I have a 2006 Honda Insight, 65 mpg winter, 70+ mpg summer. A bike fits in the back with the front wheel removed, but I had a receiver installed so I could carry two bikes. That said, bikes on the back decrease fuel economy . . . a lot! Approx. 10 mpg less with bikes on the back.
Here is a photo of my car with the bike rack on:
Rick / OCRR