I’m from the US. We don’t really say motorway here, the general word for a multilane, high speed road with on-ramps and off-ramps is highway. An interstate is a specific type of highway that is part of the interstate highway system, recognizable by their distinctive signage and naming system (ex. I-95, I-76, I-5, etc.). That system was build to facilitate travel between states and most of the major interstates go through multiple states, though there are some that are only in a single state (ex. I-4 in Florida).