Running through woodland terrain in southern Calhoun County, M-66 passes through Athens, along Graham Lake and continues to the outskirts of Battle Creek. The highway widens first to a four-lane, limited access expressway south of the Lakeview Square Mall before becoming a full freeway at the interchange with I-94. It is at the transition to freeway that M-66 starts its concurrency with I-194. I-194/M-66 is known as the Sojourner Truth Downtown Parkway, but the locals still use the former semi-official nickname, "The Penetrator". The southern section of the freeway has the highest traffic levels along M-66 as measured by average annual daily traffic (AADT) in the survey conducted in 2009. The Michigan Department of Transportation (MDOT) calculates the AADT value as a tally of the average number of vehicles using a given stretch of roadway. I-194/M-66 carried 25,200 vehicles on the average day during the year; 980  trucks were included in that traffic. The freeway continues north into downtown Battle Creek along part of the Kalamazoo River and crossing a branch of the Canadian National Railway and Norfolk Southern Railway before ending at the at-grade intersection with Hamblin Avenue. I-194 ends, and M-66 continues northeast out of the Cereal City on Division Street and then northeast on Capital Avenue along the Battle Creek River.