Earlier quoted context omitted.
What was the stack used to write such a system? Was it a lot of C++? And what storage systems did they use? Sounds pretty cool.
The system as a whole used C, C++, Python, and some Java/JS-family stuff in the infrastructure backends. You can find a long tail of other languages scattered throughout the organization, like Go, Rust, Lisps, and Swift, etc. I wrote a fare-cost-calculator in Mathematica awhile ago, as an example. As for storage systems, no idea. The stuff I know was all custom, but I was deep in the stack most of the time and don't…
It all makes sense now. Astounding its legal to use C/++ in a safety critical situation.