Greenway’s ‘partners’

There is nothing so immutable as a public subsidy — and so it is hardly surprising that what was originally billed as a process to “wean” the Greenway Conservancy off public funds will continue at least for another six years.

But the agreement announced Monday to assure future funding for the ribbon of parkland that replaced part of the old Central Artery also puts in place a private sector element, so that those businesses that benefit from having the artery as their front lawn will contribute to its upkeep in the future.

There are, of course, still some problematic details. Aren’t there always. But the framework is a reasonable one.

The agreement will have MassDOT contributing $1.25 million to start — down from its current $2 million-a-year subsidy. That figure would be gradually reduced to $750,000 by 2020.

The city of Boston has already committed to setting up a $5 million trust fund that would generate $250,000 a year for operating costs. That, of course, is dependent on legislation aimed at creating an exemption to permit the building of a residential tower at Winthrop Square.

Under the 10-year lease agreement reached with MassDOT, another $1 million a year would come from a Business Improvement District — that figure would increase to $1.5 million after 2020. At least 20 area businesses have already agreed to be part of that effort, but it too requires legislation.

Now Boston is decades behind the times in its use of BIDs to make and fund improvements in public spaces. Boston has one — for Downtown Crossing — and that took more than a decade to get off the ground. New York City currently has 74 BIDs, generating $134.7 million in private funds in fiscal 2016. The first one began operation in 1982.

The Greenway BID — with the power to levy assessments on its member businesses — will have to be up and operating in short order.

Transportation Secretary Stephanie Pollack conceded, “For purposes in negotiations, we made it clear that if others didn’t step up, I was prepared to zero it [state funding] out. And I was.”

Presumably that threat still holds if any of these moving parts goes south.

And with new contributors signing on, the Conservancy itself should have more watchful eyes on its spending. Nothing wrong with that.