Northeast - Southhold to Southampton

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I rode from Southhold to Southampton, it was a good ride in that the roads had a nice wide shoulder/bike lane. The only drag is the bridge over the peconic river which does not have a meaning shoulder and the cars are going by at 55MPH. Any ideas how to advoid the bypass bridge? Riding into downtown Riverhead is a huge detour and might not be that safe.
I've ridden through downtown Riverhead, and I didn't notice anything particularly unsafe about it. Traffic goes pretty slow, and there are a lot of pedestrians around the aquarium, but no problem. In fact the aquarium is a nice place to stop for a rest; you can watch the seals &c swimming around. At least, when I rode through there with my daughter, that's what she wanted to do! (but she was 9 at the time).
Downtown is not the question its from the circle out, in the area known as Riverside.
I rode from SH to Southold but this time I went by way of Sag Harbor and took the ferry.
It was a much nicer ride.