Phobias

Ever dealt with a phobia? I have a long standing one that was always in the background since I was in high school. Now it has become more pronounced and I am wondering how best to deal with it. I have a fear of heights, especially when I am driving a mountain road on the outside edge. This started when I was a teenager driving to Surfside, Texas over the bridge over the Intercoastal Canal. It hit me big time this trip when I drove the Trail Ridge Road in Rocky Mountain National Park. I dealt with it also at Arches and Canyonlands National Parks and even today driving to Cove Palisades State Park in Central Oregon.
As I was driving the Trail Ridge Road my phobia was a real problem for me. And, as much as I tried to reason my fear away it remained. I am a good driver. I know how to control my vehicle. The road is plenty wide. I am not going to fall off. There are a lot of other people on the road in both bigger and smaller vehicles. They are not falling off the road. Many of them are probably horrible drives and they are not running off the road. All of these thoughts and more ran through my head but the fear remained. It is unreasonable fear. It is fear that cannot be reasoned away. It is real.
How to people overcome phobias such as this? I'm going to do some reading because I am determined to understand and overcome this. So that I can stand on the edge of the canyon, as I couldn't today.