These are variable length barriers designed to prevent a car that is leaving the road from hitting a hazard - perhaps going over a cliff, striking a tree, or crossing the interstate into oncoming traffic.
Subtype
Device - Details on specific devices are given in the subtype pagesLength - This is calculated from the line drawn on the mapSource - This is used for documenting imported data, if it is a user added feature it can be left blankWikiURL - This navigates users back to one of these pagesNotes - A free text field for folks to describe this particular deviceGeometry - This is calculated based on the drawn line or pointRoadType - This includes road detailsThe sources for the specific subtype and device names are documented here.
Below are some of the places we import actual mapped features from.
Mapillary is a key partner for Safety in Numbers and thier object detection AI gives us the rough location and type of several types of features.
Here is a good article on Mapillary object detection. For specific definitions, take a look at their API documentation