Shoulder lines are generally interrupted outside built-up area to make the driver be aware the presence of crossing bicycles and pedestrians, driveways and stopping cars. Wider roads sometimes have a single, but in most cases have a double centre line. Interrupted center lines mean overtaking is allowed, a solid line means overtaking is not allowed, depending on which side of a double line is solid. Smaller roads and roads where bicycles are allowed generally do not have center lines, and many country roads have no lines at all. Sometimes there is a center line only in sharp curves.