The Nevada Highway Patrol says closures at the state's busiest freeway interchange have caused backups in Las Vegas, and they're asking drivers to be aware of the project dubbed "Car-nado."

Trooper Chelsea Stuenkel said the Thursday backups came after drivers headed south on Interstate 15 apparently missed warning signs saying the ramp to northbound U.S. Highway 95 was closed. Many ended up turning around near Las Vegas Boulevard, clogging traffic.

More closures are set for Friday morning on northbound Interstate 15, which typically carries more traffic.

It's part of a $1 billion project to smooth traffic through the city's congested Spaghetti Bowl interchange, a chokepoint on Interstate 15 that links Los Angeles with Salt Lake City.

It's Nevada's busiest stretch of highway in and sees 300,000 vehicles daily, about one-tenth of the state's population.