I live in Northamptonshire, and my mum in Yorkshire. To visit her using public transport, I have to get DH to drive me to Milton Keynes (30 mins drive if traffic is ok, but have to allow nearly twice as much again, just in case, as it only takes an accident on the M1 to block up all routes to MK), then a four hour 15 min coach journey to Huddersfield (after Sheffield it takes a very circuitous route to Huddersfield) that costs over £30 return, followed by a five mile local bus journey, then a 15 min walk with my luggage.
Then the same in reverse to go home again.
Assuming there are no big delays en route, one way takes about six hours from door to door.
The return journey for one person costs nearly £40, plus the car petrol to/from Milton Keynes.
By car, it takes 2 hours 15 mins door-to-door and the return journey costs under £30 in petrol for up to 4 people.
As I absolutely hate driving, and have an old-ish car that I don't want to go far from home in anyway (plus the fact that DH is no longer willing to either drive there or accompany me on these visits), I have made all recent visits using the coach journey as described, but until such travel becomes both quicker, easier and more cost effective, there is no way most people would choose this option over the car. It just isn't practical for most people!
Do I feel that my use of public transport here is of any benefit to the environment? No, not really!