Advocates say transit-oriented development could be a good solution if done right. But in order for it to succeed, they say it’ll need to be both affordable and environmentally sustainable. Building in wetlands like the area around Fairfield Metro requires infrastructure that can mitigate the effects of climate change and reduce the impact of wastewater on a vulnerable environment. The Crossings at Fairfield Metro is the largest of the proposed developments. One building is already under construction. Eventually, the sprawling complex will include nearly 700 apartments, a hotel, an eight-story concourse building and more than 40,000 square feet of office space. That’s based on an ambitious expansion of the project from the developers, Accurate Builders, in March.