WATERVILLE — Residents got a first look Monday at what the downtown would be like if two-way traffic were returned to Main and Front streets. Vehicle traffic on Main would move through downtown more slowly, there would be areas for pedestrians only, and sidewalks paved with brick-like blocks. Commuter traffic would be diverted more toward Front Street, and it would be easier for motorists to get through town because they would’nt have to follow the one-way streets. That was the scenario sketched out for residents Monday by officials from Gorrill Palmer, a consulting firm from Portland that has been working with the city and Colby College on a traffic and parking study. “It’s actually the beginning of a new chapter of what happens next and how do we turn theory into action,” Mayor Nick Isgro said.