The zipper merging advocates suggest that utilizing all open lanes up to the point where one of them is no longer open, then taking turns merging into the remaining lane. There are studies that indicate that this is more efficient -- that traffic actually moves faster when zipper merging. I have to wonder whether these studies took place under real-life conditions or were mathematical models, because I have never seen a video of this working smoothly. Sure, I've seen plenty of animations illustrating how it should work, but nothing showing real cars in real traffic smoothly zipper merging.
I'll concede that there are certain scenarios where it theoretically should work better than everyone moving over as soon as the "lane closing" sign appears. One might be in bumper-to-bumper, slow moving traffic where every lane is already occupied. Trying to move over right away would require vehicles slowing down to create gaps in the traffic flow to allow people to merge early. This would slow down everything. In this situation it's unlikely that one could move over very easily. But when the traffic got to the choke point, both lanes would need to slow down enough to allow alternate merging into the open lane. It's not clear to me that zipper merging would cause traffic to move faster, although it would prevent the traffic from extending back so far as to block exits, which is a benefit. You'd still need to deal with the human tendency to think of themselves first -- drivers would all need to follow the rules, but I'm not convinced, for the previously stated reasons, that traffic would move any faster.
Now if traffic is moving at, or close to, the speed limit, and and there are enough naturally occurring gaps between vehicles (as there should be -- 1 second for every 10mph) then it should make absolutely no difference when you move over to the open lane. In fact, if vehicles are sliding out of the lane that is closing when there is a natural break in the flow of traffic in the other lane, rather than waiting until the merge point, traffic should continue to move at the same rate. If everybody waits until one of the lanes disappears, both lanes are going to have to slow down to allow each lane to alternately move forward. The only way zipper merging works in this scenario is if (1) space between vehicles in the lane that is staying open is maintained and (2) drivers in the lane that is closing merge into the space left for them without slowing or stopping and (3) no one is a jerk. In my opinion the probability of "1" and "3" is 50-50 at best; the probability of "2" is going to be pretty low -- drivers are going to be naturally hesitant about pulling in front of another moving vehicle and hoping that they allowed enough space and time. The natural reaction will be to at least slightly slow down, causing a chain reaction, slowing everyone down. Then there's the question of why, in some scenarios, is anyone even in what is usually designated as the passing lane?
Rules about the left lane on multi-lane roads is another of the things that irritate me. In most states the far left lane is for actively passing slower vehicles only. The reasoning is that drivers should be free to drive at the speed limit -- if a vehicle is traveling below that speed, other drivers should have the option to safely get around them. It makes sense to me. But I hear a lot of complaining from drivers who are stuck behind someone in the passing lane not going fast enough. Technically, if you stay in the left lane while not actively passing slower traffic, it's a traffic offense that will earn you a ticket. What I see most though, are people griping that someone driving at the speed limit is preventing them from exceeding the speed limit! I even recently saw a video where a member of law enforcement proudly ticketed drivers "camped out" in the left lane at the speed limit, while ignoring people speeding around them. Logically, if I am driving at the speed limit in the passing lane, why does anyone need to pass me? By passing someone driving at the speed limit they are exceeding the limit and breaking the law! I have no idea whether most highway patrolmen ticket people for hogging the left lane, but I know they'll nab you for speeding if they catch you.
Personally I drive 5 mph over the speed limit on the interstate. Illegal, I know, but I'm gambling that the cops are going to let it slide and I've never received a ticket for driving between 1-5 mph over the limit. (It's a misconception that cops can't pull you over for going less than 5 mph over, but they usually won't) Some days the middle and right lanes are full of people who are driving slower, so rather than constantly changing lanes to pass car after car of slower vehicles I stay in the left lane for long stretches. In those situations I feel no obligation to enable someone who wants to break the law even more than I'm already breaking it. If someone comes roaring up behind me when I'm already doing 80 in a 75, they're just going to have to wait until there's a clear stretch of road in the middle lane for me to get over to. Chances are they're going to thread the needle through small gaps and pass me in the center lane or even way over on the right. Not my problem. Now, if I have an open middle lane, that's where I'll be.
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