Merging

When a road narrows, multiple lines of cars may have to slide together to fit into one line. This is "merging".

Some traffic signs may state "Merge In Turn", meaning that left and right columns should zip up like the two sides of a metal fastener down the front of a coat. Watch out for markings called "deflection arrows", telling which lane should merge into the main line of traffic. Principles are the same if you need to change lanes.

So, read far enough ahead to [1] check what's behind, [2] signal if someone could benefit (and it's safe), then [3] balance your speed and remaining distance to keep checking when it's safe to move over, without stopping completely.