The fire was reported at 6:40 p.m. near Exit 42 for Route 57 in Westport, according to Assistant Fire Chief Brian Meadows.
Engine 6 arrived and reported that car was fully involved in flames in the breakdown lane, Meadows said. Engine 2 arrived shortly afterward, and both companies worked to extinguish the fire, he said.
One lane of travel was temporarily shut down during firefighting operations, he said.
Connecticut State Police assisted at the scene with traffic control. The last fire department unit cleared at 7:42 p.m. Saturday.
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