Compare driving and train travel costs.
This comparison includes the cost drivers usually leave out of a fuel-only sum: wear and depreciation at a per-mile rate. Nine cents a mile is a conservative figure covering tyres, servicing, and the mileage-related share of depreciation, and on a 500 mile round trip it adds 45 dollars — often more than the difference between the two modes. Rail fares are per person and rise with party size, so two travellers is roughly where driving starts to win on cash cost, and four almost always does. Station parking is a small but real addition on the rail side that catches people out on multi-day trips.
Drive vs Train Cost
Driving = round-trip miles / mpg x fuel price + round-trip miles x wear rate; train = ticket x 2 x travellers + station parking
Yes, if you want the true cost. Fuel alone understates driving by roughly half on a long trip; a per-mile wear allowance of 9-25 cents brings it into line with what the mileage actually costs you.
Because advance fares are yield-managed and can be a fraction of the walk-up price. Booking weeks ahead frequently halves the rail figure, which shifts the crossover to three or four travellers.