Stuck Behind A Prius

As I drove to work today I decided to take out my iphone and snap a quick shot of something that summarizes what frustrates the heck out of me on a daily basis.

 During my daily commute to and from work there are 3 things that I can almost guarantee that will happen:

1. I'll some how get stuck behind a Prius.
2. The Prius that I get stuck behind will almost always have just merged into the fast lane ahead of me only to slow down to 55MPH messing up my nice pace of 70-75 MPH.
3. The Prius in front of me will almost always leave about 10 car lengths of space in front of them while they continue to drive at a snail like 55 MPH. 

I'm always amazed at how frequently this happens and I try to think about what the heck is wrong with these Prius drivers that makes them feel the need to merge into the fast lane if they're not going to keep pace. 

My questions for Prius drivers are:

1. If Prius driver is going to continue to drive 55 MPH, why not stay in the middle lanes?  Why do they feel the need to merge into the faster lanes only to continue to drive at the same slow speed that they were driving in lane that they decided to merge from?  Obviously they are not in a hurry to get anywhere, so why get into the fast lane?
   
2. WTF is up with the 10 car lengths of space that Prius driver almost always leaves in front of them?