Tire pressure

My tire pressure was way too low on the front two tires of my Civic Hybrid. I inflated the tires this morning and although I seemed to get better mileage before I got on the freeway, the overall result wasn't that different. I got 58 mpg on the 40 mile trip to work. I think I should be closer to 70 on the way home, assuming I can find a truck to draft behind.