In my experience, calle is the most common word used for road. Camino is usually used for a trail.

I use:
"calle": for street or avenue
"camino": for road
"carretera": for main road
"autopista": for highway
"calle principal": main street

The above is simple. I have been in Mexico and very small dirt roads have been called "camino" and "carretera".

Daniel, My experience has been similar. I have seen different words used for the same road. However, I was trying to at least narrow it down to a single use word for road. Remember, none of these people have any type language background, so I was attempting to not overwhelm them with multiple words.

Vance

Daniel, My experience has been similar. I have seen different words used for the same road. However, I was trying to at least narrow it down to a single use word for road. Remember, none of these people have any type language background, so I was attempting to not overwhelm them with multiple words.

Vance

Then I would suggest camino, because it carries the connotation of path as we also use road in English...road to happiness, path to enlightenment, et. al.

calle = a street between buildings
camino = road, track or path, not necessarily paved, often used for countryside tacks.
carretera = any paved road intended for cars
autovía = a highway with less restrictions than a "autopista"
autopista = a highway

Daniel, My experience has been similar. I have seen different words used for the same road. However, I was trying to at least narrow it down to a single use word for road. Remember, none of these people have any type language background, so I was attempting to not overwhelm them with multiple words.

Vance

I think they could handle 2 words, use "calle" in town and "camino", out of town. "Camino" is also used for a path, trail or country road (as lazaruz says).