Connecticut Route 166

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Route 166
Spencer Plain Road
Map of Middlesex County in southern Connecticut with Route 166 highlighted in red
Route information
Maintained by CTDOT
Length	1.62 mi[1] (2.61 km)
Existed	1935–present
Major junctions
West end	Route 153 in Westbrook
Major intersections	I-95 / Conn. Turnpike in Old Saybrook
East end	US 1 in Old Saybrook
Location
Country	United States
State	Connecticut
Counties	Middlesex
Highway system
Connecticut State Highway System Interstate US State SSR SR Scenic
← Route 165 → Route 167

Route 166 is a minor state highway in southern Connecticut running from Westbrook to Old Saybrook. The route primarily serves as a connector from I-95 to the Saybrook Manor section of Old Saybrook.