WASHINGTON (CNN) -- Americans taking to the roads during the July 4 holiday weekend are almost certain to encounter a traffic bottleneck somewhere, but the biggest is likely to be west of Portland, Oregon, the American Highway Users Alliance said Thursday. The road between Oregon's Willamette Valley, where Portland sits, and the Pacific coast is known for recreation, wineries and beauty. This weekend, it will also be known for slow traffic, the group said in a study titled "Are We There Yet?" Interstate 64 in the Tidewater region of southeastern Virginia is second on the group's list of vacation bottlenecks,...