But not completely interchangeable in neither Swedish nor English. All streets are roads, but all roads aren't streets. Roughly, gator are more what you'll find in the city, while vägar connect the cities.
Roads and streets really are interchangeable in English though. Especially in a sentence like this. Imagine a politician only paving within the city because his constituents said they want "new streets" instead of "new roads"
No, folk isn't used for a single individual. In the singular, ett folk is used like 'a people' – about a group of people. In the sentence above, most likely the population of a whole country or city, seen as a group.