While driving using the VW Travel Assist (lane keeping) system, the vehicle was unable to ‘see’ the lane markings and Travel Assist disconnected. When this happens the display of the lanes changes from green to gray, but there is no warning. In the case where i was traveling about 30 MPH it took less than a second for the vehicle to steer off the road. The Adaptive Cruise Control remained engaged as the Travel Assist disengaged. Considering that VW has programmed in white and red warnings plus a sound to require the driver to control steering about every 10 seconds it seems to be minor addition to trigger those warning lights and sound if the Travel Assist disengages.