Congratulations, cross-lake commuters. You managed to defeat gridlock on Interstate 90 despite losing three westbound lanes Monday morning.

So now it’s time for another challenge — a fundraising visit, from midafternoon Tuesday into early evening, by President Obama, whose exact route is always a Secret Service secret. The trip, like previous ones, includes an Eastside stop, but any freeway closure in the region can have ripple effects.

The president’s visit, along with the usual second-day traffic surge surrounding a major highway project, could add suspense and time to the trip between Bellevue and Seattle.

Seattle Mariners baseball games, at 7:10 p.m. Monday, Tuesday and Thursday and 12:40 p.m. Wednesday, will add traffic throughout the project.

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On Monday, commuters headed to work earlier than usual, and in lesser numbers.

Traffic volume was two-thirds above normal before 6 a.m., then plummeted to 40 percent below normal the next hour, 60 percent the next two hours, and 40 percent in the 9 o’clock hour, compared with usual counts.

The trip from Issaquah to Seattle maxed out at 35 minutes at 6:35 a.m., compared with the typical 21 minutes at that time. The backup briefly stretched three miles to Eastgate; then by 8 a.m. it was virtually gone.

Afternoon traffic was stop and go, but for less than a mile.

“A lot of folks took alternate routes, carpooled or stayed home. They did what we hope they will do the rest of the week, and that’s take wheels off the road,” said Travis Phelps, spokesman for the state Department of Transportation.

Only one mainline lane is open westbound, along with one oncoming lane from I-405, until 5 a.m. Friday.

That makes the situation fragile, Phelps said, because one fender-bender or stalled car could crimp the traffic flows more than normal.

The Seattle area’s tendency on the opening day of a freeway-lane closure is for traffic to be manageable. After eluding a “carmaggedon,” drivers return the second day.

Congestion fluctuated this way during the I-5 Sodo joint repairs of 2007, then stabilized into daylong backups of three miles. During the “Viadoom” closure of the Alaskan Way Viaduct, for Sodo-area demolition in October 2011, the fourth day was worst, causing diversions and jams as far away as Bothell.

This week, workers are replacing the 92-foot expansion joint across the deck of the I-90 East Channel Bridge. The southern half of the joint was replaced over the weekend, and concrete was being chipped out Monday afternoon to replace the north half. The job ends with a 30-hour operation to weld the halves together, then set concrete on the deck edges to embed the steel joint into place.

The high-occupancy-vehicle lane is being converted to general use past the work zone, leaving buses vulnerable to other traffic.

There was ample space Monday in the Eastgate park-and-ride garage, where bus drivers said passenger counts seemed normal.

Sharon Andrews, of Bellevue, said Metro bus 271 got her to work at the University of Washington in only a half-hour, or 10 minutes faster than usual, after she boarded at 7 a.m. She attributes part of her early arrival to UW students who left town, but the same thing happened for her daughter, who rode from Issaquah to Seattle.

“Traffic was a breeze, it was very light,” said Andrews. “My daughter was surprised too.”

More people than usual commuted in the bike lane Monday, regular cyclists said.

By afternoon, cars were lining up to merge at the East Channel of Lake Washington shortly after 1 p.m., setting the stage for some afternoon slowdowns.

Staff reporters Alexa Vaughn and Colleen Wright and deputy business editor Rami Grunbaum contributed to this article. Mike Lindblom: or 206-515-5631