I think there is another way round to use multi-lane traffic is to use andi06's road system. If you place the '1-way traffic' spiline road (from andi06's road pack) laid in parallel all in the same direction of travel, and the same in the opposite direction (e.g. for near-side driving:
--->
---> (northbound traffic)
--->
==== (central reservation)
<---
<--- (southbound traffic)
<---
(obviously its opposite for off-side driving)), you would essentially get a 'motorway/freeway' type road.
This is particullarly useful for those with who has TRS04/06 as well as Trainz Classics/Railways.