Depending on time of day but by the time someone drives from the burbs to downtown San Antonio they’d be halfway to Austin.
They’d have to pay to park at the station and then pay to get around Austin.
Regarding flying versus train NYC to Philly anyone with a car would drive because getting to the airport in NYC would take almost as much time as driving to Philly. Once you get to the Philly airport you’d have to take a taxi or train to downtown Philly regardless.
The only reason someone would fly from Philly to NYC is if they had a connection to somewhere else. That would typically be international.