If you're traveling this holiday weekend, you might want to know the most efficient way to merge--and it's not what most drivers consider to be common courtesy.

Say you're driving along in the center lane on a traffic-filled highway, and the left lane is ending in a few hundred yards, due to construction or the way the road is built. The polite drivers in that left lane put their blinkers on right away, and move over as soon as someone lets them in. The rude drivers zip to the end of their lane--passing you and many other drivers in the center lane. Then they merge in as soon as they can, effectively cutting in front of you and other center-lane drivers in the process.

You might be annoyed enough to respond to one of those rude drivers with an obscene gesture. But guess what? A lot of studies show those rude drivers are helping traffic flow better. It makes sense if you think about it: Those apparently rude drivers are putting more of the roadway to use and thus helping speed things along, in much the same way water flows faster through a funnel than through a straw.

It makes such a big difference that a number of states have undertaken projects to actually teach drivers to stay in the closing lane until the end, and then take turns merging in (or "zipper merge") right at the end of the lane. Colorado posted zipper instructions to its Facebook page. It also experimented during a highway project a decade ago with signs along the about-to-close lane that said "Use both lanes during congestion," then "Use both lanes to the merge point," and finally, at the end of the closing lane, "Take turns. Merge here." According to The New York Times, that experiment led to a 15 percent increase in traffic flow through the work zone and a 50 percent shorter line.

Kansas, not to be outdone, created its own hokey animation telling people why they should zipper merge.

There's only one problem with all this. Most drivers still consider people who drive past a waiting line of cars and then merge in at the front of the line to be unconscionably rude. So much so that, researchers found, many drivers will actually straddle two lanes or tailgate the car in front of them in an attempt to prevent this behavior. People are liable to give you the finger if you fly to the end of the closing lane and then zipper-merge your way into the next lane--or maybe worse. One traffic exec in Colorado, seeing a closing lane due to construction, rushed to the end of that lane to put zipper-merging into action--and another motorist responded by throwing a burrito at her car.

So while you're on the road this weekend, if you're in heavy traffic and your lane is ending, feel free to zoom to the end and merge into the next lane at the head of the line. But if you see someone wielding a food item, you might want to duck.