PostGIS Solution to Create Parallel Lines for Two-Way Travel Direction

For almost all GIS road network data, if there is no physical barrier (e.g., road median or center island for pedestrians) separating the two directional traffic flows, the road segment will be represented by single link. When you need to show the two-way traffic on a map, you need a function to separate the single link into two parallel links for visualization purpose. The most popular transportation-GIS software tools such as ArcGIS and TransCAD do not provide a ready-to-use function for this link dualization job. Thanks for the release of PostGIS 2.0; it includes a new function "ST_OffsetCurve" that can do this job easily. For details of the function, please refer to the PostGIS function documentation:

http://postgis.refractions.net/docs/ST_OffsetCurve.html