Depending on how much of the DLC's you own, this achievement might take a while. You'll need to complete a delivery on all oversize routes in the map. So if you own more dlc's (Going East, Scandinavia, etc) you'll need to do more routes and thus the achievement takes longer.
First off, you'll need to do Special Transport DLC routes, so those are the ones with escort vehicles which you have to stay in between, delivering huge cargo. If you go to quick jobs and then filter on sender - ascending (sending company), you'll get all Special Transport dlc cargos first, as they don't have companies attached (sending nor receiving).
As of patch 1.38, there are 36 routes that need completing if you own all dlc. The routes you'll need are (depending on which dlc you own, some might be available, others not):
*** Spoiler - click to reveal ***
- Berlin to Szczecin
- Bratislava to Graz
- Brussel to Amsterdam
- Dortmund to Hannover
- Dresden to Wrocław
- Glasgow to Aberdeen
- Köln to Amsterdam
- Košice to Budapest
- Linköping to Kalmar
- Luxembourg to Liège
- München to Innsbruck
- Nantes to Civaux
- Olsztyn to Białystok
- Praha to Nürnberg
- Reims to Strasbourg
- Sheffield to Birmingham
- Stavanger to Oslo
Patch 1.31:
- Cardiff to Birmingham
- Dijon to Geneve
- Linz to Brno
- London to Felixtowe
- Napoli to Terni
- Nice to Nice
- Palermo to Catania
- Szeged to Debrecen
- Trelleborg to Esbjerg
Patch 1.35:
- Krakow to Banská Bystrica
- Odense to Hirtshals
- Plymouth to Dover
- Pori to Helsinki
- Saints Petersburg to Saint Petersburg
- Toulouse to Montpellier
- Verona to Parma
Patch 1.38:
- Istanbul to Edirne
- Pleven to Sofia
- Reșița to Târgu Mureș
It doesn't matter which cargo you deliver, but along the way, if you at least do one of each, you'll nab most of the other achievements in this dlc, like:
Doing these without any damage will also give you: