New York City is thriving again. New businesses, new construction and new residents have created an economic boom -- and generated billions in unexpected revenue for the city budget.

None of this new development would be possible without the Metropolitan Transportation Authority, which runs the subways, buses and commuter trains. And as the MTA tries to fund billions in mass transit investments over the next five years, it's only fair for NYC government to make a reasonable contribution to enhance and expand the mass transit network.

The MTA's transportation assets are worth about $1 trillion, and 80 percent of that -- some $800 billion worth -- is located in the five boroughs. The subway system is one of the largest in the world, with 468 stations, more than 840 miles of track, 6,400 subway cars and more than 6 million rides on our busiest days.

Yet, the city has historically contributed just a fraction of the MTA's capital costs. The MTA has invested more than $115 billion in rebuilding the transit network since 1982; barely $7 billion came from the city. The rest came from the state of New York, the federal government and the MTA.

When NYC and the MTA were both reeling from the fiscal decline of the 1970s, it was understandable that city government said it had nothing left to give. That's no longer the case. From 1982 to 1986, the city contributed an average of $136 million a year. As the city's own Independent Budget Office found, if that kept up with inflation, it would equal $363 million a year today. Instead, in recent years the city has contributed just $100 million a year to the MTA's capital needs.

NYC must contribute more to the MTA capital plan. We have absorbed millions of new customers while barely expanding the subways; much of the system is more than a century old. Maintaining and improving our subway infrastructure, much less upgrading it with new signals, more countdown clocks and modern tap-and-go payment systems, will cost billions. So will buying new subways and buses and expanding the Second Avenue Subway to East Harlem.

All of this work and much more will cost $26.8 billion over the next five years. That's a lot of money -- but the price of doing nothing is even higher. The MTA has contributed $7.7 billion to the plan, and at Gov. Andrew Cuomo's urging, we have committed to cut another $2.2 billion by using smarter "design-build" procedures and reforming procurement. The governor, in turn, has committed to invest $8.3 billion over the next five years.

We have asked NYC to contribute $3.2 billion over the next five years -- less than 12 percent of the cost of the program. That works out to $325 million a year as well as $1.5 billion to expand the Second Avenue Subway to East Harlem. This is a reasonable and appropriate request.

As we saw during superstorm Sandy, New York can't function without a strong and reliable MTA. The subways were once plagued by crime, fires, derailments and breakdowns, and it has taken more than $115 billion to fight back from decades of deferred maintenance. Maintaining that progress is vital -- and so is finding the money to make it happen.

Tom Prendergast is chairman and chief executive of the Metropolitan Transportation Authority.