Light control is probably the biggest challenge to a good projection setup. The subterranean nature of London's subway is pretty much ideal in that regard, and now CBS Outdoor has brought its cross-track projection (XTP) system to the Tube. The Piccadilly Circus, Euston, Bank, Liverpool Street and Bond Street stations have been outfitted with a total of 23 14-foot screens that are getting HD video ads beamed onto them, sans audio (thankfully). There are plans to build out to 150 XTP screens and compliment them with 2,000 digital screens Tube-wide, which all fits in with CBS Outdoors' plans to bathe subway riders in advertisement. If ad-targeting tech is brought into the equation, we see some potential for really embarrassing hilarity. Meanwhile, London readers are encouraged to let us all know how the picture XTP quality is holding up!