~1.5 billion train journeys a year is “functional”.
Annual train ticket form my small town (25 miles from the Zone 1 of London) is over £5,500. Five GRAND. For the pleasure of standing every time and a much higher risk of getting mugged.
£15k will give you REALLY nice bike or pretty new car. After third year you're saving thousands. Of course if you decided to buy something old and used, you're saving from the second quarter of the first year on.
It's only functional because not everyone can afford another car to work.