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This paper reviews past evaluations of the Lyon–Turin High-Speed rail project undertaken since the project was designed. It investigates these evaluations and summarises their methodologies and main results. Moreover, it analyses in detail the latest official Cost–Benefit Analysis (CBA) carried out in 2019 in Italy and investigates the criticisms formulated on this evaluation. Our findings reveal that the tunnel project had been approved despite the lack of an evaluation that would reach the minimal requirements of being simultaneously documented, open to public scrutiny, computationally correct, based on parameters consistent with evidence, on a sufficiently detailed representation of supply and demand, and properly considering the risk of cost overruns. Regarding the 2019 CBA, the most salient criticisms focused on the Rule of Half and the inclusion of taxes. These criticisms appear, under review, ill-conceived, which suggests a possible misunderstanding of some fundamental outcomes of transport economics. From a methodological point of view, our results confirm that there is no inconsistency in the mainstream approach of CBA, in which taxation is included in the calculation and transferred user benefits are computed with the Rule of Half.