Good to hear from the expert!
Some builders would push conventional limits when it came the length of their Pratt trusses. The Lafayette Bridge Company was building Pratt's in the 1890's up to around 190 feet long that would have required a Whipple truss 10 years earlier. The Elkhart Bridge & Iron Company trumped that in the 2nd decade of the 20th century by hitting 200 ft. with a single span Pratt.
Along with the length of these spans extra height was needed to increase the depth of the trusses. Usually, these spans are fitted with substantial sway bracing to manage the added height. This span is surprising in that only 2 panel points have added bracing, with the remainder using only laced struts.
More impressive to me than the height of this bridge is the size of the panels. If the length given is correct, then these panels are pushing 19 ft. which is impressive. It also further helps to explain why the trusses are so tall.
That is an interesting question, especially as the bridge has such a narrow deck width. This bridge does seem to have a rather tall truss.
Does anyone know why it was built with such a high vertical clearance?