Ten years after it first introduced the OnStar safety and navigation system, General Motors Corp. is making a significant upgrade, called Turn-by-Turn Navigation, which will allow customers to get real-time directions as they're driving, according to the Associated Press.The Turn-by-Turn Navigation system will debut on the Buick Lucerne and the Cadillac DTS in March and will gradually be added to other GM vehicles. GM says it will be available on approximately 1 million cars and trucks by the 2007 model year.Right now, OnStar owners can press a button to dial an operator and get audio directions based on their location, which is pinpointed by satellite. The directions are read off immediately. The system lets customers tape the directions and play them back as they drive, but it doesn't keep track of the vehicle's progress as it follows the route. With the new system, drivers will call an operator and ask for audio directions, which are downloaded by the operator. A computerized voice will come on and talk the driver through each step of the route as they're driving. If the driver leaves the route, the system will alert the driver and recalculate the directions based on the new location.The exact cost of the Turn-by-Turn Navigation option was not divulged immediately by GM, but a spokesman said it will be less than $34.95 per month customers currently pay to access directions from OnStar because it is less labor-intensive.Around 4 million drivers now have GM’s unique OnStar service. GM plans to make it standard on all its vehicles by 2007.