Yep, what John said, you need to contact your municipality for them to come and survey how much more driveway you are allowed. They also spraypaint where you can and cannot dig aswell (ie. water pipes, gas lines etc.) You also have to pay them to have the curb cut where the extension will be, which you also need permission to do.
I just had mine done in September so if you have any more questions, let me know.
Joey