The Science of Traffic Patterns

Roundabouts, zipper merging, diverging diamond intersections…all of these are designed to improve traffic flow but seem confusing on the surface. After all, most of us were not taught to drive this way. Many people don’t know how to drive through roundabouts and diverging diamond interchanges because those are fairly new in the United States. Once they learn, they worry that other drivers in the same flow who haven’t learned how to navigate them could cause an accident.

Round and Round
Roundabouts incite anxiety in many drivers because they either aren’t sure how to drive in them yet, or they know others don’t know either, which is a recipe for an accident. These drivers often believe stop signs and stop lights are much easier to understand. However, studies have shown that roundabouts actually reduce injury crashes by 72-80% and all other crashes by 35-47%. They also keep traffic moving, causing fewer delays.

Do the Zipper Merge
Have you heard of a zipper merge? It's not the latest dance craze. A zipper merge occurs when a lane is closed ahead. The zipper merge encourages motorists to use both lanes of traffic until reaching the merge area, then take turns moving into the open lane. Most of the time, signs are posted well in advance of the closed lane, seemingly giving drivers have plenty of time to get over. Because of this, drivers who aren't aware of what the zipper merge is are usually  irritated by the driver doing the zipper merge. They don't realize that when drivers use the zipper merge method it helps maintain the speed of traffic and drivers can merge safely. It might seem counterintuitive, but when all drivers do it, it works. The downside to zipper merging is most drivers don’t see it as more efficient. Instead, they think it’s rude, which sometimes incites road rage. The reality is zipper merging reduces the overall length of traffic backup by as much as 40 percent.

Diverging Diamonds—A Driver’s Best Friend?
Diverging diamond interchanges are another new traffic flow designed to make driving through an intersection more efficient. They are designed to prevent drivers from crossing paths with other drivers. What makes it scary is it looks like you are driving on the wrong side of the road, but in this case you’re supposed to in order for it to work. These intersections direct drivers to turn left by crossing over to the other side of the interchange and then crossing back before leaving the interchange. From an aerial view, it looks like an infinity symbol. This pattern results in fewer accidents, a reduction in entering ramps the wrong way and better sight distance at turns.

Although changes in traditional driving patterns can be difficult to navigate and maybe even a bit scary, when they are used properly, they keep traffic moving right along in a more efficient manner.