From papal visits and UN week to upcoming postseason baseball games, New York City is used to days when it's harder than usual to navigate its roads.

Each time, there's a familiar clarion call, when the powers that be urge New Yorkers to please, please use mass transit. After all, when streets are closed, and drivers are going nowhere fast, you can still get uptown underground.

It's easy to take our subway safety net for granted. But the net already has plenty of holes. Trains will run -- never mind run reliably -- only if they're funded and cared for.

Despite recent ads from the transit union, the city is in little danger of returning to its doomsday past of muggings, graffiti-scarred trains and piled-up trash. But a future of shutdowns, slowdowns and stoppages, of crowded platforms and broken-down trains and tracks, is possible if the $30 billion MTA capital plan remains unfunded.

The alternative, state Comptroller Tom DiNapoli said this week, may be more debt and higher fares and tolls. But commuters' wallets are already stretched. Higher fares, tolls and fees aren't the answer. And a deteriorating subway system is equally unacceptable.

The state committed to contributing $8.3 billion, and MTA chairman Thomas Prendergast has asked the city to chip in $3.2 billion. But city officials say they're waiting for detail on how the state will provide its funds, though that seems like a delaying tactic, because that decision will be determined in the 2016 budget. The city also wants assurances that its contributions really will go to the MTA.

Meanwhile, the money is missing and plans for repairs and upgrades are stalled. It's a regional system that needs regional cooperation and solutions. City, state and MTA officials have turned the rails into a political battlefield. They should hammer out an agreement and fund the plan.

Perhaps Mayor Bill de Blasio should take a few subway rides during rush hour. Commuters would be glad to show him what they go through, and how quickly the situation could worsen. Perhaps, then, he'll do his part to make the MTA capital plan -- and a more reliable, repaired, improved subway system -- a reality.