• key=crossing:cantilever
• Values: yes/no
  
• Description: Metal cantilever that extends over the road, and usually has a crossbuck/saltire and/or flashing lights mounted to it.
• key=crossing:contact:emergency
• Values: <string>
• Description: A designated contact number for contacting emergency operators.
• key=crossing:contact:railroad
• Values: <string>
• Description: A designated contact number for contacting the railroad.
  
• key=crossing:contact:state
  
• Values: <string>
• Description: A designated contact number for contacting state government.
  
• key=crossing:quiet_zone
• Values: yes/no
• Description: Locomotive engineers/operators are not to sound the horn at these crossings. There is often some sort of additional sound-producing device at these crossings.
  
• Federal Railroad Administration page
• key=crossing:traffic_signal
• Values: control/interconnected/no
  
• Description: In Urban environments, highway intersections and level crossings are often adjacent to each other and therefore the level crossing is integrated into the traffic signal controller. "control" is to indicate a crossing where traffic signals replace the typical alternating crossing lights and other standard protections. "interconnected" is when the traffic controller program will alter from typical operation when a train is approaching. It could be a red light for traffic in that direction, a temporary no right/left turn restriction, or a number of other scenarios.
  
• key=crossing:wigwag
• Values: yes/no
• Description: Old type of crossing protection consisting of a pendulum swinging back and forth. There's approximately 100 left in service in the U.S.
  
• Wikipedia page

The inventory reports also list the count of crossing lights, crossbucks/saltires, and other such warning devices. I am unsure if these would be useful enough to tag, however.

In addition, the integration of traffic signals at highway intersections with level crossings leads to a problem of grouping together elements of the entire junction, or even just the level crossing with itself. This is a problem with highway junctions in general. I think it could be a good idea to co-opt the complex junction relation from Proposed_features/Junction. This would also allow level crossings of multiple tracks to be grouped together. They way I would structure it is:

• Relation tagging:
  
• key=type=junction
• key=junction=level_crossing
• key=ref:fra_crossing
• Value: <string>
• Note: While not an approved value, this is the value I have been using for marking the ID used in the FRA's Crossing Inventory.
• Any of the tags used for the level_crossing node, as many of them are better applied to the relation than the node.
• Relation roles:
• (blank)
• Used on: Anything else
• Description: Used to include anything else that isn't listed below. The only thing I can think of that could be is the segment of track that is embedded in the roadway. I have tagged this in the past as key=embedded=yes/pavement/metal/wood/plastic (plastic includes rubber). The highway section between stop lines/traffic signals could be added as well, as I suppose those are part of the junction as well.
  
• level_crossing
  
• Occurance: 1 or more.
  
• Used on: key=railway=level_crossing or key=railway=crossing
  
• Description: This is where the railway track intersects a highway or pedestrian path.
  
• traffic_signal
  
• Occurance: 0 or more
  
• Used on: highway=traffic_signals
  
• Description: Any traffic signals that are part of this junction. This assumes that the traffic_signal is not mapped at the intersection of roadways.
  
• stop_line
• Occurance: 0 or More, mutually exclusive with traffic_signal
  
• Used on: Nodes tagged with key=highway=stop_line
  
• Description: This is where vehicles are to come to a stop, in cases where a traffic signal would not otherwise be tagged at this position.
  
• location_hint
• Occurance: Optionally one. Mutually exclusive with.
• Used on: Any node.
  
• Description: A hint to a renderer as to where a good place to put the the junction number or name on the map.

Anyways, just seeing what other thoughts you have. I cannot say that all of the terminology used in tags or roles are optimal.