All I can speak for is CA, and my recent observations in WY. The CHP went to the right side approach probably 15-20 years ago (altho some dummies still walk up on the drivers side). They did that because we were having so many officers picked off by passing traffic while standing at the drivers door. In years past I have actually had my butt brushed by a passing car doing about 75. That might have something to do with my grey hair falling out. In WY I have seen officers do nothing but left side approaches, then go back to sit in their vehicle to take care of the paperwork. Not a good place to be sitting when someone rear ends your patrol vehicle. Not to mention your delayed response when the bad guys you are writing a ticket to decided to jump out and blow you away...