The fact that people could see signs like this and literally not understand what they mean makes me weep. No wonder people are constantly holding up huge lines of traffic by not understanding proper lane discipline.
It would be nice if we had a system in place requiring that people actually knew this kind of stuff in order to obtain and renew a drivers license.
I think they are just variations of the same directive. People who post signs don’t always look up the official or recommended wording, and there may not be one in this case, so they make stuff up.
We used to have a sign like one of these (I don’t remember the exact wording). It was on a long hill upgrade. The 2-lane highway widened to 3 lanes, with 2 of them partitioned to the up side. It was your only chance to pass a slow truck for miles, so you hoped he would read the sign, then move over before you reached the crest of the hill and lost the opportunity. If he didn’t move over quickly, you were tempted to pass on the right, and halfway up the hill, he would decide to move right and everyone got frustrated. It was a mess.
Thank goodness the entire route has been replaced with a modern, 4-lane divided highway.
(bolding mine)
A+
This!
Dear, sweet OG, just [SIZE=“7”]THIS![/SIZE] 
D&R
I was driving on a bunch of mountain roads last week and saw a lot of those signs, so we have them also.
However the freeway I go on has a two lane to one carpool merge on the left, so the middle non-carpool lanes often are moving a lot faster than the carpool lanes at this point. Thus the independent lane rule makes sense for us.
A couple decades ago when i drove in CT a lot they had signs on I-84 directing everyone to use the center lane unless passing (left) or going below speed limit (right). I was going the speed limit in the right lane once and had a trooper flash his lights at me and chase me out of the right lane back into the center because I wasn’t going slow enough to be in the right lane.
That’s odd… Maybe they have very short and crowded on-ramps or something like that, so they figure it’s more efficient for people to yield the right lane to them.
I wonder if they have a similar rule in Canada. A few years ago, I took a trip from the Middle of Nowhere, Connecticut to Toronto, Ontario. Nobody was using the right-hand lane at all, but chose to be overcrowded in the left lane going approximately 40 to 45 miles per hour (by my speedometer) in a 100 kilometer per hour zone. I didn’t want to offend the nice Canadians that left me a clear path around them, so I made good use of that wide open lane. Even the people coming down the ramps would promptly merge into the slower traffic to the left.
Overall, it seemed like silly herd behavior to me, but I wasn’t about to complain, as it directly benefited me in that case. I may be in favor of “keep right except to pass,” but I’m not going to poke along at 15 or 20 under the speed limit to avoid passing people on the right either.
Even if they were getting out of my way on the “wrong” side, it was much nicer than upstate New York, where people would keep right until they saw you passing, at which time they would promptly pull to the left in front of you. Any time I ever drove on the New York Thruway, it always seemed like people were going out of their own way to get in mine.
Personally, I always adhere to the "Lead, follow or get the fuck out of the way!" style of driving. 
Can’t hardly go wrong with that. 
The “keep right except to pass” rule only makes sense in places where there are long, straight stretches of lightly used highways.
As soon as traffic reaches a noticeable density, enforcing such a rule will quickly start slowing down traffic.
Theoretically, if you take such a rule strictly, you can end up with one lane of bumper-to-bumper standstill traffic and one vacant lane.
I’m not following your logic.
Massachusetts has what I consider a textbook example of a keep right law.
Nothing in that law requires you to get out of the left lane to merge into slower moving or stopped traffic.
Even Maine’s law provides that you can use the left lane for both “… overtaking and passing another vehicle…” (cite). Ours does require moving over at the “earliest opportunity.” Again, that does not mean merging into slower moving traffic; it means you get out of the way once you’ve passed them.
I am studying to be a traffic engineer, and part of this is watching videos to observe how traffic moves (fun stuff to a traffic nerd…). Watching traffic through intersections in England always makes me dizzy!
I think the point they were trying to make is that there is so much traffic on the highways Acsenray is mentioning that there is no discernible point in which you are not overtaking another vehicle. Does this mean a person can stay perpetually in the left lane as long as there are more vehicles to pass? Or should they follow the law more closely and move back over into an already congested traffic lane? If everyone did this, one lane would be far more congested than the other for no real purpose.
I have always seen it as slowest lane is far right, middle lane is faster, and left lane is fastest. Unless it’s late at night (11pm or later), the highways I happen to travel on are always congested to the point where all lanes are filled at least comfortably to overfull, and a person in the left lane can be perpetually overtaking someone else. So, we treat the far left lane as simply “the fast lane” where if you’re going fast enough, feel free to travel in it, and if not, move over. I prefer this outlook.
Here’s the straight dope and the federal law on the use of such signs, from the Manual on Uniform Traffic Control Devices, 2009 Edition http://mutcd.fhwa.dot.gov
Section 2B.30 KEEP RIGHT EXCEPT TO PASS Sign (R4-16) and SLOWER TRAFFIC KEEP RIGHT Sign (R4-3)
Option:
01 The KEEP RIGHT EXCEPT TO PASS (R4-16) sign (see Figure 2B-10) may be used on multi-lane roadways to direct drivers to stay in the right-hand lane except when they are passing another vehicle.
Guidance:
02 If used, the KEEP RIGHT EXCEPT TO PASS sign should be installed just beyond the beginning of a multi-lane roadway and at selected locations along multi-lane roadways for additional emphasis.
Option:
03 The SLOWER TRAFFIC KEEP RIGHT (R4-3) sign (see Figure 2B-10) may be used on multi-lane roadways to reduce unnecessary lane changing.
Guidance:
04 If used, the SLOWER TRAFFIC KEEP RIGHT sign should be installed just beyond the beginning of a multi-lane pavement, and at selected locations where there is a tendency on the part of some road users to drive in the left-hand lane (or lanes) below the normal speed of traffic. This sign should not be used on the approach to an interchange or through an interchange area.