Honolulu’s troubled rail project has sat at the threshold of disaster so often that it’s hard to keep track of every twist and turn.

But the resignation of Dan Grabauskas, the embattled executive director of the Honolulu Authority for Rapid Transportation, certainly signifies a crossroads.

Grabauskas’ contract renewal had languished in limbo for weeks longer than it had in previous job-performance evaluations. So it was hardly a surprise when he stepped down on Thursday, having plainly lost the HART board’s confidence.

But now the episode stands as a decision point, perhaps the last chance the agency will have to reset the project.

The decision the HART board must make without delay is on a new chief executive who is primed to hammer through the 20-mile, 21-station project to completion.

A qualified candidate needs deep experience with the construction industry and the ability to troubleshoot problems that arise, holding contractors accountable.

This is an awkward moment for such a transition. Colleen Hanabusa, who chaired the HART board for the past year, is likely to resume service in the U.S. House of Representatives, a forecast based on clear polling data.

Further, the project, now an estimated $1.3 billion short of anticipated tax revenues, occupies the starring role in the latest political drama.

That’s the showdown between Mayor Kirk Caldwell, seeking re-election in November, and his rival, former U.S. representative and City Council member Charles Djou.

While the search for Grabauskas’ replacement begins, Michael Formby will serve as HART acting director; he has stepped down from the HART board and from his position as director of the city Department of Transportation Services. It’s a reasonable appointment, given the circumstances. But the reassignment can’t erase Formby’s history as a Caldwell Cabinet member.

This added political component runs counter to the aim of a quasi-independent agency: keeping political considerations at bay.

HART must keep its distance from the coming general-election uproar.

Finally, hard deadlines loom in a few weeks. The Federal Transit Administration is demanding a “recovery plan” — a blueprint for closing a yawning gap in project funding.

The FTA doesn’t expect a final plan until year’s end, but HART will meet with FTA officials Aug. 29, crafting a preliminary version.

Despite all the complications, however, the changing of the guard was a necessary move. Grabauskas was touted as someone with transit operational expertise, but if the project is ever to reach that stage, the process of construction must be managed expertly first.

The outgoing director inherited some bad decisions the city made at the outset, before HART was constituted.

Some looming problems were not made public when they should have been. The delayed revelation about the costly risk of constructing close to high-power electrical lines provides the most vivid example.

Still, Grabauskas’ error lay primarily in adopting an insufficiently aggressive stance in contract management. He said at several points that leaving subcontractor management to the general contractor was industry best practices.

That may be true, but the complications and rising costs of this particular project demanded a more hands-on approach. The next director also needs a firm technical grasp of transit construction, enough to recognize when things are going awry.

It’s not only the job at the top that is so crucial.

The HART board of late has become more aggressive in probing cost overruns and other problems. However, much of the most pointed questioning in the past year has come from Hanabusa and Formby, who are retreating from that role.

These two expected openings on the board must be filled with equally assertive public advocates.

They should continue to press for transparency in project management. They should support the project but do so with eyes wide open.

And it would be optimal that they, too, come with construction industry experience to question on the public’s behalf.

The board also must retain, even sharpen, its aggressive posture.

There is no time to lose in assembling a new team. The newly reconstituted board and management team must be capable of analyzing new options for solving the project’s financial woes.

Completing rail to its planned Ala Moana Center terminus is the imperative for a city that needs a fully functional, multimodal transportation system.

It will take all hands on deck to meet that challenge.