Hit a 13'6 ¹/² bridge.

They have an interesting way of dealing with heavy snow, mainly by melting it.

And I figured the measurements were to keep their measuring devices clean, and a 1 inch wide tape measure will usually reach up high enough to hook over the top. I run lots of Chicago, so I have a good sense of what can be cleared with a 13' 6" trailer, but an airbag malfunction raising it higher and hitting something hasn't happened to me, yet.

And remember the Lake Street Ell.