This study compared whether commercial motor vehicle drivers spent less time looking at the roadway while cruise control was engaged. The trucks in the study were equipped with commercially available systems that provide adaptive cruise control (ACC), which uses radar to regulate headway in addition to speed when following a lead vehicle. Three metrics were analyzed to assess drivers’ eye-glance behavior during periods of traditional cruise control usage, full ACC usage, and manual car-following: total eyes-off-road time (TEORT), durations of glances off-road, and number of glances off-road. Drivers were observed to spend less time looking at the forward roadway when cruise control was engaged. Drivers were observed to spend less time looking at the roadway when ACC was engaged compared to when manually following a lead vehicle. This difference appears to be due to the truck drivers taking longer glances away from the roadway rather than taking more frequent glances away from the roadway. These differences are important for system designers to consider, as drivers are expected to maintain their attention on the roadway while using driver assistance technologies.