IDP issued in the U.S. is mere translation of the original driver’s license and it specifically indicates drivers still need to have original driver’s license from driver’s home country in possession beside IDP. My understanding is that such is situation because in the U.S. IDP is issued by a private organization, not a government entity responsible for maintaining driver’s license.

However, in Japan IDP is issued by the Metropolitan Police Department. IDP issued in Japan is an official document indicating a person is permitted to operate certain vehicles. Looks like rental car agents at Narita Airport was not aware that IDPs issued outside of Japan does not work same way as IDP issued in Japan. I am surprise that rental car agents, especially one work at Narita Airport are not properly trained in this. But again, same time people from various countries with driver’s license in various languages, rental car agents likely will not able to decipher name on the original license nor able to figure out validation date on the original license.

I guess same thing can be said about rental in the U.S. When Japanese person show IDP and original Japanese driver’s license to car rental agent at Chicago O’Hare airport, the car rental agent will have no idea what is written on the original driver’s license. Will have no idea about name, address, validation date, etc. All the agent can figure out is that the picture on the original driver’s license looks like the person standing in front.

About the scanners on toll roads in Japan, I think those measures how many cars are on the road. Use to determine congestion and average speed of vehicles on the road. I think information from those scanners are used to provide traffic condition and traffic information.