Missing the point

Yes taxation rates matter. But France-Spain and France-Belgium trains are expensive to take *because the capacity is too low*

If you reduce ticket prices on those routes you WON’T TRANSPORT MORE PEOPLE. Just different people. As the trains are full anyway

So, Clement Beaune, how are you going to get more TGVs to Barcelona?

https://www.euronews.com/green/2023/08/10/france-is-raising-taxes-on-flights-to-pay-for-trains-should-other-european-countries-do-th

Why are flights cheaper than trains in Europe?

Train travel is often more expensive than flying. Could taxing aviation to invest in the rail industry help change that?

euronews
And if your response is “ah but rail firms will add more capacity”, I’d point you to Thalys that hasn’t upped capacity in 2 decades despite rising demand and sky high prices. And SNCF that runs just 2 TGVs to Barcelona a day. Both easy to solve, both not done.
@jon appart from cross-border rail, do you know how other countries finance their infrastructure ?
French HSL are pretty well used close to max capacity, track fares are of the most expensive in Europe, yet apparently the network operator struggles, and SNCF barely breaks even on those lines.
Could EU-laws allow to finance tracks solely by the state (charging train operators only for saturation at specific times)

@tristramg Italy pretty much did just that. So yes that’s possible.

But I’d argue France’s HSLs are inefficiently used. You’ve got a morning and afternoon peak with saturation, but big gaps rest of the day. Also don’t underestimate station access charges too - that strongly mitigate against running only half full trains.