Prince Tu'ipelehake, 56, and Princess Kaimana, 46, died Wednesday night, according to Senter Uhilamoelangi, a distant relative and longtime friend of the prince.
Uhilamoelangi said the couple had arrived in the area earlier this week to discuss political reforms with members of the region's Tongan community. Uhilamoelangi, a Tonga native and East Palo Alto resident, helped arrange the visit.
San Mateo County Coroner Robert Foucrault confirmed that two members of Tonga's royal family died in the crash. But he would not release their names until the Tongan government made an official announcement.
The driver of the red Ford Explorer carrying the two also was killed, the California Highway Patrol said.
Edith Delgado, 18, of Redwood City, allegedly was racing her car at speeds up to 100 mph on a highway in Menlo Park, about 30 miles south of San Francisco, when she tried to pass the SUV in which the royal couple was traveling, said highway patrol Officer Ricky Franklin.
Delgado's car slammed into the driver's side of the Explorer, causing it to swerve across several lanes before tumbling to a stop on its roof, Franklin said.
Delgado, who was not injured, was jailed on suspicion of vehicular manslaughter and engaging in a speed contest, Franklin said.
Tonga, a 170-island archipelago about halfway between Australia and Tahiti, has a population of about 108,000 and an economy dependent on pumpkin and vanilla exports, fishing, foreign aid and remittances from Tongans abroad.
Now the last monarchy in the Pacific, Tonga has been a Polynesian kingdom and a protectorate of Britain, from which it acquired independence in 1970. It is ruled by 88-year-old King Taufa'ahau Tupou IV.
Tu'ipelehake, a nephew of the king, was the leading reformist in the royal family. He was head of a national committee studying democratic reforms for the kingdom.