It’s a bit tricky but as I far as I know France gov can’t by design reserve the profit from any tax to a specific use. It’s all pooled for the global budget, an

It’s a bit tricky but as I far as I know France gov can’t by design reserve the profit from any tax to a specific use. It’s all pooled for the global budget, and the pooled money is dispatched according to the agreed plan each year. But any new project requiring significant financement needs to propose actions to balance its cost to get approved, thus in this instance the project to invest in roads and rails is backed by this tax. The projected tax amount just needs to be roughly the same as the new project’s cost.