Paramedics took the victims — a man and a woman — to The Queen's Medical Center in serious condition, said Donnie Gates, assistant chief for the city's Emergency Medical Services.

Capt. Kenison Tejada, fire department spokesman, said the victims suffered leg injuries. Neither victim was pinned in the SUV, he said.

The boulder fell at 8:13 a.m. Police said it was about nine feet across, but firefighters reported it to be about five feet across.

Westbound traffic was backed up for about an hour. State road crews were able to move the boulder to the side of the freeway by 9:30 a.m.

It appears that the SUV pushed the boulder before stopping, Tejada said.

State transportation officials were trying to determine this morning where the boulder came from, said Scott Ishikawa, spokesman for the state Department of Transportation.

"There is a quarry in the area but we are not sure where the rock came from," he said. "It didn't come from state property, that's for sure. It came from private property. We will spend the rest of the day out there."

Falling boulders have killed people, damaged homes and disrupted traffic on several occasions in recent years.

• The Navy is spending $225,000 to strap down a 60-ton boulder perched more than 100 feet above a private Moanalua Valley home after a survey of the property discovered the potential for it to fall.

• On Sept. 14 National Park Service Ranger Suzanne Roberts died when she was struck by a boulder that fell 40 feet. She had been clearing rocks from a remote East Maui road in Haleakala National Park when she was killed.

• On May 13, a 10-ton boulder — that looked as big as a compact car — plunged down a Nanakuli hillside and came to rest against a house. Within days the state moved to demolish and remove the boulder after 39 residents from 11 area homes were evacuated. It was determined the boulder had slipped from state land less than 30 feet away.

• On May 10 , as 11/2-ton boulder tumbled down a Nu'uanu hillside, narrowly missing Rose Hamakado as she stood in her back yard. The incident occurred on the same street where a 2002 boulder crashed into a home and killed a young woman sleeping there.

• In May 2003 a six-ton boulder perched on a Kalaheo Hillside ridge in Kailua was removed without any movement because of concerns by residents that it could fall onto homes below.

• In May 2003 landslides onto Kalani'anaole Highway near Castle Junction prompted the state to spend 19 months and $7.8 million to reshape the dangerously eroding cliff into a gently sloped, landscaped hillside.

• On Aug. 9, 2002, a 5-ton boulder crashed into a Nu'uanu home, crushing and killing 26-year-old Dara Rei Onishi as she slept.

• In December 2002 26 families at the Lalea condominium project in Hawai'i Kai were forced to move out of their homes in after two dumpster-sized boulders fell onto cars and buildings on Thanksgiving. Geologists determined the area was unsafe. Developer Castle & Cooke and landowner Kamehameha Schools spent $5 million to have crews sweep the mountain of loose boulders and take other steps to make the condominium safe again.

• In October-November 2002 rockslides onto Kalani'anaole Highway near Makapu'u Beach resulted in some road closures in East Honolulu while officials worked to prevent more landslides.

• In December 2001 a 12-foot boulder landed in the middle of Kalaniana'ole Highway by Queen's Beach. There were no reported injuries from the rockfall.

• On March 6, 2000, large rocks fell across Kamehameha Highway near Waimea Bay and closed the road for three months.

• On May 9, 1999, eight people died and 50 were injured in a rockslide at Sacred Falls on the Windward side of O'ahu. The tragedy closed the popular and scenic park, which has yet to re-open.