Hi,
They are and can be used interchangeably in most contexts. However, "streets" are usually found in towns and cities and often have houses and shops along them, whereas "roads" sometimes do not if they are in rural areas. Having said that, a road may have buildings on either side, but its primary function is to provide a route for transportation.
For example, I would say, "The road through the countryside from City A to City B is very scenic and peaceful." Here, it would not be natural to use "road" unless the two cities are seamlessly connected.
To summarise, in cities, the two terms can be used interchangeably, but in rural areas, streets that predominantly connect towns and cities are usually called roads.
Hope that helps :-)