The first and second men are contradicting each other by calling each other liars, and the third man supports the second man (Bruce). Therefore either the first man is lying and the other two are telling the truth, or the first man is telling the truth and the other two are lying.
If the third man were telling the truth and either road were fine, then the directional answers of the first two would be either both true or both false (depending upon whether their statements were considered exclusive). Since the first two contradict each other, the third man must be lying.
Therefore only the first man is telling the truth, and the road on the right is the right road to Trigoon.
