Yes, it is possible. How likely it is, is another question altogether. Gravel is a low value commodity, and the shortline would have to be hauling a lot of it in order to afford the expense of building it. The most likely explanation of why such a bridge would exit on a gravel hauling shortline is if the shortline was a small segment of what was formerly a longer, wealthier route. That said, since you're General Operations Directore of the route, you can do what you want, reasonable backstory or not.
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