A giant inflatable plug that can be filled with 35,000 gallons of water at a moment’s notice could have prevented some of the flooding that crippled New York City’s transit in the wake of Sandy, according to an expert working on the technology.

This isn’t a case of Monday-morning quarterbacking. The technology is still in the lab. But the impact of this month’s superstorm on transit and the possibility that it’s a harbinger of things to come has focused attention on adding the plugs to the disaster-response toolbox.