Huge City/HWY MPG difference

Factual Questions
1

I was reading the savage on Wheels review of the Chevy Cruze. What jumped out at me was the difference in mileage, City 27, Highway 46.

All but a few vehicles get better mileage highway vs city, but 19 seems like an awfully big jump to me.

Is it because it’s a diesel, or are there other factors here?

2

gearing, possibly. it could have an incredibly tall 6th gear to keep the engine barely loping over idle at highway speeds. a diesel would probably have the torque to keep from obviously lugging.