score:5
The two signs are WA-5-L "Left Reverse Curve" and WA-4-L "Left Reverse Turn".
The difference between a curve and a turn is how much the road turns/curves, and how much you should slow down to go through the turn/curve, i.e. the same different which exists between "turn right" and "curve right" (full list here).
In both cases, the road first turns/curves left, then turns/curves right. The opposite signs (WA-5-R and WA-4-R) also exist.
If there are more than 2 curves, then WA-6-L "Left Winding Road" is used (if the first turn is to the left, otherwise WA-6-R).
Haven't found the equivalent for Alberta, but BC have a "Manual of Standard Traffic Signs & Pavement Markings" which gives (pages 69 to 72) the procedure to determine the max advisory speed, and from that and the max legal speed, the type of sign which should be used (turn or curve).
Upvote:-2
The page has an error.
Both of these signs mean a left curve followed by a right curve, also called an S-curve. That also exists in a mirror-image for a right then left.
This is distinct from "winding road" which means a whole ton of curves, sequence not specified, so you could have that exact sign with a first curve to the left.
As others say in answers, the different styles of sign reflect different sharpness of the curves ahead. They use the words "Curves" and "Turns" to indicate the relative sharpness and the necessity for you to adjust speed.
If you ask me that's too subtle, and where speed reduction is needed, a warning sign to that effect should be included. I also don't consider that to be proper use of the word "turn". A "turn" to me is a sharp 90, as at an intersection.
Upvote:7
For drivers, the difference is that turns usually are more difficult to manoeuvre than curves and may require a greater attention and a lower speed.
For the technical differences, this is explained in the guidelines from Alberta Transportation: TURN AND CURVE SIGNS, REVERSE TURN AND REVERSE CURVE SIGNS. The difference between a turn, sharp curve and curve is outlined in the table provided in the first document, based on the difference between recommended safe speed and the normal speed limit on the road.
Note that these guidelines are recommendations and the provincial or local infrastructure department may decide to adopt a sign different from the guideline recommendation if needed by the circumstances (e.g. using reverse turn signs on a reverse curve where accidents are more frequent).