Mount Vernon is at the intersection of two trails that make up part of the Ohio to Erie Rail Trail system. The Heart of Ohio Trail goes southish towards Columbus and ultimately the Ohio River at Cincinnati, while the Kokosing Gap Trail follows the Kokosing River northeast toward Gambier, Howard, and Danville, and ultimately to Lake Erie at Cleveland.
This bridge is part of the Downtown Connector Trail, a very short section connecting the two trails mentioned above. You used to have to use surface streets to get from one to the other. It was a short distance, but there was traffic. This is much better.
There are, of course, a ton of old railroad bridges on the rail trails. I've always loved the way the red orange rust of the metal looks contrasted against the blue sky. Honestly, I haven't explored the Heart of Ohio trail much at all (it's newer, and I haven't biked much lately)(and by much I mean at all), but the Kokosing Gap Trail is really just a lovely, shady joy with amazing views of the river and convenient stops at regular intervals.