I haven't quite found a solution for buffering selected line segments of a road network without extporting the selected line segments to a new file and then buffering. I want to avoid creating a bunch of new datasets for this task. Either environment will do (ArcGIS application or Python). Any suggestions?
Run the Buffer geoprocessing tool from ArcMap on the layer with the selection. Most geoprocessing tools operate on the selected set by default, if present.