Connecticut 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 (2.61 km) | |||
| Existed | 1935–present | |||
| Major junctions | ||||
| West end | Route 153 in Westbrook | |||
| I-95 in Old Saybrook | ||||
| East end | US 1 in Old Saybrook | |||
| Location | ||||
| Country | United States | |||
| State | Connecticut | |||
| Counties | Middlesex | |||
| Highway system | ||||
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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.