625 ILCS 5/11-1409: Driving on mountain highways.

The driver of a motor vehicle traveling through defiles or canyons or on mountain highways shall hold such motor vehicle under control and as near the right-hand edge of the roadway as reasonably possible and, except when driving entirely to the right of the center of the roadway, shall give audible warning with the horn of such motor vehicle upon approaching any curve where the view is obstructed within a distance of 200 feet along the highway.