I would say that if you are the one trying to merge into traffic, you do not have the right of way, nor is anyone required to let you in. You need to either slow down or speed up if someone is already in the lane you're trying to get into.
I try to move over a lane when I can in order to let someone merge, but when another vehicle is already on the other side of me, I can't do it. All too often I encounter drivers who seem to think I should move over, even when there is another vehicle on the other side of me. Often these people will show their displeasure by pulling behind me within inches of my back bumper, blowing their horns and displaying digital salutes. I am simply not going to crash into another innocent driver in order to accomodate these jerks.
2013 Surveyor SP220
2010 Silverado LT 5.3 V8
The world is a great book, of which those who never stir from home
read only a page. - St. Augustine