Colonia Route 31

Colonia Route 31 is a server highway route that runs from the city of Cairo in the northwest to Belvedere Village to the southeast, passing through Suffolk Village and New Nassau. Route 31 starts on Cleopatra Street in Cairo and heads south until Cairo Village Plaza, where it turns west along Alexandria Street. It exits the city on this street and turns south along Dawson Highway, where the roadway opens up to a divided highway and begins a concurrency with Vanderbilt State Route 27.

Just north of Suffolk Village, the road intersects Route 131, an auxiliary route, before continuing south into Suffolk as Main Street. In the south of Suffolk, Route 31 makes a turn towards the east, while also separating from State Route 27, which continues south over the Major Thomas Jones Memorial Bridge as Interstate 27. Route 31W also begins at this intersection and heads west into Vanderbilt City. As Route 31 exits Suffolk, it takes the name of Islip Avenue.

Route 31 passes through New Nassau as Forest Avenue, constantly changing direction while generally heading eastbound in the direction of Belvedere. It passes several prominent buildings, most noticeably the Paumanok Marketplace and the Kings Point Apartments. It soon exits New Nassau and continues east into Belvedere's village limits before making a turn to the south, where the route ends.