That's not a distinction I've ever encountered (from Indiana, US). I'd have said they were interchangeable, but if you told me there was a difference, and asked me what it was, my best guess would have been that a street is urban and a road is rural, just based on experience with whether something tends to be named "XXX St" or "XXX Rd". Wiktionary tells me that a street is within a single city/town, while a road runs between cities/towns, which I guess seems about right to me?