But, the thing with adding things like wear and tear/insurance etc into the mix with a car, is that you already own the car, so, insurance etc is not factored in as it’s something you would be paying regardless of your trip to the airport.
In fact, one could say that it makes the rail option more expensive, as you are still paying for the dormant parts of the car like insurance, tax etc, but are now using rail so the tax etc isn’t being put to use.
Then there is ‘multiple occupancy’, so to speak. That means a car journey is going to cost broadly the same whether one person, or 4/5 travel in that same car. The same cannot be said for a train whereby every person has to pay the same amount.
Your 60/40 split in favour of the train also includes, as you say, availing yourself to the BEST advance offers, it’s not always that easy to grab these bargain basement fares. I used to commute between Manchester and London by rail quite a lot. I wasn’t a novice, I knew when broadly the best times to book were, but even then, the fats were not always that cheap.
Swings and roundabouts really, and like I say, I’m also taking ease into the equation, which for me, no matter which way you try and swing it, a train from me to the airport is far from easy. In fact, to get to my closest rail station, I have to take........a car! Defeats the point then really, doesn’t it! (And I know just me singularly is very anectodal evidence, but there will be thousands like me in the same situation that don’t have access to a high frequency rail station, nor one without a taxi/car journey to the station to begin with).