I seen a shipping container bridge. It was meant for ATV's and a
tractor. As far as a car of truck, I believe it would get a little narrow.
I have also seen a flat rack for a bridge, basically, a shipping container without sides. I like this better than the container but it is still a little narrow for my liking.
Railroad flatbeds run around 85' and support a lot of weigh symmetrically from the centerline and are wider.
I am a civil engineer by education. I worked for Amtrak for three years in their bridge dept. That was awhile ago now and I traded that work in for something different.
I see there are two schools of thought about whether to use poured abutments or pilings. or this picture.