That would imply that the US has several trillion dollars invested in its highway system, correct? Does that number pass the smell test to you?
Wiki reports that our ~45,000 mile interstate highway system cost about 425 billion, or a hair under $10 million a mile, in 2006 dollars. That's under a twentieth of what the LA transit folks are quoting. (I think they're doing creative accounting by reclassifying part of construction as operating expenses, which is a frequent trick in this field, but I've got nothing to back that up.)
If I commuted by car I would've personally paid a hell of a lot more for the privilege. The up-front cost of the infrastructure is not the only consideration...
This does not speak to operating costs.
Mass transit fairs are usually subsidized from general tax revenues - user fees usually cover something like 10-25% of actual costs.
You don't just pay for gas, you pay for the car to put it in.