Lane Speed Divergence, sometimes called Speed Differential, is something we really have to pay attention to.  When we see it, we are looking at multiple road hazards all bunched up together.  It may not kill us (then again it may), but it can quickly send us and our favorite buggy to the body shop.

This exciting little happening can be defined as when one or two lanes of traffic are moving very slowly or perhaps not at all, while an adjoining lane is boogying along at a significantly greater speed.  How we handle it will depend on which lane we’re in.

There are three primary situations where we can suddenly find ourselves in a Lane Speed Divergence situation and it behooves us to both watch for them and recognize them when we see them.

First, there is the HOV lane divergence, specifically where the HOV lane is only separated from the other lanes by bright white iridescent double lines with zebra stripes with exclamation points blatantly indicating that the lanes should not ever be crossed.

So we’re comfortably bopping along in the HOV at limit plus 15 or 20 along with everyone else in the lane, and we suddenly realize that the regular lanes are hovering around at about limit minus limit.  Yup – we’re happily buzzing by them while they’re lucky if they can put 10 mph on the board.  And we’re doing it with only those silly little zebra stripes (and maybe a couple of extra inches between the lanes), separating us from those humble types blazing along at almost a dead stop.

Hmmm!

As we happily gloat at our good fortune it might be prudent to expect that one of those frustrated pokeys in the other lane is going to lose it and jump into our lane.  It may be because his side view mirrors aren’t adjusted correctly or possibly he has suicidal instincts but when he jumps the lane right in front of us, we’re going to have nowhere to go unless he has 550 horsepower to very quickly come up to our speed – and applies it!

Next, there is the interesting little situation where an exit lane backs up traffic onto the parkway or highway that we’re on.  This can get really exciting.

If we happen to be in the left through lane and all of that traffic is backed up in the right lane, there are two things to watch out for.  You probably don’t have to worry about the exit traffic jumping into your lane because, duh – they’re exiting right?  But what about that gal who accidentally got trapped in the lane and isn’t going to exit?  She’s going to be desperately watching for an opportunity to hop back into our faster lane and get on with her life.  If she does it right in front of us, that “on with her life” thing may become kind of meaningless.

Then of course, there’s the puppy in front of us that was texting at 65 miles per hour and suddenly realizes he’s missing the exit.  He now has to jam on his brakes in our lane, slow down and somehow wedge himself into the exit lane traffic.  When he performs this act of bravery there are two things we have to consider.  First, we have to stop short to avoid hitting him.  If we’re successful with that endeavor the next trick is not to get rear ended by the traffic in back of us.

Finally, there is the Merge.  Three or more lanes are being reduced to three or more minus one.  There are usually pretty Yellow signs for some distance warning of the event and it is at this point where we will have to decide whether or not to be an early merger or a late merger.

If, upon spotting the warnings we elect to immediately move out of the lane being closed, or to stay in the ones remaining open, we are an early merger.  If we stay in the lane being closed or move into it we are late mergers – choosing to remain in the usually faster lane until the last minute.
 

Tom Vanderbilt in his book “Traffic, Why we Drive the Way we Do” does an excellent job of describing the pro’s and con’s of each of these options.  There are more than we might think so we won’t delve in to them here, but the majority of drivers will be early mergers and this is where Lane Speed Divergence develops.  The lane being closed will usually empty out early, creating a neat little opportunity to buzz on by the drivers in the “to remain open lanes” until the merge is finally forced.

If we choose either lane at first blush and stay in it to the bitter end, cool.  It’s when drivers change their minds about half way through the happening that problems can develop.  It’s kind of like the HOV situation.  Some one gets frustrated while in the slow lanes and decides to hop into the faster lane.  If we’re “late merging” we really want to be ready for this potentially traumatic event.

There are three things to consider when faced with Lane Speed Divergence.

The first is to immediately set the situational awareness button to at least code Orange when we first see the divergence developing.  We really want to know everything that’s going on around us. 

If we’re in the slower lane and elect to hop over into the faster one, we really want to be sure we have enough room and horsepower to make it happen safely.  Be especially careful about any blind spots and definitely watch for the driver behind us that decides to do the same thing at the same time.

Keeping a safe distance from the cars in front of and around us is always a good idea but it becomes critical in a Lane Speed Divergence situation especially if we’re in the faster lane.  Yup, it may give someone the opportunity to hop in front of us but that’s okay.  In this situation, we probably don’t have too many escape options and any space we can keep between us and the cars around us can mean the difference between safe passage and body by crunch.