Commuters exit a Metro train at Washington’s L'Enfant Plaza station on May 24. (Nicholas Kamm/Agence France-Presse via Getty Images)

IT’S BEEN six years since regional leaders learned, in the aftermath of Metro’s most lethal accident, that the transit system’s safety oversight body was a toothless phantom — underfunded, ineffective and impotent. In those six years, the drumbeat of mishaps, maintenance disasters and quotidian delays has mounted while safety has continued to deteriorate — along with ridership and passenger confidence.

Now, after unprecedented intervention by federal transit regulators, who are providing the safety oversight that was so glaringly lacking, and threats from the U.S. transportation secretary himself, leaders in Maryland, Virginia and the District have finally stirred from their long and irresponsible slumber. They have produced a plan, in the form of coordinated legislation, to set up a functioning commission to oversee safety in the rail-transit system. Unfortunately, the plan has a fatal flaw.

The commission would be broadly endowed with investigative and regulatory powers, invested with the authority to issue subpoenas, rejigger Metro’s budget to prioritize safety and slap the agency with warnings and fines if it fails to comply with corrective orders.

That sounds promising, almost as if Virginia Gov. Terry McAuliffe (D), Maryland Gov. Larry Hogan (R) and District Mayor Muriel E. Bowser (D) were dead serious about reestablishing trust and accountability in a transit system on whose shoulders the economy of the nation’s capital depends.

So why would they at the same time subvert that same project by carving out a zone of secrecy in which to shroud the new safety commission’s work, including investigations it would conduct of incidents that could affect and imperil hundreds or thousands of passengers?

In an agency whose shortcomings of accountability are so glaringly obvious, why would the workings of the agency’s oversight body be encumbered, by design, by a similar absence of accountability? It’s doubtful there is any surer way to accelerate the loss of public confidence in an agency already reeling from it.

Yet that is precisely what Ms. Bowser, Mr. McAuliffe and Mr. Hogan are proposing. They would establish the Metrorail Safety Commission, at an annual cost of about $6 million — that, at any rate, is what the Federal Transit Administration currently spends in its role of direct safety oversight of Metro. And, then, according to the legislation drafted for approval, they would exempt the commission from the two states’ and the District’s open-meetings and freedom-of-information laws.

Moreover, according to the legislation, the commission “may withhold from public view the contents of any investigation report” it might produce, even after submitting it to the mayor and two governors.

It seems to have slipped the minds of the measure’s authors that Metro is a public agency, funded by taxpayer dollars, serving a broad constituency of citizens who are entitled to know how their safety has been assured, or not. It is simply untenable that Metrorail, already the subject of intense scrutiny, should have its safety overseers granted a cloak of invisibility.