Matt;
Not a simple answer, I'm afraid... here is a pic of the end of the bridge:
The flared portion at the bottom of the bridge is 6 3/4". The straight section above the flare is 5" wide, and the top section is 6" wide. Without the water base, the BOTTOM of the Fastrack section attached to the bridge is 5 1/4" high. The bases of the Fastrack trestles are 5 1/4" wide. The tallest of the Fastrack graduated trestles, and all of the elevated trestles are 5 1/2".
Hope this helps.