My worst-ever Insight commute was on December 15, 2000. Went 25 miles home in five hours at 2-3
mph on iced-up roads - 25mpg. Considering I went the first 4-5 miles before traffic turned into a parking lot, it potentially was as bad as 20mpg from that point on.
I can't talk about snowbanks, but last month along Hwy 287 west of Witchta Falls, I tried to park on a dirt road along the highway. Some spots had six-inch sand and was almost trapped, so I returned to the highway.