2001 Honda Civic I used to get better Mileage from my Honda

Not sure the part of the country you live in but cold weather will beat down that mileage as a starter. Next I would look at the air filter. Check the PCV valve for operation. What about a look at the plugs to see if they are burning good and that the gap in set right? The list of things to check is long. I suppose you notice no difference in the way the engine runs or handles.

I usually make a habit of putting fuel injector cleaner in my engine every time I get an oil change done. It certainly can't hurt. Have you tried anything like this?

Check your tire pressure too - that'll definitely have an impact on your economy. Just make sure you take the reading when the tires are cold, or driven less than 1 mile to a service area for an accurate reading.

Winter's rough because of Salt, Sand, and other junk on your car. You can try washing it too, this will help eliminate surface friction.

In terms of highway, my 2000 Civic LX gets around the same mileage. I have an 11.8 gallon tank, and I'll go around 400 miles purely highway before I have to fill 'er up. City though I'm looking at around 300.