The molten rock could make the road impassable and force drivers to find alternate coastal routes in the north and south. That could add hours to commute times, doctor's visits and freight truck deliveries.
“I am very nervous about it being cut off,” said Frank Manley, a licensed practical nurse whose commute is already an hour and 45 minutes each way from his home in Hilo to a Kaiser Permanente clinic in Kailua-Kona.
If the highway closes, he anticipates driving two-and-a-half to three hours in each direction. Manley fears he might lose pay if an accident or other traffic disruption along an alternate route delays his arrival.
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The lava is oozing slowly at a rate that might reach the road next week. But its path is unpredictable and could change course, or the flow could stop completely and spare the highway.
The slow-moving flow was coursing about 2.7 miles (4.3 kilometers) from the road Friday, U.S. Geological Survey scientists reported.
There are more affordable housing options on the island's east side, home to the county seat, Hilo. But many jobs at beach resorts, in construction and other industries are readily available on the west side, where Kailua-Kona is located. Saddle Road, also known as Route 200 or Daniel K. Inouye Highway, connects the two communities.
The state Department of Transportation took steps Thursday to remove potential traffic obstacles on the northern coastal route by reopening a lane across Nanue Bridge that was closed for repairs.
Hilo also is one of the island's major harbors, where a wide variety of goods arrive by ship before proceeding across the island by truck.
Hawaii County Councilor Susan “Sue” L. K. Lee Loy, who represents Hilo and parts of Puna, said she's concerned about big rigs traveling across aging coastal bridges.
“It’s going to take a lot to rethink how we move about on Hawaii Island,” she said.
Manley said he would have to get up at 3 a.m. to reach work by 8 a.m. If he left at 5 p.m., he wouldn't get home until 8 p.m. “That drastically reduces my amount of time that I would be able to spend with my family,” he said.
Tanya Harrison of Hilo said she would need a full day off work to travel to her doctor in Kona.
There are more than 200,000 Big Island residents. Amidst throngs of tourists, delivery trucks and commuters forced to reroute, Harrison said she couldn’t imagine the congestion.
“It might even be quicker just to fly to Honolulu,” she said of the hour flight. “There’s no line at the Hilo airport. Fly over, see the doctor, come back would actually be quicker than driving.”
Outrigger Kona Resort & Spa plans to provide rooms at a Kailua-Kona hotel so its dozen or so Hilo-based employees can avoid the long commute five days per week.
A shutdown could also affect major astronomy research at the summit of Mauna Kea, a 13,803-foot (4,207-meter) peak next to Mauna Loa that is home to some of the world's most advanced telescopes.
The road heading to Mauna Kea's summit is midway between Hilo and Kona. If lava crosses Saddle Road on either side of Mauna Kea Access Road, many telescope workers would be forced to take long, circuitous routes.
Rich Matsuda, associate director for external relations at W.M. Keck Observatory, said telescopes may need to adjust staff schedules and house workers at a facility partway up the mountain for a while so they don't have to commute.
There's also a chance the lava flow may head directly across the lower part of Mauna Kea Access Road, which could block workers from reaching the summit. Matsuda hopes they'll be able to use gravel or other bypass routes if that happens.
The telescopes previously have shut down for multi-day or weeklong winter storms. “So we’re prepared to do that if we have to,” Matsuda said.
Hilo resident Hayley Hina Barcia worries about the difficulty of reaching west-side surf spots and relatives in different parts of the island.
“A lot of my family is on the Puna side and we have other family in Kona," Barcia said. "We use this road to see each other, especially with the holidays coming up, to spend time, so we’re looking to have to go several hours longer to go the south way or taking the north road.”
Geologists with the Hawaiian Volcano Observatory said if Mauna Loa follows historical patterns, they expect the eruption, which began Sunday night, to continue for one to two weeks.
Since then, traffic has clogged the road as people try to glimpse the lava. A handful of resulting accidents included a two-vehicle crash that sent two people to the hospital with “not serious injuries," Hawaii Police Department spokesperson Denise Laitinen said.
U.S. Rep. Ed Case and U.S. Rep. Kaiali’i Kahele sent a letter to President Joe Biden saying Hawaii County would need “immediate help” to keep island communities safe if lava flow blocks the highway. The two Hawaii Democrats noted that restricted access could hinder emergency services because one of the island’s primary hospitals is on the east side.