One of the first things Gabe did when he moved out of his parents' house was learn to drive. Aggie refused to teach him, claiming he was too protective, so Lucifer volunteered.
For the most part, Lu was a good teacher, and Gabe a good student. However, just like during school, Gabe froze when it came to public performance. He was perfectly fine driving back roads and parking lots. He was even cool off- roading at the dry lake bed just outside of town. But get him into city traffic, and it was like he suddenly forgot everything he'd learned. Other drives made him paranoid. He never knew what they were going to do, and he didn't like that.
After several abortive attempts to get Gabe to actually take his road test, Aggie finally agreed to be his co-pilot. It took his angelic lover babbling at him about unimportant little things for him to relax and drive comfortably. It was decided: Aggie would go with him for the road test.
Unfortunately, the DMV wouldn't allow Aggie to ride along, so he made himself invisible and sat behind Gabe, murmuring low enough that the test proctor couldn't hear him. It was in this way that Gabe managed to pass his driving test on the first go.
Now, whenever Gabe has to drive somewhere alone. he brings a CD of Aggie talking to keep him calm.