City straphangers enjoyed one day last month — just one day — without any delays from signal failures during the morning rush, a new report says.

On Aug. 23, a Thursday, the error-plagued subway system managed to pull itself together and avoid signal breakdowns between 6 and 10 a.m., according to a study by transit advocates from the Riders Alliance and Straphangers’ Campaign.

Still, there were other delays: on B and Q trains from a tripped emergency break and on No. 4 and 5 trains because of a sick passenger, the transit advocates noted.

The study’s findings are simply unacceptable, said John Raskin of the Riders Alliance.

“Every one of those signal malfunctions throws thousands of people’s daily lives into chaos,” he said. “In a functional transit system, that would be a rare event that merits an apology. In 2018 New York, it has become routine.”

The L train, which has an upgraded signalling system, was the only line not to hit a signal snag during August.

The subways had their worst day of the month a week earlier — on Aug. 14 — when there were 15 signal delays and 13 mechanical delays.

D and R trains were tied for worst performance in August, with 11 signal delays and five delays caused by mechanical issues.

Last summer, Gov. Cuomo declared the subways in a state of emergency, and in May, New York City Transit boss Andy Byford unveiled an ambitious, $37 billion Fast Forward Plan to upgrade signals within a decade, though questions remain about how it would be funded.

Raskin and other transit advocates said they have the solution.

“It’s time for Gov. Cuomo and members of the state Legislature to pass congestion pricing,” Raskin said, referring to the plan to toll drivers entering Manhattan below 60th Street.

Cuomo’s own Fix NYC panel has recommended congestion pricing, but he never said whether he fully supported the plan and then signed a budget that included a watered-down version only applying to for-hire vehicles, calling it a “first step.”

Cuomo spokesman Peter Ajemian, referring to the funding issue, told The Post on Sunday, “The Riders Alliance time would be better spent convincing those who need convincing — members of the Legislature and City Hall.’’

Cuomo rival Mayor de Blasio favors a millionaire’s tax to fund the subways over congestion pricing.

Meanwhile, MTA spokesman Jon Weinstein disputed the study’s overall findings, arguing the system has “stabilized over the last year thanks to intensive investment and maintenance” and that a new initiative to reduce delays is “already paying dividends.”