Depends on how you drive it.
Depends on how you drive it. You don't need to drive it slow to get good fuel economy. You need to step on it and get it up to your cruising speed then let off and start cruising. It acceeleration that eats the gas and the shorter you are accelerating and longer crusing will get you the best MPG. Barely stepping on the pedal and slowly getting up to speed is making your time during acceleration longer then as oppose to just smashing on to quickly get to your crusing speed.
Also repeated cols starts eat up a lot of gas. The Prius has to warm the engine and to do so burns more fuel. Not to mention keeping the heat up when it's cold will force the engine to stay on longer. Definitely the colder the weather worse MPG you'll get.