SAN FRANCISCO, Dec. 20 (Xinhua) -- The major interstate highway, Interstate 5 in Washington state on the U.S. west coast, reopened more than 50 hours after a passenger train derailed Monday, which killed three people and injured scores of others, authorities said Wednesday.

The Washington State Patrol said the two left lanes of Interstate 5 were opened to public traffic as of Wednesday afternoon, with a set reduced speed of 45 mph (about 70 km per hour).

It said all three lanes of the highway will be opened by Thursday morning.

The Interstate 5 highway, which runs largely parallel to the Pacific coast of the continental U.S. from Mexico to Canada, has been completely closed after an Amtrak train (the National Railroad Passenger Corporation) went off the tracks in DuPont south of Seattle Monday and spun several rail cars onto Interstate 5 below.

The two-day road closure has caused a heavy traffic crunch that affected the whole region near the accident site.

Monday's derailment was one of the major rail accidents in recent years in Washington state. The cause of the tragedy is still under investigation.

The U.S. federal transportation authorities have sent a 20-member team to the state to probe the accident.

Preliminary findings showed that the train was travelling about 50 miles (80 km) per hour faster than the speed limit near a curve with a limit of 30 miles (48 km) per hour.