"This road is the shortest."
Translation:Den här vägen är kortast.
It is actually an accepted translation already. As to why Den här vägen är kortast has 'This road is the shortest' as a main translation, I think whoever wrote the sentence probably felt that that was more idiomatic in English than 'This road is shortest'.
I think gata generally refers more to a street (i.e. in a built up, urban area) and väg is a road. (could be anywhere)