In 1987, the Board of Supervisors passed legislation urging Muni “to take certain steps to minimize air-pollutant emissions,” and get workers trained “in the latest emissions-reduction techniques.”

Fine words. But, in 1996, representatives from the San Francisco budget analyst’s office staked out bus yards in the wee hours and observed Muni employees idling diesel coaches for up to four-and-a-half hours; “Pollution Menace at Muni, Audit Finds,” screamed the eventual front-page headline in the San Francisco Examiner. That story revealed the city analysts’ grim tabulation of Muni’s dirty habit: Those idling buses needlessly discharged the equivalent amount of pollutants as 56,000 cars — every single day.

In 2013, your humble narrator staggered up to a Muni yard at 4 a.m. and documented that it was all still happening. The first rays of sunlight revealed an oily haze enveloping the yard—the byproduct of scores of buses idling for hours on end.

Idling a bus for more than five or 10 minutes, by the way, is not only wasteful and unnecessary, but is also a violation of state law.

As such, Muni buses’ onboard computers came equipped with a pollution control program that shut off idling vehicles’ engines after a pre-set amount of time. But Muni workers sabotaged it, placing blocks on the bus’ brakes, and fooling the computers into thinking there was a human behind the wheel. Those buses could idle indefinitely.

The practice of idling buses for hours — damaging their engines, wasting money and fuel, and polluting the environment — has been a problem at Muni for decades. And, a few months ago, the phone calls started coming in: It’s still happening.

Muni workers claimed that Muni’s newest, greenest hybrid buses, the New Flyer Xcelsior diesel-electrics, were idling for hours on end at city bus yards. But this time, Muni has ensured there’s no need for crude work-arounds like blocks being placed atop the brakes.

Instead, the pollution-control program that automatically shuts down an idling bus was — and is — simply not enabled on the high-tech New Flyer buses’ onboard computers. Confronted with this allegation by Mission Local last week, Muni confirmed it to be true. Those buses can idle indefinitely.

Problem solved.

The green laurels of the New Flyer diesel-electric hybrid buses were used to justify a price tag approaching $750,000 a pop — roughly twice what a regular diesel bus costs. And yet. last week Muni quickly copped, in writing, to what yard workers and drivers had said on background: Our “green” hybrid buses are operating without a pollution-control program that has been an industry standard for municipal transit vehicles since the Reagan administration.

Muni spokeswoman Erica Kato admitted to this. But she claimed there’s a really good reason for it.

She explained that the first batch of New Flyer buses was obtained in 2013 by piggybacking on a procurement operation set up by the state of Minnesota. Muni says this streamlined the process because the buses’ specifications were already set and there was no need for requests-for-proposals or other bureaucratic hassles. And yet: “The specifications did not include an automatic shutdown for idling,” Kato confirmed, “and we continued with that specification in future purchases.”

Getting in on Minnesota’s procurement plan may have delivered Muni its buses faster. But anyone trapped indoors in Anoka and forced to listen to A Prairie Home Companion during the goodly portion of the year when Minnesota resembles the ice world of Hoth knows that our city and the Land of 10,000 Lakes are not similar places. As such, proper specs for our buses and theirs will vary a bit.

It makes some sense not to force an idling bus to shut down every 10 minutes during a Minnesota winter; you may not be able to start it up again, and passengers will experience impromptu cryogenics. It’s true, San Francisco did experience a freak snowstorm back in 1976 — but, in the 41 years since, Muni has idled away oceans of fuel, and we haven’t seen snowflake No. 1.

Muni, however, ensures us we shouldn’t worry about idling buses. Its employees “continuously monitor for idling through enforcement,” Kato writes. “We are well aware of the laws and abide by them.”

It takes a Costco-sized allotment of chutzpah to make a statement like this: Muni has a decades-long, well-documented history of being well aware of the laws and not abiding by them. Its inability to obey the laws generated a budget analyst’s audit the size of a Sears Roebuck catalog; its workers for years manually overrode the failsafe device — and, in its newest, priciest, “greenest” hybrid buses to date, it simply eliminated the failsafe altogether.

But who needs a failsafe? Muni has posted operator bulletins for its drivers. Everyone is aware of the laws. So what’s the problem? “Given the dearth of idling complaints,” Kato notes, Muni sees no reason to consider auto-shutoff programs now or in the foreseeable future.

(While Kato says such a program would probably have to be purchased and uploaded into the buses’ computers, a maintenance source told us it’s potentially already on the computers — and merely needs to be switched on).

Considering that much of Muni’s excessive idling occurs in the dead of night, in bus yards the public doesn’t visit, and amid a culture in which this was tolerated and even encouraged for generations, the “dearth of idling complaints” is no surprise. But just because nobody is complaining doesn’t mean nobody is watching. In the end, the one blowing the whistle on Muni’s idling bus problem may be the bus itself.

Idling a car is more efficient and uses less fuel than turning an engine on and off again. Turning the engine off and on is hard on the starter. Idling is the best way to warm up the engine, especially in cold weather. Idling does not cause damage to a vehicle’s engine.

All of these widely held beliefs are false. But don’t take our word for it: bring it up with the scientists at the Oak Ridge National Laboratory, where the above well-worn myths were refuted in a 2016 publication.

Idling, in fact, is spectacularly bad for an engine — as you’d expect extended, low-temperature operation to be. That’s why, Mission Local has learned, excessive idling — of the sort Muni workers claim is still going on in the bus yards — can void the warranty on the Cummins diesel engines powering the New Flyer hybrids. The same onboard computer in which the idling shutdown program is not enabled is also recording all the engine data for the life of the vehicle.

The public and Muni higher-ups may not see what’s going on at 4 a.m. in remote bus yards. But the buses do. When they idle for 15 minutes, half an hour, hours on end — it’s all being dutifully recorded by those very buses.

If, in the future, engines begin to prematurely conk out, the computers’ collected data could shine a light on our transit agency’s pre-dawn idling. A costly light.

Unlike Muni, it seems Cummins would rather hold onto its money; its engines’ onboard computers serve as the tell-tale heart betraying transit agencies’ poor practices. You’d think this bottom-line financial incentive would spur Muni to stop wantonly idling its buses — but people have been thinking that for years and years.

Muni has long idled its buses indefinitely and, barring decisive action, will continue to do so indefinitely. It does so despite the explicit instructions of the manufacturer of its diesel engines, and against the recommendation of every vehicle manufacturer on God’s green Earth. It does so in the face of economic, mechanical and environmental rationales, and in violation of common sense and common decency.

That may yet change. But, for now, it remains to be seen what, if anything, will inspire Muni to throw idling under the bus.