Radar is a geolocation-tracking feature on billboards owned by Clear Channel Outdoor. The company launched the service in 11 U.S. markets earlier this week. Privacy advocates worry that the company will be able to collect massive amounts of information from smartphones in cars driving past. But Clear Channel receives aggregated and anonymous data from its partners, not personal information, a company official says. Senator Al Franken, a Minnesota Democrat, has asked the company to answer questions about privacy implications of the service.”]