According to this [1], taxes on gasoline are much higher than 40 cents/litre (50 cents in Spain, 68 cents in France).

If you buy a train ticket in advance, you definitely are in that price scale. I looked up train rides one month in advance [2] and a ride from Madrid to Spain is now 175€ to 210€, right in the range of the train ride.

But hopefully, Europe-wide CO2 taxes will start to price in externalities and remove the finger from the scale in favor of flights.

[1] https://taxfoundation.org/gas-taxes-in-europe/ [2] https://www.raileurope.com/en/journey/madrid-paris-14skjpm