[xyzzyz]

> One interesting thing that points out is that internal combustion engines are also about 15% less efficient at cold temperatures.

They are less efficient at cold engine temperatures, but more efficient at cold air temperatures. This means that in cold winter, once the engine warms up (which might not take place on short routes), internal combustion engines are more efficient than in summer.

[anamexis]

That may well be, but it seems like the 15% is a high-level number that takes a lot of factors into account, such as power used by heating accessories, and the fact that cold air is denser (more air resistance).

https://www.fueleconomy.gov/feg/coldweather.shtml

My original wording was inaccurate, as it's more about ICE-powered vehicles than the engines themselves.

[xyzzyz]

That sounds reasonable: note that I said that on short routes the engine might not have a chance to warm up.

Your source, however, quoted this 15% figure for city driving, I think that’s worth stressing as well. I wonder if they have any data for highway driving. I’m too lazy to Google, though.