I am a new prius owner, one week. i drove it home, about afifty mile drive, drove it back to the dealer to have leather installed and drove it home again. Each of those trips i averaged at least 56 mpg. Here at home ,whe we go shopping etc we drive between 15 to 29 miles and my mpg is 44. The terrain is about the same. Why the big difference? By the way we love the car. MEMMO
The short trips don't allow the engine to warm up to optimal temps. You're probably stopping, allowing the engine to cool while you shop, then starting again. Be sure to read my Article.