Modeled after bridges used by railroads the world over.
LDD file included!
About this creation
Designed using 24 of these parts, ( www.bricklink.com/catalogItem.asp?P=15706 ) this bridge fits even my tallest trains. It can fit up to 10-stud-wide locomotives, leaving 1 stud on each side for clearance. It also can fit 12 2/3 bricks tall train cars, but only barely: the clearance is less that a third of a brick in difference.
The tallest train car I own is this one: a caboose based on the prison car from the Lone Ranger "Constitution Train Chase". (set 79111). This car fits the bridge by a hair less than a third of a brick.