I posted this in another thread on the same subject. Most of the time the reason that you do not achieve current EPA fuel economy values is due to forces outside your control. Some factors are certainly within your control though.
Factors affecting your FE ( and everyone else's also, btw ) in decending order of importance...
1) Towing anything is a huge penalty possibly as much as a 50% reduction in FE
2) Lots of weight in the vehicle, passengers cargo etc. ( EPA tests are done empty )
3) Short trips under 10 min - deduct 20% from your 'Norm'
4) Snow, Rain, sleet - deduct 15%
5) Strong head wind - deduct 10%
6) Cold weather - deduct 5 - 10%
7) High speed driving 0ver 70 miles per hour - deduct 5 - 10%
8) Many starts from a dead stop ( going from stop sign to stop sign to stop sign ) - deduct 5 - 10%
9) Terrain - fortunately 'what goes up..' usually this balances out on a RT
10) Winter fuel - deduct 2 - 5%
Now these are cumulative, so short trips with a lot of stops ( -20% )( -5% ) in winter ( -7% ) on slick pavement ( -15% ) can result in as much as a 40 - 50% loss from your personal 'Norm'. The bright side of this is that your 'Norm' is higher than most others at 39 mpg. If your Norm was only 26 mpg for example you might expect to get 13-15 mpg.
This is really really important when you consider how much more fuel you use in cold weather but also how much less you use relatively to a an ICE-only V6 driver. ( See below )
TCH 'Norm' @ 39 mpg uses 25.6 gal per 1000 mi driven
TCH 'Winter' @ 25 mpg uses 40 gal per 1000 mi driven
ICE 'Norm' @ 26 mpg uses 38.5 gal per 1000 mi driven
ICE 'Winter' @ 15 mpg uses 66.7 gal per 1000 mi driven
In 'Normal' driving an ICE driver will
only use about 13 gal more than a TCH driver for every 1000 mi. In 'Winter' however, that ICE driver will now use over 28 gal more than a TCH driver for the same 1000 mi.
Enjoy your hybrid

. It will be Spring soon.