rankin bridge: weight limit

[Derrick J Brashear]

Not exactly pertinent but it started me thinking. In the last week or two 
the Rankin Bridge got a weight limit: 24 tons, 40 tons for "combinations". 
Was there any case where weight limit restrictions (on the number of cars 
which could be on a structure at a time) was used as a signal input? E.g. 
if the bridge could hold one car, signals would prevent additional cars 
from entering? Obviously not relevant to this bridge which was relatively 
new in the streetcar era, but something that came to mind as I returned 
from dinner today.

-D