Design a bus simulation metric

In an AI-assisted interview, you are given an unfamiliar codebase of roughly 10,000 lines that implements a bus traffic simulation. You may use an approved AI assistant to search the codebase, summarize files, and help locate logic. You are asked to: (1) explain the responsibility of specific classes and identify where particular behaviors are implemented, (2) make small targeted code changes safely, and (3) design and implement a new metric for simulation efficiency. Describe a strong end-to-end approach for understanding the codebase quickly, validating AI-generated answers, choosing a meaningful efficiency metric, instrumenting the simulator, and testing the result.