Don't be surprised if bike lanes on Seattle streets are a little empty this weekend. The bicyclists will be back -- they've just gone to Portland for a day or two.

About 9,000 bicycle enthusiasts will be leaving the city on two wheels for Portland on Saturday morning, the official start of the Group Health Seattle-to-Portland Bicycle Classic.

Those who complete the trek will pedal more than 200 miles before crossing the finish line in Halladay Park in northeastern Portland.

Most riders are expected to take two days to complete the journey, though about 2,200 participants have said they plan to make it to Portland in one day.

About 18 percent of the cyclists signed up are first-time riders, Cascade Bicycle Club spokeswoman M.J. Kelly said.

"The casual cyclist who does some training can definitely do this," Kelly said.

The bicycle club coordinates the event, which is in its 28th year. The first year, 183 bicyclists participated.

Paul Wantzelius of Maple Valley was one of those first bicyclists, and he's participated in the ride every year since then -- even after experiencing a heart attack last year.

"I actually just ended up taking two days instead of one," he said. "The ride is not difficult for a 200-mile ride. It has a few rolling hills in a few places but it's not really hilly."

The cyclists will be set off Saturday in 10-minute waves starting at 4:45 a.m. at the University of Washington's E-1 Parking Lot on Montlake Boulevard Northeast. Their route will run past Spanaway, Centralia, Castle Rock and Longview before crossing the Columbia River into Oregon.

The route will run along public roadways, and although participants have been urged to proceed with caution, "you can be sure there will be a few cyclists who won't pay as much attention," Kelly said. "We ask motorists to be careful."

The event sold out in June, but there may be a few riders who want to sell their tickets Saturday morning, Kelly said.