"The safest route is the one on the left."
Translation:O caminho mais seguro é o da esquerda.
Comparison of superiority is very similar to superlatives. What might change (except for the irregular adjectives) is the usage of the. Ex: Meu carro é mais seguro do que o seu = my car is safer than yours. Meu carro é O mais seguro (my car is the safest). The safest car (O carro mais seguro).... if you'd like further information, just ask, once the examples are many of them. As for "one",there are many contexts where it doesnt occur in Portuguese comparing to English, especially when "one/ones" are used for not repeating the subject/object/noun in the sentence.