A lot of them here are typically under the influence, usually alcohol, sometimes a combination of drugs and alcohol.
Other wrong ways are confused elderly drivers, who maybe shouldn't have a drivers license any longer.
Our simple diamond interchanges make it too easy for drivers to get on the freeways the wrong way. Cloverleaf interchanges are more difficult to accidentally get on the wrong way, but take up a lot more real estate around the interchanges.
ADOT is installing at least one diverging diamond interchange along the Loop 202 South Mountain Freeway segment in Ahwatukee (Phoenix). I believe it's been claimed that it could reduce the chances of a wrong way driver, without taking up any more real estate than a simple diamond interchange. However, reading about it (link below), it may not actually do so, according to the 4th paragraph.
Diverging diamond interchange - Wikipedia
Every time the issue of a wrong way driver comes up, there are several calls for wrong way spikes to be installed on the off ramps. However, engineers from several state DOT's across the country have studied that idea, and have come to the conclusion that they would not work, for several reasons. They are not designed for right way traffic travelling over 5mph, there would need to be a series of speed bumps down the exit ramps to slow exiting traffic down to 5mph, which can lead to long backups onto the freeway mainline, and increase the possibility of rear end crashes. They clog up too easily, and are high maintenance because of that. High speeds and clogging increase the chance of breakage, which can then damage tires of right way traffic. They are also not motorcycle friendly. And sometimes, first responders have to travel the wrong way on an exit ramp in order to get to an incident scene. So, wrong way spikes are not an effective solution to wrong way drivers on the freeways.
John
Peoria