Avoid 3rd Street

3rd St. is labeled as a bike route, but don't do it. At least, not west of Wilton.  Traffic isn't so much of a problem - there is actually plenty of room for you, your bike, and the plenty of stuff you'll pile onto your bike after visiting the various stores (such as Trader Joe's) on 3rd.

The unfortunate problem with 3rd St. is that, while the main part of the road itself is kept up quite nicely, the shoulders are very poorly maintained. Riding on a 3rd St. shoulder definitely requires a mountain bike. If you enjoy feeling everything inside of your body vibrate as you bounce from broken concrete to broken concrete, you'll enjoy this particular bike route. If not, here is the best alternative I've found so far:

2nd Street will get you as far east as Hudson.
Pop onto 3rd until you get down to the next light, but break the law and use the sidewalk. It is also poorly maintained, but at least you aren't jumping about in traffic.
At the next light, bounce down to 4th St., which you can take to Wilton. Once you've gotten as far as Wilton, 3rd will actually be okay.