Northbound traffic on I-5 in Lynnwood was snarled during the heart of the Wednesday evening commute after the truck crashed into several cars near 164th Street Southwest at about 4:15 p.m.

State Patrol Trooper K.C. Scott said 42-year-old Tony Tucker told investigators that he was tired and had nodded off at the wheel just before he hit the car in front of him. The Bellingham man was mumbling and slurring his speech when troopers arrived, Scott said, but no drugs or alcohol were found in the man's truck.

Scott said Tucker volunteered a blood sample but it will take several weeks for toxicology tests on the sample to be completed. While the truck driver was seen being handcuffed at the scene of the crash, Scott said that he has not been arrested and was released.

If the toxicology do not show that Tucker was using drugs or alcohol he will likely be cited for negligent driving for falling asleep at the wheel, Scott said.

Tucker has prior convictions for assault and disorderly contact. Scott said Tucker has a valid commercial driver's license.

A 30-year-old pregnant woman who was in one of the vehicles that was struck was injured and taken to Harborview Medical Center in Seattle where she was expected to recover.

Troopers initially thought the woman may have gone into labor after the crash, but her husband told KOMO News that she was not in labor.

The freeway was blocked for about 30 minutes as crews worked to clear the wreck, and traffic remained snarled for several hours Wednesday evening.