A: You should choose "inaccessible" as the Crossing Type if you cannot access the crossing at all. For example, many crossings on railroads and limited access highways are completely inaccessible. The database will make no assumptions about the passability of these crossings because they were not assessed.
If you can access one side of the structure but the reason that you can't assess either an inlet or outlet is that the stream is piped or buried, then choose “buried stream” as the Crossing Type. These types of crossings receive low passability scores by default.
If the crossing is not a buried stream, but you can only access one side of it, then you need to decide whether you can make reasonable estimates about the inaccessible inlet/outlet based on the characteristics of the other end of the crossing and what you can see from the road. Sometimes it is obvious that you are dealing with a 36" round pipe that will look pretty much the same at one end as at the other (e.g. same dimensions, same substrate or lack thereof). You would then need to determine whether the view from above is sufficient to decide issues like: inlet grade, outlet drop, scour pool, tailwater armoring, and physical barriers.
If you can make reasonable estimates for all the fields, then label the crossing type as “culvert”, “multiple culvert”, or “bridge” and fill out the form with measured or estimated values. If you are not confident that reasonable estimates can be made, then label the crossing type as either “partially inaccessible” and then collect as much data as you can.