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I had driven this route once from CZ to Bulgarian' coast via Romania and it was rather traumatizing journey. First of all, Romanian roads are very bad shape even on Eastern Europe standard which will be compounded by crossing over mountain ranges of the Carpathians. Second problem are also lack of safety on the road, numerous pedestrians and other individuals, especially in the countryside. The third problem is insufficient road amenities on long journey. Once you reach Romanian/Hungarian borders, you will be fine. Hungarian roads and highway system is probably the best in Eastern Europe and it is country where four lane roads and highway connect all major cities and border crossing with Budapest. So once you get past Arad or Oradea, you can utilize good quality Hungarians roads (M3, M5) which will bring you all the way to Slovakia (M1). This will bring you to Slovakian highway system that is connected to Czech system (D2-D1-D9/D5) all they way to German border crossings. To travel on Czech or Slovakian roads, you will need a sticker that you can purchase on the borders or gas station. Police do check cars with foreign license plates if they pay this highway duty.