Department of Transportation crews opened one lane of westbound Cary Parkway.
The road between Two Creeks Road and Lake Pine Drive was shut down last month after investigators say a teen set a fire in the culvert causing the road to collapse March 21.
Eastbound lanes opened Saturday.
It took investigators only days to find out who they say was responsible, 17-year-old Tristan Zammit.
The Cary High School student confessed. A search warrant showed investigators believe Zammit was trying to burn his name into the side of the pipe, which was coated with flammable tar to prevent rust.
That warrant then showed a fellow Cary High School student told police that Zammit sent a text showing what he had done.
The fire caused $480,000 in damage. It is money investigators say the apologetic teen will have to help pay for.
Zammit will find out his fate in court April 25. He faces 60 days in jail and a hefty fine.