Three months ago, the Bay Area Rapid Transit system that serves San Francisco and surrounding counties launched a “blitz” to deter morning rush-hour fare evasion at four stations.

The results were startling: Proof-of-payment citations rose 13 percent, new ticket sales rose 10 percent, add-value transactions to existing tickets rose 29 percent and, most significantly, average weekly calls to police dropped 45 percent.

This rapid turnaround came about simply, after authorities staffed stations with extra police officers, fare inspectors and BART managers wearing bright yellow vests so that anyone trying to jump a fare gate or use a bypass door had his way blocked.

These results should come as no surprise to anyone familiar with the Broken Windows theory of policing developed by James Wilson and George Kelling. The theory’s simple premise: Responding proactively to minor crime (fare evasion, for example) also reduces serious crime.

Before he made New York City the safest large city in the country as NYPD commissioner, William Bratton put Broken Windows into effect as the head of the New York Transit Police, directing his officers to focus on fare evasion. Bratton’s achievements were transformative.

Frisco’s BART “blitz” is a reminder that the lessons of Broken Windows policing still hold. By putting people at the gates who looked to be in charge — neither the fare inspectors nor the yellow-vested managers were badged police officers — BART was able to cut crime in those stations almost in half.

As Broken Windows predicts, those willing to commit serious crime often start by committing minor crimes, like fare evasion. Keeping such people out of the transit system means that everyone paying the fare is safer.

The data also put to rest two common arguments against fighting fare evasion — and, by extension, against Broken Windows policing. Advocates claim enforcing laws against fare evasion criminalizes the poor. People don’t evade fares out of malice, the argument goes, but because they’re struggling and can’t spare the cash.

But the sharp rise in BART fares paid post-“blitz” shows that fare-jumpers can pay — they just chose not to do so, knowing that they faced no consequence.

Plus, the large increase in add-value transactions demonstrates that it isn’t only poor people who jump the turnstile. People who already have a ticket or transit card are more likely to be regular riders, perhaps commuters, who figured that they may as well skip paying the fare since no one was watching. Jumping the gates instead of buying a valid fare remains a choice, not an involuntary circumstance.

Another argument against Broken Windows policing is that monitoring petty transactions is a waste of resources because the money spent paying public employees to do this exceeds the revenue from fines or additional tickets. Some of the police officers involved in the new BART policy worked overtime, and their additional salary may have exceeded the value of fines and extra fares.

But this argument discounts the cost of the approximately 40 police calls that didn’t occur as a result of stationing guards in the stations. Yes, causation isn’t correlation, but the correlation is a strong one. Each response to a crime is expensive, but the social benefits of establishing public order are incalculable.

Letting people get away with jumping turnstiles leads to a deterioration of the transit environment. When some commuters become cheats, some cheats become thieves — and some thieves become muggers, a progression Broken Windows seeks to interrupt.

BART has seen ridership drop by almost 8 million in two years, a loss of tens of millions of dollars of revenue driven in part by the drug use, litter and even mass robbery plaguing the system. For every potential cheat who turned around when seeing an official at the turnstile, thousands of paying customers saw a transit agency finally in charge of its own stations and trains.

Reinforcing law and order in San Francisco’s transit system can help bring back those lost riders and their money, but only if BART stays the course. Meanwhile, New York City, Broken Windows policing’s first proving ground, might consider re-applying its enduring lessons before the bad days ­return.

Phillip Sprincin writes from the Bay Area. Adapted from City Journal.