prolog help producing route finder

Hey any help is greatly appreciated complete newb to prolog, trying to produ
ce a route finder, i'm given this program to start with;

% chicago.pl
:-use_module(library(lists)).
%road/3
road(bourt,chicago,5).
road(chicago,canter,30).
road(canter,gaton,30).
road(canter,idmouths,25).
road(staple,onbur,20).
road(staple,gaton,40).
road(staple,tiv,15).
road(gaton,tivworthy,30).
road(onbur,idmouths,10).
road(onbur,tiv,10).

What i need help with is i have to produce a predicate trip/3 which is a bi-
directional version of the above road/3, i think it only involves writing 2 
rules of which the comments are;
%trip/3
% rule 1
% you can make a trip of distance DIST from A to B
% if there is a road of distance DIST from A to B
% rule 2
% you can make a trip of distance DIST from A to B
% if there is a road of distance DIST from B to A

Any help with this would be appreciated. Thanks.

%trip/3

trip(A,B,DIST) :- road(A,B,DIST).
trip(A,B,DIST) :- road(B,A,DIST).