It is the onion, and is flippant, but as a general belief it touches upon a basic truth -- everyone would love if everyone else used public transit, leaving the roads available for our use.
This is occasionally used as an argument in favor of cheaper or free public transit: that even from a self-interest perspective, it makes sense for road users to subsidize public transit, as a way of effectively paying other people to get off the roads and out of their way. However most road users don't seem to see it that way.
As with most articles from the Onion, there is an element of truth, but if you look at a city with good public transit options (NYC is the only one in the US) over 50% of commuters travel by public transit. If you look at cities with adequate but not great public transit options (DC, Boston or San Francisco) more than 30% of commuters travel by public transit.
It is the onion, and is flippant, but as a general belief it touches upon a basic truth -- everyone would love if everyone else used public transit, leaving the roads available for our use.