###New Answer, After Re-Reading the Q
It appears that I completely misread what the question is asking for. Some of what I answered previously is still relevant so I'll leave it at the bottom.
UsingFor the suggestion that you call it a crossing (read below)least ambiguity and greatest recognition, I would suggest using words such as available, and engaged to describe the crossing.
Basically, the key thing to keep in mind is that the bridge is not 'open' or 'closed', it is usable and not usable. Regardless of which way you're crossing, by boat or by road, the bridge can only be one of two states for you, usable
or not usable.
On that basis alone, I think you should be able to find a variety of relevant words and phrases to refer to the state of the bridge, relative to you.
My overall suggestion, after quickly perusingas a few synonyms of usable, is:
“ Is the crossingCrossing accessible?”- A place at which one may safely cross something (Source: Google)
###Old Answer, Not Exactly Answering the Q
I think you could sufficiently describe this with the term Crossing.
It usually refers to places where roads intersect with railways, but according to the definition it is not limited to railways, but rather “a place at which one may safely cross something, especially a street”. It does fit that particular definition, because it is a mechanism used for vehicles, people and bridges to safely cross the intersection.
I really think it could lend itself perfectly to this situation. Most people would understand what you mean immediately.Fairly unambiguous alternatives:
“When will the crossingcrossing be openaccessible?”
“When will the crossingcrossing be availableavailable?”
“When can we use the crosscrossing the bridge?”
“When can we use the crossingcross the bridge?”
As an unnecessary bonus, I'm also recommending two words that can be used to describe the boolean state of the bridge. The bridge can be either: