. Clarify scope. Identify the obvious bottleneck. Pick a reasonable storage and reasonable scaling approach.
L5 / SeniorTarget
All of the above plus: explicit failure handling, durability vs latency trade-offs, choose the right batching/caching strategy, articulate why.
L6 / Staff+
All of the above plus: organizational concerns (rollout, migration, on-call), quantitative analysis, multi-region considerations, what could go wrong with the proposed solution at 10x scale.

Insider Notes

**Common mistakes:** Treating the system as a pure ride-hailing design and ignoring the internal vehicle lifecycle / spot management component; Not modeling the vehicle state machine explicitly, leading to unclear transition logic; Forgetting concurrency issues when multiple dispatchers try to assign the same vehicle **What passers do:** Explicitly modeling the vehicle state machine with legal transitions before jumping to services; Addressing spot-allocation consistency (locking mechanism) proactively; Proposing concrete, measurable performance metrics with justification **Why people fail:** Focusing only on the customer-facing ride request flow without addressing internal fleet/spot management; Skipping data model and jumping directly to high-level boxes without detail; Unable to articulate relevant metrics beyond generic 'latency and throughput' **Edge cases probed:** Vehicle runs out of charge while in a regular (non-charging) spot before being dispatched — needs re-routing to charging spot; All charging spots are occupied when a vehicle needs to charge; Customer cancels request after vehicle is already dispatched; Simultaneous ride requests when only one AVAILABLE vehicle exists (race condition in assignment) **Alternative approaches:** Event-driven with Kafka for state transitions (Decouples services and enables replay/audit of vehicle state history, but introduces eventual consistency — a vehicle might appear AVAILABLE briefly while already being assigned in another partition.); Centralized monolithic coordinator (Simpler to reason about strong consistency for spot allocation and dispatch, but becomes a single point of failure and bottleneck at scale.); Geospatial dispatch (if multi-lot or large lot) (Use PostGIS or Redis GEO commands to find nearest available vehicle to a requested exit gate — more accurate but adds infrastructure complexity.)
Waymo · System Design · Last reported September 2025