I was reading this Consumer Report's blog report on the '08 CTS by one of their testers - Gabe Shenhar who's a Mechanical Engineer and a former BMW driving instructor.
Quote » When pulling the turn-signal stalk toward you, there is no flash-to-pass if the headlights are off as they would be during the daytime. This is a feature so basic and universal, it never dawned on me GM would omit it.
The new CTS' optional HID (High Intensity Discharge) headlights use bi-xenon bulbs for low and high beams. Apparently, GM was concerned about bulb longevity, or wanted to save some money by omitting a dedicated lamp solely used for flashing. Subsequently, we discovered that our Buick Enclave lacks flash-to-pass as well.
Flash-to-pass (a.k.a "optical horn") is used to communicate with other drivers for warnings or courtesy. It often means "Please let me pass, I'm going faster than you." Other times it means "Go ahead, I'll wait." In the extreme, less communication between drivers can have an adverse safety consequence. It is particularly odd that the CTS lacks this feature. After all, the car is intended to be sold in Europe--and, in particular, Germany--where stalk flashing on the autobahn is the second most used feature after the gas pedal. How hadn't anyone discovered this on the way to and from the Nurburgring track, where the CTS was developed?
And after looking at the comments following the article -
Apparently, no one in America uses their headlights to flash people to pass or for warnings or courtesy.
Is this your experience? I use my headlights all the time to signal other drivers - either for passing on the left lane on the highway or to tell people or cars to change lanes, or move.