Is there an international standard on the frequencies used by car toll tags?
Is there an international standard on the frequencies used by car toll tags?

That doesn't matter to your use case, your question is whether your standard interferes with your wifi, and I don't know the standard your car-tool collection points use. Neverless, yes, there are standards. Multiple standards.

I'm guessing that the Car-toll tag system uses the same frequencies used by Wifi.

Generally, systems operating in unlicensed / ISM bands are required to operate in a manner that avoids harmful interference with other system. I'd be greatly surprised if that wasn't the case for toll collection systems.
Even if they were operating on the same frequencies, that would pose no problem: the amount of data exchanged with the toll station would be very small, the communication hence very short, and since Wifi is a collision-detect and collision-avoidance system anyway, not any special in any way then say, you carrying a smart phone that actively pings previously seen SSIDs, or you bringing a bluetooth device, or a lot of other things.
So, I don't think &quot;interference with commercial infrastructure&quot; to be a likely reason. Also, why would your maps drop out? That kind of software is designed to work without connectivity for seconds to minutes, not for the milliseconds that your car and a toll system would be interacting. Same for music playback: your media player prefetches whole songs as quickly as possible, usually. I've never seen an audio player with less than half a second of raw audio buffer when streaming from anywhere. A data connection not being flawless all the time is normal, even for wired internet (Ethernet, DSL, cable, fiber...).
Probably, it's just software quality. Your car's wifi/entertainment system is running on shared resources as the toll collection system, maybe; maybe it's just &quot;confused&quot; by some broadcast messages sent over the car's internal communication buses.