On 31 December 2010, an Embraer ERJ190 being operated by Air Canada on a scheduled passenger service from Denver to Chicago was about to begin the take off roll from the full length of runway 34R at Denver in normal day visibility in accordance with ATC clearance when the flight crew observed the headlights of a vehicle approaching along the runway towards their position. The aircraft held position and advised ATC who had previously been unaware of the presence of the vehicle.