System designHardsd-g399

Subject Eta predictionLevel Senior–Staff~50 minCommon in ML systems · Algorithms & data structures interviewsIndustries Technology

Question

Design an ETA prediction service that powers a navigation app serving 1M route requests/minute. ETAs must reflect live traffic that changes minute-to-minute, must be returned in <100ms p99 for a route that may span hundreds of road segments, and must stay accurate across rush hour, incidents, and weather. You have a fleet of probe vehicles feeding live speeds. Describe how you ingest live traffic onto the road graph, compute the ETA, serve it at low latency, and reconcile the physics-based segment model with a learned correction.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

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