A common commute for me would be to extend the 5 mi. commute into 30 miles rolling terrain on the way in. And then on the way home, I'll do whatever interval makes sense. On KY(kill yourself) days, I'll turn off halfway home to do hill repeats on the LHAR (local hilly-ass road [that's Furman Rd. around here]). On recovery or normal days, maybe some one legged drills or fast spin or something.