Alberta driver's knowledge test: what is the difference between these two signs?

[alxms10]

Hi guys

I am preparing for the Alberta knowledge test. In principle, what is the different between the two signs below which seem to tell the same message, The one on the left is a designated lane sign and the one on the right is a permissive sign. Does anyone know?

 

[k.h.p.]

The black one is used on roads to tell you what direction is lane is intended to go. The white one is used at intersections to tell you how to proceed b

 

[alxms10]

The black one is used on roads to tell you what direction is lane is intended to go. The white one is used at intersections to tell you how to proceed b

This is great, I never really thought of it that way. Thanks very much k.h.p. for clarifying this