So ROI is coming to a billboard near you. The story yesterday in the Tribune, of a Chandler, Arizona company’s technology that can ID the radio station of a car passing by, is almost like the story of RFID tags for patients.

But not quite. MobilTrak detectors are attached to billboards that read the radio frequencies of vehicles on California freeways –not the identities of the cars themselves. Then, by coss referencing this with radio listener demographics, companies can serve up ads that are relevant.

That’s the theory. In practice, it will be limited to digital billboards, and targeting will not be able to serve on-to-one ads (since many vehicles with very different demographic could pass a billboard at any given time.) But at least, the information could give advertisers hard numbers to go by.

In a world where everything in marketing is more or less measurable, this is one more piece in the ROI puzzle.