Rush hour traffic at a busy Edmonds intersection was snarled for a couple of hours Tuesday afternoon after an excavator being used for a city road construction project at 212th Street Southwest toppled into a 12-foot-deep hole.

The driver of the excavator suffered a sprained ankle, a strained shoulder and bumps and bruises during the mishap, Edmonds Public Works Director Phil Williams said.

The incident occurred around 5 p.m. near Edmonds-Woodway High School when shoring boxes were being set for a detention vault. A bank gave way, and the excavator fell into the 12-foot-deep hole, which is 30 feet wide and 70 feet long, Williams said.

The excavator operator was taken to the hospital and later released, and 212th Street was closed between 76th and 80th while the excavator was pulled out. The road was reopened around 7 p.m.

Marshbank Construction, which has a contract with the city for the 212th and 76th construction project, is investigating the cause of the mishap, Williams said.

The intersection improvement project, which began in April and is expected to be complete by Thanksgiving, includes adding dedicated left- and right-turn lanes on 76th Avenue, and new traffic signaling that will allow simultaneous flow of traffic north and south. In addition, while the area is dug up, the city is moving overhead power and utility lines underground and upgrading its water, storm and sewer facilities.