Mayor Nancy R. Rossi said in a release that the project developer is setting up detour signs and digital sign markers near Elm and Main streets to give motorists notice of the road closure and traffic change. The development company is led by John P. Dionis, vice president of development for Simon Premium Outlets, based in Morristown, N.J., and Matt Armstrong, executive vice president of The Haven Group LLC, based in Dallas. The Haven’s demolition phase is expected to begin shortly after April 27 with the environmental remediation of some commercial structures, followed by the acquisition of demolition permits for each property, officials said. Once completed, The Haven is expected to encompass 26 waterfront acres featuring dozens of luxury retail shops, restaurants and a promenade. The project is expected to generate between 800 and 1,200 jobs and several million dollars in municipal tax revenue and fees, officials said.