Q: In the diamond lane, what does the single white line with two yellow lines next to it mean?

HOVLANE

 

Any kind of yellow line signifies oncoming traffic on the other side of the line.

A solid white line means you can not legally change lanes across that line. If you’re in the diamond (HOV) lane, you must wait until the line becomes dotted/dashed and then change lanes.

Reference:

White Lines, Yellow Lines, Solid Lines, Broken Lines – BC Driving Blog

Using HOV Lanes – DriveSmartBC