The National Transportation Safety Board has concluded its investigation into the crash of a tour bus in Littleton last year saying no action is required.

The crash occurred on March 21stand involved a tour bus carrying 23 Korean tourists, a guide and a driver. It was coming from Canada and was headed for Boston.

The NTSB report found the bus was delayed at the border for about four hours because one passenger lacked the proper documents. By the time it headed south a snowstorm moved into the area and the interstate was covered with snow.

The driver lost control on Interstate 93 in Littleton and the bus overturned, seriously injuring five people.