Gov. Andrew Cuomo and the state Legislature have finally found a new revenue source for the MTA: the app-based for-hire vehicles that serve more than 600,000 riders every day, most of them on the narrow island of Manhattan.

These cars, along with taxis, will soon generate $400 million a year, which — when combined with new funds from the municipal treasury — will provide a nice pot with which to boost mass transit.

This is a major victory for all subway and bus riders, since the revenue will naturally grow in future years, and especially if the fee per ride goes up along with subway fares.

And what could be fairer than to compel people who live and work in Manhattan to pay when they get into a private vehicle on crowded city streets?

The car-service fee also lets New York City raise funds without a massive new bureaucracy to collect taxes, by just requiring a change in the software now in cellphones, taxis and for-hire vehicles. We’ll soon have an opportunity to deploy advanced technologies that collect fees from trucks and autos without massive and costly camera systems, without an electronic version of a Trump-style “wall” around Manhattan.

And we’ll raise much more money than the London congestion-pricing system and American cities that have imposed fees on Uber and Lyft services.

There’s a strategic logic to the new fees, too: Contrary to the conventional wisdom, tolls on cars entering Midtown Manhattan won’t end congestion. In 2016, there were 132,000 fewer cars entering the borough’s core than in 1998, a decline of more than 15 percent.

Yet Midtown Manhattan congestion got worse, because the traffic isn’t caused by cars entering Manhattan but, increasingly, by Uber and Lyft vehicles circulating within it. So it makes sense to target them with new fees.

Even so, we can only hope to reduce, not eliminate congestion, a task that is actually tougher than raising money. As Cuomo’s Fix NYC panel noted, congestion in Manhattan is due to a multiplicity of forces: internet-based truck deliveries, tour buses that cruise slowly down major avenues, a failure to enforce traffic laws, the use of streets for construction projects, providing parking spaces, often on weekdays for low or no charge as well as the surge in for-hire vehicles.

Manhattan’s 19th-century street grid was not designed for 62 million tourists and 8.4 million residents. That is why we depend on our 100-year-old subway more than ever.

With the new revenues, we can now do the hard work of fixing the system and making it more attractive to commuters, with the hope that some will ditch their cars for the subway and relieve congestion even more.

Perhaps a seasoned transit pro like new New York City Transit president Andy Byford can bring our subways into the 21st century. Modernizing the signal systems in the subways and purchasing new subway cars are essential to moving the 5.6 million weekday subway riders.

Fact is, our system is an aging gem that has suffered from neglect and underinvestment. Every generation is tested by a subway crisis. In the 1930s, New York City took over the privately operated subways then facing bankruptcy.

In the late 1960s, Gov. Nelson Rockefeller created the Metropolitan Transportation Authority, combining the subways and the commuter railroads with the Triborough Bridge and Tunnel Authority, to draw upon bridge and tunnel tolls. Today, approximately $1 billion a year in TBTA toll revenue subsidizes subways and commuter rails.

In the early 1980s, Govs. Hugh Carey and Mario Cuomo brought in fresh blood to lead the MTA, buy new subway cars and buses, remove graffiti and cut crime on the subways. We now face a new crisis of mobility. We have just raised new revenues for mass transit but now need strong management to spend this money wisely. No one should expect the federal government to save the system. We are on our own.

Above ground, we must also start to enforce traffic laws, tow double-parked limousines and reduce on-street parking. Below ground the urgent goal is to fix dysfunctional labor work rules and control MTA construction costs.

During the past 25 years, New York City brought down crime, closed failing schools and opened up the waterfront. There is no excuse to let our subways decline further, while motorists clog our roads.

Mitchell L. Moss is director of the Rudin Center for Transportation at NYU’s Wagner School of Public Service.