LAS VEGAS -- According to Metro police, a shuttle bus crashed into a guard shack near the CityCenter construction site on the Strip.

The wreck occurred at 1:28 p.m. Thursday near Las Vegas Boulevard and Harmon Avenue.

Police said the driver of the 2007 Chevy C550 shuttle bus, William Tolbert, 43, of Las Vegas, was traveling in the only eastbound lane on the Harmon Avenue Interstate-15 overpass.

George Vaieland, 66, of Las Vegas, was standing in a guard shack which straddled the westbound lane and the median.

Jordan Grissette, 20, of Las Vegas, was walking westbound on Harmon Avenue, in the westbound lane, on the north side of the guard shack.

Pedro Alfaro, 20, of North Las Vegas, was traveling westbound on Harmon Avenue in a 2007 Kawasaki mule and stopped east of the guard shack.

Police said as Tolbert crested the Interstate-15 overpass, he lost control and began sliding sideways. His vehicle then struck the median, a concrete barrier and the guard shack.

Officers said Alfaro was struck by flying debris, and Grissette and Vaieland were hit by the shuttle bus.

Grissette was in critical condition, and Vaieland was in serious condition Thursday night. Alfaro had minor injuries.

There were no passengers on the bus, and Tolbert was not injured.

Officials have not said how this will affect a NASCAR hauler parade that is scheduled for the area, but roads have been shut down on the Strip in preparations for the parade.

Police are investigating to see if speed was a factor in the wreck. The collision remains under investigation.

The CityCenter construction project has had its share of problems: Four construction workers have been killed while at work.