The nature of an emergency is that nobody knows when it’s going to happen. So it goes without saying that an emergency road should be available at all hours, and enable vehicles to pass in either direction.

That doesn’t appear to be the rationale of the National Park Service, which is in charge where Chain of Craters Road — the thoroughfare in question — crosses the Hawaii Volcanoes National Park.

The park service has insisted that the lava-covered portion can be rebuilt as a one-way, gravel-paved road, and that this will suffice for emergency purposes.

That stance needs to be amended in the coming weeks before the current eruption causes further problems for the besieged Puna and Pahoa districts.

The necessity for a two-lane reconstruction is plain. State Highway 130, the primary commuting route for residents of Puna, could be bisected by the lava flow headed in that direction.

This circumstance is nothing new to the island’s residents, of course. The 19-mile Chain of Craters Road, built in 1928, has been overrun by lava from Kilauea eruptions several times in the decades since.

The NPS is constrained by current federal environmental laws, but can avoid preparing an environmental impact statement for an emergency road.

The disagreement between the feds, and the county and congressional officials who are pressing for a functional two-lane route, appears to be over what’s enough for emergency use. The park service understandably wants to avoid the delays, costs and environmental impacts of a two-lane highway built to federal standards.

However, that is not what’s needed for Puna residents on an emergency basis, who simply need some way to get in and out of their community as needed. What’s completely unsuitable is the proposal for one-way out in the morning, one-way in during evening hours that the park service suggests.

Not everyone has work commutes or essential errands that fit that time frame, for starters, and handling medical emergencies with medevac service is excessively costly and impractical.

For its part, local government seems to be addressing the problem with proper urgency. This week Gov. Neil Abercrombie issued an executive order that conveyed the state’s 3.68-mile stretch of Chain of Craters Road to Hawaii County for use as a county highway.

But travel in two directions must be allowed to pass on the entire Chain of Craters Road, because the only other possible access routes, Railroad Avenue and the coastal Old Government Road, are insufficient for the traffic loads. It may need to be a bit narrow at some points, where the dense lava will be more challenging to carve away, but it still should be possible to provide enough space to allow cars to travel in both directions, at lowered speed limits.

With some luck, the immediate concern may become moot. Hawaii County Mayor Billy Kenoi has said lava could overrun Highway 130 by mid-month, cutting off about 8,500 residents. The flow has slowed, though, making predictions all but impossible.

One outcome ought to be a sure thing, though: Local and federal authorities should be able to come to terms on a reasonable accommodation for a community that’s endured enough in the last few months.