It didn't fit !
Well, what do you do when the tunnel is too low ? you drag your container behind your truck through the tunnel ... ok, it's not ideal, the container might have got a little bit scratched but it worked.
This convoy was not the first to pass through in this way. The trucks with their containers were called 'DROPS'. These tunnels were near Vares on the Skoda route to Tuzla (Siman Han) from Santici (Thanks to Don for this info).
See also this video at YouTube.