It really depends on when the road was built. If the road is new it would be built to a standard size however if the road is a country area or village it can really be any size it likes. In rural and remote Scotland many of our roads are very narrow and there are often single track roads with passing places. In older towns and villages there are roads which are hard to squeeze a car through. Get to know the area you are modelling and take a few pictures of what you are trying to recreate and use this as a basis for your model.