Ridership fell this morning on the Sounder commuter trains, as hundreds of people apparently reverted to driving, and some possibly to express buses, to take advantage of the relatively uncrowded highways.

A total 4,956 people rode the five trains to Seattle, or got off in south-end suburbs, this morning. That's 864 fewer than Tuesday, and 1,763 fewer than the record 6,719 riders who filled the morning trains on Monday, the first weekday of the big I-5 project.

Still, the trains are still drawing a bigger crowd than usual; Sound Transit says that on a typical May weekday, 3,371 people took morning Sounder trips on the south-end line.

Transit spokeswoman Linda Robson said the trains will take on renewed importance Thursday morning, when a third lane closes on northbound Interstate 5 near Spokane Street, in the next phase of construction. She said there is plenty of space at four temporary park-and-ride lots that are going virtually unused: in downtown Kent, Sumner High School, the fairgrounds in Puyallup, and a Tacoma Dome surface parking lot.

Increased transit use is helping the region avoid severe gridlock, but greater numbers of commuters continue to bypass I-5 by detouring, canceling unnecessary trips, telecommuting, or taking time off work.

More information at soundtransit.org