How to build a bridge

A support for the demolished Long Island Bridge in Boston Harbor. Craig F. Walker / Globe Staff

The Walsh administration recently took steps forward on its plan to rebuild the Long Island Bridge and create a new addiction recovery campus on the city-owned island in Boston Harbor. The news arrived amid ramped-up opposition to the proposal from the mayor of Quincy and other elected officials. Officials there cite concerns about construction traffic on Quincy's streets and lack of community input, and are even floating threats to ban construction trucks. They proclaim they are ready "to do what we need to do to fight this ill-conceived project."

Those objections are overwrought — but they do underscore the work that Walsh will need to do to convince Boston and Quincy residents alike of the merits of his project.

The old bridge, which allowed the city to access the island through Quincy streets, was shut down in 2014, after engineers discovered urgent structural problems. The island used to house a homeless shelter and other services. It was a source of friction between Quincy and Boston even then: Not only did the vehicles serving the island annoy neighbors, but Boston blocked any public access to the island.

It's tempting to dismiss Quincy's objections as just NIMBYism — and there's definitely plenty of that going around — but critics have exposed the city's failure to articulate just what it envisions for Long Island, and why it is the right place to realize those visions. Right now, it's a proposed bridge to a vague idea, not a full plan.

Bostonians deserve more details in exchange for committing nearly $100 million for a structure. What is the opportunity cost for Boston of the new bridge? Where are the viability studies showing that Long Island is the best locale for a new recovery center in the area? Will there be further development on the island? If so, what kind? After a major expenditure of their tax money, what sort of public access will Boston residents have to their island?

In a briefing with reporters last week, the Walsh administration said it still has no answers to such questions. Essentially, the mayor is asking Boston's taxpayers to take a big leap of faith.

The data is clear that demand for treatment beds is higher than the supply, but for $100 million just to build the bridge, are there other sites that would yield more bang for the buck? The city has resisted the sort of analysis of alternatives that normally accompanies big projects, saying that to study other potential sites would only mean more delays. “For us, it’s about access and equity. We can’t wait for us to do an assessment of whether we could find a place [on the mainland],” said Marty Martínez, Boston’s chief of health and human services.

The concept of a recovery campus is a good one. Walsh deserves credit for recognizing that fighting the opioid epidemic requires much more than the outdated 28-day treatment model. Substance-use disorders, particularly opioid abuse, are chronic and progressive illnesses. A recovery campus that offers a chain of services — detox, rehab treatment, work and training opportunities, supportive housing programs — elevates the probability of success tremendously. Long Island has potential.

But asking taxpayers to cough up $100 million for a bridge — plus whatever the recovery center will cost — without due diligence and consideration of alternatives is unwise. Because the island housed social services before doesn't mean it's the best or most cost-effective place to put them now. Walsh will find his sales pitch much easier, in both Boston and Quincy, if his administration does the legwork to demonstrate that it has a fully formed plan, and that Long Island is the best place for it.