In the US, Interstate Highways with 3 digits are either spurs (first digit an odd number e.g. I-195, I-395) or circumferential "belt" highways (first digit is even e.g. I-695). The 2nd and 3rd digit refers to the major highway (e.g. I-95) that they are a spur or beltway off of. The Beltway plus the Key Bridge section forms a complete circle around the city (or did until the bridge collapsed). So it's not really confusing if you understand the numbering system which is quite different from British practice AIUI.
What is probably more confusing is probably that we have so many different categories of highways - Interstate, US highways (both part of the Federal system), state highways with their own numbering systems, and sometimes lower categories such as numbered county roads, farm to market roads (Texas), etc. Whereas you just have M, A, and B roads.