The crash happened in the New Haven County town of Middlebury at about 8:10 p.m. on Monday, March 14, according to Connecticut State Police.
A 2003 International 4000 Series 4300 was driving slowly in the left lane on I-84 westbound near Exit 16 when a 2019 Ford Transit-150 struck the rear of the truck, police reported.
Both vehicles came to an uncontrolled rest in the grassy median, police said.
The driver of the Ford, a 25-year-old Newtown man, was hospitalized with serious, possibly life-threatening injuries, authorities said.
The driver of the International, a 59-year-old North Haven man, was not injured, police reported.
Police said the investigation into the crash is ongoing.
Authorities asked witnesses to call Trooper Quaglino at 203-267-2200.
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