Design a Pickup Area Driver Queue

Problem Statement

Design an internal pickup area driver queue service for Uber. Given a pickup area such as an airport staging lot or a geofenced pickup zone, internal systems should be able to fetch the current driver queue for that area. When a driver enters the area, they join the queue. When they leave the area, go offline, or become ineligible, they are removed.

At minimum, the system should support:

• maintaining queue membership for many pickup areas in real time
• adding drivers when they enter a pickup area
• removing drivers when they leave, go offline, or get matched elsewhere
• returning the current ordered queue for a pickup area
• preserving correct ordering even with duplicate, delayed, or out-of-order events

This is not the same as a heatmap or global dispatch optimizer. The core challenge is closer to a real-time geofence membership and ordered state management system:

• how you decide a driver is "in" a pickup area
• how you maintain a stable queue order under continuous movement
• how you make queue reads fast while processing event streams correctly
• how you keep the queue consistent across driver status changes, reassignment, and failures

This walkthrough follows the System Design interview framework and stays focused on what you can explain clearly in a 45-60 minute onsite.

Reported Interview Signals

• The prompt can sound deceptively small, but interviewers usually want more than a CRUD queue.
• A strong answer clarifies what defines queue order and what events remove a driver before drawing architecture.
• Interviewers often push on duplicate enter/leave events, GPS jitter near boundaries, and how to avoid scanning all drivers for one area.
• This question is more about stateful stream processing than about raw map rendering.

Disclaimer: This is a sample interview-prep structure, not the only valid design. In the interview, clarify whether queue order is strict FIFO, whether temporary exits reset position, and whether "return queue" means the full queue or only the next few eligible drivers.