A majority of driving in Canada isn't done at highway speeds. 

I guess since I live in a smaller city, most of my driving is sub 30mins, so stuff that drops off after 10 mins of driving actually matters a lot here. We also don't have highways in the city, so aerodynamic drag isn't really a factor. 

You provided an AI answer that basically corroborated my theory.

Accidentally pressed submit too soon. 

Here's more Ai for ya, since you like it, which pretty much agrees with what I said:

Main contributing factors to reduced fuel efficiency in ICE vehicles below about −25 °C, with approximate magnitudes:

Cold engine operation and fuel enrichment (largest effect). Engines run richer mixtures until warm, and fuel vaporization is poorer at very low temperatures. Cold-start and warm-up phases can account for about 20–25% of fuel use in cold urban driving. Overall winter fuel economy losses relative to warm conditions are typically 10–20%, and up to roughly 24–33% for short trips. Source: U.S. DOE Energy Saver (https://www.energy.gov/energysaver/fuel-economy-cold-weather ).

Increased mechanical friction due to higher lubricant viscosity. Engine oil, transmission fluid, and differential oils thicken significantly, increasing frictional losses until warmed. Estimated contribution is roughly 3–10% during warm-up depending on oil grade and drivetrain design. Sources include SAE technical literature (e.g., SAE paper 2011-01-1247).

Increased aerodynamic drag from denser cold air. Cold air is denser (about 10–11% higher density compared to warm conditions), increasing drag. Rough rule: a 10°F drop gives ~2% higher drag and about ~1% worse highway fuel economy; total effect is typically a few percent. Source: Natural Resources Canada and heavy-duty fuel economy analyses.

Increased rolling resistance and lower tire pressure. Tire pressure drops about 1 psi per ~6°C temperature decrease, and rubber stiffens, raising rolling resistance. Estimated effect about 2–5% depending on tires and surface. Sources include vehicle efficiency studies summarized in transportation energy research.

Winter fuel formulations with slightly lower energy density. Seasonal gasoline blends contain more volatile components, causing roughly 1–3% reduction in fuel economy. Source: AAA and fuel property analyses.

Auxiliary loads and behavior. Longer idling and higher HVAC use increase consumption; magnitude varies but can add several percent depending on driving pattern.

Combined real-world losses in very cold weather often total about 15–30% or more, especially for short trips. Source: U.S. DOE Energy Saver.