Eastbound lanes were also slowed to a crawl by onlookers.
Officials said the cause of the accident was due to an 18-wheeler fishtailing in the rain near NC Highway 751.
Other vehicles followed which caused a bus to hit four cars, spawning more wrecks about 100 yards back.
Authorities said paramedics took four people to Duke Hospital and one to UNC for treatment of minor injuries.
The most severe injury reported was a broken wrist.
Motorists traveling through the Triangle were urged to get off I-40 at the Durham Freeway (Exit 279B) and follow that to I-85 South and back to I-40.
By 6 p.m. westbound lanes had reopened to slow moving traffic, as crews continued to remove wreckage and clean up the scene.