Do in traffic miles on the highway count towards "highway" miles?

Hi. I've been wondering how good the mileage my 2007 Toyota Camry gets. fueleconomy.gov says it should be getting about 21 mpg in the city and 30 mpg on the highway. But for the most part the only highway miles I put on it are to and from work during rush hour traffic both ways. So I'm wondering if the miles I spend on the highway commuting are actually getting me those 30 "highway" miles or is it closer to the 21 "city" miles since I'm in stop and go traffic?