The clash broke out when police evicted protesters who for two days had blocked a stretch of highway between Turin and Bardonecchia.
As police cleared their barricades, protesters set fire to tyres and threw rocks at police, who responded by launching tear-gas grenades, ANSA reported.
The high-speed rail link — projected to cost €20 billion ($26 billion) — would allow a connection between Paris and Milan in just over four hours compared to seven at the moment and between Lyon and Turin in less than two hours.
The project is considered a strategic European transport corridor.
Part of the population in the scenic Val di Susa is against the project, which is expected to be completed in 2023, and it has become a focus point for wider social protests against the Italian government.
On Monday, a leader in the protest movement was gravely injured when he climbed onto an electricity pylon during a demonstration.
More demonstrations are planned on Thursday in Rome.