My speed driving my motorhome is 62-64mph. I'm about 60' long and don't have the power or brakes or maneuverability to change speed as quickly as a car. If I move over to the left lane to let someone in then by the time they get in and ahead of me there is usually a line of cars behind me getting PO'd because I'm in the left lane driving much slower than they are. Many times they whip around the right side of me and I'm blocked from getting back in the right lane. So it is much safer for me to remain in the right lane. The person merging can easily adjust their speed to merge either before or after me. So no I won't usually move over for someone to merge unless there is no one coming up behind me. It's all about safety.