The Federal Railroad Administration issued its record of decision Wednesday, clearing the final technical hurdle for construction to start next year on a 65-mile span from Merced to Fresno.
The decision supports the California High-Speed Rail Authority's so-called hybrid alternative, which state officials say is the least costly approach and the one that is least harmful to the environment.
Lawmakers approved the first phase of the planned 800-mile line this summer. The system's total price is at least $68 billion.
The project still faces legal hurdles that could delay construction. Groups representing Central Valley farmers claim in lawsuits that the state failed to conduct thorough environmental reviews, as required by state law.