public transport (if it exists) can ofter be many times slower than cars and far less reliable
Which was sort of my point, however there are ways public transport could be improved to make using it easier, but they'd only be viable if people wanted to use them which sort of implies some kind of coercion and a chicken-and-egg situation.
For example, there are vague plans to re-open the branch line I mentioned earlier which runs near my house. It would directly connect Caerphilly to Newport and enable a lot more people to consider commuting by train than do at present.
There are much more firm plans to vastly increase capacity on the valley lines. The one that runs through Caerphilly currently only has one train per hour into Cardiff from the extremity of the line at Rhymney, with three more per hour originating and terminating several miles down the line at Bargoed. Part of the improvement plan (which also involves buying new trains) will see that increase to four per hour from Rhymney and an additional two from Caerphilly.
Trains running more often from Rhymney, and with an increased overall capacity on the line, makes commuting into Cardiff (which a lot of people do) by public transport more viable. It also make leisure use of the line more viable.
That said, nothing beats London's underground where some platforms see a train arrive every ninety seconds. Dream on!