A speeding Jeep Cherokee flipped over a wall on the H-1 Freeway's airport viaduct and fell about 30 feet to the ground yesterday, killing one man and critically injuring another.

Police said alcohol probably was also a factor in the 7:20 a.m. accident.

It was one of two fatal traffic accidents on O'ahu yesterday. About 2:15 p.m., a 26-year-old motorcyclist was killed in a head-on collision with a truck on Kaukonahua Road near Wahiawa, police said.

The names of the victims were not immediately disclosed.

Police said the white 2000 Cherokee was traveling east on the airport viaduct when it apparently went out of control, hit the concrete barrier along the right shoulder and went airborne. It landed on a grassy traffic island at the intersection of Kamehameha Highway and Middle Street, just before the on-ramp to the H-1 Freeway's westbound lanes.

One man died at the scene. The other occupant was taken to The Queen's Medical Center in critical condition.

Police said it appeared that the man who died was the passenger in the Cherokee, and the police opened a negligent homicide investigation. However, paramedics said the 26-year-old man who died was the driver.

Just after 11 a.m., tow trucks turned the wreckage on its side to allow fire rescue workers to cut open the vehicle and get the dead man's body out. The injured man had already been taken to the hospital.

Eastbound traffic on the H-1 viaduct was diverted to Dillingham Boulevard. Westbound traffic was diverted to Nimitz Highway for most of the morning. On- and off-ramps reopened after both men were removed from the wreckage.

In central O'ahu, police closed Kaukonahua Road between Wilikina Drive and Kamananui Road from about 3 to 6 p.m. while they investigated the motorcycle accident.

Police said a 26-year-old Kane'ohe man was operating a 2004 Honda motorcycle, traveling toward the North Shore at high speed.

The motorcycle went out of control, ran onto the grassy shoulder of Kaukonahua and back onto the roadway, police said.

It crossed the center line and collided with a Honolulu-bound 2004 Chevy pickup truck about 1,100 feet west of Wilikina Drive, police said.

The motorcyclist died at the scene. The driver of the truck — a 27-year-old Wai'anae man — and his passenger suffered minor injuries, police said.

The deaths were the 27th and 28th traffic fatalities on O'ahu this year, compared with 25 at this time last year.

Reach Loren Moreno at lmoreno@honoluluadvertiser.com.