bonzer’s mention of CERN makes me wonder: Are there any tariffs, duties, or other import/export regulations that apply to the protons in the particle beam?
Cripes. I thought Vancouver BC was the only train station with preclearance precisely because the train made no additional stops before the border. They don’t do that on the VIA/Amtrak train from Toronto through Niagara Falls because people get off in Niagara Falls, Ontario.
The classic answer to this is, of course, the Large Hadron Collider that straddles the border between France and Switzerland. Without a shadow of a doubt the largest such structure in the world and one that incurs onto both territories to the greatest extent.
In case you wonder about the name Morokulien it’s made up from Norwegian moro and Swedish kul, both meaning fun in English.
Yes, each particle is charged. 
Relatively few, I understand.
The runway at Coolangatta airport doesn’t straddle an international boundary, but it does cross the NSW/QLD border. In summer, when the two states are in different time zones, you can have the fun of losing or gaining an hour as you land or take off.
Last week I stumbled across this National Film Board documentary about the town. It was made in 1955. I wonder what life is like there now…