Intersection road_segment shouldn't contain road_block

Hi, I’m trying to understand the relationship between road_segment and road_block layers in the map. My understanding so far is as follows:

  1. a road_block is always associated with a road_segment(via road_segment_token)
  2. when a road_segment is not intersection, there’s always at least 1 road_block within it
  3. when a road_segment is intersection, there’s no road_block associated with it (which makes sense because we can’t define traffic direction at an intersection)

I’m looking at the singapore-onenorth map to verify my understanding but interestingly I found some outliers. In this map, there’re 3 intersection road_segment that have road_block association. For example:

nusc_map.render_record('road_segment', '9ebcd1ea-4ea4-462e-847f-1e7563f4229d', other_layers=['road_block'])

As shown above the road segment(‘9ebcd1ea-4ea4-462e-847f-1e7563f4229d’) and road block(‘25aab928-44b2-45b8-93e9-3414044b25f8’) share the same area, but when I look at the local patch overlayed on the lidar base map this polygon doesn’t look like an intersection.

The other two cases are similar with this one. So I wonder if the is_intersection field of these three records are incorrect?

Another relevant question is the relationship between lane and road_block, it seems reasonable to assume that lane is the building block of road_block, but the two are not linked in the dataset, I wonder if there’s any reason for this?