Some of Comet’s double deckers were marked up at 16’ 5", made you wince a bit.
If any car transporters run over 16’ thats the driver doing it unofficially (or its a small outfit), some yards had beams across the exit, if you were over 16’ you were going nowhere.
Suspension bounce to be catered for, the bridge might be 16’6", but with soft air suspenders bounce could get it too close for comfort.