Different countries drive on different sides of the road. This is named for the side the driver sits on. The UK is the main right-hand drive (RHD) country. Most countries that were British colonies are RHD. The EU and most other countries are LHD. The US was British but is LHD. Canada (next to the US) is LHD. When you are building a truck LHD or RHD is not important. Australia builds US type Mack and International trucks with RHD.