What is the "gore area"?
Wikipedia has a nice description of the gore area. In summary, the gore area is the triangular space between the highway and an entrance or exit ramp. The gore area is defined by the white lines painted on the road that meet in a point where the highway and entrance or exit join.
There is also the "physical gore". This is the unpaved area of the gore area and therefore smaller than the gore area. For purposes of the gore area violation, we are dealing with the entire gore area.
The gore area is often referred to as the "gore point", probably because of the point that is formed by the joining of the highway and entrance or exit.
What is the violation?
If your vehicle enters the gore area, you are committing a traffic violation according to A.R.S. 28-644(A)(2). The one exception is if your vehicle breaks down and you are unable to stop outside of the gore area. In that case, you may temporarily stop your vehicle in the gore area.
Why is this a traffic violation?
Vehicles entering the gore area is a safety issue. You may notice while you are out driving that many gore areas contain concrete barriers. As discussed above, the physical gore is no paved. Highways and entrance ramps are designed to guide vehicles on and off the highway safely. If you are crossing a gore area while you are trying to exit the highway, you have missed the opportunity to do so safely and run the risk of driving off the road or hitting a barrier. Additionally, other motorists on the highway are not expecting a motorist to be approaching from a gore area.
Arizona made crossing a gore area a violation after an Arizona Department of Public Safety officer was struck and killed by a motorist entering the gore area.
This is a civil violation and if found responsible, the court will impose a fine. However, if it results in serious injury or death, it can result in a criminal charge. This is also a 3-point violation like civil or criminal speeding.
If your vehicle was breaking down and you were unable to stop anywhere other than the gore area, that would be a good defense. You might be able to argue that another driver's reckless driving forced you into the gore area to avoid a collision. You might be able to argue that the citing officer was not in a position to observe whether or not you were in the gore area.
Saying you crossed the gore area because you would have missed your exit otherwise is not a good defense.