[rayiner]

For things like endowments, the general assumption is that you can get a 4% yield that keeps pace with inflation, without touching principal. So you'd be up to $300 million per year today. That's about $2.50 per BART ride of $750 per year per BART rider, which is a believable number.

The problem that you're ignoring, however, is that the relative cost of building infrastructure today is far higher than it was in the 1970s. If you built BART today, it wouldn't cost $10 billion in today's dollars. NYC's recent projects are running $1.5-3.5 billion per mile of subway track. BART has 28 such miles. That's $42-100 billion, not including the other 70 miles in the system.

So what if BART had cost $8 billion ($50 billion in today's dollars) instead of $1.586 ($10 billion)? Instead of having to great $2.50 of value per ride to justify the investment, you're up to at least $12.50. Or $3,750 per daily BART rider. Is each BART trip generating that much value compared to doing the same trip in a car?