Calling ST_INTERSECTION() on two partially overlapping linestrings returns a single POINT , rather than the list of overlapping segments.

For example:

SELECT AsText( ST_INTERSECTION(
LinestringFromText('LINESTRING( 3 5, 2 5, 2 4, 3 4, 3 5 ) ') ,
LinestringFromText('LINESTRING( 3 5, 2 4, 2 5, 3 5 ) ')
));

Note that the two linestrings share (3 5 , 2 5) and (2 5 , 2 4) and yet ST_INTERSECTION returns only POINT(2 5). Postgis returns MULTILINESTRING((3 5,2 5),(2 5,2 4))