Find a 2 lane road that is suitable. Clone it so you have your own copy to edit. Open the clone for edit and add the lines fo the config .txt file:
isfreeway 1
(1 = asset will be a freeway model allowing the use of and multi-lane roads)
numlanes 2
(The number of lanes to be generated.
Default lane spacing is 3.4 metres.
Note that for kind track, traffic will flow in one direction for all lanes)
Now lay two road splines, one in each direction and you should have what you want. I believe there are some roads on the DLS that already do this.