There is a free-travel zone that extends across the southwest US that generally goes as far north as I-10. Mexican nationals may travel in that area without having regular visas - I think that this is part of the La Paz Agreement. There is a similar free-travel area for US citizens south of the border. Checkpoints that are the equivalent of border crossing checkpoints are set up north of this area. I go through the one on I-25, about 30 miles north of Las Cruces, New Mexico, all the time...it generally involves slowing almost to a stop and waving a driver's license or other form of ID at the BP agent. I can see someone with non-US credentials having to do some more explaining - my Panamanian niece always carries her passport and entry visa when traveling that way. Ferry terminals in Washington? Well, sure - that's how many people enter from Canada. I'd like to see some information indicating that the BP is running these checkpoints on East-West highways or anywhere at all besides the southern border.