Welcome, bentjazz. If you're making short trips in cold weather, 30 mpg may be all you can expect to get until Spring and Summer come. I rented a Yaris automatic in New England for a week, and averaged 42 mpg for three tanks.
Keep your maximum speeds down - 55 or 60 mph on slower highways always beats 70 mph on the interstate. 40 mph on a frontage road will average 50+ mpg.
Coast as much as possible. Most people still have their foot on the gas half a block from red lights and stop signs. I start coasting to them 3 or 4 blocks away - in neutral, so my engine is turning 750 rpm instead of 1500 rpm.
Plan your routes to minimize stops. Even with our fuel-sipper 1NZ-FE engines, starting from a stop nets <10 mpg going to the next stop sign 2 blocks away. If you minimize those stops and starts, you can get that 50 mph cruising mpg, instead of that 8 mpg stoplight drag race wastage.
If your Yaris doesn't have an instantaneous mpg meter built-in, consider getting an
Ultragauge for $60.
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