You will probably have to go to each states DOT for that data.
I know in my state even though Interstates are Federal roads our DOT manages the traffic flow. However, I don't think they do a constant collection of traffic flow.
1. Looking for a file with Lat-Lon for US Interstate Interchanges. 2. Looking for a file with traffic counts passing each Interstate Interchange.
You will probably have to go to each states DOT for that data.
I know in my state even though Interstates are Federal roads our DOT manages the traffic flow. However, I don't think they do a constant collection of traffic flow.
I agree with Robert that each State DOT would be the only place you might find something like this. Interchanges between Interstates have a wide variety of designs across the US, so a single Lat/Long point to define them is not the way I would think you would see them defined and maintained in most GIS databases. Multiple stations at pretty widely spaced positions would be needed to track any traffic counts in most cases. My state DOT only lists ramp counts by County Post Mile (see ramps here and all other counts here for what is published). You would need the state network to translate these LR reference to a Lat/Long. The contact for my state is on the second link and you would have to contact them to see if they have the data in any format that is closer to what you want.
As the local DOT for my County we have not obtained such a network from the state or translated the state's counts using Lat/Long or these post mile positions using our own Countywide GIS Centerline network even though we are probably one of the more GIS oriented large Counties in my state. Although my County attempts to maintain our own unincorporated count stations locations on the County maintained network using GIS point locations, those locations are initially only defined descriptively. They currently require a separate geocoding process that is only periodically done at a much later date and those geocoded points are only for our internal use. The two way counts for my County's roads are only publicly published descriptively by offset direction from each cross street here with the explanation of the count data provided here.
