Network Analyst works with network datasets that model the connectivity and attributes of the road networks. The type of attributes that Network Analyst works with are "costs" that can be minimized for finding a shortest path. Network dataset's can model historic "costs". Generally this is the free flow travel time on an edge as well as the slow down based on a time profile. So the historical traffic is about the change in the travel time NOT the volume of cars going by which is what ADT models. The live traffic maps that you see are based on slow downs on various roads. The traffic volume can be one way to infer the slow downs but that is not the goal of network analyst. It consumes traffic slow downs for travel costs per road segment.
You can read more on this topic here:
What is traffic data?—Help | ArcGIS Desktop
BTW, it was not clear from your post what you wanted to achieve with traffic volumes data.
Jay Sandhu