Merging Guidelines

A driving lane may be blocked with orange pylons or signs for construction, a collision or many other reasons. When traffic merges into one lane, signs will be in place to warn drivers. Drivers should signal and merge into open lane when safe to keep traffic moving. In light traffic, it makes sense to merge as soon as possible.

On a busy street, when traffic is backing up, the zipper merge is most appropriate. A zipper merge means drivers use both lanes of traffic until the lane ends with a "merge" sign , when drivers from both lanes take turns merging in "zipper" fashion into the open lane. Vehicles in the merging lane must signal, and drivers in the through lane must each let one vehicle merge. 

Why use the zipper merge?
Zipper merging keeps traffic moving and is more efficient for drivers in both lanes. It also creates a sense of fairness and equity that all lanes are moving at the same rate. Zipper merging also helps reduce:

• differences in speeds between two lanes
• the overall length of traffic backup
• congestion on freeway interchanges

How is it different from a regular merge?
When most drivers see the first sign of construction, they quickly move to the lane that will continue through the construction area. This is appropriate when traffic is very light; however, in high-traffic/high-speed areas, this driving behavior can lead to unexpected and dangerous lane switching, serious crashes and road rage.

With the zipper merge, as you see the “lane closed ahead” sign and traffic backing up, select the shortest lane and stay in it up to the point of the "merge" sign. Then take turns with other drivers to safely and smoothly ease into the open lane. Don't worry about being “polite”. Drivers in the through lane must take turns merging.

It’s important to note that this makes the traffic flow more quickly and efficiently for drivers in both lanes. The key is to merge as late as possible.

So, I'm supposed to merge late?
Yes! As you see the “lane closed ahead” sign and traffic backing up, move into the shortest line up to the point of merge. Then take turns with other drivers to safely and smoothly ease into the remaining lane. Don't worry about being “polite”. When traffic is heavy and slow, it is much safer for drivers to use both lanes until the point where traffic can orderly take turns merging. Vehicles in the merging lane must signal and drivers in the through lane must each let one vehicle merge.