The Speciaal Transport and Mack Dag is an annual event at utrecht in The Netherlands. A lot of large heavy haulage vehicles converge on the Veemarkt cattlemarket site, along with a lot of preserved Macks and FTF’s.
I will - as a guide, it is always either the last w/e in Sept or 1st w/e in Oct. Also, check Mammoet or Nooteboom websites as they have a lot to do with the organisation of the Utrecht show.