A year of declines has concluded with FOX drawing its lowest average rating for NASCAR since the net began airing races in ’01.

Excluding the rain delayed Coca Cola 600, 12 NASCAR races averaged a 5.1/11 rating and 8.5 million viewers on FOX during the 2009 season, down 11% in ratings and 9% in viewers from a 5.7/12 and 9.3 million last year, and the lowest rated season ever for NASCAR on FOX.

Last Sunday’s Autism Speaks 400 drew a 4.0/10 final rating on FOX, down 11% from a 4.5/11 for the same race last year.

Every single, solitary NASCAR Sprint Cup telecast on FOX — all twelve races, the Budweiser Shootout and Daytona 500 Qualifying — saw declining ratings this season. 10 of the 12 races saw double-digit declines, including the last nine.

Despite the declines, NASCAR on FOX easily topped its competition. The 5.1 rating for NASCAR races on FOX is 65% higher than the 3.1 average for the ’09 NBA Playoffs (not including the ongoing NBA Finals) and 16% higher than the 4.4 for last year’s MLB Playoffs (including the World Series).

Additionally, the 8.5 million viewers is 42% higher than the 6.0 million for last year’s college football bowl games (including the BCS), and is only slightly off from the 8.9 million viewers for last year’s NCAA Tournament (including the Final Four).

Ratings for NASCAR on FOX in 2009.

Asterisk (*) indicates race was moved to another day because of rain.