Passenger Wayne Balacky, 21, of Danbury, died at the scene. The driver, Jauseheema Perkins, 19, also of Danbury, died several days later.
Construction has begun, and the gates should be working by April 30, the Connecticut Department of Transportation says.
Gates were originally planned to be installed as part of a realignment of the nearby intersection of Long Ridge Road, Side Cut Road and Simpaug Turnpike. But "environmental and right-of-way issues" delayed the realignment project until late 2014, the DOT says.
An investigation found the crossing's warning lights were flashing when the car tried to cross the tracks in the fatal Dec. 30 accident, the DOT says. The crossing is near the West Redding station on Metro-North Railroad's Danbury branch.
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