A one-car accident on the slopes of Mauna Kea that killed two people last month resulted from worn brakes, an investigation by Big Island police determined.

Philip Patrick Y.M. Lung, 34, of Honolulu, and Yuko Aizawa, 33, of Osaki-Shi, Japan, died March 27 after Lung lost control of a rental car and drove off Mauna Kea Access Road above the Visitor Information Center.

The rented 2006 red Jeep Wrangler traveled down a steep embankment and overturned.

Aizawa, a student at Central Pacific College, was in the back seat and was thrown from the Jeep. Lung had just quit his job at the English-language school in Waikiki for Japanese visitors. Lung's wife, 31-year-old Ryoko Lung, who was sitting in the front, suffered serious injuries.

"Riding the brakes" wore them out, said Chris Loos, a spokeswoman for Big Island police.

Loos said the Jeep was in low gear and descending from the mountain when Lung lost control.

The Jeep was rented from Dollar Rent A Car. As part of written rental agreements, Dollar and most other Big Island car rental agencies prohibit the use of their vehicles on unpaved roads such as those above the Mauna Kea visitor center.

A representative at Dollar declined comment and referred questions to the company's legal office in Tulsa, Okla. Dollar representatives in Tulsa could not be reached for comment.

The road above the Mauna Kea visitor center, which runs from the 9,000-foot level to the summit of the 14,000-foot dormant volcano, is "unpaved, rough, steep, winding and dangerous," according to a description on the Web site of the University of Hawai'i Institute for Astronomy, which maintains facilities on the mountain.

Only four-wheel-drive vehicles are permitted on unpaved portions and observation officials recommend that drivers use low gear and drive under 25 mph.

"Vehicles should be in good working condition with good brakes and sufficient fuel to return to Hilo or Waimea. Emergency services, including medical assistance, may be two hours away," according to the Web site.

The accident was the 11th and 12th traffic fatalities on the Big Island this year.

Reach Rick Daysog at rdaysog@honoluluadvertiser.com.