The New Haven area has some attractive waterfront running overlooking Long Island Sound. These are some options just east of I-95:
Long Wharf Dr. and Park has lovely waterfront running along a dedicated path, for 1.5 miles. Great views! Access from Vietnam Veterans Memorial Park ROUTE MAP
Front St. Just north, there’s also really nice waterfront running from Criscuolo Park north to Quinnipiac Terrace near I-91 in Fair Haven, mainly along Front St. It’s possible to combine with the the Long Wharf route (above) using Long Wharf Dr./East St./Chapel St., but it does go through an industrial section for ~1 mile (although there is a bike path). See this MAP for the 4.5 mile combined route, one-way.
From New Haven center it’s 1.7 miles along Grand Ave. to get to Front St.
East Shore. There’s some great waterfront running in East Haven. We recommend the 3.4 miles from East Shore Park, south to Lighthouse Point Park. Combination of park trails, shore path, and road, with water views much of the way. It’s not one dedicated path — there are some road sections, so helpful to have this MAP of the route.