I think this is considered a through truss because the two sidewalks go through the trusses. It's definitely an oddity that is hard to classify, though.
Massachusetts does have a bridge with a somewhat similar configuration with steel trusses:
And half the time the NBI lists pony or through trusses as deck trusses or vice versa, so really, the NBI data is often... not especially helpful in determining the bridge type.
A pony truss is technically just a sub-category of through truss. So, either one it technically correct. In the NBI Coding Guide for bridge inspection there isn't even an option for pony truss, they are just lumped in with the through trusses. So in conclusion it is not all that uncommon to see a pony truss listed as a through truss since all the data is based off the NBI.
I hope that makes it as clear as mud.
Have a good day,
Not argumentative. I really want to know. How is this through truss when there are no lateral braces or portal braces over the roadway?
This bridge is the focus bridge on the Historic Bridge Foundation's brand new Facebook page:
WSDOT is asking for public input on the future of the McMillin Bridge. The McMillin Bridge is a unique concrete through truss, and the only one to my knowledge of this scale in the United States.
WSDOT is considering leaving the bridge in place for historic purposes but they are also considering removing the structure so input is valuable to the process.
If you believe this is a historic structure worth preserving I encourage you to email or call the project office.