The MTA’s leaders released a fine five-year capital plan this week, though by its nature it dodges the toughest issues about the agency’s future.

The plan is a winner for subway and bus riders, with spending on signal modernization as well as station accessibility and new buses and trains. The signal upgrades, in particular, are vital to improving service.

The first questions come on the revenue side. Mayor Bill de Blasio’s likely to resist the plan’s call for $3 billion in new funds from the city when the state is willing to “only” kick in the same amount. But 78% of the plan’s outlays are for the city’s subways and buses, a lot more than in the past — and Gov. Andrew Cuomo has beaten the mayor on similar past fights over MTA funds.

More dicey is the assumption that the MTA will yield $25 billion in capital funds from a new internet sales tax, congestion-pricing tolls and a new tax on homes worth more than $2 million. If any or all of those sources comes up short, the agency might have to fall on borrowing even more than the anticipated $9.8 billion — which would force future fare and toll hikes.

The only possibility we see for a good surprise is the project MTA chief Pat Foye has been working on for the last two years: contracting reform. The agency routinely pays through the nose on major construction projects — even London and Paris public-transit agencies get work done for far less.

But the capital plan could also be thrown off-course by major problems with the MTA’s operating budget. And everything there turns on negotiations with the MTA unions, since all its labor contracts have expired.

The Transport Workers Union, which reps city subway and bus workers, has already put its members on a war footing, and it launched a “rulebook slowdown” disrupting rush-hour bus service in Brooklyn last week as a sample of what might come.

If the TWU leads a scorched-earth resistance to any work-rule and overtime reforms, even if the MTA offers to share the savings with its workers, all bets are off.