The state-run Metropolitan Transportation Authority is hiring 500 state cops without giving them a clear goal to meet. Meanwhile, the New York Police Department, which has some 2,700 officers traditionally policing subways and buses, is pulling back on criminal enforcement in the transit system.

The risk is that the two police forces will end up working at cross purposes. To avoid that, the MTA should rethink its approach to its biggest low-level scourge, fare evasion. As with many things transit, Europe does it better — and with more civilians, not cops.

The MTA loses money on fare evasion. In September, the authority told its board it would lose about $274 million for a full year, up from $189 million the previous year, from the 4 percent of subway riders and 25 percent of bus riders who don’t pay.

Customers — many of them poorer and working-class New Yorkers who toil hard to pay their fare — also suffer crowding and nuisance from ­passengers who get on for free or who use the subway system for something other than transportation.

But there is no political appetite for mass arrests for low-level crime underground. Indeed, most fare enforcement is civil. From January to October, police gave out 63,334 fare-evasion summonses, essentially $100 tickets. That was up from 41,450, a whopping 53 percent, from the previous year. By contrast, the NYPD made 2,794 “theft of services” arrests in those nine months — down 47 percent, from 5,235, in 2018.

As the MTA seeks more control over policing its system, it can make civil enforcement more efficient and consistent.

The authority will roll out its new fare-payment system, the OMNY tap card, over the next three years. That gives the MTA board an opportunity to switch to a European-style “proof-of-payment” enforcement system.

What does this mean? Rather than getting one chance to catch fare evaders at the turnstile, officials could ask riders throughout their journey for proof that they paid — proof given by having each rider tap his or her OMNY card (or credit card) against an official’s mobile machine.

The MTA could give people two hours from fare payment to complete their trips.

Rather than issue a summons, the deterrent would be a “penalty fare” — something the MTA board could also implement. In London, the penalty fare is about $90, half that if paid within three weeks. In Paris, the penalty is about $35, payable on the spot. (Carol Kellermann, former Citizens Budget Commission head, recently wrote about her experience with Parisian enforcement after failing to retain her ticket.)

Proof-of-payment is better in a few ways. First, it would deter people from illegally selling MetroCard swipes: buying a few monthly passes, disabling fare-vending ­machines in a station and then selling a “swipe” for a lower price. The swipe would be worthless, as anyone entering on a stolen swipe would still be subject to showing proof of payment later.

Second, it would be more consistent. MTA officials could ask ­every third person on a random bus for proof of payment or stop every other passenger about to exit a busy station and ask him for a quick tap to prove he had paid.

Consistent enforcement would create data to drive more targeted efforts: Officials would learn quickly which lines or stations suffer more evasion and step up inspections there.

Police don’t even have to be on the front lines of much of this work. Civilian workers in teams could ask people for proof of payment, with police in the background to serve a backup role for passengers who won’t cooperate, just as in Paris and London.

Third, a proof-of-payment system would make it clear that the subway is for getting from one place to another. It isn’t a homeless shelter, mental institution or backdrop for illegal vending and performing.

The city and state should give people sleeping on trains better options, including 24-hour drop-in centers along major train lines with showers, computers and cots, without the bureaucracy of an overnight city shelter. But outreach workers should be firm, in tandem, that ignoring the use of the train as anything but transportation isn’t compassionate.

Likewise, proof of payment would reduce the incentive for ­illegal performers and vendors. A penalty fare would wipe out much of the day’s profits.

The vast majority of New Yorkers already pay their fare, no matter their financial circumstances. Penalty fares would just further entrench what is already perfectly normal behavior.

Nicole Gelinas is a contributing editor of City Journal. Twitter: @NicoleGelinas