Of the approximately 100,000 km of High-Speed Rail (HSR) lines in the world today, half are in operation and half are planned or under construction. The implementation of HSRs are planned in various countries with different characteristics to pursue different objectives. Today, the results are known, and therefore, the differences between the planned and achieved objectives can be verified. Italy is one of the countries that first built an HSR, and now, at the national planning level, Italy has decided to implement an HSR in Southern Italy. The problem is therefore not “whether” to realize an HSR but “which” type of HSR to realize. Italy is an important case study at the international level because it is possible to extend the HSR network in three different ways: upgrading existing lines by increasing the speed to 200 km/h, building a new line with speeds of 300 km/h with heavy freight trains, and building a new line with speeds of 300 km/h without heavy freight trains. The problem is how to find the best alternative in order to pursue sustainable development while considering national planning. To solve this problem, at the intermediate level between planning and design, the theoretical Lean, Agile, Resilient, Green (LARG) paradigm is proposed and applied. This approach can be extended to all countries that are launching massive and expensive programs to construct HSR lines or to upgrade existing lines.