Vehicle Registration System

Vehicle Title and Registration Records

Design a government-style records system for vehicle titles and registrations: ownership changes exactly once, every change leaves a permanent audit record, and lookups return only what each caller may see.

Overview

A vehicle registry is the legal record of which vehicles exist, who owns each one, who has lent money against it, and whether it may be driven on public roads. A title proves ownership; a registration is the yearly permission to drive, tied to a plate; a lien records a lender's claim until the loan is paid.

This is a records problem, not a scale problem. A few hundred thousand changes a day is light work for one database. What makes it hard is that every change is a legal fact: an ownership transfer must happen exactly once, a lien cannot be silently lost, and years later someone must be able to prove who changed what and why. Meanwhile police, insurers, toll operators and the public look up plates and VINs hundreds of times more often than records change, and each may see only certain fields.

In the United States, two outside rules shape the design and are worth naming. The Driver's Privacy Protection Act (DPPA) limits when personal information from motor vehicle records may be disclosed and lists the permitted uses. The National Motor Vehicle Title Information System (NMVTIS) lets a state check a vehicle's title history, including salvage and junk brands, before issuing a new title. This topic describes a general design, not any particular agency's system.

Questions to ask first

How many vehicles? — About 30 million registered in one jurisdiction
How many changes? — Renewals yearly, 15% change owners a year, 2 million new a year: about 100,000 changes a day
Who looks things up? — Police, insurers, toll operators, the public; about 50 million lookups a day
Channels? — Online portal, branch counters, dealers, mailed forms keyed in by clerks
May a lookup be a few seconds stale? — Yes for most fields; a stolen flag must reach lookups within seconds
How long is history kept? — Permanently for titles; lookup logs for a period the law sets

What you will be able to do

Model titles, liens and plates so the database itself rejects impossible states.
Transfer ownership exactly once, even when two channels submit the same sale.
Make every workflow safe to retry with an application ID.
Keep an append-only, tamper-evident audit trail.
Serve high-volume lookups from a filtered read model that shows each caller only permitted fields.

Key concepts

System of record
One current title per VIN
Row locks
Idempotent applications
Append-only audit log
Hash chain
Purpose-based access
Read model
VIN check digit

Functional requirements

Title a new vehicle, assign a plate and record the owner
Transfer ownership, carrying brands (salvage, rebuilt) forward
Record a lien, and release it when the lender reports payoff
Renew a registration after insurance, emissions and payment checks
Flag a vehicle stolen, salvage or junked, and clear a stolen flag
Look up by plate or VIN, returning only fields the caller may see for the stated purpose
Show the full history of a vehicle to authorized staff

Non-functional requirements

Strong consistency for ownership: two transfers of one vehicle can never both succeed
Every change is recorded in an append-only log with who, when, why and the evidence
Every request is safe to retry; a retried transfer or payment never happens twice
Lookups answer in under 100 ms at p99 and stay up 99.95% of the time (targets we chose)
A stolen flag reaches lookups within seconds; other fields may lag a few seconds
Every lookup is logged with the caller and the stated purpose

Interview questions

How do you guarantee that ownership changes exactly once?
Why not use a microservice per entity and a saga?
How do you build the audit trail?
How do you serve 50 million lookups a day?
How do you keep personal information from leaking through lookups?
How do renewals work when the insurance check is slow?
How do you stop title washing?
What about disaster recovery?