IT’S HARD to overstate the financial, logistical and street-level disasters that would follow the collapse of Maryland’s $5.8 billion Purple Line project, years in the making and midway through construction through close-in suburbs north of D.C. A state judge made that very point late Monday in forbidding contractors from walking off the job Aug. 22, as they had threatened while the state and its private-sector partners haggle over a reported $755 million in cost overruns.

The judge’s order grants the project a three-week reprieve but does not remove the real and growing risk that the 16-mile light-rail line project may fall apart, a victim of mounting delays and expenses arising from specious litigation and evident mismanagement. If that happens, Maryland and its taxpayers may be left holding the bag.

The losers would include Gov. Larry Hogan (R), whose legacy, and perhaps presidential hopes, rest partly on the biggest infrastructure gambit he has undertaken; the state, its finances already sapped by the pandemic; residents of Montgomery and Prince George’s counties, who are facing torn-up streets, half-dug tunnels and unfinished bridges; and the idea that the private sector is a reliable partner in public-transit projects in the United States.

Not to be overlooked is the reputational damage to the corporations whose abandonment of the Purple Line would give future business partners pause. They include Meridiam, which is among the bidders to build and manage another large public-private initiative proposed by Mr. Hogan, to add toll lanes to Maryland’s portion of the Beltway and Interstate 270. That project’s prospects will dim if the Purple Line deal disintegrates.

The private-sector consortium building the Purple Line says problems beyond its control have added at least 2½ years to the construction schedule; it is entitled to scrap the deal if delays add more than a year. Talks are ongoing between the state and its private-sector partners, who are building and helping finance the project and would reap much of its revenue over 30 years. At least that was the idea, before a groundless lawsuit, sluggish land acquisition and unanticipated design changes demanded by a water utility and a nearby railroad. Now, the contractors have given notice that more than 700 workers will be laid off if no agreement is reached.

Officials insist the state can take over the project if the partnership fails. At best, that would mean further delays; at worst, it could mean an indefinite halt in construction with no apparent funding source to pay scores of subcontractors awaiting payment — “inestimable amounts of additional damages,” according to Circuit Court Judge Jeffrey M. Geller.

Mr. Hogan, on assuming a one-year term as leader of the National Governors Association last summer, highlighted the urgency of upgrading the nation’s infrastructure and touted Maryland’s innovative public-private partnership to build the Purple Line. Lately he’s been conspicuously silent about it, at least in public. If there is any hope for a rescue, he needs to be the point man for the state, which has already sunk more than $1 billion into the project.

The rescue is worth it, for the same reason the Purple Line has always made sense as a lifeline for older neighborhoods and job hubs, and for commuters with no suburb-to-suburb transit options. No one can afford to let a project of this importance go to seed.

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