Perhaps
nothing can cause such a universal emotional response in drivers as the
dreaded lane-ending-merge like the ones when a lane is closed for road
work or a crash. We all know the drill-- most people move
out of the truncated lane early while a few seemingly self-important people take
advantage of the empty lane to cut in at the front of the
line, causing incalculable road rage amongst those waiting patiently in the through lane.
Even some of those people cutting in at the
front feel the stress of that tense, last-second merge while
knowing that they're now the target of disdain of dozens of people
behind them. It's even worse for the innocent, well-meaning
motorist who tried to get in earlier but was blocked by self-defeating
road vigilantes.
Drivers properly executing a Zipper Merge (Photo source: ABC7/WJLA-TV)
In Texas and most states, legally,
there is
no requirement to merge until the taper point. Therefore, this
situation exposes a deep-seated philosophical argument: Is it better to
merge early, like most folks do, or wait and merge "late", i.e. at the point
where the lane ends?
Fortunately, recent research and
experimentation is helping to inform the debate. Unfortunately,
like so many things in
life, the answer isn't cut-and-dried-- it depends on the situation.
Most
drivers are either taught, or learn on their own (often instinctively),
to merge early. That
just seems to be the "right" thing to do on so many
levels. And sometimes it is indeed the right thing to do.
But traffic
experts have discovered in recent years that
sometimes it's actually the wrong thing to do, and the late merge has
now become the recommended procedure in a number of states including
Minnesota, Wisconsin, Washington, Missouri, and Kansas, as well as in much of
Europe, where in Germany it's actually the law. (German zipper-merge sign at
left.) It's also supported and recommended by the AAA.
The "Zipper Merge" The "late
merge", known more descriptively as the "Zipper Merge", is
when drivers fill up both lanes and then take
turns merging one-at-a-time
at the
point where one lane ends. That one-at-a-time merge is where
the "zipper" name comes from.
Research has shown that this method is
safer and helps to keep things moving more smoothly through the merge
point because drivers are cooperating and creating gaps, thus
eliminating brute force injections into the through lane. It's
those sudden, unexpected forced merges, especially from a standing
stop, that causes shock waves in the traffic flow that creates the
stop-and-go conditions often seen in these situations.
Here is why it works:
When people take
turns and
know that's the expectation, they can gradually open a gap earlier
while still
moving.
Drivers in the closed lane can better predict where they'll
merge, align themselves, and merge smoothly and safely without having to stop.
Because
everyone keeps moving, it eliminates shockwaves in the traffic
stream, which reduces the risk of rear-end collisions, and drivers feel
less stressed because traffic is still moving.
By using the full capacity of
the truncated lane, the length of the backup is reduced correspondingly.
These circumstances together result in a smoother, safer, and more
consistent traffic flow, and studies have shown it can reduce congestion by up to 40%.
(Source: Oregon Dept. of Transportation)
Here's maybe the best reason to use the Zipper Merge One big benefit of the Zipper Merge that is rarely recognized or mentioned, but may actually be the most important
reason for many early-merge adherents, is this: The Zipper Merge fills
the lane that is closed, thereby preventing opportunistic drivers from taking
advantage
of an empty lane to zip past everyone and cut in the front of the line. That
alone makes it worth the price of admission to me. Furthermore, if both
lanes are used, they will tend to even themselves out, which then makes
it fair for everyone, i.e. the person you let in at the merge point
will have been waiting about as long as you have.
But for it to work, everyone has to be on the same page The
biggest obstacle to implementing the Zipper Merge is that pretty much
everyone has to buy into it and play along in order for it to work. If only
a handful of people do it and the other drivers aren't aware of it,
then it gives the appearance that the zipper-mergers are just taking
advantage,
and many of them may therefore feel like that's what they're doing and
will
abandon it.
Furthermore, it's hard to break such a
deeply-ingrained habit and belief system. I myself know the
benefits of the Zipper Merge, but I still often feel that visceral need to
merge
early.
Therefore, a significant public education campaign,
along with signage in work zone merge area, is needed to make the program work. Studies have
shown that when this is done, the benefits are
realized.
This
humorous description of the Zipper Merge is by a Canadian, but is still applicable to the US:
But there still is a situation when
merging early is better
The Zipper Merge works best when traffic is already congested
and
moving slowly through a bottleneck, which is frequently the case. In
that situation, merging early provides absolutely no benefit to anyone.
But in those instances
when traffic is
free-flowing through a lane drop (like in the photo below), then the early merge is the best
thing to do. Merging
early in this situation is safer and helps to
maintain the free-flow of traffic because, as mentioned before, drivers
who wait until the very last minute often need to slow considerably or
even come to a
stop in order to merge, or will sometimes just shove themselves into
the through lane. Someone in the through lane then has to slow
considerably or even stop to allow them to merge, which then causes the
person behind them to slow or stop, and the dominoes fall from there
and becomes the genesis of a
traffic jam or, worse, a rear-end collision. Merging well in
advance in that
situation allows drivers to find
and enter a gap when other drivers only need to make minor
adjustments to their spacing while maintaining speed, thus preserving
the
traffic flow.
So
to summarize (and because many people like things boiled-down to
simple bullet points):
When traffic is already slowing
or congested, use the Zipper Merge. Merging early is pointless and even counterproductive in this situation.
When traffic is free-flowing,
merge early. Doing so in this situation is safer and can prevent congestion from forming.
This is an example of a time NOT to use the Zipper Merge (Photo source: Oregon Dept. of Transportation)
Zipper Merge status in Texas
While
the Zipper Merge is being promoted in other states and by AAA, and is even the law
in places like Germany, it's still virtually unknown in headstrong Texas. TxDOT
studied it over a
decade ago, but it has not been officially adopted for widespread
use. A
blog posting by TxDOT's San Antonio office a while back was the
first mention of it I've seen in Texas in recent years, and TxDOT's
Waco
district reportedly implemented it at select
work zones in the Temple area for a time. Perhaps as more
states implement it and have good results with it, Texas will join the
party.
Other
sites of interest There are a lot of sites about the Zipper Merge,
but here are a few good ones.
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Cable median barriers
Fortunately, recent research and
experimentation is helping to inform the debate. Unfortunately,
like so many things in
life,
The "late
merge", known more descriptively as the "Zipper Merge", is
when drivers fill up both lanes and then take
turns merging one-at-a-time
at the
point where one lane ends. That one-at-a-time merge is where
the "zipper" name comes from.
