The temperatures dropped below freezing in places overnight, causing black ice to form, the National Weather Service said early Wednesday.
There were reports of slippery surfaces in several spots in the Connecticut River Valley, the service said, and even more in the Boston area.
“Exercise caution and take it slow, give yourself extra room between other motorists,” the weather service warned.
Black ice is dangerous because it is hard to see.
By 5:30 a.m., some crashes and spinouts already had been reported. One happened before dawn on Midland Drive in Tolland, where a car crashed into a utility police, according to Tolland County 911.
No one was injured, they said.