For an idea that actually has been batted about for several years — it’s included in the Central Oahu Sustainable Communities Plan — the First Responders Technology Campus still needs to be much better explained to the taxpayers before any serious investment in its development proceeds further.

The First Responders … what? The public may adopt a blank stare and be surprised to learn discussions about an early concept for this project began in 2014, on a site originally pegged for a second phase of the Mililani Technology Park, a Castle & Cooke Inc. expansion project that failed. The state bought the site for $9.8 million in 2017.

Initially the campus was proposed as a centralized headquarters for the state’s sheriffs division. It since has morphed — so much so, beyond any apparent urgent need, that it has the look of a boondoggle in search of a purpose, one that is likely to cost hundreds of millions of dollars.

This facility is being planned on 243 acres of former plantation land, and is intended to be used by 19 state, county and federal entities. They include law enforcement, fire, defense and other emergency response agencies, in both individual and shared capacities.

One key argument for providing the campus is that it could replace existing facilities that are in the inundation zone. While that’s true enough, it’s unclear why it’s necessary to have a project of such startling scale.

It includes roughly the office space of a 37-story tower, but in sprawling low-rise form; classrooms; a 450-seat auditorium, 293,000 square feet of storage space in warehouses; a helipad atop a parking garage; an indoor shooting range; outdoor training facilities, which could include structures for practice raids and rescues, an obstacle course, a rappelling tower, running track and vehicle driving course.

There are amenities, too, such as a fitness center, competition swimming pool, locker rooms and retail space, as well as a community center and fully-staffed kitchen. And there’s lodging — a hotel for visitors, a dorm for recruits and 400-500 workforce housing apartments.

More than half the property would be largely undeveloped, 150 acres for Hawaii National Guard search-and-rescue training.

Just the initial, infrastructure-centered phase, is expected to cost over $100 million. Construction, which could begin next year, would be spread out over several phases. Already, nearly $7 million has been spent to complete a market study, conceptual plan and an environmental review. A full environmental impact statement would follow — and that is one opportunity the public should take to weigh in.

Among the agencies that are committed to help produce the campus are: Honolulu police, fire and emergency management departments, state land and public safety departments, the Hawaii Emergency Management Agency, the University of Hawaii, the Federal Fire Department, U.S. Marshals Service, Federal Bureau of Investigation and the U.S. Office of Homeland Security Investigations.

It’s woefully unclear, though, who would develop what and when, and how construction costs would be shared.

Those are government operations with disparate objectives and training requirements. Coming up with project elements that serve all of their needs would be at least somewhat duplicative of the independent facilities.

One driving force behind the project was to consolidate existing facilities, saving on separate maintenance costs. Unless and until that objective is locked in, the campus should not merit a high funding priority.

Given the money pit already dug for Oahu’s rail project, and given unmet needs such as land for housing, the public may not share this vision — and are at least justified in regarding it with a jaundiced eye.