Tesla has spent about $8.5B on R&D in the past decade. Of course, not all of that was spent on FSD, but let's assume it was.

Let's also assume our hypothetical public transport is built in San Francisco. San Francisco recently spent $1.5B on a 1.7 mile subway line. It will also take a decade from when work begun to its opening next year.

That works out to be a 9.7 mile subway that opens in 2032.