here is an informative article from the City of Lethbridge about merging;
http://www.lethbridge.ca/living-here/getting-around/Streets-and-Roads/Pages/LateMerge.aspx
Late (Zipper) Merge
When a lane is closed for construction, motorists may be instructed to use a technique called a late or zipper merge. A late merge occurs when motorists use both lanes of traffic until reaching the defined merge area, then take turns merging into the open lane. Vehicles in the merging lane must signal, and drivers in the through lane must each let one vehicle merge. This technique has proven to make the traffic flow more quickly and efficiently for drivers in both lanes.
There are several benefits of the late merge:
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Reduces differences in speeds between two lanes
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Reduces the overall length of traffic backup
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Creates a sense of fairness and equity that all lanes are moving at the same rate
How is it different from a regular merge?
Typically when drivers see the first “lane closed ahead” sign in a work zone, they slow too quickly and move to the lane that will continue through the construction area. This driving behavior can lead to unexpected and dangerous lane switching, serious crashes and road rage.
With a late merge, when you see the “lane closed ahead” sign and traffic backing up, stay in your current lane 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”. Drivers in the through lane must take turns merging.