Coastal erosion isn’t the only danger to roads in Hawaii — a fact once again highlighted after weekend rain caused rockfall to pummel the main road on Oahu’s North Shore.

Incidents like this have prompted lawmakers in the House to advance a bill Thursday that would require the Department of Transportation to conduct more regular rockfall inspections; essentially doubling the current frequency of once a decade and requiring additional inspections after heavy rain.

The move came a few days before rockfall shut down part of the Kamehameha Highway and a few days after a boulder crashed through a woman’s home in Palolo Valley; an area famously susceptible to landslides and geological instability.

“The Honokohau Valley, the Kahakuloa area, Hana, we’ve had major landslides and rockslides there after heavy rains,” said Rep. Elle Cochran, who introduced House Bill 653. Cochran represents West Maui, where roads leading to and from Lahaina have been prone to rockfall.

A total of almost 168 miles of roads in the state are exposed to risk of rockfall and landslide, according to a 2021 DOT report. That same year the DOT also published a GIS map of the state’s roads colored to denote susceptibility to rockfall.

Sunday’s rockfall struck part of Kamehameha Highway that goes by Waimea Bay, severing the North Shore’s main arterial road for almost the entire day. It’s a stretch marked red for “very high” risk on the DOT map. Buses that ordinarily travel the length of Kamehameha Highway were rerouted to turn around at the site of the incident, forcing passengers to get out and walk or bike across if they wanted to transfer to the other side.

“Took me two hours to drive home yesterday,” said North Shore resident Karen Gallagher, who said she had to go around the other side of the island.

Fellow North Shore resident Bob Leinau, who worked at Waimea Valley for 35 years, said he brings up the rockfall issue every time the region gets a fresh elected official. That same area of road saw heavy rockfall in 2000 leading to months of road closure. There was some brief official focus on preventative measures in other vulnerable places like Makapuu, but not so much by Waimea.

“I understand how priorities shift, but erosion doesn’t go away. Erosion generally progresses,” Leinau said.

The events can also be costly.

In 2019 heavy rains required months of repairs on the Pali Highway and required about $20 million to fix.

The bill advanced without much fanfare. Two pieces of testimony were submitted in support including one from the DOT — which currently performs formal inspections every eight to 10 years — along with “windshield inspections” they perform while driving by each year according to communications manager Shelly Kunishige.

More frequent inspections would require more funding from the legislature the DOT said in their testimony. 

The DOT also uses this money for equipment like mesh netting and concrete barriers to hold in rocks, plus drones to more efficiently inspect problem areas.

Many of the communities most susceptible are remote enough that road closures can cut them off from external resources.

House Bill 653 passed the House Transportation Committee last week and now awaits a hearing in the House Finance Committee.